(Submitted February 17, 2002)
Could dark matter be composed of mini-blackholes formed at the time of
the Big Bang?
This is a very good question. We at "Ask an Astrophysicist"
know that it's currently not considered to be a major constituent of dark
matter, but we're not sure if we know all the reasoning behind this.
Here is what we do know.
Stephen Hawking proposed primordial (i.e., created just after the Big Bang)
black holes in connection with his work on black hole evaporation:
This process (Hawking radiation) should have destroyed the lowest mass
primordial black holes by now, and should currently be destroying ones
that started out with the mass of a small asteroid. However, no
mini black holes have been discovered to date, through Hawking radiation:
or through other means.
Note that the number and the masses of primordial black holes depend
sensitively on the nature of density fluctuation in the early universe.
We have learned a lot on this topic since Hawking made the original
suggestion: the Cosmic Microwave Background as measured by COBE is
extraordinarily smooth on the one hand, while we now know of large-scale
clustering of galaxies, on the other hand. As we understand it, current
models of density fluctuations that account for these observations do not
predict a large number of primordial black holes. Therefore, they are
probably not a major component of dark matter.
You might want to fallow this up with the Dark Matter FAQ site at Berkeley:
Hope this helps,
Koji & Ilana
for "Ask an Astrophysicist"