Spinning Black Hole's Edge Rotates At Nearly the Speed of Light

astroengine writes "Astronomers have directly measured the spin of a black hole for the first time by detecting the mind-bending relativistic effects that warp space-time at the very edge of its event horizon. By monitoring X-ray emissions from iron ions (iron atoms with some electrons missing) trapped in the black hole's accretion disk, the rapidly-rotating inner edge of the disk of hot material has provided direct information about how fast the black hole is spinning. Astronomers used NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) — that was launched into Earth orbit in June 2012 — and the European observatory XMM-Newton measured X-ray radiation as a tool to directly infer the spin of NGC 1365's black hole. 'What excites me is the fact that we are able to do this for the very massive black holes at the centers of galaxies but we can also make the same measurement for black holes in our galaxy ... black holes that resulted from the explosion of a star ... The fact we can extend this from billions of solar masses to 10 solar masses is pretty cool,' Fiona Harrison, professor of physics and astronomy at the California Institute of Technology, Pasadena, Calif., and principal investigator of the NuSTAR mission, told Discovery News."

Comments

know your audience

[Anonymous Coward]

i love how this summary explains what an ion is, but assumes i know the definitions of black hole, x-ray, and solar mass. great writing, folks!

Re:know your audience

[Anonymous Coward]

Are you..... are you.... serious?

Re:know your audience

[cyberchondriac]

Ion not an astrophysicist, but ... I did like the way they explained angular momentum. I think everyone sort of knows what a black hole is by now; who hasn't had an x-ray? and mass is just high school chemistry, if not junior high.

Re:know your audience

[oodaloop]

Of course, it doesn't define accretion, earth, relativistic, radiation, mass, electron, or spin either. If you don't know anything about physics, go post on 4chan or something.

Re:know your audience

[alen]

didn't graduate high school

or did you go to school before the big bang?

Re:know your audience

[Anonymous Coward]

As opposed to not knowing what an ion is? If you slept through high school chemistry, Slashdot is happy to dumb everything down for you.

Great evidence of how far this place has fallen.

Re:know your audience

[Anonymous Coward]

i love how this summary explains what an ion is, but assumes i know the definitions of black hole, x-ray, and solar mass. great writing, folks!

I love how that part of the summary is plagiarized from the page one of the first article linked and the link takes you to page two!

Re:know your audience

[Anonymous Coward]

Actually, one of my big complaints about Science Channel styled science shows is the need to take up 3 minutes by giving a definition of a black hole every time they mention a black hole.
 
Take note, podcasters like Pamela Gay: if we haven't gotten the concept of a black hole down by the 10th poscast you've done on the subject then we're just not going to get it.

Re:know your audience

[Idbar]

It seems like you got caught in the mind-bending relativistic effects of the summary.

Re:know your audience

[140Mandak262Jamuna]

Till I read the summary I thought ion is a iron with the letter r removed. Now I know what is removed is not r but electrons. Got it.

Re:know your audience

[Anonymous Coward]

Actually, one of my big complaints about Science Channel styled science shows is the need to take up 3 minutes by giving a definition of a black hole every time they mention a black hole.

Take note, podcasters like Pamela Gay: if we haven't gotten the concept of a black hole down by the 10th poscast you've done on the subject then we're just not going to get it.

Being a science populizer is a freaking hard thing to do right. And to be honest, the astronomy cast podcasts are independent of one another, so reiterating the definition of a black hole or other "esoteric" astrophysics objects is a good thing for the lay audience.

Re:know your audience

[Anonymous Coward]

Exactly.

And even more importantly, why did they leave out possible implications for time travel?

Re:know your audience

[K. S. Kyosuke]

i love how this summary explains what an ion is, but assumes i know the definitions of black hole, x-ray, and solar mass. great writing, folks!

You forgot "space-time", "event horizon" and "accretion disk".

I'm also astounded by the discovery of black holes resulting from an explosion of a star. So far I thought that a black hole is a result of an implosion of a star. This is a major new discovery!

Re:know your audience

[MouseR]

You can thank anonymous postings for this.

Re:know your audience

[nedlohs]

That's the point. It wastes a bunch of words explaining what an ion is.

If you don't know what an ion is the rest of the words are going to make any sense anyway.

Re:know your audience

[Anonymous Coward]

didn't graduate high school

or did you go to school before the big bang?

I, in fact, had my big bang after graduating from high school. So, yes, it's pretty much possible that he did.

Re:know your audience

[vux984]

I think everyone sort of knows what a black hole is by now; who hasn't had an x-ray? and mass is just high school chemistry, if not junior high.

Ions are elementary chemistry as well, and are covered early on in school, grade 7 or 8 at the latest I think. Acids and bases, potato batteries, etc.

And knowing what an "x-ray exam" is doesn't tell you anything about what an x-ray actually is, nor what they are doing near black holes.

Re:know your audience

[Artraze]

And relativistic effects and thus why any of this is even mildly interesting. I guess they explained accretion disc too, though, so that's something.

But beyond that, what I find most awesome about it is that it's completely unnecessary for understanding anything about this. They could've said "X-ray emissions from walruses (large flippered marine mammals) trapped in the black hole's accretion disk" and it wouldn't have really made any difference to 99+% of the audience, aside from causing us to wonder why walruses were in space at all. It's really quite bizarre that the author felt a need to elaborate on that one.

Re:know your audience

[thomasw_lrd]

You're obviously not from the deep southern United States.

Mass is at least college level, maybe graduate level.

Re:know your audience

[Anonymous Coward]

That's the point. It wastes a bunch of words explaining what an ion is.

If you don't know what an ion is the rest of the words are going to make any sense anyway.

Q.E.D., I guess.

Re:know your audience

[voidphoenix]

It's both, iirc. Star goes supernova, the remnants collapse into a black hole.

Re:know your audience

[PhxBlue]

Probably so folks wouldn't think it was a typo, e.g., iron iron.

Re:know your audience

[smpoole7]

> I'm also astounded by the discovery of black holes resulting from an explosion of a star.

Really massive stars (greater that 250 solar masses -- i.e., 250 times as massive as our own Sun) most assuredly do explode, and *very* violently, leaving behind a black hole. It's believed that this is a key source for gamma ray burst events. It's also thought that many of the first stars in the universe, not long after the Big Bang, exploded this way, spewing jets of metals at relativistic speeds.

To be fair to you, it's now known that there are actually several different types of supernova. Some core collapses do occur without a big earthshattering "kaboom." The really massive stars explode due to photodisintegration, and result in a hypernova -- a ridiculously intense, you-don't-want-to-be-within-a-hundred-light-years kind of thingie. :)

http://en.wikipedia.org/wiki/Photodisintegration

http://en.wikipedia.org/wiki/Supernova

Re:know your audience

[gmuslera]

In that US regions almost everyone would deny all of this, no matter of the education level. The light coming from the accretion disk of that black hole is coming here from before 6000 years ago, when the universe, earth, man, and everything else was created by the almighty god.

Re:know your audience

[HairyNevus]

As opposed to not knowing what an ion is? If you slept through high school chemistry, Slashdot is happy to dumb everything down for you.

Great evidence of how far this place has fallen.

I don't think anyone who spells out "Slashdot" rather than typing"/." (you know because then the website would be http:///..com. The whole joke behind why this site is called what it is) is in a position to comment on how far it's fallen. I also don't see how the person who submitted the article explaining the simplest concept in the summary but not the more advanced ones is anything more than curious/funny. Hardly something to read into about the site as a whole.

Re:know your audience

[Anonymous Coward]

No no, a mass is what happens in a Church you heathen.

Re:know your audience

[nedlohs]

I didn't want to have to define not, so I just skipped it.

Re:know your audience

[maxwell demon]

No no, a mass is what happens in a Church you heathen.

Ah, now I understand why the Higgs particle is the god particle: It is causing what happens in a Church!

Re:know your audience

[Anonymous Coward]

If people ask, just tell them it has a lot to do with 'synchrotron radiation'. They'll automatically assume you're talking about something out of a superhero comic book, and if they ever find out you weren't, they'll feel stupid. :D

Re:know your audience

[maxwell demon]

That's the problem of non-interactive speaking. When explaining it to someone directly, you'd ask: "Do you know what a black hole is?" and if the other one says "yes" you'd skip the explanation (but keep in mind that you might have to do it anyway if it turns out that his understanding of black holes is wrong).

Re:know your audience

[Anonymous Coward]

I thought an atom missing one ore more electrons was called a catiom

Re:know your audience

[BrokenHalo]

Familiarity with ions isn't necessarily universal - I had a chemistry professor at uni whose wife (a smart enough lady in other regards) told me her attempt to get to grips with chemistry at school ended with failure to understand ions.

Re:know your audience

[Anonymous Coward]

I think the extra 'R' gets attracted to the electron; because opposites attack or something. That makes it an electrRon. And I think that the frisbee from Tron is how the 'R' particle moves around.

Pretty sure that is how it goes.

Re:know your audience

[pyro_peter_911]

In that US region almost everyone would deny all of this, no matter of the education level. The light coming from the accretion disk of that black hole is coming here from before 6000 years ago, when the universe, earth, man, and everything else was created by the almighty god.

I'm an atheist with a college degree who works daily with salt of the earth types in the Bible Belt. In general, physics understanding is spotty around here but actual Young Earthers are extraordinarily rare (to the point where I've never actually met one). You're unlikely to find someone who can tell you the difference between weight and mass and if you want them to use a torque wrench make your specs in foot pounds instead of Newton meters. However, pictures of Jesus riding a T-Rex are taken as ridiculous jokes since, obviously, they weren't contemporaries.

Hell, the guys in the oil and gas industries make their fucking paychecks based on a fundamental understanding of geology, evolution, and the time scales involved.

You may want to question your assumptions more in the future if you would like your worldview to more accurately reflect reality.

Peter

Re:know your audience

[Anonymous Coward]

Ions are elementary chemistry as well, and are covered early on in school, grade 7 or 8 at the latest I think.

Unfortunately, even if that is how education works, it is not how people's memory or pop culture reminders work. Since my field is plasma physics and I do a lot of outreach stuff, I constantly have to explain to people what an ion is, and am happy if they remember the structure of an atom (most roughly do). At the same time, I get a lot of questions about black holes, and people know a little about them without prompting and can remember at least roughly what the event horizon is.

Re:know your audience

[Anonymous Coward]

Assumptions? They're not assumptions. They are a core part of his religion.

Re:know your audience

[Neil Boekend]

So child abuse is mass?

Re:know your audience

[Anonymous Coward]

Unlike the slashdot readership, not everyone pursued natural sciences in high school.
I know at least one dude in marketing who knows in rough terms what a black hole is but doesn't know what an ion is. Because of this he uses the English word for ion when he tries to sell lithium based batteries.

Re:know your audience

[Nyder]

Ion not an astrophysicist, but ... I did like the way they explained angular momentum. I think everyone sort of knows what a black hole is by now; who hasn't had an x-ray? and mass is just high school chemistry, if not junior high.

Mass is chemistry? damn public school education.

Re:know your audience

[mbstone]

Now I know that steam ions are what actually remove wrinkles from shirts.

Re:know your audience

[Anonymous Coward]

So brave!

Re:know your audience

[Anonymous Coward]

Supernovae...

Re:know your audience

[RaceProUK]

Cation - Positive ion

Anion - Negative ion

I think that's the right way round.

Re:know your audience

[Impy the Impiuos Imp]

Spacetime -- What you have plenty of all alone in your room.

Accretion disk -- The growing circle of used kleenex around your bedroom garbage can.

Event horizon -- The zipper of a girl's pants, and there's no way to know, even in theory, what's on the other side.

Re:know your audience

[sFurbo]

Star can't be heavier than 100 solar masses, as the solar wind (stellar wind?) becomes so strong that it tears the star apart.

Re:know your audience

[sFurbo]

Hmm, I see that the WP article about photodisintegration you linked to does mention stars of that mass. The hypernovas could be what Phil Plait meant by "incredibly violent paroxysms that are second only to the star going supernova". Anyway, I am going to withdraw my objection, as I am not going to disagree with neither Phil PLait, nor with Wikipedia in this matter.

Re:know your audience

[Anonymous Coward]

The exact upper bound on mass for both stars in general and normal star formation processes are still something being worked out and depends a bit on the modeling.

Re:know your audience

[Sigg3.net]

But I failed my X-ray exam, you insensitive clod!

Re:know your audience

[cyberchondriac]

Heh .. our school did chemistry before physics, so I got the first solid exposure to the "concept" in chemistry class. There's a lot of overlap, in any case.

Re:know your audience

[cyberchondriac]

Assumptions? They're not assumptions. They are a core part of his religion.

Whose religion? gmuslera's ? Check your sarcasm detector, it might be a little off..

Re:know your audience

[TheCarp]

And I know someone who was in a school with all new labs when the Chemistry teacher left and some other random teacher was put on as the chemisty teacher.... so everyone in their 8th grade class had an entire year of going into class, being given a paraphraph from the chemistry book with words removed, and being asked to read the chapter and fill in the words.

she, quite predictably, has no idea what an Ion is.

Re:know your audience

[Anonymous Coward]

I think you meant steam ions remove winkles from shits.

Re:know your audience

[peawormsworth]

i love how this summary explains what an ion is, but assumes i know the definitions of black hole, x-ray, and solar mass. great writing, folks!

I liked the way it is titled "...At Nearly the Speed of Light", but without bothering to mention the measured speed. For those who want real information: "84 percent of its theoretical maximum". Where I assume theoretical maximum is at or near the speed of light.

Re:know your audience

[Anonymous Coward]

Even with the decline in article quality, the comments are where the real meat on /. is. Just learning about something as cool sounding as photodisintegration exists and finding out that it is as cool as it sounds is completely worth the shoddy summary.

Re:know your audience

[smpoole7]

> Star can't be heavier than 100 solar masses

Just one example: http://en.wikipedia.org/wiki/R136a1

Estimated at 265 times solar mass. I was going to use the Pistol Star (located in the center of our galaxy), but its mass is disputed.

Slate is wrong. Or rather, they're repeating something that was believed about 20 years ago. Astrophysicists have known for some time now that stars > 100 solar masses are quite possible.

Re:know your audience

[smpoole7]

And I apologize to you, I didn't see your retraction before I posted a response to you.

This stuff fascinates me. I understand just enough about it to keep my own head from collapsing into a black hole, but only barely. :)

Re:know your audience

[hacksoncode]

FWIW, it was really called the "God-damned particle"... science journalists and fussy professors just shortened that name.

Is the hole rotating, or just the disk?

[ShanghaiBill]

Have they shown that the black hole is rotating near c, or just that the accretion disk is rotating near c at the event horizon? The accretion disk and the black hole are not necessarily spinning in sync. If they mean the accretion disk, then, like DUH: if it wasn't rotating near c, it would fall straight in and there wouldn't be a disk.

 

Re:Is the hole rotating, or just the disk?

[Anonymous Coward]

Considering they are experienced researchers, how likely do you think is the latter?

Re:Is the hole rotating, or just the disk?

[Anonymous Coward]

By monitoring X-ray emissions from iron ions (iron atoms with some electrons missing) trapped in the black hole's accretion disk, the rapidly-rotating inner edge of the disk of hot material has provided direct information about how fast the black hole is spinning.

So the summary indicates that measuring the accretion disk somehow tells them exactly how fast the non-emitting portion is spinning.

The useful answer is in the link from the above quote:

Risaliti and his colleagues measured X-rays from the center of NGC 1365 to determine where the inner edge of the accretion disk was located. This Innermost Stable Circular Orbit - the disk's point of no return - depends on the black hole's spin. Since a spinning black hole distorts space, the disk material can get closer to the black hole before being sucked in.

So they calculated the spin of the black hole by comparing the observed orbit to the calculated orbits possible from the calculated mass based on observable gravitic effect on nearby objects. Yes, there's uncertainty there, but until someone discovers a new detail in astronomy, that's as accurate as we can get.

Re:Is the hole rotating, or just the disk?

[Anonymous Coward]

The accretion disk and the black hole are not necessarily spinning in sync.

Let's consider angular momentum for a moment. A cloud of gas and dust falls toward a black hole. As it is drawn inward the cloud begins to orbit the black hole forming an accretion disk. As the now ionized gas moves inward, it spins faster and faster. As the matter crosses the event horizon, it is flying around at super speeds. But the event horizon isn't the end. It continues falling inward toward the singularity. Conservation of angular momentum would suggest that it's rotation would continue accelerating as it fell. Faster and faster as it is compressed toward infinite density.

How fast? Well, if the accretion disk near the event horizon is "near the speed of light", I suppose the stuff inside the event horizon would have to be going 'even nearer the speed of light'.

Re:Is the hole rotating, or just the disk?

[The Grim Reefer]

Have they shown that the black hole is rotating near c, or just that the accretion disk is rotating near c at the event horizon? The accretion disk and the black hole are not necessarily spinning in sync. If they mean the accretion disk, then, like DUH: if it wasn't rotating near c, it would fall straight in and there wouldn't be a disk.

I realize this is /., but did you not even read the first sentence of the summary?

Astronomers have directly measured the spin of a black hole for the first time

It's not that someone has discovered or theorized about it. They actually measured it. Which I find to be pretty damn interesting.

Re:Is the hole rotating, or just the disk?

[ceoyoyo]

That's not actually what happens. The event horizon, among other things, is where general relativity predicts that time will stop. So anything at the event horizon will take forever (literally), from the point of view of an observer at relative rest in flat space, to experience any passage of time. Which means nothing can ever cross the event horizon and continue to fall inward. The event horizon is, very literally, the end.

Re:Is the hole rotating, or just the disk?

[Anonymous Coward]

Black holes can evaporate in a few billion years, and then their event horizon disappears. So an event horizon is not the end, just some temporary area with slow time.

Re:Is the hole rotating, or just the disk?

[Chris Burke]

Black holes can evaporate in a few billion years, and then their event horizon disappears. So an event horizon is not the end, just some temporary area with slow time.

A black hole of one solar mass will take 10^67 years to evaporate from Hawking Radiation -- and this time is proportional to the cube of the mass, so think about those SMBHs out there with billions of solar masses. That's a mind-bogglingly long time. You might think it's a long time waiting in line at the Department of Transportation, but that's peanuts compared to black hole evaporation...

And that's only after the CMBR has been red-shifted into near non-existence since until then the black hole is absorbing more energy than it is losing.

Though there are in theory primordial black holes (ones created in the moments after the Big Bang) that would have a lifespan measured merely in billions of years.

Re:Is the hole rotating, or just the disk?

[Anonymous Coward]

There is a region around a spinning black hole (the extent of which depends on how fast it is spinning) in which essentially matter cannot not spin. You can either think of it as requiring faster than light travel to stop spinning or more technically as the light cones of all particles being such that they point around the black hole. So there is a strong connection between the speed of matter spinning around a black hole even though they might not be in exact sync, there is some synchronization, even more assuming models of the accretion disk are accurate.

Re:Is the hole rotating, or just the disk?

[Anonymous Coward]

Considering they are experienced researchers, how likely do you think is the latter?

Considering this is slashdot, how likely do you think the summary is accurate?

Re:Is the hole rotating, or just the disk?

[Anonymous Coward]

Depends on your frame of reference. From the point of view of an observer moving with the disk material, there's no (relative) motion at all. There's acceleration, and it is mighty, for it is the centripetal force overcoming the inertia of the disk material (a.k.a. the centrifugal force in the rotating reference frame). From the point of view of an observer far away in "flat spacetime", the material is embedded in spacetime that is rotating with the black hole (q.v. frame dragging = Lense-Thirring effect) and the matter is also affected by gas pressure (densities can be pretty high near the ISCO) and radiation pressure, especially from the jets. While the velocity of matter is limited to the speed of light *relative to the spacetime it's embedded in*, spacetime is not limited in such a way. Frame dragging normally doesn't matter. Near the surface of the Earth, it's something like 0.1 nanosquats per fortnight (actually, ~10^-14 radians/second). At the surface of the Sun, it's slightly bigger (~ 10^-13 radians/second). Near the surface of a rapidly rotating neutron star, this can be krad/s and it's not hard to see that freely falling material can appear to have velocities a large fraction of the speed of light when it's embedded in spacetime zipping along so aggressively.

Godel, Tipler, and Gott studied consequences of frame dragging and the absence of a speed limit for the hunks of spacetime in which matter is embedded. They found that on a patch of spacetime moving a significant fraction of the speed of light, an object could accelerate itself to a significant fraction of the speed of light relative to the patch so that an observer far away on a flat patch of spacetime would see the object's clocks run backwards -- i.e., the object would seem to be running backwards in time. We now know that the environment near a rapidly spinning black hole *that we can find* is inhospitable to devices we can make -- the copious X-ray bombardment is deleterious enough and the MegaKelvin disk material isn't doing us any favors, so maybe we can't profitably use this trick... unless we can start finding rapidly spinning black holes that aren't emitting gobs of radiation. (In which case, how did we find it?.)

tl;dr:
So the short extension of your quip is: "... I suppose the stuff inside the event horizon would have to be going '[faster than] the speed of light [from the point of view of a remote observer]'."

Re:Is the hole rotating, or just the disk?

[miniMUNCH]

First things first... how does a singularity, i.e. a 0-D object, have 'spin'? Author please explain how you can attribute spin to a black hole. I think something got mixed up in the message of what the NuStar scientists actually figured out and what got reported here.

From simple classical arguments, it is not surprising that, from conservation of angular momentum, matter traveling into the black hole could reach 'observed' angular speeds up to the speed of light. Very cool that we have moreorless observed this angular velocity limit.

Re:Is the hole rotating, or just the disk?

[Anonymous Coward]

Physicists talk of 1D objects having spin all the time, but usually it is in the context of fundamental particles. It is also possible for gravitational fields to convey angular momentum just as electromagnetic fields can convey momentum and angular momentum.

Re:Is the hole rotating, or just the disk?

[fatphil]

> I realize this is /., but did you not even read the first sentence of the summary?

> > Astronomers have directly measured the spin of a black hole for the first time

Don't stop there - it continues:

"... by detecting the mind-bending relativistic effects that warp space-time at the very edge of its event horizon."

So they measured a property of something which is *nowhere near* the black hole. The event horizon isn't the black hole, you know. They've not *directly* measured any property of the black hole itself. Just think about it for 1 moment - they were detecting X-rays. You don't get any X-rays from the black hole itself.

It's a dreadfully worded article, they seem to bounce between the black hole and its event horizon on a whim, not understanding that the two are not interchangeable concepts.

Then again, it's not the best science in the universe either. They gathered the data and interpreted noisy results in order to confirm an expectation:
"It was my expectation, and the main scientific rationale for the project. Of course many colleagues would rather expect absorption as the right explanation ... but the whole project has been conceived to solve this puzzle,"
I.e. there no attempt to falsify the theory, only an attempt to confirm it.

It only becomes good science when the guys who expected absorbtion confirm their results.

Re:Is the hole rotating, or just the disk?

[Anonymous Coward]

The event horizon is part of the structure of the black hole. It might not be a physical structure, but nonetheless, it is part of the black hole and very closely related to some of the properties of a black hole. Additionally, for a rotating black hole, there is the ergosphere immediately outside the event horizon. Otherwise, you might as well argue someone using calipers is not directly measuring something, because the contact force is based on electronic structure and not the nucleus of an object's atoms.

Re:Is the hole rotating, or just the disk?

[Bengie]

They found that on a patch of spacetime moving a significant fraction of the speed of light, an object could accelerate itself to a significant fraction of the speed of light relative to the patch so that an observer far away on a flat patch of spacetime would see the object's clocks run backwards

I was under the impression that time dilation only affects matter moving through space time, and that gravity and frame dragging are not "proper acceleration" and relativity does not apply to this improper form of acceleration.

Same reason why space falling into a black hole can drag an object faster than c.

WRONG!

[Anonymous Coward]

"speed of light" is meaningless -- because it's not a constant. Might as well talk about the "speed of a honda civic". Maybe it's been souped up with a v8 engine and can hit 200mph. Or maybe it's sitting in rush-hour traffic doing 0.

Maybe they mean "speed of light in a vacuum without gravitational interference". But this a is a black hole (the very definition of gravitational interference) so the speed of light may be a constant, but it's not the constant you're thinking of. In fact, it slows down to 0.

Re:WRONG!

[jgtg32a]

The speed of light is influenced by gravity?

Re:WRONG!

[kenaaker]

Of course the capitalization of the title is a dead give away. It was nice to self label the contribution.

The speed of light in a vacuum is a constant. It never changes.

Time, on the other hand, is different almost everywhere. My hypothesis is that the the speed of light and time have switched places in someones private universe.

Re:WRONG!

[Westwood0720]

Gravity certainly bends light. But as far as slowing it down, I always thought was a constant represented by the letter "c".

Re:WRONG!

[thechemic]

I had a Honda Civic that could go the speed of light. It sucked because nothing ever showed up in the rear view mirror.

Re:WRONG!

[SJHillman]

Speed is distance over time. If time slows down, then light will appear to slow down to an observer in another frame of reference. However, speed is unaffected, it takes the same amount of time to cover a set distance within the same frame of reference - it just appears to be slower to an outside observer.

Re:WRONG!

[Anonymous Coward]

So many people (a number of whom who should know better) get this totally wrong because you always here that a black hole has "such powerful gravity that not even light can escape!!!111!!!"
 
This is another failing of Science Channel styled science shows*. They neglect to tell you that light doesn't escape because the gravity well created by a black hole warps space, not because photons are pulled on by gravity. It may sound like I'm splitting hairs since the overall end result is the same but a lot of people mistake it as meaning that light is sucked in to the black hole because particles with mass are also sucked in. This also doubtlessly leaves people scratching their head over the misconception that maybe the gravity is forceful enough to actually attact the light.
 
* Yeah, I'm the guy who complained about definitions being used too often in another thread.

Re:WRONG!

[thechemic]

I think you should have somebody take a look at your shift key.

Re:WRONG!

[AK Marc]

c is a constant represents the theoretical maximum speed of light. The problem is that the speed of light is not constant. Light slows down in a medium.

Re:WRONG!

[Anonymous Coward]

In some mediums, light moves faster than it does through a vacuum. c is the speed of light in a vacuum, not the "theoretical maximum speed of light"

Re:WRONG!

[AK Marc]

It may sound like I'm splitting hairs since the overall end result is the same but a lot of people mistake it as meaning that light is sucked in to the black hole because particles with mass are also sucked in. This also doubtlessly leaves people scratching their head over the misconception that maybe the gravity is forceful enough to actually attact the light.

Light has momentum (which "require" mass in more classical thinking). Light is "moved" by gravity (which indicates mass). If mass distorts space so that it makes light and particles behave the same, then why is it a misconception to think of light as a particle? It's both a particle and a wave, thus *is* a particle.

Re:WRONG!

[AK Marc]

If it's anything like my last Honda Civic, that's because the mirror fell off and is sitting under the passenger seat.

Re:WRONG!

[Turminder Xuss]

Doesn't the light have a constant speed for all observers but it's frequency is shifted for an observer in a different frame of reference ?

Re:WRONG!

[Anonymous Coward]

Wrong, so very wrong.

Re:WRONG!

[DragonWriter]

This is another failing of Science Channel styled science shows*. They neglect to tell you that light doesn't escape because the gravity well created by a black hole warps space, not because photons are pulled on by gravity.

Most of the Science Channel-style science shows I've seen that cover the issue not only cover that light doesn't escape the gravity well because the gravity of the black hole warps space, but also covered that that's how all gravity works, not just a special variation related to "black holes" as the source or "light" as the affected entity. (As do the more technical, less Science-Channel-ish, works that I've seen addressing the same subject matter.)

It may sound like I'm splitting hairs since the overall end result is the same but a lot of people mistake it as meaning that light is sucked in to the black hole because particles with mass are also sucked in. This also doubtlessly leaves people scratching their head over the misconception that maybe the gravity is forceful enough to actually attact the light.

The "sucked in" analogy is exactly as accurate (or inaccurate) applied to light as it is to "particles with mass".

Re:WRONG!

[maxwell demon]

So many people (a number of whom who should know better) get this totally wrong because you always here that a black hole has "such powerful gravity that not even light can escape!!!111!!!"

Which actually is correct (except for "here" instead of "hear" :-)). What's wrong is the imagination that this is because the light is slowed down when going outwards (actually in some sense the light is slowed down, because the time as seen from outside is slowed down; but that's independent of the direction, and of course locally it is still going with c). The real reason is that the spacetime (not space, spacetime) is curved in a way that there's no way out when going at light speed or below. That is, the outward-going light is still going with light speed, but will not get out, but eventually reach the singularity. Yes, that seems paradox, since the singularity is "in the middle" (which isn't entirely accurate either; for a non-rotating black hole it is actually in the future), but that's because we are not very good in imagining curved four-dimensional spacetimes.

Re:WRONG!

[roc97007]

...and even with the headlights on, you couldn't see it coming.

Re:WRONG!

[maxwell demon]

No, time is the same everywhere, too. Only the length of timelike paths depends on how you move. But ultimately it is not too different from the fact that the length of spacelike paths depends on the way you take. Except that for spacelike paths, the direct path is the shortest, while for timelike paths, the direct path is the longest.

Re:WRONG!

[MozeeToby]

In some mediums, light moves faster than it does through a vacuum.

No, it doesn't. Not only does such a material not exist, it is proven beyond any reasonable doubt to be impossible.

c is the speed of light in a vacuumm

Hey! You got something right!

not the "theoretical maximum speed of light"

And right back to wrong. Nothing can travel through space (empty or otherwise) at faster than c, that is the central concept of relativity.

Re:WRONG!

[oodaloop]

And you're always adjusting the in-dash clock.

Re:WRONG!

[gmuslera]

Time and space are influenced by gravity, and speed depends on both.

Re:WRONG!

[TapeCutter]

Three dimensions.are mind boggling enough, once you are inside the BH, light is bent such that all directions are pointing towards the "middle", it's sort of like the 3D equivalent of asking which way is north when you are at the south pole.

Re:WRONG!

[maxwell demon]

In some mediums, light moves faster than it does through a vacuum.

No, it doesn't. Not only does such a material not exist, it is proven beyond any reasonable doubt to be impossible.

That depends on what exactly you mean with the "speed in the medium".

You certainly can have a phase velocity larger than c, and AFAIK you also can have a group velocity larger than c. What you cannot have is a signal velocity larger than c.

Re:WRONG!

[maxwell demon]

Actually it is already a misconception that particles are sucked in. Particles can fall in, but they also can orbit the black hole (as long as nothing else is in the way), just as they can orbit earth. If they get too close they no longer can orbit the black hole for the simple reason that they would need to go faster than light to do so.

Re:WRONG!

[Anonymous Coward]

Not to repeat what other replies are saying, but I think maybe you mean "In some mediums, charged particles can be found travelling faster than the speed of light in that medium". Are you thinking of cherenkov radiation?

Re:WRONG!

[maxwell demon]

For a non-rotating black hole in Schwarzschild coordinates, the radial vector inside the horizon gets timelike, that is, the singularity is not really "in the middle" but "in the future". This quite intuitively explains why you cannot go "outward": The "outward" direction is actually the past direction.

Now, Schwarzschild coordinates are not the full story, but neither are Eddington-Finkelstein coordinates (which obviously are what you had in mind). The complete structure of the Schwarzschild solution can only be seen in Kruskal coordinates, where you on one hand quite literally see that the singularity is in the future (for any world line starting outside the black hole and entering it), but you would still be able to evade it if you could travel faster than light (while in Schwarzschild coordinates it looks as if you'd have to travel backwards in time).

Anyway, light is not "bent towards the middle", that's only the result of non-ideal coordinates where the singularity appears spacelike while it is actually timelike.

For rotating black holes, things are more complicated (there are two horizons, the singularity is spacelike, but not a point, and inside the black hole there occur closed timelike curves).

Re:WRONG!

[Anonymous Coward]

Please explain time, please explain whether it is continuous or not. And if you have time explain further relative to this case :)
thanks

Re:WRONG!

[Chris Burke]

Light has momentum (which "require" mass in more classical thinking). Light is "moved" by gravity (which indicates mass)

Also light has energy which is mass in Relativistic thinking, and is moved by (and moves other things by) gravity which is due to it's energy (same as mass).

This is confusing because people think of "mass" as the things photons don't have and matter does (which is true if we mean intrinsic mass), but also think of "mass" as the thing which effects/is affected by gravity and makes objects resist acceleration, when that's actually the relativistic mass (= energy).

It's both a particle and a wave, thus *is* a particle.

A photon is a quantum mechanical particle, which is a thingie which behaves kinda like a classical particle and kinda like a classical wave but not exactly like either.

However the key thing about quantum mechanics is that stuff is quantized... like particles are. So we call them particles. There is no misconception in doing so.

Re:WRONG!

[Flamerule]

In some mediums, light moves faster than it does through a vacuum.

No, it doesn't. Not only does such a material not exist, it is proven beyond any reasonable doubt to be impossible.

Your statement would seem to be contradicted by this theory on faster-than-c speeds between 2 Casimir plates.

Re:WRONG!

[mestar]

It does not. It only looks that way due to the reactions with electrons.

You must also think that light travels in a straight line?

Re:WRONG!

[Anonymous Coward]

GR assumes time is continuous. There have been some theories that space and time may be quantized, but none so far have any great evidence pointing their way, and some have evidence pointing away from them when they were able to make predictions that are measurable. Further research on the topic is on going. Even if it turns out space-time is not continuous, it would probably only be relevant to small black holes, which is where the idea got a big jump when trying to deal with information theory and small black holes.

Re:WRONG!

[ThePeices]

c is a constant represents the theoretical maximum speed of light. The problem is that the speed of light is not constant. Light slows down in a medium.

meh, you are almost right.

C is a constant that represents the maximum speed of light *in a vacuum*.

That "in a vacuum" piece is quite important. The medium itself has no effect on the constant c ( constant is a constant), but each medium has its own value of light propagation speed which is *always* less than c.

Think of 'c' as the speed of reality.

Re:WRONG!

[ThePeices]

I take your reasonable doubt and counter it with un-reasonable doubt.

Thats more than enough for many people, sadly.

Re:WRONG!

[AK Marc]

That's your misunderstanding, not theirs. Particles are indeed "sucked in" (if by sucked in, we presume they mean "accelerated towards"). Yes, the language is messy, but the very fact they aren't using the technical terms indicates a manner of linguistic slop, and some allowances should be made.

If they get too close they no longer can orbit the black hole for the simple reason that they would need to go faster than light to do so.

So you are saying that the singularity curves time-space so much that you'd have to travel infinitely far to be able to leave a black hole, and speed is irrelevant. The light orbits the singularity inside the event horizon, and will never leave, nor contact the singularity itself. Or something like that.

Re:WRONG!

[AK Marc]

You must also think that light travels in a straight line?

Light thinks it does, just like standing on a trampoline and rolling a ball, the ball travels in a straight line, in a curve around you. Gravity curves space such that light travels in a straight line, and the universe curves around it.

Re:WRONG!

[AK Marc]

C is a constant that represents the maximum speed of light *in a vacuum*. That "in a vacuum" piece is quite important.

If there is no material in which light travels faster than C, then your clarification is irrelevant.

Re:WRONG!

[Anonymous Coward]

The propagation of the electric and magnetic fields slows down in bulk when going through media. It does involve the electrons the vast majority of the case, but that doesn't change that the light is actually slowing down. It is not like that light is simply bouncing between atoms except for when you get to light with really short wavelengths.

Light in a vacuum does travel in a "straight line" although the definition of straight line usually becomes a geodesic when dealing with curved surfaces.

Re:WRONG!

[Anonymous Coward]

There is a distinction to be made between sucking and pulling (as far as physics...). But for others trying to use that to make some point about gravity are missing the actual point. It is a leaping off point to describe the behavior of pressure and air, to give examples of how atmospheric pressure does useful things for us. That is where the distinction is pedagogically useful, and not so much insightful into gravity.

The light orbits the singularity inside the event horizon

The only place the light can fully orbit the black hole is exactly at the event horizon, and it is an unstable orbit that would be destroyed by any other near by matter. Once inside the event horizon, light cones all point inward to the point that even at the speed of light, you could not remain at a constant radius from the center.

Re:WRONG!

[taj]

Objects in Mirror are closer than they appear.

Re:WRONG!

[AK Marc]

The only place the light can fully orbit the black hole is exactly at the event horizon, and it is an unstable orbit that would be destroyed by any other near by matter. Once inside the event horizon, light cones all point inward to the point that even at the speed of light, you could not remain at a constant radius from the center.

So light slows down inside singularity? Because at the speed of light, it would be in a stable orbit at the event horizon, right?

And an unstable orbit is an orbit, still a "full" orbit.

Re:WRONG!

[Jesus_666]

Objects in Mirror are bluer than they appear.

FTFY

Re:WRONG!

[Anonymous Coward]

There is no inside the singularity, it is a 0 dimensional point or a 1 D ring in GR (which may be wrong about that and superseded by a new theory in the future...). And regardless, the speed of light is constant, both inside and outside the event horizon. If you look at an expression showing what speed is needed for an orbit, you get something below the speed of light outside the black hole (as long as it is in the same direction as a spinning black hole, or either direction for non-spinning black hole), the speed of light right at the event horizon, and above the speed of light inside the black hole.

And by fully orbit, I mean go in a repeating pattern around the black hole. You could in principle call the parabolic trajectory of an object dropped to the ground an orbit even though it intersects with the Earth, and in the same sense any trajectory within the event horizon will intersect with the singularity. The trajectory of any object or light within the event horizon will never return to the same radius as it previously was. The trajectory of light outside the black hole would only pass any given radius at most twice, absent a third compact object that could spin it back around. That would be analogous to a hyperbolic classical orbit, it goes in, either crosses the event horizon never to leave, or comes out to never come back to the black hole.

The only place that light can orbit, as in visit the same radial distance more than twice, would be exactly at the event horizon. But it is impossible outside of some deficit in GR to get light into such and orbit, and any light in such an orbit would leave the orbit in the presence of any other matter additional matter outside the black hole. That is why it is unstable, because the smallest push will change the trajectory into something that will never come back.

Re:WRONG!

[voidphoenix]

"speed of light" is meaningless -- because it's not a constant. Might as well talk about the "speed of a honda civic".

I thought "the speed of a honda civic" was "fast and furious"... :)

Re:WRONG!

[Neil Boekend]

So light slows down inside singularity? Because at the speed of light, it would be in a stable orbit at the event horizon, right?

Yes and no. Light doesn't actually slow down. Time does. If a photon, at 300.000 km/s, gets close to the event horizon time slows down, so while it may still move 300.000 km in a second, that second takes longer and longer to pass. At the event horizon it takes an infinite amount of time.
Therefore if you are looking at it from the outside (and if the light you are using to look with doesn't have these pesky relativistic effects we are talking about) you'd think the photon has stopped.
[/armchair physics without much official education in the direction]

Re:WRONG!

[Anonymous Coward]

So when Milamber (in one of the books of Feist) moves the Lifestone a bit into the future to make it undetectable (you're always a bit late. You just missed it) he risked creating a black hole?

Re:WRONG!

[Anonymous Coward]

It sucked because nothing ever showed up in the rear view mirror.

It sucked because nothing showed up, or nothing showed up because it sucked?
Was your Civic black?

Re:WRONG!

[Anonymous Coward]

"c is the speed of light in a vacuum"

But is it different depending on what sort of vacuum it is in?

EG would it be faster in A Dyson than in a Dirt Devil?

Re:WRONG!

[Anonymous Coward]

What's funny about this is if it isn't a constant, then why's it widely considered a limit?

When talking to the astrophysicists here, questioning their belief that the speed of light is unbreakable often gets the same reaction as questioning that the Bible happened to a fundamentalist Christian.

Science and religion really are two sides of the same coin.

Ironic captcha: tenant

Re:WRONG!

[Anonymous Coward]

Umm, there have been several tested and failed models of variations in the speed of light to account for various cosmological scale effects. Additionally, at the small scale, chances in the speed of light alone would have messed up spectroscopic data that we have a plethora of now showing it doesn't.

Re:WRONG!

[AK Marc]

If time slows to zero at the event horizon, then no matter could ever enter a black hole, right?

Re:WRONG!

[AK Marc]

The problem is that uneducated people hear terms and take them in the non-scientific meaning, which often conflicts with reality. Science is like all tech fields. Nobody outside the field knows or cares about the terminology. 10 Gbps fiber is "baseband" and 128kbps DSL is "broadband" from the original definitions. But idiots misused the terms so much that the field gave up and neither term has any meaning anymore beyond "broadband" means "feels fast" and "baseband" means the floorboard that holds your carpet in place, or whatever "regular" people think of when they hear it.

The current scientific models seem agree that nothing can be accelerated from below the speed of light to above it, nor decelerated from above the speed of light to below it. There is nothing that indicates that nothing may travel faster than the speed of light, just corollaries that indicate that if anything is, we'd never be able to detect it. That you don't understand that (or are lying about what you believe) doesn't change reality, or what it's widely considered to be.

Re:WRONG!

[Anonymous Coward]

From the frame of reference of a distant observer, it appears no matter crosses the black hole. Instead, the matter gets closer and closer, but more and more red shifted, so it will still essentially disappear from view as all emissions are red shifted way into the radio region and emitted energy drops.

This comes about because essentially all observation from a distance needs to be carried by a signal that is at the speed of light or slower. When climbing out of the gravitational well removes a lot of energy from the photons, so they get red-shifted. And for more difficult to explain reasons, the speed of light is still the same, instead the meaning of distance gets messed up from such a point of view, so it is as if the signals are having to travel from very far, but still at the speed of light.

From other frames of references, things will cross the event horizon with no change, and particularly from the view of something falling into the black hole, the center is reached in a short, finite time.

Re:WRONG!

[AK Marc]

The next question that brings up is, "What is the minimum energy of a photon?"

Re:WRONG!

[maxwell demon]

I don't know the book (I hope I don't have to hand in my geek card because of this :-)), but if the Lifestone is a bit in the future, shouldn't you be a bit too early? If I arrive at the place where an event shall happen, and the event is ion the future, I'm too early. If I'm too late, the event is already in the past.

Anyway, in the Schwarzschild solution, the singularity being in the future means you will get to it, because you simply cannot avoid going to the future.

Re:WRONG!

[maxwell demon]

Well, in General Relativity time is continuous, and it is a dimension of spacetime. Spacetime is four-dimensional, with three space dimensions and one time dimension. Actually the time dimension only differs from the space dimensions by the sign in the metric (which basically means that as soon as time is involved, things are often reversed to what we are used in space, but the important part is that it makes it impossible to rotate the time dimension to a space dimension or vice versa; the metric is basically an onject which tells us how to measurte distances and angles). Also, while there are three space dimensions, there's only one time dimension (this makes it impossible to just turn around in time, as we can do in space). Note that this doesn't mean there's only one time direction; you can rotate the time axis in spacetime. That's known as boost; it's exactly what you do if you accelerate. Note that this is even true if you use a Newtonian spacetime, as one can easily convince oneself by simply drawing the world lines (i.e. the line describing at which place an object is at each point in time; to draw it, you certainly have to remove at least one spacial dimension). What's new in Special Relativity (which basically is a special case of General Relativity, namely the case of flat spacetime) is that also the space axis is turned on a boost, and in a way that the speed of light is the same in both systems. The time which elapses for you between two events is just the length of the world line (measured with the space time metric, with the different signs for space and time coordinates). Due to the different sign, the direct way is the one which takes the most time (unlike in space, where a detour makes the way longer). That's basically because if you detour in space, the change in the orthogonal direction adds to the distance, while for time, it gets subtracted (actually it's in the square of the distance where this addition/subtraction occurs, but the qualitative effect is the same: Moving in other dimensions at the same time adds to a length of a spacial path, but subtracts from the elapsed time, which is the length of the world line). This difference is generally known as twin paradox (the travelling twin makes the detour, and therefore he needs less time, and thus is younger than the waiting twin when he returns).

Now General Relativity adds to the mix that the spacetime is curved (and the curvature depends on the energy and momentum of the matter inside). That works in principle the same way as for example the curvature or earth's surface. For example, imagine two people meet somewhere at the equator, and one goes 5000 km west, and then 5000 km north, while the other first goes 5000 km north, and then 3535.5 km west. Then they get (approximately) to the same place, although the second one has gone a shorter distance. Quite similarly, someone going closer to the black hole and then remaining there will need less time than someone first waiting far away from the black hole and only then going close to it to meet the other one.

Note that the analogy goes even further: After going first north and turning west, to keep going west you have to constantly turn right (i.e. to accelerate in the direction of the pole). If you just went straight on, you'd start moving southwards, as if the pole would push you away. The acceleration causes you to keep at fixed distance from the pole. Similarly, the observer going close to the black hole (assuming he does not orbit it) has to accelerate away from it to not fall in; again this is the effect of curvature (of spacetime in this case). However spacetime around a black hole is curved in a way to make unaccelerated motion go towards it instead of away from it, thus the acceleration has to go away from it (orbiting is another way to keep from falling in; this option is not available in the earth surface analogy).

Re:WRONG!

[Anonymous Coward]

In principle you could probably have a photon with a wavelength comparable to that of the observable universe, which would give an energy of almost 10^-52 J and associated with a temperature of 10^-29 K. Constructing an antenna or object that efficiently couples at that wavelength and sticks around long enough for attohertz frequencies might be another issue, and there is probably a lot of junk in the way further hindering that, even assuming there is not some unknown effect over such large distance scales that would block it.

For stuff falling into a stellar sized black hole though, it would quickly red shift out of view. Within one second, visible light would be redshifted to frequencies on the order a few Hz, which would have a wavelength larger than the black hole. After about an hour or so you would reach wavelengths on the size of the universe, and after about a day even high energy gamma rays would be redshifted to such an extreme value. (For a large black hole, like the one at the center of the galaxy, multiply these time scales by 10 million).

I would have to think for a while about the implications are of releasing a photon with that large of a wavelength is. Although I don't know how much it would matter, as it may very well just be easily absorbed by any intermediate matter, and if not, would be too weak to detect anyways. You could have something as outputting equivalent to the total luminosity of the milky way galaxy, and it would come out weaker than a light bulb at the same point that the 180 billion light year photons are coming out.

Re:WRONG!

[Anonymous Coward]

There might be a misconception about particles. The idea that material can be broken down to indivisible particles dates back to Aristotle. In the 20th century we proved that, well, actually, "atoms" aren't indivisible at all; there are electrons. The Plum Pudding model gave way to the Bohr model, which postulated that actually these atomic "particles" are mostly empty space and the electrons orbit the positive core in an eliptical pattern. But really that's it, the protons and electrons and neutrons are the elementary particles.

Oops, looks like there are smaller particles. And it looks like those smaller particles are made up of even smaller particles, and so on.

It wouldn't surprise me in the least if, as it turns out, everything we think is a "particle" is just a whirlpool in an all-expansive medium. This would make our current model of physics completely wrong, and it wouldn't be the first time in history that this were the case.

Re:WRONG!

[Anonymous Coward]

It is not like they haven't and are not continuing to test and look for structure of current fundamental particles. There have even been proposals for possible component parts, but they don't quantitatively hold up. The electron has been confirmed to be structureless down to a scale of at least 10^-22 m. The electron does interact with a soup of virtual particles, but the impact of that on electrons has been known for some time and the base theory, quantum electrodynamics, has been incredibly accurate quantitatively. The equivalent for exploring proton and neutron structure and interaction of quarks, quantum chromodynamics, is much more mathematically and computationally challenging, and the upper bound on their size or substructure size lags behind a couple orders of magnitude from the electron.

For comparison, the size difference between the size of an atom and that of a proton is about four orders of magnitude. Any structure to quarks would have to be at least another four or five orders of magnitude smaller to have not been seen by previous efforts, and another four orders of magnitude smaller for structure of an electron.

Re:WRONG!

[Bengie]

Light in a vacuum is the fastest speed

Light between the Casimir plates is less c

Some particles can move through a medium faster than light can move through said medium

The particles are not moving faster than c, just faster than light in that medium.

Strange stuff still happens, but still does not violate c.

My thought...

[kannibul]

My thought has always been that black holes are black because the particles they are made from move faster than the speed of light, therefore don't give off light radiation...same with the theory of Dark Matter/Energy....they all contain particles that have aspects that move FTL, and when crossing the FTL barrier means not that it doesn't have mass, that it abnormal mass... But what do I know, I'm not a scientist, or really all that smart. Meh...one of those theories I came up with decades ago after watching too much discovery channel.

Re:My thought...

[dreamchaser]

You might as well say it's because they are made of rainbows and ponies unless you have math to support your theory.

Re:My thought...

[Talderas]

They are obviously made of strawberries and unicorns.

Re:My thought...

[Anonymous Coward]

No, the almighty flying spaghetti monster sprinkled Parmesan cheese into the universe to create stars, and shed meatballs to make black holes.

Re:My thought...

[Anonymous Coward]

But what do I know, I'm not a scientist, or really all that smart.

In the future, you should probably focus more on that and less on coming up with novel physical theories.

Re:My thought...

[PhxBlue]

They are obviously made of strawberries and unicorns.

I can't prove they're not, so it must be true! </sarcasm>

Re:My thought...

[maxwell demon]

My thought has always been that black holes are black because the particles they are made from

Black holes are not made from particles. Black holes are vacuum. Curved vacuum, that is. Yes, that's hard to understand, because our brain was not made to deal with this. But that's what the mathematics says.

move faster than the speed of light, therefore don't give off light radiation

A charged particle does emit light radiation when going faster than light. This can be observed in a medium (e.g. water) where the speed of light is slower than in vacuum, so particles there can indeed go faster than light (but still not faster than the vacuum speed of light). That radiation is known as Cherenkov radiation. It is the optic analogue of the sonic boom. If the particles could go faster than light in vacuum, they'd emit that radiation also in vacuum.

Uncharged particles would not emit Cherenkov radiation, however uncharged particles don't emit light radiation no matter what their speed is.

Spin equal to mass?

[justthinkit]

Could the near light speed rotation of the SMB be equivalent in some way to having extra mass at the core of the galaxy? In other words, does this change how much dark matter there must be?

Re:Spin equal to mass?

[justthinkit]

Apologies for self-replying...
.

In other words, if a lot of SMB material is moving at close to the speed of light, then this would cause a significant mass increase due to this relativistic effect and so the overall mass of the SMB would be significantly higher...helping to explain the current rotational speed of the stars around the center.

Re:Spin equal to mass?

[Anonymous Coward]

No. Black holes are not dark matter. Well, I mean, yeah, they are dark. Like black dark. Like "how much more dark could they be? None, none more dark." But they are normal matter, not dark matter. The mass of (nearby) galactic core black holes is easily measured by measuring the speed of closely orbiting stars. Their velocity is entirely dependent on the mass inside their orbit, so no need to invoke dark matter.

Re:Spin equal to mass?

[Antipater]

In addition to what the AC said below, it's my understanding that the galaxy rotation problem is a matter of mass distribution, rather than just plain missing mass. Adding more mass to the black hole in the center would make all the stars orbit more quickly, but it wouldn't affect the relative rotational speed from one star to another. In a system where most of the mass is clustered in the center, the outer orbits should have a lower rotational velocity - simply changing the amount of mass at the center won't change that general idea. To explain the uniform speeds going outward from the center, you have to add mass to the edge of the system, rather than the center.

Re:Spin equal to mass?

[jkflying]

How about a bunch of black holes which are distributed around the edge of the galaxy?

Re:Spin equal to mass?

[TheTurtlesMoves]

Lots of ideas here. Why don't you run the numbers? Turns out if you do neither of these get close to explaining galatic rotation or other "dark matter" stuff. The facts are that from what we observe, the best explanation/theory right now is dark matter.

Re:Spin equal to mass?

[TheTurtlesMoves]

then this would cause a significant mass increase due to this relativistic effect.

Sorry no. Relativistic mass increase is not the same as rest mass. So no, when get a particle close enough to the speed of light and it stops accelerating. Its local gravity is determined by its rest mass not its relativistic mass.

Re:Spin equal to mass?

[Antipater]

?

What I was describing was a layman's perspective of dark matter. Or are you saying that dark matter doesn't explain galactic rotation or other "dark matter" stuff? Not snark, I honestly can't tell.

Re:Spin equal to mass?

[Chris Burke]

Its local gravity is determined by its rest mass not its relativistic mass.

No. Gravity is determined by the stress-energy tensor, and the energy component is total energy, aka relativistic mass (literally, they're the same thing). Relativistic mass is the gravitational mass is also the inertial mass.

A proton's mass -- the ratio between its acceleration and the force exerted by an electric field -- is much higher than the intrinsic mass of the quarks that make it up. It's the kinetic energy of those quarks held together by the Strong Nuclear Force that gives a proton 90% of its mass. The Higgs Field only explains that last 10%.

Similarly the gravity of the sun is far greater than just the intrinsic mass of the quarks and electrons inside it. It's the sum of all energy in the sun.

If you an accelerate an object it gains energy, and therefore (E=mc^2) relativistic mass, and also therefore increased gravity.

Oh, and yes, this means photons have gravity. Not are affected by gravity (though of course they are) but exert it.

Re:Spin equal to mass?

[Chris Burke]

What you said was quite correct.

I'm not sure what they were saying. I think maybe they meant to reply to justthinkit who was actually proposing an alternative?

Re:Spin equal to mass?

[zAPPzAPP]

If dark matter is subject to gravity (which I assume it is, if it's a source of gravity itself), then wouldn't some of it eventually end up inside black holes too?
In that case dark matter would not be able to escape from within the event horizon, just like anything else, right?

Re:Spin equal to mass?

[Anonymous Coward]

They're really dark suckers.

Re:Spin equal to mass?

[pantaril]

No. Black holes are not dark matter. Well, I mean, yeah, they are dark. Like black dark. Like "how much more dark could they be? None, none more dark." But they are normal matter, not dark matter. The mass of (nearby) galactic core black holes is easily measured by measuring the speed of closely orbiting stars. Their velocity is entirely dependent on the mass inside their orbit, so no need to invoke dark matter.

You are right that we can measure the mass of black holes pretty well so this discovery would probably not lead to any new insight about the origin of dark matter. (or in other words: the missing mass in our universe).

But your statement that black holes are composed of 'normal matter' is slightly inaccurate. Black holes are formed mainly from normal "baryonic" matter (protons and neutrons) but when this matter is absorbed by black hole, it is stripped of all it's properties expect mass, charge and momentum. So theoreticaly, black hole could be formed from more exotic types of matter or even just from photons/radiation. On the outside, it would alway look the same. This is called No Hair theorem.

Re:Spin equal to mass?

[justthinkit]

So, to my original question, does the calculated mass of our SMB, plus the relativistic mass (not sure how anyone will calculate this -- what percent of the SMB is rotating at what % of the speed of light) equal enough to explain the motions of the stars?

Re:Spin equal to mass?

[Anonymous Coward]

No, no amount of added mass at the center of the galaxy can explain the rotational profile of the motion of the stars with current theories. The motion requires either modifications to the theory of gravity, or mass located at places besides the center of the galaxy. And unfortunately, all attempts at the former that can explain the rotation profile of stars screws up somewhere else, unlike the dark matter explanation. And other black holes are unlikely to be a source of such matter, as searches looking for distortion of the light from stars due black holes passing in between places an upper bound on the number of black holes roaming the galaxy that is too small to account for the matter.

Also, we already have a good idea of the mass of the black hole at the center of the galaxy by observing its effects on nearby stars (as in a few tens of light years).

Re:Spin equal to mass?

[Chris Burke]

What the AC said as to why the SMBH can't explain the galaxy rotation curve -- the problem is that the curve is flat, meaning the orbital velocity doesn't decrease with distance from the center as one would expect regardless of the amount of mass at the center. See the graph on the right, here. All increasing mass at the center would do is change the values on the Y-axis. The curve shape would be the same.

As far as measuring the relativistic mass goes -- turns out that's easy! Put an object on a scale, and you are measuring its relativistic mass. Measure the gravitational force exerted on some object by another, and you are measuring it's relativistic mass. All of your everyday notions of what "mass" means and the ways in which you measure mass are measuring relativistic mass.

It's actually figuring out the intrinsic mass that's hard. And for a black hole, it's both impossible and irrelevant. The properties of a black hole do not depend at all on the intrinsic mass of whatever went into it. In fact it was proven that in General Relativity that you can't tell what made a black hole, or what has gone into it since, by observing the black hole. The resulting object is the same regardless. This is called the "no hair" theorem for what I'm sure are hilarious historical reasons.

one question

[Anonymous Coward]

But does it run Linux?

Re:one question

[gameres]

do black holes blend?

Re:one question

[Anonymous Coward]

do black holes blend?

The Mixmaster singularity might.

light is influenced by gravity

[Anonymous Coward]

http://helios.gsfc.nasa.gov/qa_sp_gr.html

" Yes, light is affected by gravity, but not in its speed. General Relativity (our best guess as to how the Universe works) gives two effects of gravity on light. It can bend light (which includes effects such as gravitational lensing), and it can change the energy of light. But it changes the energy by shifting the frequency of the light (gravitational redshift) not by changing light speed. Gravity bends light by warping space so that what the light beam sees as "straight" is not straight to an outside observer. The speed of light is still constant."

Dr. Eric Christian

Re:light is influenced by gravity

[Westwood0720]

I knew it was something along the lines of that. I recall something about during one of the World Wars a telescope being confiscated for thoughts of being spies, but was given back the day before some astronomers wanted to view the stars behind the sun during a solar eclipse. They did in fact able to see the stars behind the sun showing the world that the sun's gravity bent the light the went around it. This may not be 100% accurate, but I know its something along those lines.

Seems obvious to a naive engineer!

[140Mandak262Jamuna]

In my limited understanding of these things, (mostly from articles meant for mass consumption, not scholarly journal papers), I imagine a black hole to be so massive not even light can escape its gravitational pull. Which technically means the escape velocity is the speed of light. So anything at the event horizon should be at the speed of light. This is of course, a naive view. The escape velocity is based on Newtonian, not Relativistic, physics.

Re:Seems obvious to a naive engineer!

[Anonymous Coward]

ARGGG!!!! Light not escaping a black hole has NOTHING to do with it's gravitational pull. Light has no mass. Multiply any number by zero and you always get zero.

Re:Seems obvious to a naive engineer!

[marcosdumay]

Only if that thing is orbiting at the event horizon, what is another way to say that nothing can orbite there. If the object is just falling, it can be slower.

Re:Seems obvious to a naive engineer!

[Anonymous Coward]

Light doesn't have a rest mass, but it most certainly has momentum. Perhaps you need to review what E=MC^2 means, Light is affected by gravity as witnessed numerous times in astonomy. Perhaps your "ARGGG!!!" should be directed at yourself.

Re:Seems obvious to a naive engineer!

[Anonymous Coward]

Light is affected by the warping of space-time. If you want to talk about relativity maybe you need to learn it yourself.

Re:Seems obvious to a naive engineer!

[Anonymous Coward]

Please feel free to explain the difference between gravity and the warping of space-time by massive objects.

Re:Seems obvious to a naive engineer!

[Anonymous Coward]

Uh, gravitational pull and the warping of time-space, although have the same base cause, are different effects. Sorry if this is a hard concept for you and some of the moderators around here. Go ask an astrophysicist, they'll tell you the same thing.
 
Fuck it, you're probably not smart enough to Google this shit for yourself. I'll just point the way.
 
Was that easy enough for you to understand, fucktard?

Re:Seems obvious to a naive engineer!

[ceoyoyo]

No, what you said is insightful. IIRC, anything freely falling into a black hole from infinity would arrive at the event horizon travelling at the speed of light. You're also perfectly free to calculate an escape velocity based on relativity. But this measurement is an (indirect) measurement of the rotation (or at least the angular momentum) of the black hole, not the accretion disk.

Re:Seems obvious to a naive engineer!

[SpazmodeusG]

You seem to be unaware of the definition of gravitation.

The effects of the warping of space-time by mass is called gravitation. Your "OMG it's not gravitational pull it's the warping of space-time" line of argument makes no sense considering that gravitation is simply the name we give the warping of space time by mass.

Re:Seems obvious to a naive engineer!

[Anonymous Coward]

I'll even make it more clear for all the dumb fucks who argued with me and all the mods who just promoted bad science:
 
  Enter Albert Einstein. In 1915 he proposed the theory of general relativity. General relativity explained, in a consistent way, how gravity affects light. We now knew that while photons have no mass, they do possess momentum (so your statement about light not affecting matter is incorrect). We also knew that photons are affected by gravitational fields not because photons have mass, but because gravitational fields (in particular, strong gravitational fields) change the shape of space-time. The photons are responding to the curvature in space-time, not directly to the gravitational field. Space-time is the four-dimensional "space" we live in -- there are 3 spatial dimensions (think of X,Y, and Z) and one time dimension.
 
I am so sick you you dumb geek cunts acting like you know shit about something when it's obvious that you don't. You've spread misinformation, you've fucked up. Yet you'll hold your head up proud and will likely continue to spread your bullshit while patting yourself on the back because, in your own little minds, you're the smartest kids in the room. Fucking learn how to use Google. Fucking learn the science instead of thinking that a couple of shows on TV is a real science education. You're fucking dumb and you shouldn't have any mod points for being a fucking fucktard. It just floors me how much you same bitches shit on anything you think is outside of your precious "nerd" circles when it turns out you don't speak the truth any more than anyone else and you don't give a shit to take the time to confirm your bullshit instead of coming off like a smart ass.
 
Go back to reading comic books and watching shitty sci-fi movies. Apparently that's where your "science" education comes from.

Re:Seems obvious to a naive engineer!

[Anonymous Coward]

I find it amusing that the article you linked says we haven't been able to measure a photon's mass, but that it might be as high as 4x10^-48 grams.

Also, I'm a different AC, but I'm still not convinced, based on what you've linked and other articles I read, that gravity != space-time curvature, where for certain conditions Newton's law of universal gravitation applies (but not when talking about light, obviously). I don't see gravity being rigidly defined as the force calculated from Newton's law anywhere. At most, you might say that gravity is caused by space-time curvature, but I've never seen any words besides yours that say gravity and space-time curvature are different effects of the same cause.

In any case, it's not very useful to split hairs about stuff like this. Even general relativity is an approximation, since we know it breaks down at the quantum level and at event horizons.

Re:Seems obvious to a naive engineer!

[Anonymous Coward]

I'm guessing you didn't follow the conversation and probably didn't bother to read the cited article either. Again, gravitational pull (which works with mass) and the warping of time-space are not the same effect. They have the same cause but they are not the same effect. The OP used the term "gravitational pull". This is categorically false.Why can't you understand this?
 
And if you want to debate it some more go find an astrophysicist who agrees with you that gravitational pull and the warping of space-time is the same effect and I'll consider it. Until then go back to your armchair political debating. You don't take the science seriously enough to be willing to understand the systems that science represents.

Re:Seems obvious to a naive engineer!

[meglon]

Yeh, the article seems to imply it's a direct measurement, when it's not. And i agree, the OP made a very insightful comment on what can be a really tough thing for a lot of people to grasp.... and me without mod points /sigh.

Re:Seems obvious to a naive engineer!

[Anonymous Coward]

The photons are responding to the curvature in space-time, not directly to the gravitational field.
 
You really don't read this as the warping of space-time isn't the same thing as the gravitational field? Ok. You use a bit of good rhetoric to your credit but this pretty much says that the curvature of space-time is what the photos are reacting to, not the gravitational field. Gravity is the base effect of the two phenomenon but they're not the same thing.
 
As far as the mass of a proton, all they are saying is that if a photon has mass that we haven't found it yet and we're pretty far down as far as what we know about what the mass isn't. There still isn't a shred of evidence to suggest that photos have mass.

Re:Seems obvious to a naive engineer!

[Anonymous Coward]

Um, no from your "evidence" link

"The strong gravitational field of the star changes the paths of light rays in space-time from what they would have been had the star not been present"

So, you originally say "Light not escaping a black hole has NOTHING to do with it's gravitational pull." then use a source which says " gravitational field of the star changes the paths of light rays"

You busted yourself

-- MyLongNickName

Re:Seems obvious to a naive engineer!

[rocket rancher]

In my limited understanding of these things, (mostly from articles meant for mass consumption, not scholarly journal papers), I imagine a black hole to be so massive not even light can escape its gravitational pull. Which technically means the escape velocity is the speed of light. So anything at the event horizon should be at the speed of light. This is of course, a naive view. The escape velocity is based on Newtonian, not Relativistic, physics.

In Einstein's theory of general relativity, the Newtonian concept of mass doesn't really exist, being spread out over the Einstein curvature tensor on one side of the general relativity equation and the stress energy tensor on the other. Calculating the radius of a gravitational field where the escape velocity is equal to c is straight forward in both Newtonian mechanics and general relativity, and produce the same value, the so called event horizon (Scharzschild radius, technically) but something interesting happens when the gravitational field is generated by a rotating object -- it drags spacetime around with it. This would cause the orbital plane of an object to precess, something that Newtonian mechanics completely misses but was predicted nearly a century ago when people first started exploring solutions to Einstein's equations. Being able to directly arrive at the rotational rates of a wide variety of blackholes (which is what this announcement is all about) means that both frame-dragging and the no-hair conjecture concerning the characterizability of blackholes with just three Newtonian values -- mass, charge, and angular momentum -- can in principle now be studied more rigorously.

Re:Seems obvious to a naive engineer!

[Anonymous Coward]

You can start with the classic text on the matter:
http://books.google.com/books?id=w4Gigq3tY1kC&printsec=frontcover#v=onepage&q&f=false

Gravitation is how matter warps spacetime. There's no distinction to be made between that and gravitational pull. Next time do your own research before going off on some rant about how no one takes this seriously. Or better yet, listen when a crowd of educated people are telling you you're a dipshit.

Re:Seems obvious to a naive engineer!

[Anonymous Coward]

And if you want to debate it some more go find an astrophysicist who agrees with you that gravitational pull and the warping of space-time is the same effect and I'll consider it.

I am a physicist, and those effects have become synonymous under GR. One of the major important results of GR is that gravity now has a geometric description, and that any object in free fall/force free movement follows a "straight line" which is updated to include the concept of geodesics over a non-flat space. The only difference the mass makes is how much inertia the object has and what gravitational field it itself creates , otherwise photons and any other particle following geodesics is the same concept (and the components of the stress energy tensor don't distinguish between energy from rest mass from kinetic energy, or distinguish between photon's ability to carry momentum or a massive particle's ability to do so).

Re:Seems obvious to a naive engineer!

[RandomStr]

...I imagine a black hole to be so massive not even light can escape its gravitational pull. Which technically means the escape velocity is the speed of light. So anything at the event horizon should be at the speed of light. ...

Also consider that at the event horizon, space-time itself is travelling at the speed of light towards the black hole.

So when the medium light is travelling through is travelling at the speed of light, light can't escape; i.e. the event horizon...
Think swimming upstream when the current is faster than you can swim; the steepness of the hill has little consequence.

Having said that, I'm also not a physicist, but I also came that same conclusion...

Re:Seems obvious to a naive engineer!

[Sigg3.net]

My understanding is less limited, and I think black holes (or African American holes) is more like picking up the phone and it's your mother-in-law.

There is no escape.

While Event Horizon is a great sci-fi/horror from 1997.

Re:Seems obvious to a naive engineer!

[Bengie]

It doesn't matter.. pun? Gravity bends space, not "pulls in matter". A black-hole is pulling in space at speeds greater than c, which means light cannot escape.

Nothing can move through space faster than c, but space itself can move faster than c. How do you think the universe expanded to its current size in less time than it takes for light to move through it? Big bang happens, and then space expands much much faster than c, giving us our cosmic background radiation.

Re:Seems obvious to a naive engineer!

[Anonymous Coward]

Your quote doesn't differentiate between how gravity works on photons and how it works on things with rest mass... because it is the same, both respond to the curvature. And it is wrong to differentiate between such curvature and the gravitational field, as in GR the gravitational field is the Einstein tensor, which is a direct expression of space-time curvature. That is different and more complicated than how people think of the previous Newtonian gravitational field, but it still comes down to just one effect in GR.

Apparently that's where your "science" education comes from.

My education came from getting my PhD in physics with an emphasis on astrophysics, plus years of experience working on relativistic plasma physics modeling of accretion disks. The bigger question is not where you education came from, but where your attitude and zeal toward an idea that turns out to be a mistake.

Re:Seems obvious to a naive engineer!

[Anonymous Coward]

anything falling into a black hole from infinity, would never arrive at the event horizon.
Dammit. infinity and singularities are nothing more than broken mathematical models. Stop projecting them into the physical world.

Re:Seems obvious to a naive engineer!

[Anonymous Coward]

Anything falling into a black hole from inf^H^H^H really far away, would never arrive at the event horizon*, which, quite some time ago, has been shown not to be a singularity with the appropriate coordinate choice.

* As seen by someone else far away, because light signals take longer and longer to get to them as the source approaches the event horizon. From a local observer in or near the falling object, they would see it falling in just fine.

Keep going...

[mynameiskhan]

it is just that our warp tech is not yet caught up with your honda civic.

I'll belive it when I see it.

[Anonymous Coward]

Moving close to the speed of light relative to what?

As with most deep space observatiosn and calculations.... They are all built from a house of cards. Too many assumptions and too many variables. We may soon actually find out that the edge of a blackhole is not moving at all instead of at the speed of light and then a few tweaks to the first theory or a few assumption and bam, yep, now we think its not moving at all.

Re:I'll belive it when I see it.

[MozeeToby]

If conservation of momentum is preserved (and arguing that it isn't would... well, quite an extraordinary claim) black holes, and the stuff falling into them, are going to be rotating. Unless, I suppose if everything collapsed absolutely, completely, perfectly symmetrically; to an accuracy 1 part in several millions of billions). And even then, as soon as matter starts flowing in the rotational momentum is going to start climbing.

People have it in their heads that since science is wrong in the past, science will be just as wrong in the future. But there are certain things that just aren't going to change, and the laws of conservation of mass/energy and momentum are one of them.

Re:I'll belive it when I see it.

[Bengie]

We know it's rotating at some fast rate because the swirling of space puts stress on the matter and causes it to emit radiation. Swirling is caused by rotation.

Re:I'll belive it when I see it.

[Anonymous Coward]

The infalling matter will swirl on its own, as it is unlikely to get matter falling into a black hole that is perfectly symmetric, so you have some angular momentum to deal with. And since angular momentum will result in orbits and is not something you can just make disappear, you will accumulate a whole bunch of stuff into the accretion disk because it has too much angular momentum to just fall in. Instead, for stuff to fall in requires a process of transferring angular momentum between stuff in the disk, so that some matter looses the momentum and falls in, while other gains it and moves farther out (or is flung out in the jets). The light (x-rays) comes from friction and viscosity heating up the plasma in the accretion disks in this process (it doesn't all spin at the same rate).

Additionally, usually there is a point which orbits become unstable when you get too close to the black hole, but before the event horizon, so in the most immediate area around the black hole, there is a lot less stuff in the disk withing a certain radius. What the black hole rotation does is change the close by paths of light. It is easier for light to swing around the black hole in the same direction as the rotation instead of against it. So what they are looking at is for the change in the x-ray spectrum due to how light emitted by the accretion disk gets bent and dragged around. That light and disk would have been there without any rotation of the black hole too.

Information across the event horizon?

[Bugler412]

Not a physicist of any kind, but I had thought that information could not cross the event horizon? If that is true, then how can we construe that the speed of matter near the event horizon indicate the speed of rotation of the black hole? Wouldn't it only indicate the speed of that particular matter? Educate me if I'm wrong!

Re:Information across the event horizon?

[ceoyoyo]

You can measure a few properties of black holes. Their mass, charge and angular momentum. All three of these can be observed by the effects they have on nearby matter. The article isn't precisely clear, but I think they're measuring angular momentum by looking at the effect frame dragging has on absorption spectra in the accretion disk.

Re:Information across the event horizon?

[TheTurtlesMoves]

A spinning black hole is distinct because the way space time is draged with the spinning. Basically the only 2 properties left with a black hole is mass and spin.

But the real question is

[Anonymous Coward]

How do relativistically spinning black holes contribute to global warming, and what can we do about it?

Re:But the real question is

[gmuslera]

Probably the CNN question would be if supermassive black holes are caused by global warming or maybe that they started to rotate so fast due to global warming. Anyway, small things after they ask if the bing bang was caused by global warming.

Re:But the real question is

[maxwell demon]

Anyway, small things after they ask if the bing bang was caused by global warming.

Well, at the big bang, it was extremely hot everywhere in the universe. So how could that have happened except by global warming? :-)

Rotation speed limiting density?

[Bohnanza]

TFA mentions a fact that I'd read about before, that the black hole's rate of rotation increases as it collapses due to the conservation of momentum. But since no matter can actually mover faster than the speed of light, is the collapse limited by this maximum rotation rate? Would the black hole cease collapsing when the rotation rate neared the speed of light?

Re:Rotation speed limiting density?

[MozeeToby]

Matter speeds up as the black hole collapses because it moves toward the center of gravity, trading potential energy for kinetic. There's no (practical) limit to the amount of kinetic energy a piece of mass can have, if I have a baseball moving at 99.99999999% the speed of light, I can continue to accelerate that baseball to my heart's content. Though it's acceleration will appear, to an outside observer, to slow down, a baseball's energy will continue to climb at the same rate. The same is true for the particles falling into a black hole.

Re:Rotation speed limiting density?

[Anonymous Coward]

No, the speed of light does not limit the angular momentum of a black hole.

Car analogon: Suppose you can accelarate your car infinitely with a constant acceleration. Does that limit the momentum the car can achieve? No, otherwise the conservation of momentum would be violated. The momentum p = m*v can be increased infinitely, but at relativisitc speeds (v is close to c), an increase of momentum does no longer mean an increase of the velocity v (which will always be smaller than c), but an increase of the mass m.

Re:Rotation speed limiting density?

[maxwell demon]

Actually there is a maximum angular momentum for a black hole (depending on its mass). However that's independent of how that hole was formed. If the angular momentum is larger than this maximum value, you'll get no hoizon, but a naked singularity (with closed timelike curves around it, allowing time travel).

However the bad news is that you cannot spin up a black hole beyond this value. Well, maybe it is good news, after all; who knows what sort of nasty stuff we'd get from there otherwise ... ;.)

Re:Rotation speed limiting density?

[Anonymous Coward]

First, for a uniformly collapsing star, there is a limit to how much it can spin up a black hole in the process and still continue to collapse. An upper bound for this has been worked out and it is less than the absolute maximum rotation speed. You can continue to speed up the black hole by by flinging matter at it (just not radially), however, the limit coincides with the point where you would have to fling the matter faster than light to add angular momentum.

simple explanation for engineers...

[Anonymous Coward]

Light (photons) have no mass. Mass will deform the space-time fabric around the object creating a well of sorts. This "space-time well" can be very "deep" for a black hole because is so massive. So deep it can trap light.

The article talks about the implicit spin of a black hole. It is implicit because it can't be measure directly. It is based on the amount of photons (i.e. X-rays) it emits and the difference of those emissions when the black hole is not rotating, is rotating against the debris spiraling into it (accretion disk), or is rotating with the debris spiraling into it. There seems to be correlation between those emissions and the the rate and direction of rotation relative to the accretion disk.

Too simple?

[bughunter]

FTA:

Imagine a sphere more than 2 million miles across - eight times the distance from Earth to the Moon - spinning so fast that its surface is traveling at nearly the speed of light. Such an object exists: the supermassive black hole at the center of the spiral galaxy NGC 1365.

If it were a rigid body,

Rotation Rate omega = Tangential Speed nu / 2pi * Radius r = 186 280 mi/s / 6.2832 * 2e6 mi = 0.014824 cyc/sec = 0.88942 cyc/min

Roughly one revolution per minute. Not an amazing rotation rate for objects of scales we're used to, but for something 2 million miles across it's pretty impressive.

Now, an event horizon is anything but a rigid body, so I could be waaaaay oversimplifying. But the article says "imagine a sphere..."

Anyone care to extend the math to apply to something other than the theoretical physicist's favorite imaginary object?

Re:Too simple?

[meglon]

The event horizon is nothing more than a point in space determined by the mass of the singularity inside it, so thinking of it as something tangible, while it may help to visualize it, really doesn't do justice to what's really going on. Consider, everything inside that threshold is revolving around the central point as well, including the empty "space."

Definitely a place you'd want to bring a camera to.

Re:Too simple?

[Neil Boekend]

But not a too expensive one, because if you drop it it'll surely get damaged.

Thought experiment

[PhxBlue]

If I were to build a disc with its inner ring located near (but not inside) the event horizon of this black hole, and an outer ring located a few million kilometers away, at what speed would the outer section of the disc spin? What would happen along that outer edge?

Re:Thought experiment

[bughunter]

It would be ripped to shreds by tidal and frame dragging forces, heated to millions of degrees by frictional heating, emit some very lively photons, and the resulting plasma would become part of the accretion disc.

And this is assuming you could even get it in place without the same result befalling the construction crew, their equipment, and raw materials.

Re:Thought experiment

[bughunter]

Oh, and also, you'd never live to see the completion of the object because time dilation caused by the mass of the singularity would cause all motion near the event horizon to slow to a virtual stop, as seen by an observer at a reasonably safe distance.

Of course, you can always go visit it yourself to check on the progress... we won't wait for you, though.

Re:Thought experiment

[bryonak]

If I were to take a very long, very rigid (say: diamond) stick with me on one end and someone else sitting on the moon on the other end, then by pushing the stick a bit back and forth we could communicate via the Morse alphabet (ignoring orbital movement, wind drag, etc. for a moment). You'd obviously need something even more rigid (and stronger) than diamond, but keep in mind that light takes some 1.3 seconds for that distance, so this is the maximum speed information can be transmitted with.

This means that the stick must be "soft" enough such that the pressure wave from morsing propagates through with slightly under light speed, so we have an upper bound for the hardest and strongest material in the universe.
I doubt that this would be sufficient to withstand the much larger dimensions involved with this black hole, so even with the "best" material, see the comment above mine.

Re:Thought experiment

[Anonymous Coward]

Oh, and also, you'd never live to see the completion of the object because time dilation caused by the mass of the singularity would cause all motion near the event horizon to slow to a virtual stop, as seen by an observer at a reasonably safe distance.

And that's also why the event horizon itself never seems to form. A black hole is an asymptotic entity for us outsiders. That's also why we will never get to suffer the consequences of the singularities inside a black hole—for us black holes will never have insides.

Re:Thought experiment

[PhxBlue]

Oh, and also, you'd never live to see the completion of the object because time dilation caused by the mass of the singularity would cause all motion near the event horizon to slow to a virtual stop, as seen by an observer at a reasonably safe distance.

So, kind of like a government contract, then?

Re:Thought experiment

[meglon]

Like a government contract given to a private company, yep.

Re:Thought experiment

[IndustrialComplex]

The only thing slower than a contract given to a private company is a task order given to another government agency.

"What, you mean you guys gave me money to do something, and the closest intersection point between our two offices is at the Cabinet level? Yeah, I'll get right on that."

Re:Thought experiment

[meglon]

Government bureaucracy is cliche, but at least it's usually not near as expensive as doing all the same things, for the same costs, minus the profit and fraud that private companies bring to the mix.

Re:Thought experiment

[Anonymous Coward]

for us black holes will never have insides.

Unless you happen to bump into one and jump in... then the insides will be visited quite quickly from your frame.

Re:Thought experiment

[Anonymous Coward]

From the frame of reference at rest just above the event horizon, the stress from crossing the event horizon would be infinite, so there would be no material possible that could be lowered below the event horizon from a stationary spot above it. The interesting part is that for a frame in free fall at the same point, there would be almost no such stress (might be some differential stress depending on how big of a black hole you are dealing with and how long of an object you are letting fall) and hence nothing that particularly marks the event horizon for a person in free fall.

Re:Thought experiment

[Anonymous Coward]

for us black holes will never have insides.

Unless you happen to bump into one and jump in... then the insides will be visited quite quickly from your frame.

That conjecture is not scientific because it is not testable even in principle—any more than religious statements about life after death.

Re:Thought experiment

[Anonymous Coward]

It is a direct consequence of GR. If you can find fault with GR, you can falsify such a statement. The statement may not be directly falsifiable, but so is the stating, "If I drop something such that it is unobstructed and not buoyant on the Earth's surface, it will fall even if no one ever observers it." You can't falsify that something will fall if never observed, but you can except it to under the one basic assumption that science, religion and pretty much day-to-day life is based on: things tend to act the same way.

Reflections

[Culture20]

Are they sure they're not seeing the light-speed reflections of another source? If I shine a laser at the moon and wiggle it, I can make the dot "move" really fast.

Physicists!

[CHIT2ME]

Don't you just love armchair physicists!!!

Ironic

[Anonymous Coward]

Ironically I iron my clothes with iron iron ions

Re:Ironic

[Neil Boekend]

I've switched to plastic iron ions. Much cheaper.

Relativistic Braking?

[bill_mcgonigle]

If the matter on the outer edge of the disc is spinning near the speed of light, and if that matter is gravitationally bound to the rest of the disc and the black hole itself, then eventually the outer edge of the disc should act as a brake on the entire black hole's spin rate (because it can't exceed c). If it were to experience additional imparted momentum, what would happen to spacetime at the edge? I'm curious what the frame-dragging implications of this are.

Is this simply a matter of the amount of energy needed to approach c is so large that even galactic-sized energies aren't significant?

Unlimited Power

[Anonymous Coward]

Could we no use the spinning black hole at light speed to beam unlimited energy to sol? Do this before this gets erased. My time on this planet is limite

I was blind-sided.

[Anonymous Coward]

I was blinded by the black hole. No wonder I can't see it. All I see is all the starry affects circuling the galaxy around my head. Maybe, I need new gravitional lensed bifocal glasses due to my age.

Bronie

[DarthVain]

Someone's been watching a bit too much Friendship Is Magic...

"Nearly the Speed of Light"

[walter_f]

Spinning at "nearly the speed of light" is o.k.

Note: Anything faster will certainly not be approved.

Signed,
A. Einstein
Chief relativity supervisor

are what?

[Trogre]

The enemies of Democracy are what?