Big old black hole

[arcticpenguin]

http://xxx.lanl.gov/abs/astro-ph/0303062

Someone claims to have measured the mass of a black hole 13 billion light years away by a novel method. They came up with a mass of 3 billion (3x10^9) times the mass of our sun.

This needs some 'splainin', since black holes are supposed to grow slowly over time.

[garys_2k]

Originally posted by arcticpenguin
http://xxx.lanl.gov/abs/astro-ph/0303062

...black holes are supposed to grow slowly over time.
They are? Why, and from what "original" size?

I've never heard anything that actually prevented big black holes, but I can see where that type of growth may be problematic. Perhaps some biggies were left over from the big bang?

[arcticpenguin]

Here's the commentary by ScienceNow: http://sciencenow.sciencemag.org/cgi/content/full/2003/324/1 (subscription only)

[Andonyx]

Since our sun is too small to collapse into a black hole wouldn't any black hole have to start out with significantly more mass than our sun?

I mean the hole is not 3 billion times the VOLUME of our sun.

Granted 3 billion is more than just significant, it's a huge difference, even on a stellar scale, But I also don't know what size an "average" black hole starts at. I thought the smallest stars that turn into black holes are around a million times the mass of our sun.

[Crossbow]

Well, there is a large black hole is at the center of our galaxy (which is pretty big for a galaxy).

So I expect that this black hole is what remains of one really, really big galaxy, or the remains of several smaller galaxies.

[arcticpenguin]

Originally posted by Crossbow
Well, there is a large black hole is at the center of our galaxy (which is pretty big for a galaxy).

So I expect that this black hole is what remains of one really, really big galaxy, or the remains of several smaller galaxies.
"What remains"? The object being measures existed 13 billion years ago. There shouldn't have been a lot "remaining" at that time.

[garys_2k]

I've read that black holes are suspected in the centers of most globular clusters (thousands of stars), and I would suppose that most galactic center black holes are surrounded by material in relatively stable orbits.

However, as CB alluded, if there was a galactic collision it would likely REALLY cause instability and a biggie could sweep up a lot of stars.

[garys_2k]

Originally posted by arcticpenguin

"What remains"? The object being measures existed 13 billion years ago. There shouldn't have been a lot "remaining" at that time.
You're right! That would make the universe ~700 million years old at the time we're observing it.

Likely a big bang remnant.

[Agammamon]

http://archive.ncsa.uiuc.edu/Cyberia/NumRel/BlackHoles.html
Basically a star above 1.5xsun's mass can collapse into a black hole. Black holes grow over time through because mass is drawn in from their vicinity. Black holes also shed mass through a QM mechanism. Small black holes can actually shed mass faster that they can accumulate is and eventually dissapear. Large holes can from simply through the accumulation of mass, by small ones require some external force to compress a mass into a critical volume.

[FireGarden]

I gave an estimate for the doubling time of a black hole (in a different thread) of about 45 million years. But the equation I used wasn't particularly designed for that.

The equation I used was based on this:
If gaseous matter orbiting a black hole is spiralling in, then it has angular momentum to lose. It does this through interaction (friction/viscosity) with the inner rings of an accretion disk. This process allows the infalling matter to lose gravitational energy through radiation. This radiation in turn provides a counter pressure against the gravitational attraction of the black hole. It can reach a limit where if it exceeds this, the radiation would be blowing away matter more powerfully than the black hole attracts it. This puts a limit on the luminosity of an accreting object of given radius, and also a limit on the rate at which matter can accrete in this fashion.

From that, I estimated 45 million years to double the mass of a black hole (If the matter was available).

But if an object merely falls into the black hole, rather than spiral down in a viscous disc, all its gravitational energy will be turned into kinetic energy and no radiation. If the matter is available in this way, then the doubling time for the mass of a black hole could well be less than 45 million years. I suppose this may become a possibility in galactic collisions, but in most cases (like the centre of our galaxy) matter would orbit the black hole, and so have to spiral in.

I don't see how saying the big bang did it helps in this case.
You still have to force the matter in, and force it in rather quickly to reach 3 billion suns in 700 million years. Matter resists compression. Even ignoring angular momentum, there has to be a limit to how quickly you can stuff matter into a black hole.

I don't know,
First we worried that they may grow too quickly... Now we worry whether they grow fast enough!

[garys_2k]

Couldn't "black hole stuff" be just one of the ways matter was left after the bb? In other words, maybe some of the early soup happened to form into that? Or is there some reason that a black hole ALWAYS has to form from ordinary matter?