Re: Chandra and black hole abundance

From: Robert Bradbury (
Date: Sun Jan 16 2000 - 01:29:44 MST

On Sat, 15 Jan 2000, John Clark wrote:

> Robert Bradbury <> Wrote:
   ... I had discussed the problem of nanoprobes encountering black holes.
> I don't think that's a serious problem. A stellar black hole is only about 15 miles
> in circumference (black holes don't have a meaningful radius) so the chance of
> hitting one directly by accident is almost nil, and a probe moving at 2% of the
> speed of light a near direct hit is what you'd need to get into trouble.

This is a good point (Mentally I drop the fact that these objects are
really compact). So the real problem is not so much falling into one
but whether or not you can detect any radiation emitted from infalling
matter and avoid the high radiation doses, or perhaps more importantly
doing the course corrections after one that you didn't "see" drags
you off course. Perhaps one of our rocket engineers would like to
comment on how much fuel/energy you would need to correct the deflection
caused by a 1g nanoprobe coming within a few AU of a standard stellar
mass black hole?

> Chandra just discovered the closest known black hole to earth, it's
> 1600 light years away. What would be really interesting is if it can find
> any mini black holes, those about as massive as a mountain and made in the
> first second of the Big Bang. Such a beast would be super hot but so tiny that
> it would not be very bright, if one is found it would have be nearby and that
> would mean mini black holes are common.

But that would seem to imply, that there "should" be more astronomical
phenomena associated with encounters between "small" black holes and
planets, stars, etc. My impression is that even the smallest black
holes should be able to "eat" stars? Is that not correct?
Of course this depends on their density. I suppose there might also
be the question of whether or not in the early history, most of the
micro-black-holes got aggregated into the massive black holes that
serve as the galaxy seeds.

An interesting image though -- you have to form structures that
suck matter out of the universe in order to organize the remaining
matter into structures that can support life... I think I hear
the twilight zone music in the background...


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