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

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: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?

[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.