Re: How can we 'see' a blackhole?

On Mon, 12 Feb 2007 01:07:17 -0500, "Greg Neill"
<gneillREM@xxxxxxxxxxxxxx> wrote:

I need to find some figures on the expected infall time
for matter in an accretion disk (i.e. persistence time
for the disks of a non-accreting black hole). I'll
keep browsing.

Just for fun, I did a back of the envelope calculation. Assuming the
black hole is traveling 20 km/s and sweeps up all the interstellar
matter (1e-21 kg/m^3) across a 10 km cross section, and that it
completely converts the mass to energy, the output will be 1.4e8 J, or
the equivalent of 34 kg TNT per second. In practice, the energy would be
less. I doubt we could detect such an energy source at any appreciable
distance. You'd need a black hole that already had one of these stable
accretion disks before it got launched, and then you'd need it to pump a
lot of its own energy into the disk, but without driving material out of
the disk, which can only collect new material at about 1 microgram per
second. Sounds unlikely to me.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
.

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