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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
So, does that mean that in time, the blackhole will swallow up the star?
-Cyc
/.'s 10 Millionth
where Enron's accountants found work.
"...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.
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.
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
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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
Since when do black holes occupy so much space (I thought they were points)?
They're big points.
RMN
~~~
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
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!
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!
"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?
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".
Several things wrong in here. First, it's the huge density at the center of the galaxy that would lead you to think a black hole might form there. Yeah, the density is big there because it's way down in a gravitational potential well. But intense gravity doesn't create a black hole-- quite the other way around, in fact.
Second, spiral galaxies are *not* spiralling down the drain. Most of the stars in a spiral galaxy orbit the center approximately circularly; they aren't spiraling in any more than the earth is spiraling into the Sun. So why the spiral shape? Spiral shape can come from a couple of differnet things. In some galaxies, they are density waves. Think of them as a cosmic "traffic jam". In some places, the stars are closer together than other places; in those places, densities are higher, and gas clouds get compressed, and more stars form (which is why spiral arms are bluer). As the wave passes through those stars, they will spread back out. It's similar to sound waves (which are density waves), or, indeed, clumps of cars on freeways (which seem to maintain their identity even though they don't always have the same cars in them-- you pass through them, so for a while you're a part of the clump, but eventually you get past the clump).
Other theories of spiral structure formation are based on the differential rotation; when a big group of stars form, the differential rotation will tend to stretch it out into a little spiral arm segment. These theories are probably more responsible for spiral structure in galaxies where the arms are ratty and choppy. The density wave theory is probably more responsible in "grand design" spirals where you can trace one long arm all the way from the center out to the edge.
One thing spiral galaxies are definitely not however are stars spinning down the drain the way water spins down a drain. It may look obvious, but it's wrong. (Yes, there are ways to get material to sink down to the center of galaxies, but generally it's a whole lot easier with gas and dust than with stars. Gas and dust are viscous fluids, but stars are basically collisionless.)
-Rob
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
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
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.
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...
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
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.
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.
> 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.
Roger Penrose talks about it in his book `the emperor's new mind', and here is an excellent link
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
our galaxy does suck.
The best education consists in immunizing people against systematic attempts at education. - Paul Feyerabend
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.
How about this one: What if our known universe resides inside a black hole, and black holes act just like quantum particles? Our universe could be just an elementary particle that acts as part of a sand grain on a super-universal beach.
If that could be true, how about tiny universes residing in each of our tiny elementary particles?
Think about a proton having a half-life. At that point, all the matter in that little universe has collapsed into little black holes, and it's time for that bugger to move on.
Blah, blah, blah, and so on.