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There's a Hole in the Middle of It All
Apparition writes "CNN is reporting that the star at the center of our galaxy is actually a super-massive black hole. The article then claims that it occupies a volume of space about 3 times that of our solar system. If my math is correct, about 230 million suns could fit into that same volume, so it doesn't impress me that the claimed mass of the black hole is only between 2.6 and 3.7 million times that of the sun. So what is up here? Since when do black holes occupy so much space (I thought they were points)? And how can something with a density only 1/100 of our Sun be called super-massive?" I think the article is talking about a maximum possible size of the object, due to limitations on the resolution of our instruments. Nature has a no-registration story about the research. Update: 10/16 23:44 GMT by M : There's an article with more information on space.com, and a press release from the European Southern Observatory.
RB
The size of the black hole isn't the volume taken up by its mass. It's the volume inclosed by the event horizion.
If light enters that volume, it never(ish) gets out.
I am a Karma Library.
The large size is probably the event horizon for the black hole.
The event horizon is the sphere within which not even light can escape from the black hole. It is the dark area the the black hole appears to take up.
The actual size of the object would be much smaller
There should be a moderation category "Dumbest Comment EVER"
So, does that mean that in time, the blackhole will swallow up the star?
-Cyc
/.'s 10 Millionth
where Enron's accountants found work.
Yes, black holes are a point (that's called the singularity), but they're talking about the size of the event horizon, or point of no return. So this particular black hole has a mass of 2.6 to 3.7 million or whatever suns, but its event horizon is larger than the solar system.
With a black hole this big, you can actually cross the event horizon, and not be torn apart because the change in gravity over a certain distance (6 feet or so for your height) isn't great enough. Smaller black holes will rip you apart quicker though
"...until the super-massive black hole eats up our galaxy, and do you think M$ will survive?"
It's nice to see that graduates from the Bob Saget School of Comedy are getting journalism work.
According to my Astronomy course, Super-Massive black holes are less "violent" than their smaller brothers because most of the mass is concentrated at the center in a very very small space. Their event-horizons are very large because of this mass, which makes them seem not as dense as we would assume. With a small black hole, the event horizon is very small, and thus the effects near the point are much more drastic because mass that passes the event horizon is "consumed" immediately. I realize I am simplifying quite a bit, but hopefully you get the point.
I've always thought it was obvious that super-massive blackholes lie at the center of galaxies. The intense gravity at the center should create one, and spiral galaxies are all just pinwheeling "down the drain".
I would bet there are black holes at the center of ALL spiral galaxies like our Milky Way. Other shaped galaxies may just be at earlier stages of evolution (such as elliptical) before their holes have formed.
the scientists in the article seem to assert that this is CONCLUSIVE proof of a black hole's existence. but i remember reading a few months ago about a schism in the physics community - a sizable segment of the community is disputing the theoretical existence of black holes! i wonder how this discovery will affect that debate....
smd4985
The "size" of the black hole refers to the size of its event horizon (a.k.a the Schwarzschild Radius), which is R = GM/2c^2. For a huge value of M ("supermassive"), the event horizon is very large: once you cross this, there's no coming back, and our physics stops at the edge. But since R is so large, the tidal forces are small at the event horizon - much smaller than the tidal forces at the event horizon of a smaller black hole. (Chew on it for a second and it makes sense).
The "actual" naked singularity is in fact a point, but we have no way of probing anything inside the event horizon. So calculating the density of a black hole is misleading...
"I will take the Ring," he said, "though I do not know the way."
Theoretically the mass of the galaxy itself should be enough to hold it together. Even the black hole could have originally been formed from matter collecting at the center of gravity of the galaxy.
Would this be the proverbial drain that we're all swirling around to our eventual demise?
Just wondering.
-Goran
Carpe Scrotum - The only way to deal with your competition.
From the very center, this galaxy sucks.
"What's inside is unknown (and presumably unknowable)"
:-P But in theory, even if for no purpose and getting no proof, a probe could make it past the event horizon, if only an extremely small amount. Maybe even a manned module. I forsee these "suicide trips" in the future, as opposed to a KevorkianBot.
Actually, it is completely knowable. It's just impossible to relay that information outside the event horizon.
This would seem to imply that, in theory, a very large black hole could have rather low density inside the event horizon. It seems to me that a black hole could spontaneously form around a particularly dense cluster of stars if it was large enough and they all happened to clump together.
But my head starts to hurt thinking about what happens to physics when a region of normal space suddenly finds itself inside a black hole like that. I am definitely not a physicist, so I can't explain what goes on inside a black hole, or if my globular cluster black hole is even possible.
Crispin
----
Crispin Cowan, Ph.D.
Chief Scientist, WireX Communications, Inc.
Immunix: Security Hardened Linux Distribution
Available for purchase
> (and presumably unknowable)
You could go in and find out, but due to time dilation, you would see the rest of time flash before your eyes, and then witness the end of the universe. You wouldn't be able to tell anybody though, because no signals can escape unless they travel faster than the speed of light (which is of course impossible). You would also be dead, but that's another story.
-- Wibble
As the above reply suggests, the galaxy's own mass should be able to hold it together. Just like the sun holds together the solar system and the Earth holds itself together.
/.-ers might be a recent paper that describes the universe as a cyclical entity (no "big bang"), by representing it as a pair of branes (world sheets, see string theory...). The end result is there's an event (a "bounce) that might look like the Big Bang, but it's really just a collision between the branes.
Black holes are good candidates for causing a galaxy to accumulate. It can be kind of hard to explain what causes galaxies to form.
I'm getting off-topic, but I don't care...
One of the favorite explanation comes from irregularities in mass distribution as evidenced by perturbations in the cosmic microwave background. That's one of the reasons that the CMB became such a hot topic, it offers insight into the origin of large scale order in the universe.
Also of interest to
Like anything else in cosmology, it's all rather speculative (at least as compared to many other physical models).
Find the link on your own (/. might've even covered this topic).
That's Florida.
.sig last updated Jan. 14, 2000
An object can orbit a black hole just like a planet can orbit the Sun (or a star). The Sun will not swallow or pull in the Earth any time soon. Black Holes are not cosmic vacuum cleaners that "suck" up everything around them. If you're in a stable orbit, it would be just like orbiting a Sun.
That said, there is evidence from general relativity that due to graviton radiation (gravity particles), large orbiting bodies slowly move closer to each other. The gravitons leaving such a system take energy out of the system slowly bringing the orbiting bodies together. This effect is (AFAIK) theoretical, although many people are currently working on ways to detect this graviton radiation and show that it is coming from systems like this. So in this case, yes, eventually (think eons) the star and the black hole would slowly move towards each other (the star would move more since it the least mass of the two) and in this type of collision, the black hole wins.
Who said Freedom was Fair?
Radius = 2 * "Universal Gravitational Constant" * "mass inside event horizon" / pow("speed of light",2)
For a black hole the mass of our sun the radius is:
Radius = 2 * (6.67 * 10^-11m/kg/s^2) * (2 * 10^30 kg) / (3 * 10^8 m/s)^2 = 2.964 km
When you check my math make sure you get your units right. A black hole three times the size of our solar system would be quite massive, and you should be impressed.
Also, I saw a program on Discovery Channel a while ago (6 months+) which had an interview with an observational astronomer in which he claimed to have observed movement in the center of our Galaxy which was consistant only with a supermassive black hole. I guess he finally published.
Galium Arsenide is the material of the future, and always will be.
We already know there's a powerful telepath living on a planet there and he needs a space ship. If there had been a black hole in the center of the galaxy, you'd think someone would have mentioned it.
The article is referring to a determination of the orbit of the star closest to the galactic center. The periasteron (closest point in the orbit) is 17 light hours from the galactic center. This implies that the mass necessary to create that orbit is concentrated within that radius. The only thing in our current cosmic zoo that fits 3 million solar masses inside of 17 light hours is a black hole. The event horizon itself should be smaller than that, but not by much.
What is an interesting question is where the Roche limit is for these parameters, and how close this star is to that limit. (In other words, how much closer can the star get before it is ripped apart.) I seem to remember that it is possible to set up conditions so that the Roche limit is inside the event horizon. Obviously, the physics around there are very strange.
- r = 2GM/c^2
where G = 6.67e-11 m^3/s^2*kg (the gravitational constant) and c = 3e8 m/s (the speed of light, of course). Plug in 3 million sun-masses (the sun weighs 2e30 kg), and you have- r = 8.9e9 m = 5.5 million miles = 0.06AU
So unfortunately, the event horizon isn't three times as big as the solar system. The earth's orbit is 1AU (that's how the unit is defined). The event horizon barely stretches past the surface of the sun (7e8 meters)!So much for that idea!
at the middle of the galaxy was some calm looking planet with a grey-haired guy that Sybok is looking for. Thanks for bringing up horrible memories of ST:V!
"The objective of securing the safety of Americans from crime and terror has been achieved." -- John Ashcroft
"but really, wtf could hold an entire GALAXY together but a black hole?"
I am (or rather, was) an astrophysicist. The answer is the rest of the galaxy holds it together, a bit like the gravity of the Earth is what holds the Earth together. The galaxy has the mass of billions of stars - so any stars not at the center are being pulled towards the center.
In answer to the original poster, the 'size' of a black hole is its event horizon radius:
R = 2GM/c^2
where
G = universal gravitational constant
M = mass of the black hole
c = speed of light.
Quattuor res in hoc mundo sanctae sunt: libri, liberi, libertas et liberalitas.
This is a small misunderstanding. Many people seem to think that a black hole has super gravity or extra strength power just because its a black hole. Actually, it all depends on the mass.
For example, if our sun suddenly turned into a black hole, we wouldn't get sucked in. We'd still orbit our new black hole sun the same way we orbited our old normal sun. Just because it became a black hole doesn't mean its mass changed. And since its mass didn't change, we would still orbit the same.
Ditto for our galaxy. If we didn't have this black hole at the center of the galaxy, but instead 3.7 million suns, everything would orbit just the same
---
A black hole is just God dividing by zero
Actually, a point with no volume would have infinite density, but finite mass. Density is defined as Mass/Volume.
Let's set mass = k, and volume = x okay?
Lim(x->0) k/x = infinity.
What's inside a point with infinite density? Who knows, but we do know that our universe has finite mass, just like black holes....
points to ponder.
God save our Queen, and Heaven bless The Maple Leaf Forever!
p.s. I may be wrong about which book mentioned it, but it was one of those uber-cool sci-fact books by a reputable physicist, like Feynman or something. Really. I'm serious.
-Ansel.
G=C800:5
The sun is about 800,000 miles across. The diameter of pluto is about 7,000,000,000 miles. The volume of a sphere with that diameter is about 4.3e+28 miles. You could fit something on the order of 5e+22 suns in that space.
Since when do black holes occupy so much space (I thought they were points)?
They're big points.
RMN
~~~
"A language that doesn't affect the way you think about programming, is not worth knowing" - Alan Perlis
the only problem is, for the brief instant it was within the event horizon almost all of eternity would pass outside it, so we would most likely get the results a bit late :(
Jeremy
It is doubtful that a probe could even get substantially close to the event horizon intact. Gravitational tidal forces would rip it to shreds. No need to even mention the intense radiation...
*** Quantum Mechanics: The Dreams of Which Stuff is Made ***
Of course this is all based upon classical arguments, and without a theory of quantum gravity we can't be sure. However it hasn't stopped Hawking and Penrose arguing about "cosmic censorship principles" :)
Jon Erikson, IT guru
If the information inside the event horizon cannot be communicated to the outside of the event horizon, then none of your statements about what goes on inside the event horizon are empirically provable. You may want to consider using qualifiers such as "may" and "might" to indicate the conjectural--and ultimately unprovable--nature of your claims.
Any sufficiently well-organized community is indistinguishable from Government.
Theoretcially (we'll likely never have building materials struturally sound enough to test this) light should behave in almost exactly this manner close to a black hole. For example, say you've built a circular torus space station around a black hole. If you're within a certain radius to the singularity, but still outside the event horizon, light will bend towards the blackhole, allowing your vision to see 360 degrees around the torus. You can stand in one point and see your back an apparent distance equal to the circumfurence of your imaginary torus away. Closer than that radius means that the torus would appear to bend the wrong way.
The next Slashdot story will be ready soon, but subscribers can beat the rush and slashdot the links early!
Not really. As has said before, earth would have to be 1cm across to be a black hole. All the matter in the universe would only have to be about 15 billion light years across, or roughly the size of the universe.
A deep unwavering belief is a sure sign you're missing something...
If my memory serves me, I believe that there is a nearly confirmed black hole at the center of M15 (a globular cluster). However the conditions for it's creation are probably still up for debate. A bunch of semi-simultaneous stellar collisions at the core is not out of the question though.
Shop Smart, Shop S-mart!
Our sun is about 10^30x2 kg while the earth is 10^25x0.6 kg That makes the sun about 10^6 times heavier than the earth([1])
This black hole now is about 2.6 to 3.7 times that heavy when compared to a sun of the size of our own.
Our planet roates around the Sun at about 150,000,000 km at a speed of ca. 29.658 km / s if my math isn't wrong.
That other sun rotates around the black hole at about 17 light hours at a speed of 240.652 km / s (if I am not mistaken here either).
The speed of that sun is more than 8x the speed of the Earth, generating a significantly higher centrifugal force.
Now, that sun is 127.5 times further away from the black hole's event horizon than Earth is from Sun.
At the same time, the increased distance should provide a significantly lower gravitational pull than the 3.6 x relative weight of the sun could provide.
As this sounds completely bogus to me, I'd be happy if someone could enlighten me how this is supposed to work.
- The explosion is too small: everything comes back again. If they miss, they orbit each other (circular (special case of ellipse:) or elliptical)
- The explosion is just right: everthing is gone forever but eventually stops at infinity. Straight line or parabolic trajectory.
- The explosion is too big: everything is gone forever and never stops, not even at infinity. Straight line or hyperbolic trajectory.
The size of the explosion needed for each case is easy to find from the escape velocity/energy (E=1/2mV^2). For V (velocity due to explosion) < Ve (escape velocity), you get 1; V == Ve, you get 2; V > Ve, you get 3. The main difference between cases 2 and 3 is the velocity in case 2 has a zero asymptote while in 3 it has a non-zero asymptote.Bill - aka taniwha
--
Leave others their otherness. -- Aratak
"I think the article is talking about a maximum possible size of the object, due to limitations on the resolution of our instruments."
I'm sure this editorial comment was well-intentioned, but the article would have been much better off without it. What the article refers to corresponds closely quite nicely to the Schwarzschild radius of a supermassive black hole.
A very massive black hole will necessarily be much less dense than the Sun, and can even be less dense than the Earth.
The simple reason is that (assuming a static, spherically symmetric mass distribution) the mass of an object is directly proportional to its Schwarzschild radius. But density is proportional to mass divided by radius cubed.
So if you double the mass of a black hole, you must necessarily double its radius. By definition this increases its volume eight-fold, and so its density is decreased by a factor of four.
So as you consider larger and larger black holes, you must see that their densities are smaller and smaller.
If you are in the market for a comparatively easy textbook that will teach you more about general relativity, I recommend Exploring Black Holes by Taylor and Wheeler. If you have a firm grasp of calculus and freshman physics, you will be able to handle it. It is more expensive than a normal book, but cheaper than the average textbook.
Comment removed based on user account deletion
Very much like those things you find at a Krispy Kreme shop, but with a lot less frosting...
Does this mean that the voice we will hear at The End of Time will be saying "OOOhhh... donuts..."
How come Slashdot never gets Slashdotted?
Some theories, including string theory, prevent the collapse to a point. But whatever a black hole is, the event horizon of the reported hole cannot be that large for the expected mass. It's just way, way out of scale for a black hole with a reported mass between 2.6 and 3.7 million times that of the sun.
I'm an American. I love this country and the freedoms that we used to have.
And how can something with a density only 1/100 of our Sun be called super-massive?
:)
It's just not super-dense!
actually.. there would be almost no tidal effect at the edge of a black hole and the radiation would be nearly negligible.[according to Roger Penrose... who is smarter than I am]
lysergically yours
The spin is what stops them from collapsing into an even bigger black hole. The stars in a galaxy are always pulled towards the center of the galaxy but always (except for some unlucky ones) miss the center/each other. WHy did the spin start in the first place? I believe the prevailing theories go for uneven mass distribution and turbulance.
Bill - aka taniwha
--
Leave others their otherness. -- Aratak
So the radius is directly proportional to the mass and since the "density" goes with 1/r^3, the "density" will decrease with 1/r^2. This is of course only valid for euclidean space, which we don't have in the vicinity of a black hole.
***Quis custodiet ipsos custodes***
The author's confusion here seems to be regarding the differences between a blackhole and its singularity.
A black hole is just that -- a black hole. It is a region of space from which nothing can escape (approximately; black holes do very slowly radiate heat). In other words, the volume a black hole occupies is defined by the Schwartzchild radius: the point beyond which the escape velocity exceeds c.
A singularity is the "center" of a black hole; it is an infinitely dense point in space, of enormous mass.
Interestingly, black holes may have some useful properties for astronomers. Light heading towards a black hole will be refracted around it and bent; in essence, the black hole acts like a magnifying glass.
social sciences can never use experience to verify their statemen
I don't want to shock anyone, but it is possible that they got the facts wrong. A small black hole (about 2.5 solar masses) has a horizon of a few kilometers (order of magnitude 10km). I am guessing the hole is a few times the size of the SUN not the solar system. That is really huge for a black hole.
Eh? Could you explain what you're talking about here? Because as far as I know, Hawking and Penrose's work has nothing to do with the likelihood of black holes forming. Indeed, one of the things about black hole formation in that no matter how unsymmetrical the initial state the end result is highly symmetrical, possessing no distinguishing features other than mass, charge and angular momentum... the "black holes have no hair" theorem.
Or are you talking about the recent results in M-theory proving Berkentstein's semi-classical formula for black hole entropy? If so, I'm still not sure what that's got to do with black hole formation... it strikes me you've got things confused...
Jon Erikson, IT guru
Black hole? Geez, where have these people been? Everyone knows that the galaxy's core exploded years ago!
End of lesson. You may press the button.
I can't believe how Milky-Way-centric that Slashdot still is. The bias is incredible. Nowhere in this story does it identify which galaxy, as if we all live in the same galaxy. For chrissake, people, it's the Internet.
Jeez.
-Waldo Jaquith
The size issue: the companion star's orbit tells us the maximum possible size of the central object. If the orbit is 17 light hours across, the primary is at most that large. It can be smaller, just as our Sun's diameter is smaller than the orbit of Mercury.
The proof the central object is a black hole is that nothing else can fit millions of solar masses into a sphere 17 light-hours across. The black hole need not fill that volume. More precisely, the event horizon need not fill that volume.
Singularities, point masses, event horizons: the size of a black hole depends what you mean. The singularity is the postulated point of infinite density: outside observers can't see it because it's inside the event horizon. The event horizon is the point of no return; in classical terms, the escape velocity equals the speed of light at the event horizon. The gravitational force is finite at the event horizon, and need not be extreme if the black hole is very, very large. If the universe is closed, we are all inside a black hole now, and will experience singularity at the Big Crunch.
But it isn't useful to think about the inside of a black hole. Different physics might apply -- lots of smart people think so. From the outside, as another poster wrote, all you get to observe is the black hole's total mass, total charge and total angular momentum -- that's plenty to work with in astronomical observations.
As to matter 'spiralling in', or the entire galaxy being sucked in by 'infinite gravity': Earth isn't being sucked into our Sun, is it? Unless you're quite close to one, the gravitational field of a black hole essentially (asymptotically) follows an inverse square law, like the gravity from any object. (When you get close, in units of the Schwarzchild radius, you do indeed 'spiral in' because the field strength increases faster than inverse square. The precession of Mercury's orbit is used to measure the deviation from inverse-square near our Sun, and is one of the 'proofs' of Einstein's General Relativity.)
The other mechanism for 'spiralling in' is loss of orbital energy due to friction, as in the accretion disk around neutron stars, for example.
That is all. Return to your homes and families. :-)
je ne suis pas un fou
I found this cool earth orbit physics toy and demonstration while reading one of my favorite web logs, Sensible Erection. (I, uh... Read it for the articles.)
/drag the screen to put a satelite in orbit.. see how long it lasts...
"This is the coolest this i have seen all week, click
pull off a moon only orbit for maximum kudos"
The physics for object orbits are incredible. This is a great demonstration of the exact effects you describe, and should apply to the questions and comments about orbits around a black hole.
Enjoy!
P.S.: You have no idea what a breath of fresh air it is to be able to visit cool links that aren't being slashdotted to hell and back.
>Actually, it is completely knowable. It's just
>impossible to relay that information outside the
>event horizon.
What about this Quantum communication idea. You know, the one where one quantum part or something will cause an equal change in it's twin quantum part no matter distance. Would these quantum parts not communicate across the event horizon?
I'm no physics major... I specialise in computers but methinks this quantum thing has much promise.
Codifex Maximus ~ In search of... a shorter sig.
Average orbital radius of Pluto's orbit is 3660 million miles.
1.2010984306567283*10^7
3 5*10^6
rs=3660000000;
Volume of solar system (based on assumption that the solar system is considered a sphere) in cubic:
vs=(4/3) Pi rs^3
2.0536757052608588*10^29
Mass in the solar system is approximately 2*10^30:
ms=2*10^30
2.*10^30
Density of the solar system is given by the mass divided by the volume:
ds=ms/vs
9.73864
Mass of the unknown object is between 2.6 million and 3.7 million times the mass of the sun (which is 99% of the mass of the solar system):
mo1=2.6 10^6 * ms
5.1999999999999997*10^36
mo2=3.7 10^6 * ms
7.4*10^36
The volume of the object is about three times that of the solar system:
vo=3 vs
6.161027115782576*10^29
The density of the object is given by the mass divided by the volume:
do1=mo1/vo
8.440151134344576*10^6
do2=mo2/vo
The ratio of the density of the object to the density of the solar system:
r1=do1/ds
866667.
r2=do2/ds
1.23333333333333
Thus, this unidentified object is between 8.6*10^5 and 1.23*10^6 times as dense as the solar system. This is very dense, and puts it into the category of a super-massive black hole. These guys are scientists.
Lack of eloquence does not denote lack of intelligence, though they often coincide.
Please mod down all the people who are currently at +5 claiming that the size of the object is really the event horizon, which is very large due to it being a supermassive black hole. This is a true statement, but it still doesn't explain the claimed size of the black hole in the article.
If you work out the schwartzchild radius of the sun using r=2GM/c^2 it comes out to around 3000 m. For the upper limit of 3.7 million solar masses that would mean that the black hole had a schwartzchild radius of around 1 x 10^10 m. This is about a factor of 14 larger than the radius of the sun which is 7 x 10^8 m.
This is no where near as large as the "volume of space around 3 times larger than the solar system" which is in the article. The poster of the article was also correct that the density was way too low. It is correct that supermassive black holes have large event horizons which are larger than the radii of typical stars like the sun. However, the average density inside of that event horizon is still denser than a neutron star.
I wish I had the 5 moderator points I had last week, I'd go to town on this story...
I can tell from the aggression present in your post that you're clearly no WIMP.
personal attacks hurt, especially when deserved
I've stumbled across NASA's Astronomy Picture of the Day site, and I've become addicted to it. Not a day goes by without me browsing back and back through the archive. Lots of wonderful images there, with explanations by a professional astronomer, in language that even I understand. And ofcourse links for people with more understanding of the stuff they are talking about.
Anyway, it's an amazing site, really worth adding to your daily-visit bookmark group. And yes, black holes in or near "our" galaxy are featured there as well.
(Not karma whoring, I've got plenty. Just wish to share this with you)
karma capped
at the middle of the galaxy was some calm looking planet with a grey-haired guy that Sybok is looking for. Thanks for bringing up horrible memories of ST:V!
And thank you for bringing up horrible memories of ST:V! He was a poor excuse for a Vulcan. Me, I like my Vulcans slim, busty and wearing skin-tight clothing, yes-siree!
GMD
watch this
Some of the more avant guard sting theorists are advancing the notion that black holes are simply really really big (as in high energy) elementary particles (i.e. strings). It'll be interesting to see if this particular theory holds any water, because it might mean high energy physicists may one day be trying to sling black holes at each other ;).
BlackGriffen
I absolutely don't believe how the quality of /. has declined. A story about a massive black hole at the center of the galaxy, and only one person even thinks to mention Beowulf Shaeffer?
Geez! And here I was, rubbing my hands in glee, loooking forward to all the elaborate puns... sigh. Nobody even meantioned a "cluster"! What's wrong? Would it have been not off-topic enough?
Too bad Niven didn't write the sequel: about how Shaeffer went back, only to discover that there are actually three black holes in the center of the galaxy, orbiting one another...
Oh, what's the use. My heart's just not in it.
"Great men are not always wise: neither do the aged understand judgement." Job 32:9
This might be a misinterpretation. In the ESO press release they say:
So that puts an upper limit on the scale of the thing, but doesn't imply it takes up all of that space.
This post is strictly my own opinion and not necessarily that of my employer.
Regarding discussions about whether the "volume" of the article implied the Event Horizon, that's what I thought it was at first also. But then I came up with some numbers that don't seem to correspond to those of the CNN article. I then checked out the original paper. The paper is formally on the observation of a star that seems to be orbiting the galaxial center, and this radius of orbiting is what they are pinning down as the a putative upper limit of the size of the supermassive object.
It would seem that the original poster's comment was correct in that this was the _Upper Limit_ of the radius of the supermassive object, and not the Event Horizon radius.
Let me clarify,
The Schwarzschild radius (Or Event Horizon) is given by
r_SCH = 2 G M / c^2
where G is gravitational constant, M is mass of object, and c is speed of light. If we use, as per CNN article (yeah, I know, good source)
M = 3 x 10 ^ 6 * mass of sun
mass of sun = 2 x 10 ^ 30 kg
s.t. M = 6 x 10 ^ 36 kg
and G = 6.67 x 10^ -11 Nm^2/kg^2
and c = 3 x 10^8 m/s^2
then r_SCH = 12 x 10 ^ 36 * 6.67 x 10 ^-11/9 x 10^16
r_SCH ~ 1 x 10^10 meters.
I looked up some values of Pluto's radius, and got about 3000 million miles, or 5 x 10^9 km, or about 5 x 10^12 m.
So this galaxial blackhole seems to have a radius 100-1000 times less than the solar system radius.
And indeed, in the final page of the Schodel paper, there is a mention that the observed radius of the orbiting star is ~ 2000 times the Schwarzschild radius, and not the actual Schwarzschild of the star. i.e. the observed radius of orbit is much much larger than the putative Schwarzchild radius.
These researchers are popular here on campus at UCLA. Also, check out some nifty pictures here.
CNN is reporting that the star at the center of our galaxy is actually a super-massive black hole
I saw a documentary about this over a year ago.
Horizon on the BBC IIRC.
I also seem to remember somebody thinks "our" black hole is "feeding again" (whatever that means).
Do you mind, your karma has just run over my dogma.
I thought that was a neat way to look at it, anyway. I don't know if it holds universally...
-Erf C.
Cthulu always calls collect...
Nope. If the universe began at the big bang, about 15 billion years ago, it would be about 30 billion light years across, no? A black hole doesn't have to be all that dense, actually. All it needs is enough mass in a volume so that the escape velocity of that volume is greater than the speed of light. I guess in a weird way, you could think of our universe as a black hole - after all, it's impossible to get above the escape velocity (speed of light) to get out. ;)
-- Give me ambiguity or give me something else!
Yeah, but we also only BELIEVE that gravity will continue to function tomorrow. However, there is a wealth of evidence that it will. There is a wealth of evidence for black holes, as black holes in binary systems have been found (of course the black hole could just be a really dim, massive object, but it still is pretty convincing).
Network Security: It always comes down to a big guy with a gun.
http://archive.ncsa.uiuc.edu/Cyberia/NumRel/BlackH oles.html
t ml
t ml
http://cosmology.berkeley.edu/Education/BHfaq.h
http://image.gsfc.nasa.gov/poetry/ask/abholes.h
The only thing necessary for the triumph of evil is for good men to do nothing. - Edmund Burke
That's why we should throw a party at the event horizon. Everyone arrives at the same time and the party lasts forever.
That or nobody ever gets there and the ride is extremely short.
I can't remember which was the inside observer and which was the outside observer. I think it mixes reference points. The same time reference point is short, and the never arrive takes forever.
Isn't relativity fun?
Network Security: It always comes down to a big guy with a gun.
So we're being flushed down a giantic cosmic toilet. Great. I know Tool said I should learn to swim, but I guess that won't be enough.
http://en.wikipedia.org/wiki/Signature_bloc
No, if the universe is 15 billion years old, it could only be 15 billion light years across. Otherwise, two points that are the furthest distance apart from each other at all times during those 15 billion years would be traveling at 2c relative to each other.
Great post. Two basic questions left unanswered in the original article, and a whole host of follow-up questions they've sparked in my imagination...
1) The orbit of this star is described as "eccentric". How eccentric? How close does the star get to the event horizon at its closest point to orbit?
2) Is the star orbiting nearly edge-on to us relative to the black hole (likely, if it's close to the galactic plane), or face-on?
With a period of only 15 years or so, are there points in that orbit at which gravitational lensing effects are significant, and can we get cool data either from lensing or relativistic effects at certain times in its orbit?
Also, how about occlusion events? Can we get data on them? Or is peri"hol"ion (perireallyfsckingbigblackholion!) stuck tantalizingly behind the black hole?
(Oh, the possibilities for a science fiction author. I mean, any species demented enough to try to evolve sentience on such a planet wouldn't need telescopes, would probably call the time their Sun was in the sky "night", and their religious leaders would probably take general relativity for granted until some hereticical freak invented Newtonian mechanics! :-)
Actually, there is a reference to this in one book or the other I've read. A black hole does not have to have infinite density, mearly enough mass to bend light back to itself. As I said before, the earth would become a black hole if compressed to around 1 cm. That is most definately not infinite density. I think you're mistaking the density of the singularity with the overall density of the black hole.
A deep unwavering belief is a sure sign you're missing something...
Assuming a football field is 100m long
(sorry, I'm British):
size of event horizon (36 light second)
= 100 million football fields
closest approach distance of star to hole
(17 light hours)
= 184 billions football fields
The world is everything that is the case
A black hole is just God dividing by zero
You mean the universe is just a bunch of cosmic core dumps? There goes the neighborhood.
Facts are boring things, because they are all just single observations. Here's an example of a fact: On October 15, 2002, I dropped a pencil. It accelerated toward the ground and stopped on impact.
Theories are a lot more interesting, because they are the generalizations that tie facts together. Here are a couple of examples of theories:
"A dropped objects falls toward the center of the earth"
"There is a universal force attracting particles of matter together that is proportional to mass and inversely proportional to the square of the separation of their centers of mass."
Basically, everything that we think we know about the universe is a theory.
> From the point of view of you (on the train), looking forward, you'll see the entire universe running about 10000 times normal speed - stars evolving in minutes - and the bullet flying away from you at 2% of the speed of light.
Argh. The sped-up universe is what a guy on the back of the train looking backwards (and the guy on the black hole probe looking up) sees.
The guy on the front of the train (and you, lowering the probe and observing the probe) sees a universe running at 1/10000th speed - a 2.0 GHz Athlon will look like it's running at 0.2 kilohertz and what-not.
Basically, non-uniform gravitational forces on an extended cloud will give it some (very slow) spin. If the cloud then collapses, conservation of angular momentum greatly speeds up the spin. If you make a very small object (such as a white dwarf, neutron star or black hole) then it will tend to spin very quickly.
So essentially the answer is - random perturbations, greatly magnified.
As another poster aludes to, this spin acts to reduce the ability of the objects to collapse to very small sizes. The more angular momentum there is in the initial gas, the less massive (and more numerous) you expect the results of the collapse to be - whether galaxies, star clusters or stars.
Quattuor res in hoc mundo sanctae sunt: libri, liberi, libertas et liberalitas.
Roger Penrose talks about it in his book `the emperor's new mind', and here is an excellent link
You've got it a bit mixed up. From memory, the elemental abundances after the big bang (prior to stars forming) was about 80% hydrogen, 20% helium, and largish fraction of 1% heaver elements.
Current composition depends on where you are (how much of the gas has been cycled through stars) but solar abundance is I think about 70% hyrdogen, 27% helium and 3% heavy elements.
Warning - all the above was from memory, and may not be accurate.
Quattuor res in hoc mundo sanctae sunt: libri, liberi, libertas et liberalitas.
I hear that to an outside observer, an object moving towards a black hole will never reach the event horizon. This seems very similary to the "Motion is impossible" problem. What if we fling YOU at a black hole? You will not slow down in relation to yourself, therefor you would reach the event horizon, right?
-- 'The' Lord and Master Bitman On High, Master Of All
The galactic year depends on how far out you are (similarly to how solar system years do.) To a good approximation, circular orbit velocity is independent of distance from the center of the galaxy (about 220 km/s), but the distance to travel is proprotional to the radius of the orbit, so the 'year' length is proportional to distance from galactic center. (This approximation fails within a few kiloparsecs of galactic center.)
The spiral pattern is misleading - it is a wave, rather than a group of bright stars that stay together as the galaxy rotates. As time passes stars enter and leave the spiral arms. There is a modest increase in stellar density in the arms, but most of the increased brightness is because the sprial arm triggers star formation, and the very bright stars live for a very short time - so they mostly occur in the arms.
Yes, the rate of star formation in the galaxy is declining, and the abunance of heavy elements increasing (although mass locked up in white dwarfs, neutron stars and black holes is probably more significant for this decline than the change in elemental abundance.) However, new, very bright stars are still being formed, so we won't entirely run out of these for some time yet.
Quattuor res in hoc mundo sanctae sunt: libri, liberi, libertas et liberalitas.
So only 3 million suns, eh? Assuming most suns in the galaxy are at least 0.1 suns of mass, and there's about 100 million suns in the galaxy, this would at the very best case amount to 20-30% of the galaxy's mass. I'm going to guestimate that this number is a bit more like 3-5%. Can anyone give a more accurate figure as to the mass of the galaxy not measured in Solar Masses? (dark matter and all)
I had always thought that a super-massive black hole might explain that 90% missing mass/dark matter theory. Or does the rotation of the galaxy suggest the matter is evenly distributed instead of being all at the center? Or is it too soon to tell?
1) the black hole that you "see" is the evento horizon
2) the point in the singularity
3) one cool thing about black holes this large is that they have the property of sucking everything in whole, no spighetification. you fall and fall and fall as light above you moves from a full view to a single point and you actualy never reach the bottom, time aproaches zero as you aproach the singularity and you realy never do reach the singularity (lim as d -> 0 T == Inf)
I am the Alpha and the Omega-3
The Schwartzchild radius is the radius, for a given mass, that will form a singularity. For a ten solar mass star, that is about 30 kilometers.
The Chandrasekhar limit gives the size limit for a star to collapse and produce a white dwarf. Most stars end their lives with a gravitational collapse, but electron degeneracy pressure (from the Pauli exclusion principle) prevents further collapse. However, for stars above ~1.2 solar masses, the gravitational collapse will overcome fermion repulsion, and the collapse will continue. Once the star's density has reached a certain point, it will collapse into a singularity. That density times the star's mass determines the Schwartzchild radius.
The event horizon is delineated by those light rays that will neither fall in nor escape from, the black hole. However, just because you cross the event horizon does not necessarily mean you will strike the singularity. Instead, it depends upon the type of black hole you've encountered.
In actual reality, you'll be fried by the blue shifted radiation coming from the accretion disk around the hole, but let's ignore that quibble.
Black holes have mass, spin, and charge. No other properties are discernable behind the event horizon. The fact that the above properties can be determined without a world-line (that is, information also does not propagate faster than light, and hence cannot escape) says something fundamental about those properties.
An uncharged, unspinning black hole is called a Schwartzchild hole. Once you cross the event horizon, you will unavoidably strike the singularity and perish.
In the other types of black holes, such as the Kerr black hole (uncharged, spinning), Reisnner-Nordstrom (charged, zero angular momentum), and the Kerr-Newman black hole (charged, spinning) it is possible to cross the event horizon without striking the singularity. Instead, you can pass into another universe.
Indeed, it's theoretically possible that you will pass through many universes. This is a one-way trip, however. If you try to get back to where you were, you will encounter the singularity and die.
Actual solution of the Einstein field equations for the holes listed above, however, produce perturbations. These perturbations, so far, cancel out the ability to miss the singularity and enter another universe.
Moving on, Hawking demonstrated that black holes evaporate. Hawking radiation is produced when half of a virtual particle pair appears inside the event horizon. Since both particles are no longer available to disappear under the Heisenberg time limit, the remaining particle acquires real energy. This energy comes from the black hole.
Since the rate of evaporation is proportional to surface area/mass, smaller black holes evaporate explosively. Indeed, no black holes smaller than a proton could exist from the big bang.
Finally, recent research shows that the universe is inflating, due to Einstein's cosmological constant (which, he ironically labelled as his "worst mistake"). That is, Hubble's constant is increasing. There will be no Big Crunch. The universe will expand at a faster and faster rate into nothingness.
There are a lot of good books on cosmology. General Relativity is undergoing a renaissance right now because of all of this important, new information.
"Invincibility is in oneself, vulnerability in the opponent." --Sun Tzu
From Gsu.edu Astrophysics: ... The Schwarzschild radius (event horizon) just marks the radius of a sphere past which we can get no particles, no light, no information.
Any mass can become a black hole if it collapses down to the Schwarzschild radius
R= 2(MG)/ c^2
Therefore at 3.7 million solar masses...
the Schwarzschild radius is
1.0919401548997975x10^10 M
Which is much smaller than our solar system (the earth orbits at 150,000,000 KM).
But I imgine that they would measure the Acreation Disk.....
The Schwarzschild radius calulation is fun. One can plot density verses radius and it becomes clear that something the size of our galaxy with density of water would be a black hole...
Space is an empty place!
DJMD - The fourth man - Planetary
Crap about event horizons aside, the article was talking about the distance enclosing the black hole and a star orbiting the black hole. The mass was deduced from observations of the orbiting star.
All together now!
There's a hole in the middle of it all, there's a hole in the middle of it all, there's a hole in the middle, there's a hole in the middle, there's a hole in the middle of it all....
There's a quark in the hole in the middle of it all....
Good judgment comes from experience.
Experience comes from bad judgment.
They merge, emitting huge quantities of
gravitational radiation in the process, and eventually settle down into a nice Kerr hole.
There is some hope that gravitational wave observatories like LIGO II and LISA will see the signature of these events (although they are expected to be rare - neutron star/neutron star, neutron star/black hole collisions are more frequent. Most people think these are the gamma ray bursts).
People are trying to figure out the expected waveform of the emitted radiation with numerical simulations, which are notoriously difficult.
The world is everything that is the case
This results in being able to move back and forth in time, but not being able to move away from the center of the black hole.
:)
:)
Really? I've never heard that before! I'm not a physicist, so I'm just talking about things that come up in common places.
But that's really cool. So, all you need to do is find a device that can make -itself- travel through time, and you could travel into the black hole, move yourself through time, and then use the device to move yourself out of the black hole . You've go yourself a method of time travel!
I'm of course somehow assuming it's easier to make a device that can travel through time without taking a person with it.
And that you can somehow get into the black hole alive.
etc.
The enemies of Democracy are
our galaxy does suck.
The best education consists in immunizing people against systematic attempts at education. - Paul Feyerabend
Are these the same scientists who said the average color of the universe was Bondi Blue, then realized they'd made a miscalculation and it's actually beige?
$x='S24;r)>63/* h@<5+oZ)32"5cz';$me='phroggy'x$];
$x=~y+ -xz+\0-Tx+;print$_^chop$me for split'',$x;
Uh, I think every galaxy has one of these in its center. I further believe that every galaxy will consequently get sucked into its black hole. Once that has been carried out successfully, the now entirely too massive black holes will begin to attract each other, during which the universe will begin collapse in on itself, at which time everything will implode within a matter of mere moments (which will appear to stretch out for billions of years due to time dilation) so that everything becomes an infinitely small and infinitely massive point. At that time, time loops over itself and the big bang happens. (I feel like I've written this before... in another life perhaps.)
A friend and I worked out a few calculations on the black hole...
Assuming it was 3 million solar masses, the diameter of its Schwartzchild limit (effectively the diameter of the black hole) would be 8.8 million kilometers, or about 6-1/3 times the diameter of our sun.
If the Earth were in orbit around this black hole at the same distance we are from the sun (assuming it wouldn't be torn to shreds by tidal stresses), a year would be 5 hours long.
The BBC have a similar story
Enjoy
Eclectic beats from Leeds, UK
handmadehands.co.uk
Has anyone got a graphical simulator for large black holes such as our friend in the middle of the galaxy. Regrettably my relativistic calculus sucks, but a visualisation of the effects would be cool.
See the "picture" at Yeah right Besides being (possibly) bogus, that picture is obviously of a Star Trek planet-eater.
One line blog. I hear that they're called Twitters now.
They discovered it made one elliptical revolution every 15.2 years, during which it came as close as 17 light hours from the centre.
Can you hear me now? Good!
One line blog. I hear that they're called Twitters now.
A black hole is a point, but it is not incorrect to describe one with such huge size as the article does. The "body" of the black hole, such as it is, is a point mass but the event horizon is all that really matters. The even horizon defines the "edge" of the black hole...or more accurately, the point at which the escape velocity exceeds the speed of light.
In Bushworld, they struggle to keep church and state separate in Iraq as they increasingly merge the two in America.
I _do_ remember however that in Larry Niven universe there is an expanding black hole in the center of our galaxy, which will destroy all of it in the next hundred thousand years or so.This is wy the Pierson's Puppeteers ( a very "prudent" alien race) decide to leave immediately this galaxy.
Ciao
----
FB
No one has mentioned the Wave Front of Deadly Radiation propagating from the center of the galaxy that the 'Pupperteer's' Flying Worlds are fleeing!?
(and definitely not that Ringworld that THEY discovered?)
.
(David Bowman, EVA near HUGE Monolithic Win-PC in orbit around Jupiter) "My God - its full of Malware!"
It doesn't matter if 'reality' expands faster than the speed of light. Since nothing in our universe can go that fast, the effective border of our universe is as far as light could have travelled since its beginning.
-- Give me ambiguity or give me something else!
Correct.
Beside the train (or on the train, looking out the window), things are foreshortened.
Both guys hold a meter stick horizontal to the ground. Each sees their own stick as being 1 meter long. Each sees the other's stick as being, say, 10cm long.
Okay, so if each guy sees the other's stick as "shorter", who's right?
And what if one guy had a tunnel 40m long, and the train was 80m long, the guy in the tunnel sees the train as being 8m long - surely he can simultaneously close a pair of doors and "catch" the 8m train in the 40m tunnel. But the guy in the train sees the barn as 4m long, and obviously an 80m train can't fit in a 4m barn. Who's right?
Answer here: A Special Relativity Paradox: The Barn and the Pole.
I probably should have talked about a reference frame. However, just how do the enormous events within a black hole affect the local physics?
"Glory is fleeting, but obscurity is forever." --Napoleon Bonaparte
Since the goal of a scientific theory is to describe reality, a theory is "correct" if it accurately describes reality, and incorrect if it does not. A theory cannot, of course, be proved to be correct--it can only be proved incorrect, by obtaining a reliable experimental result that contradicts the predictions of the theory. So, practically speaking, theories fall into two classes: those that have been shown to be incorrect, such as Newton's Laws of Motion, and those that have not yet been shown to be incorrect, and thus still have some chance (although probably only a small one) of being correct.
A theory may be incorrect, but still useful as an approximation. So, for example, Newton's and Einstein's theories of gravity are both considered to be incorrect--Newton's because it is contradicted by experiment, and Einstein's because it yields implausible results when applied at very small scales of distance, but Einstein's is a better approximation--i.e. it yields predictions that are closer to the experimentally determined values than Newton's.
All the advanced physics was interesting and fun to read, but the answer to the comment by the poster, wondering about the mass of the black hole vs the volume of space, is not a matter of black hole physics. Read carefully the sentence from the article:
"The orbital perimeter means that the entire mass of the interior object, between 2.6 million and 3.7 million times more massive than the sun, lurks inside an area three times the size of our solar system."
Get it? It doesn't say the black hole *is* 3 times the size of the solar system, it says the black hole "lurks within" a space that size. It's just a literary turn of phrase.
...you're like saying that black holes are like electrons, neutrons and protons and, like, one of these could be, like, part of an atom in some bigger universe?
That's, like, awesome, Dude.
I have discovered a truly marvelous sig, unfortunately the sig limit is too small to contain i
Newton's Laws are correct for certain conditions: they are exactly what you get when you take Einstein's relativity stuff and slow everything down to small speeds (where v/c is effectively zero). Newton's Laws are not contradicted at low speeds.
Generally in Physics, "correct" and "close enough" mean the same thing. Just about everything in Physics is an approximation; the only question is whether it's a "good" approximation, in which case it's considered "correct" (or "correct enough", at least). (As a friend of mine points out, there are two kinds of Physics theories: "wrong" and "less wrong".)
-Erf C.
Cthulu always calls collect...
They are still very, very real.
I disagree with this last statement. When things are moving slowly relative to the speed of light, and gravity isn't "too" strong, there is no difference between Newton's and Einstein's versions of things. Newton's Laws are not contradicted in these circumstances; they describe things perfectly to any precision you care to measure with (because all measurements are finite, and any differences are tiny).
(Put another way, nobody has proven that Newton's laws are in fact wrong at low energy, even given infinite precision! This is because nobody's made an experiment with infinite precision. So we assume Einstein's theory holds at low energy because it's ugly to switch theories just because you changed energy, but at the same time we use Newton's stuff because it's also right and is easier to use.)
I'm trying to make two points here. First of all, Einstein's stuff and Newton's stuff are the same at low energies (low speed, low gravity), because all the scary looking bits become zero at low energy to any precision you care to measure at. They predict the same behaviour. They work the same. They look the same. They are the same.
Which brings me to my next point: pretty much all of Physics is approximations. We approximate anything we can as long as (a) we're careful about the approximations to make sure we know when they're valid, and just how valid they are, and (b) it makes the math easier. :) We call a theory or law "true" but most of them have points where they break down. The distinction between "correct" and "so close we can't see the difference" isn't really there, or at least isn't worth worrying about.
Newton wasn't wrong. He wrote down three "laws" to describe what he saw, and he succeeded precisely. It's the people who tried to use his theories to describe high-energy stuff that were wrong, as they quickly found out. :)
Looking back, I see that this is basically a very long way of restating your other comment, so that's cool. :) But just as you say you hate it when people say "relativity is wrong", I hate it when people say "Newton was wrong."
-Erf C.
Cthulu always calls collect...
I disagree. Anytime there is motion or gravity, Newton's and Einstein's equations yield different predictions. Whether or not those differences are within the range of a practical measurement is irrelevant. There are therefore only two possibilities: Only one of them is correct (i.e. exactly accurate) as a description of reality or neither of them is correct. I don't think that it is semantics to insist that "correct" and "true" mean only one thing: an absolutely perfect description of reality to an infinite degree of precision. So a theory cannot be "true" at one time, and not true at a later time. I think talking about degrees of truth when it comes to reality makes about as much since as being a little bit pregnant. We have plenty of perfectly good terms for talking about theories that are close, but not absolutely correct under every conceivable condition--"approximation" for example. I agree that pretty much all of physics is approximation, but that is no excuse for abandoning the concept of truth. Let's preserve the conventional meanings of truth as "absolute and perfect correspondence to reality."
I'm trying to make two points here. First of all, Einstein's stuff and Newton's stuff are the same at low energies (low speed, low gravity), because all the scary looking bits become zero at low energy to any precision you care to measure at. They predict the same behaviour. They work the same. They look the same. They are the same.
There is nothing about the equations of either theory that limits it to a particular range of conditions. A true theory must yield perfectly valid results for any physically realistic value of its parameters. If it fails to do so, then it is merely approximation to the true (and quite possibly unknown) theory.
Perl, cosmology and astrophysics? This has got to be the nerdiest joke ever written on /.
It is by the juice of the coffee bean that thoughts acquire speed, the teeth acquire stains. The stains become a warning
If the mass of the black hole is 2.6 x 10^6 times that of our sun, the radius would be closer to 150 million km. (That's a very crude pseudo-calculation, so don't quote me.)
Any sufficiently simple magic can be passed off as mere advanced technology.