It's Official: Black Holes Have Lots Of Mass

KewlPC writes "Spaceflight Now reports in this article that some scientists have been able to measure the "weight" (yeah, yeah, it's actually mass, not weight) of a black hole that is (or was, 13 billion years ago) eating up the most distant known quasar, some 13 billion light years away."

Comments

Duh.

[Ayanami Rei]

Even I knew that. I mean, stuff keeps falling in them. You know that last significant figure to which they measured the weight? About 10^-8 percent of that are my keys, for sure.

Re:Duh.

[Alsee]

About 10^-8 percent of that are my keys, for sure.

Measurements show that 12% of the mass is single socks. Scientists are still trying to identify the other 88% of mass.

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Re:Duh.

[robson]

Measurements show that 12% of the mass is single socks. Scientists are still trying to identify the other 88% of mass.

Scientists have informally labeled the remaining 88% dark socks. ;)

Neat

[Anonymous Coward]

This is neat, I'd never heard of this before:

The extreme brightness of this quasar also shows that the black hole in its core is swallowing matter at the maximum rate possible. This maximum rate is called the "Eddington Limit". If the black hole were accreting matter any faster, it would shine even brighter, and the intense luminosity would actually exert enough pressure to stop any more material falling in.

So there's a limit / "max throughput" to how much matter a black hole can suck in? Very interesting.

Re:Neat

[ndevice]

this is how normal stars work too. The radiation pressure generated by the core keeps the core from collapsing into itself. - well not quite the same, but same idea.

But I haven't heard of the eddington limit before either. Neat.

Re: Neat

[Black Parrot]

> So there's a limit / "max throughput" to how much matter a black hole can suck in? Very interesting.

Yep, there's bandwidth problems everywhere.

Re:Does this say anything about its size?

[ndevice]

You might be confusing neutron stars (pulars sometimes) with these quasars.

Neutron stars are prevented from collapsing into black holes because of nuclear repulsion / neutron degeneracy (instead of electron repulsion). In fact, there's so much pressure that the electrons get squeezed into the protons of the atoms - hence neutron stars.

Black holes have enough gravity to overcome nuclear repulsion and collapse further than neutron stars. I think there's a couple theories about just what happens inside the black hole, but the commonality is that particles don't mean much whether or not you're talking about a singularity, or the non-singularity quantum foam theories.

Re:Does this say anything about its size?

[Flamerule]

Gack, I really need to go to sleep.

I'm right in saying "the Schwarzschild radius of a black hole is proportionate to its mass", but more properly it's directly proportional; i.e., the proportionality constant is 1.

Well, as long as I'm here, let's do some calculations. The article says the black hole's mass is 3 billion times that of our Sun, so multiply 3 km by 3 billion and you get 3 km * 3*10^9 = 9 billion km. To put things in perspective: the distance to Alpha Centauri is 3.8*10^16 m = 3.8*10^15 km, so this black hole's radius is only .0002% of the distance from here to the nearest star. Quite small, astronomically-speaking.

interstellar dust reddens

[barakn]

Atoms produce very specific patterns of absorption or emission in the light spectrum depending on species. A familiar example, is the solar spectrum, which is created by absorption of narrow bands in the spectrum by a large number of different elements in different states of ionization. Redshift causes the entire set of these lines to be moved towards the red end of the spectrum. They retain the spacing between themselves, so they can still be recognized in their new positions, and their new positions tell us how fast the object that created them is moving. Reddening caused by dust doesn't move these absorption lines. Instead it scatters light preferentially at the blue end of the spectrum, causing the entire end of that spectrum to dim, rather than creating narrow bands in it or moving narrow bands around. These two different processes are usually distinguishable.

Re:eddington limit and black hole evaporation

[Flamerule]

Given that in the process of evaporation, a black hole emits radiation, at some point the radiation pressure from the evaporation would balance out the force of gravity pulling matter into the black hole so then the black hole might stabilize in size.

Whoa, whoa. Yeah, a very small black hole would emit enough radiation to completely counterbalance its own gravitational force, so that matter would stop coming flowing into it. But how would that make the size stable? With no more matter coming in, the black hole would just keep emitting radiation, getting smaller, and losing mass, until it evaporates.

To put it another way, it's not a stable limit, it's an unstable limit. If a black hole is accreting mass at a rate less than or equal to this limit, the black hole will shrink and evaporate; if a black hole is accreting mass at a rate greater than the limit, it will grow.

Someone's bitter memories of high-school physics?

[tunah]

the "weight" (yeah, yeah, it's actually mass, not weight)

What was all that about? Why not just say "the mass"? This is on a site that uses computer and physics jargon and acronyms all the time, mass isn't exactly an obscure concept.

Re:Does this say anything about its size?

[Smidge204]

I'm right in saying "the Schwarzschild radius of a black hole is proportionate to its mass", but more properly it's directly proportional; i.e., the proportionality constant is 1.

Something about that seems... counterintuitive?

You're saying that if I have a black hole with a mass of x, it has radius y. Then you say if it has mass 2x, it has radius 2y?

If a black hole is a sphere, doubling it's radius increases it's volume by a factor or about 33 1/2! Since mass only doubled, it's density just dropped by a factor of 17?

I admit I'm not very experienced with black holes, but if anything it seems a black hole would condense to some maximum possible density, and it would maintain that maximum possible density regardless of how much mass you add to it... so it just seems strange that doubling it's mass would actually double it's radius.
=Smidge=

Re:Does this say anything about its size?

[Alsee]

I'm curious as to whether black holes are compacted so much that most of the space between atoms (and even subatomic particles?) is gone, or whether the repulsions keeping them apart are even stronger than the force of the black hole's gravity.

Ok, first you get netron stars where the space between atoms is gone. The entire star becomes one big "nucleus". Then there are quark stars (I think they may still be uncertain about whether quark stars exist). In a quark star the space between subatomic particles (neutrons protons and electons) is gone.

THEN you get to black holes. Once you get within a certain distance of a black hole all laws of physics other than gravity effectively cease to exist. It isn't a question of gravity being stronger then the repulsion - the repulsion no longer exists. What happens is that the repulsive force itself gets pulled in by the gravity.

Think of it this way: Imagine the repulsive force is sound and gravity is wind. A black hole is where the wind is faster than the speed of sound. No matter how strong the repulsive sound is it gets carried inwards. It can't push outwards on anything.

We don't really understand what happens at this point. All known laws of physics break down within this region. We need to discover new laws of physics. The answer will probably be found in a theory of "Quantum gravity".

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Re:Does this say anything about its size?

[taliver]

Actually, a quick googling found this:

r0=2GM/c^2 (Eqn 10.1.5)

So it is directly proportional. However, I didn't look closely at the units that they are using here, but thta shouldn't matter to the solution at hand.