
Astronomers puzzled over huge black hole in the middle of small galaxy - evo_9
http://arstechnica.com/science/2012/11/astronomers-puzzled-over-huge-black-hole-in-the-middle-of-small-galaxy/
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Empact
Wild speculation: our first evidence of advanced alien societies carrying out
the transcension hypothesis?

<http://accelerating.org/articles/transcensionhypothesis.html>

<http://www.youtube.com/watch?v=nQOyJUDTKdM>

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sambeau
If the stars are all old and the black hole is surprisingly big, could it
simply be that the black hole has swallowed most of the galaxy already?

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splat
It's generally hard to get stars to collide with black holes since even the
very largest black holes are still very small relative to the distances
between stars. There's just too much angular momentum that needs to be
removed. (Which is not to say that it can't be done -- it can, and there are
various mechanisms for doing so, but it's very difficult to do for a
substantial fraction of a galaxy's mass.) Even if this occurred, it's
nevertheless surprising that it happened in this particular galaxy, and didn't
occur in pretty much every other one.

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sambeau
Fascinating.

I'm clearly guilty of believing left Black Holes are like plug-holes in the
centre of galaxies and eventually everything will swirl down them.

So this isn't a valid picture? Do you have a more realistic one for me instead
to think about?

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splat
Far from the event horizon, a black hole acts like a point mass just like
every other star. If, for instance, the Sun were to immediately turn into a
black hole, the Earth would continue to orbit it as if there had been no
change.

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sambeau
Assuming it kept the same mass?

And even if it had a lot more mass?

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splat
Assuming it kept the same mass. If it had a lot more mass, the Earth's orbit
would be identical to it's orbit around a star with that much more mass. The
fact that an object is a black hole only becomes relevant when something
passes the event horizon. Outside the event horizon, it acts like any other
object with the same mass.

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pc86
I know next to nothing about black holes, is there any relation between the
size of a black hole and the amount of matter it's "swallowed?"

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vedant
Yes. The radius of the "event horizon," which is the spherical boundary that
serves as the point of no return, grows as it swallows more mass. For a
Schwarzschild black hole (which doesn't rotate and has no charge), the event
horizon radius is 2GM/(c^2), where c is the speed of light, M is the mass of
the black hole, and G is the gravitational constant.

The singularity at the center doesn't grow. But a black hole's "size"
generally refers to the radius of its event horizon.

Wolfram Alpha computes it for you:
[http://www.wolframalpha.com/input/?i=schwarzschild+radius+fo...](http://www.wolframalpha.com/input/?i=schwarzschild+radius+for+100+solar+masses)

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bcbrown
I learned this interesting factoid in an astrophysics class. All data is from
Wolfram Alpha:

Mass of universe: 3 * 10^52 kg

Schwarzschild radius for that mass: 4.455 * 10^25 meters

Volume of sphere with that radius: 3.704 * 10^77 m^3

Density = mass / volume = 8.099 * 10^-29 g/cm^3, or roughly 8 times the
approximate universe density

I think it's interesting that a universe-sized black hole would be a mass
within an order of magnitude of the universe's mass.

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CamperBob2
Isn't the ratio between dark matter and 'normal' matter something on the order
of 8:1 as well?

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cwkoss
Would we be able to differentiate a massive Dyson Sphere from a black hole?

