Slowly Pulling Facts from Black Holes

lee1 writes "Astronomers have proven the existence of the event horizon, the 'point of no return' that surrounds black holes. An MIT and Harvard team said they showed its existence by looking for X-ray bursts from neutron stars and more compact objects thought to be black holes." Relatedly beuges writes "IOL is reporting that by tracking the death spiral of cosmic gas at the center of a galaxy called NGC1097, scientists figured that material moving at 177 000km an hour would still take eons to cross into a black hole. 'It would take 200 000 years for gas to travel the last leg of its one-way journey,' Kambiz Fathi of Rochester Institute of Technology told reporters at a meeting of the American Astronomical Society."

Comments

Slowly Pulling Facts from Black Holes?

[Anonymous Coward]

Not another story about SCO...

Great!

[Voltageaav]

So even if God does answer my prayers and my boss gets sucked into a black hole, it'll take forever.

orbit?

[HermanAB]

Actually, I don't understand it at all. Why would the matter spiral in. Why won't it stay in orbit? What is slowing the matter down to make the orbit decay?

Re:orbit?

[HermanAB]

Makes me think of this little ditty about high falutin English:

"Father, I have spilt some butter. What shall I do?"

"Rub it briskly with a woollen cloth my son. For friction generates heat which quickly volatizes the sterine matter."

Re:orbit?

[HermanAB]

Hmmm - So friction in the revolving gas could will cause it to heat up and possibly glow, while slowing down its rotation, causing it to cross the event horizon and fall in?

Re:orbit?

[Gaccm]

Hmmm - So friction in the revolving gas could will cause it to heat up and possibly glow, while slowing down its rotation, causing it to cross the event horizon and fall in?

Yes. The only way something can fall into a black hole is by losing energy to fall it. If it doesn't lose any energy it will keep revolving around the black hole. Same thing with Earth, if Earth was in the middle of a cloud of gas that could eat away at very large amounts of the Earth's momentum, then the Earth could spiral into the Sun. Since that gas isn't there our Earth keeps revolving around the Sun, which is good for us.

Re:orbit?

[Cyberax]

Because of some obscure effects of general relativity, and not because of gravity waves as some people think. I can write you differential equations of, but I'm not going to write them here in ASCII art.

These effects are extremely weak in our Solar System, but they can be observed in perihellion precession of planets ( http://en.wikipedia.org/wiki/Precession#Precession _of_planetary_orbits ). Right now Gravity Probe B ( http://einstein.stanford.edu/ ) is in the final stage of experiment which aims to check the gravitomagnetic effect which is another manifestation of GR (and is partially responsible for decay of black hole orbits).

Re:orbit?

[DiamondGeezer]

Because there's a critical distance away from the black hole below which matter cannot orbit because the orbital speed would be greater than the speed of light. So anything orbiting that reaches the critical orbital radius (which depends on the black hole's mass) will be sucked in.

In that sense, it shows how differently General Relativity is compared to Newtonian Mechanics.

See this site for a visual demonstration and an explanation.

By the way, I've no idea where "the 200,000 years to hit the event horizon" comes from. According to GR, from our frame of reference it would take an infinite amount of time to hit the event horizon.

Re:orbit?

[Phanatic1a]

Relativity.

The closest stable orbit around a black hole is at a distance three times the Schwarzchild radius. Closer orbits exist, but they're unstable, the slightest perturbation in them will result in either an escape to infinity or an intersection with the event horizon. At 1.5 Schwarzchild radii, you have the photon sphere; at this distance, orbital velocity equals c, and it's unstable so nothing stays there. Anything closer than 1.5 radii, there are no orbits possible.

Re:orbit?

[DiamondGeezer]

The Event Horizon marks the surface where Escape Velocity is lightspeed. Circular Orbital Velocity is only sqrt(0.5) times Escape Velocity, so orbital velocity at the Event Horizon is less than lightspeed.

Yes, but there's a big difference between escape velocity which is radial, and orbital speed which is tangential.

As my link above shows, above the critical limit for being able to orbit is outside the event horizon (actually its at 3MG/c^2 expressed in metres from the singularity, whereas the Event Horizon for a non-spinning black hole is at 2MG/c^2)

If you think about it, the vector sum of tangential and radial velocity cannot be greater than c, the speed of light.

Re:orbit?

[WaterBreath]

a continuous flow of matter and light (which also has mass)

Well, that really depends on who you ask, and how you phrase the question.

Light, like everything else, has momentum/energy. Mass is one of the observable manifestations of that, but it is not the only one. The reason light is generally considered to be massless is fairly simple: When you push against the motion of moving bowling ball, or anything else with mass, you remove kinetic energy from it. When the kinetic energy is gone, the thing stops moving. But it still exists, because it has mass potential energy as well. Light, however, ceases to exist once the kinetic energy is gone. That's all the energy it has, which would indicate it has no mass.

There's still the question of "relativistic mass", which IMHO is just an artifact of trying to make relativistic effects mesh better with our Newtonian perception. The real test of whether "relativistic mass" is actual real mass would be to see if the gravity well around a massive object is stronger when it is moving than when it is stationary.

Re:orbit?

[lgw]

Qualitatively, when you get close enough to the event horizon of a black hole, gravity is messing with *direction*. At the event horizon, there is no direction which is away from the center. Near the event horizon (but still pretty close) there's no way to "fall sideways" and thereby orbit, because moving in the direction that would be "sideways" in classical mechanics is actually moving (somewhat) towards the black hole in general relativity.

Quantitatively, I can't explain it at all!

Re:What is inside a black hole?

[LordNightwalker]

I wouldn't be too sure about that. For centuries man thought it impossible to prove the existence of atoms, things so small one could never discern them not even with the best of microscopes. Right now we know about the existance of even smaller things in our universe...

So what makes you think that we'll never be able to prove the existence of places we could never visit in physical form, not even in the strongest and most powerful of spaceships? ;)

Re:orbit at greater than c

[Harmonious Botch]

You can't orbit a black hole inside the event horizon without going faster than the speed of light.

Facts

[Anonymous Coward]

A few interesting facts about black holes that some people aren't aware of:

• Black holes emit x-ray radiation and get smaller and smaller until they disappear, or "evaporate".

• Most black holes are formed from the death of large stars (larger than the sun) that run out of fuel and cannot sustain its nuclear reaction. The star loses the force pushing itself outward and is overcome by the force of its own gravity pulling inward. Eventually, the star has so much gravity and is so compacted that it "eats itself" until there is nothing left but a hole in the "fabric" of space-time, created by the gravity left over from the star.

• The gravity around the "hole" of a black hole is so strong that NOTHING can make its way back out after a critical distance.

• Even before crossing the event horizon, though possible to travel away from the black hole, it is not easy. Even light has a hard time getting out, so light being emitted from something almost at the Event Horizon but not yet inside the threshold takes a much longer time to escape and be seen by someone then it would in normal space going at 186,000 miles per second.

• The Singularity is the true point of destruction, the actual hole part of the black hole, although any object, especially a person, would be long dead before they reached the Singularity.

• Some black holes are spinning and have several event horizons called the "Ergosphere", "Outer Event Horizon", and "Inner Event Horizon".

Stephen Hawking's recent concession that black holes do not irretrievably eradicate information after all has garnered much attention. In my opinion, it is refreshing to see the public focused, if just for a moment, on an important conundrum that has fascinated theoretical physicists for three decades, and prompted much conceptual progress. The scientific issues, however, remain much less settled than Dr. Hawking's celebrated wager on the question. He most recently pronounced: "If you jump into a black hole, your mass energy will be returned to our universe, but in a mangled form, which contains information about what you were like but in an unrecognizable state." These ideas are profound and will have a lasting effect on our scientific theories as well as life as we know it.

Re:Facts

[Shimmer]

so light being emitted from something almost at the Event Horizon but not yet inside the threshold takes a much longer time to escape and be seen by someone then it would in normal space going at 186,000 miles per second.

Not true. The speed of light is a constant, even near a black hole.

As I understand it, what actually happens to the light emitted by an object approaching an event horizon is that it gets increasingly red-shifted. So an observer at a safe distance would see the object "fade" into infrared and then into ever-longer radio waves until it crosses the horizon.

Re:Facts

[Anonymous Coward]

"Black holes emit x-ray radiation and get smaller and smaller until they disappear, or "evaporate"."

Don't confuse the x-ray radiation (emitted outside of a black hole) with Hawking radiation, which is the true cause for black hole evaporation.

Re:Facts

[Anonymous Coward]

> Black holes emit x-ray radiation and get smaller and smaller until they disappear, or "evaporate".

Not really. The black hole itself emits black body radiation and the temperature of a reasonably large hole will be very low, so it's emitting radio waves. As it gets smaller, the temperature goes up, so the emissions will pass through visible light, x-ray and so on. However most large black holes have gas streaming into them from their surroundings, which gets really hot while spiralling into the black hole and this is the part that usually emits x-rays.

> Most black holes are formed from the death of large stars.

Unknown. Unproven.

Re:Facts

[Black Parrot]

> The Singularity is the true point of destruction, the actual hole part of the black hole

No, the event horizon is the methaphorical "hole in space".

Lots of physicists doubt that singularities even exist. Singularity essentially means "the math broke", a result of applying GR at scales where QM effects almost certainly dominate. If we ever get a theory that unifies GR and QM, we might discern what actually happens at the center of a black hole.

Re:Facts

[strider44]

I think you and the grandparent are getting a bit confused here on this issue (though it has been a few years since I studied Cosmology, and I may be wrong here, but I *do* try to keep abreast of the journals and recent discoveries when I have time).

A black hole itself has no temperature and emits no light. It literally can't. Hawking radiation comes from particles from before the event horizon. The actual amount of radiation is insignificant for astronomical black holes since they absorb more radiation from just the cosmic background microwave radiation than is let go through Hawking radiation. It's only really important for quantum black holes.

Stellar-mass black holes pretty much have been proven to come from the death of larger stars, more than about 3-4 stellar masses. Whether it's proven depends on how strict you are with the word "proof". Supermassive black holes *probably* started as stellar black holes, a long long time ago, maybe not. I'm not sure if anyone knows or has given proof, but if they have then I haven't heard about it. I'd like to though!

Re:Facts

[freedom_india]

A black hole itself has no temperature and emits no light.

Correction: A black hole "emits" heat, but since heat is transmitted as infra-red travelling at speed of light, it is never "emitted". So you don't get to "feel" the heat or the light. That doesn't mean the blackhole is cold.

from the death of larger stars

Stars are dense and hot, and once they shrink/collapse they will be hotter. My guess is the inside of a black hole must be much hotter than the temperate of the core of the star from which it collapsed.

Re:Facts

[penguinoid]

Not true. The speed of light is a constant, even near a black hole.

But spacetime is bent quite badly near the event horizon. Light emitted in the appropriate direction would orbit the black hole several times before entering/leaving the black hole, so while the speed of light may be chugging along at 299,792,458 m/s, the distance it travels might not be what you expected...

Re:Facts

[retro128]

Black holes emit x-ray radiation and get smaller and smaller until they disappear, or "evaporate".

Does all the matter of a black hole bleed off as X-Ray radiation? Or is all of it just folded up into the singularity, which should be theoretically impossible to get to since spacetime is infinitely warped around it?

Could the "big bang" have occurred when a singularity in another universe isolated itself and folded into this dimension? Could the whole universe be a spacetime bubble? Stuff to think about...

Re:Facts

[Wolfbone]

It doesn't actually matter what direction the light is emitted in - the "slowdown" of light occurs along radial paths too. It is, as you say, due to the badly bent spacetime that this effect is observed, but it's because of the metric structure of the spacetime itself, not the path of the light. In a "normal" (t,r,theta,phi) coordinate system - appropriate to a far away observer - where the Schwarzschild metric describes the spacetime structure surrounding a massive body at the origin, the radial coordinate speed of light (dr/dt) turns out to be (c - 2GM/rc). You get a better picture of what is happening near black holes with more suitable coordinate systems but at least here you can see that if we describe spacetime with a set of coordinates appropriate to "normal", speed of light = c conditions, "the speed of light" really is affected by the massive body.

Re:Facts

[Wolfbone]

"A black hole itself has no temperature"

Actually it is considered to have a temperature, though it's not the same thing as the temperature of ordinary matter. The analogy of black holes as thermodynamic systems (which I think arose from the study of rotating black holes and Penrose processes) is what motivated Bekenstein historically to suggest that a black hole /should/ emit black body radiation. Hawking set out to prove him wrong and - ironically - discovered that they do indeed.

Re:Facts

[johno.ie]

Your comment is purely based on the theories of Stephen Hawkings. I've read a lot of his work and I think he is mostly full of shit. For some reason he has been put on an intellectual pedestal by his peers in the field of theoretical physics. I don't believe that this is for the right reasons though, but I won't speculate what the reasons actually were. I think his theories are having a harmful effect on physics as a whole, because (1) like i said above, he's full of shit, and (2) any new breakthroughs that contradict his work are usually ignored, because they contradict him. Science advances generation by generation because its often very hard to refute a great scientists work until after he has died. I sincerely hope that he has written his last book. I sick of hearing dumbasses quoting from A Brief History of Time to support some bullshit they are trying to make me believe in.

Re:Facts

[tgrigsby]

To clarify:

* Black holes emit x-ray radiation and get smaller and smaller until they disappear, or "evaporate".

The time taken to do this for any appreciably large black hole is on the order of trillions of years. Theoretically speaking, of course. Black hole evaporation only really makes sense in high energy particle collisions.

* Most black holes are formed from the death of large stars (larger than the sun) that run out of fuel and cannot sustain its nuclear reaction. The star loses the force pushing itself outward and is overcome by the force of its own gravity pulling inward. Eventually, the star has so much gravity and is so compacted that it "eats itself" until there is nothing left but a hole in the "fabric" of space-time, created by the gravity left over from the star.

The "hole" is a mathematical construct. There is no actual hole, just a point beyond which information cannot escape, including information contained in light.

Big distance but useless figures

[Red Flayer]

310316400000000 km is the last leg of the journey?

FYI, that's 2,074,335.22 Astronomical Units, or 32.8 Lightyears, or about the distance from Sol to the Cepheids. Dang.

Too bad they don't specify how far out (radially) from the event horizon the last leg starts. Or even loosely define what 'last leg' means in this case.

Re:Big distance but useless figures

[Hobbex]

You think so three dimensionally.

(Consider relativity...)

Re:Big distance but useless figures

[Phanatic1a]

They're referring to the effects of relativity as an infalling object approaches the event horizon. The object is accelerating towards c, so as it approaches the event horizon (from our external frame of reference), its clock is moving slower and slower, and it takes longer to travel a given distance.

Wikipeding?

[bubulubugoth]

So, if there is a "googling" action, also is there a wikipedin action?
The Wikipedia entry about Event Horizon has an interesting "faq" about, orbitig the event horizon and sticking you hand into the event...
Also the wikipedia companion, talks about Stephen Hawking saying that no "event horizon" can be formed at a black hole... This article needs edition... :)
Good reading before a good sleep...
Btw, there is a neat animation about a neutron star X-ray burst


enough of karma whoring...

Re:Metric

[jfengel]

Well, you can have kiloseconds, if you want, which is on the same order of magnitude as an hour (well, a bit over a quarter of an hour).

As you note, we use metric fractions of a second (mill, nano, femto, etc) all the time. Why megaseconds (about 11.6 days) and gigaseconds (31.7 years never caught on), I can't say. Maybe it's because we're all so familiar with hours, minutes, and days, and unlike other metric/English conversions the conversion factors are at least integers, and well known integers at that (e.g. 60 seconds to the minute, 60 minutes to the hour, etc.)

I'll admit I find the European speed limits in "km/hr" somewhat disconcerting, since the latter is such a non-metric unit. Hey, let's all try to convince the EU to standardize on km/kilosec, aka meter/second.

Google units conversion, BTW, does know about megaseconds and gigaseconds.

Re:It was never in orbit

[MillionthMonkey]

What makes you think it is in orbit in the first place? It's just basic gravity. Things fall down.

You're drawing a distinction where there is none. That's what an orbit is.

If you could destroy a black hole...

[Centurix]

You'd be messing with the Phantom Zone, and we'd perish under the rule of the great General Zod!

It hurts less...

[Black Parrot]

...if you pull the facts out quickly.

Re:It hurts less...

[pintomp3]

but then it's less fun. btw, the pull out method does not work.

Too many jokes

[JakeD409]

There are way too many jokes to make about reaching the "point of no return" while being in a "black hole" to choose just one.

Re:What is inside a black hole?

[Combas]

What makes you so certain Atoms really do exist?

Oh sure, we have mathematical formulas that prove that "something" does exist and we can even do some manipulation, but what if it turns out that all this stuff thats so tiny that we can't see it isnt at all what we think it is even though it does respond in predictable ways that we can understand and measure.

Its like an old programming analogy I once read, picture a man in a box who only understands english, but has a big book on Chinese. Now programmers feed the box instructions written in chinese and the man inside is able to look up words in his book, and then he is also able to write chinese replys using the book, but he doesnt actually understand the chinese language itself. The people on the outside would think he understands chinese because they send in chinese messages and get chinese replys in return.

Maybe atoms are like that as well. We poke atoms, and they respond in a predictable fasion, but since we cant actually see them how do we really know what we're poking?

Re:Why the long time?

[massivefoot]

Conversely, someone falling into the black hole (ignoring for the moment that he would in fact be ripped apart by tidal forces) would see the entire history of the universe played out above himself as he fell in.

Well not quite. Whether he'd be ripped apart would depend on the rate of change of the gravitational field strength with distance. He'd last longer if it were a larger black hole, and if it were spinning. Also he'd see the entire future of the universe play out before him. It would also appear, well, rather blue...

Re:What is inside a black hole?

[Anonymous Coward]

That's a classic defense of dualism you're quoting, and the fatal flaw is only considering the programmer as an individual. If the book contains enough information to trick outsiders into thinking a chinese speaking person is inside, the book itself can be considered an individual, living of course only in the environment created by the actions of the programmer, but an individual none the less.

So, essentially, even if the atoms are only emulating on something more complex or different, we are still working with what we conceive of as atoms, simply at a lower level. The intermediate stage may be interesting or it may not, especially if it remains undetectable. For instance, assume a perfect simulation of the universe on a computer, the inhabitants of the universe are, philosophically, no less real than we are, they see the same phenomena as we do and think they live in a universe of atoms despite the fact that they're just data structures and algorithms emulating what our atoms would do.

Re:minor error

[DarkKnightRadick]

Light moves, generally, at c.

The problem is though, that light can be slowed down. According to several sources, light can be slowed down, although they all seem to agree that a photon travels at the speed of light no matter what, just the absorption/release/re-absorption process can slow down how quickly it crosses a given distance.

Reuters was only off by 99.99%

[xmark]

"The one-way journey from the heart of a galaxy into the oblivion of a black hole probably takes about 200,000 years..."

"...scientists figured that material moving at 177 000km an hour would still take eons to cross into a black hole."

Eons are the largest division of geologic time. There have been just four of them since the formation of the Earth. In rough terms, that's a billion years each.

Maybe the reporter can get a job working on unit conversion for the next Mars probe. (*cough*)

Re:Reuters was only off by 99.99%

[Phanatic1a]

From our frame of reference, matter moving at 177,000km an hour would still take eons to cross into a black hole. In fact, we'd never observe it doing so, by the time it crosses the event horizon any radiation from it will be redshifted to infinity.

From the frame of reference of that matter, entry into the black hole will take but an instant.

This is relativity. Always specify your FOR.

Re:What would happen..

[Gleng]

Or would they actually be destroyed by some force inside the hole itself?

Have a read about Spaghettification.

Re:minor error

[Eivind]

Yes. A photon does indeed travel at the speed of ligth. This is true for the same reason that it is true that a cow generally travels at the speed of cow.

Hint: what is the *definition* of "speed of ligth" ?

Re:Metric

[ichin4]

Fundamentally, the reason we have no metric unit of time is that there are two lengths of time we really care about a lot -- the day and the year -- and they are not seperated by a power of 10.

Actually, those metric-crazy revolutionary Frenchmen did try it. They picked the day as the fundamental unit. They then divided the year into 12 30-day months, plus a 5-6 day party at the end.

Scanning Tunneling Microscope

[Shashvat]

You can now take pictures of atoms with a scanning tunneling microscope.

Researchers at IBM even move individual atoms around to create artwork.

More here: http://www.almaden.ibm.com/vis/stm/corral.html

Re:It was never in orbit

[Intron]

Damn. I just bought that star from the International Star Registry, too.

What they don't mention

[merlin_jim]

Is the scientific reason that gas can take 200,000 years to be pulled in by the most gravitationally massive type of object possible in the universe.

It is for two reasons; first off, gravitational time dilation - time gets slower the closer you get. The gas is orbitting the black hole, which also adds relativistic time dilation.

The gas, in fact, probably orbits at just under escape velocity - thanks to a fun little effect called (IANAA) relativistic frame dragging - basically the black hole drags the fabric of spacetime around itself - and objects within about 1.5 radii of the event horizon start feeling the effect - effectively locking them into a particular path. One way to look at this is to say that time is swallowed by the black hole same as mass - and therefore objects in the vicinity of the black hole fall in because their time arrow points to its dark, dark heart.

This frame dragging should happen at speeds approaching the speed of light - and require comparable amounts of energy to change your frame. There's even some theory that infalling matter will follow gravitational field lines, like you get around a magnet - but I'm not sure how much I believe that...

Re:What is inside a black hole?

[lgw]

I think you do get it! Turing's test is just a better way of stating the problem than the Chinese Room.

The often overlooked and very insightful aspect of Turing's test is that it doesn't just apply to "artificial" intelligence. In his formulation, by communicating with an unknown entity, you can determine by conversation whether or not it is at least as intelligent as you.

While that's an interesting test for an AI (though many AI researchers have problems with it today) it also makes a very different point: given two people, both smarter than you, you can't tell which of the two is the smartest through direct interaction! Much of the scientific method and the culture of science can be understood from this simple observation.

More to an orbit

[snowwrestler]

An orbit is not just things falling down, it also requires a tangential velocity within a specific range. Gas spiraling into a black hole does have a tangential velocity, but it's not within the range create a orbit. In other words, yes, it was never in orbit.

Re:What I found intersting

[twifosp]

Even if we could travel at say, .75c, anything "near" a black hole any living thing would be hosed. The g forces of orbit insertion would likely tear our fragile bodies and crafts apart. Additionally the Xrays, gamma particles, and other nasty radiation would cook and fry everything.

Achieving neccesary velocity to not fall into a black hole would be easiest part. Even if we got into some kind of orbit, at near C speeds, you'd never leave. You'd need even closer to C speeds, and if you were near the event horizon, you'd need to actually achieve C to escape, should you ever want to extend your orbit beyond the black holes sphere of influence. IE come home. Which would require infinite energy.

SO in short, I suggest we just stay the hell away from black holes :D