Re: Chandra and black hole abundance

From: John Clark (
Date: Sat Jan 15 2000 - 11:17:21 MST

Robert Bradbury <> Wrote:

>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).

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.
A super massive black hole is a little larger, about the size of the solar system,
but there are probably only one or two this big per galaxy and so can be avoided.

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.

       John K Clark

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