Re: Chandra and black hole abundance

From: Robert Bradbury (
Date: Sat Jan 15 2000 - 14:33:41 MST

If my reading of the ABC News press release last night was correct,
there seemed to be an implication of ~1 supermassive black hole
per galaxy. Current estimates for # of galaxy are on the order of a
few hundred billion, so this would be about several hundred *billion*
supermassive black holes in the universe. The Chandra data seemed to
suggest that big black holes might come first and serve as "crystalization
centers" (matter attractors?) for the rest of the matter that makes up the galaxy.

Chandra's big find was resolving the hazy background X-ray "glow"
into distinct point sources -- *very* distant point sources.
I believe they think they are seeing high output quasars in the
early history of the universe. The quasars quiet down after
they have eaten all of the nearby matter. I believe there may
have been confirmation of several (< 10?) black holes *in*
our galaxy, that there was previously insufficient data to confirm.

Its worth noting the distinction between the "quasar" class
supermassive black holes (~1/galaxy) and the "stellar" class
black holes that are left over from big stars exploding.
What I'm unclear about is whether the paper Damien is quoting
is refering to the supermassive black holes or some extrapolations
of the "confirmed" "stellar" black holes in our galaxy to a galaxy
abundance count.

I think we need a reality check here. If we have between 200 and 400
*billion* stars in the galaxy that means we have 1 black hole per few
thousand stars??? This might be right but someone like Amara should
comment on whether the Initial Stellar Mass Function distribution
would produce supernovas resulting in black holes for ~1 in 1000 stars.

I think we need some "scientific source" URLs (rather than quotes from papers
extracted from press releases).

Now, what gets interesting is the problem of seeing those black holes.
Nanoprobes (or even non-nanoprobes) may have a hard time detecting
them early enough to avoid falling into or being irradiated by them.
The question is whether you have to have a Chandra-mass telescope to focus
the incoming X-rays? If so, you are definately no longer a nano-probe.
So, we have yet another possible problem in the realm of interstellar
travel (in addition to cosmic radiation and hitting dust particles).

On Fri, 14 Jan 2000, Eugene Leitl wrote:

> I wonder what it means for local hole density. How many lightyears is
> it to the next on the average?
> Damien Broderick writes:
> > My newspaper tells me very briefly that the latest X-ray telescope data
> > suggest`at least' 100 million black holes in the galaxy. That's not very
> > many, not for the dark matter problem (but every little helps).
> >
> > Damien Broderick

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