[ExI] Has the mystery of Dark Matter been solved?

BillK pharos at gmail.com
Thu May 26 14:40:38 UTC 2016

On 25 May 2016 at 09:33, Anders wrote:
> Likely just to annoy John, there is a recent paper (
> http://arxiv.org/abs/1603.08522 ) arguing the early supermassive holes could
> be due to direct collapse of gas clouds. I cannot judge the likelihood of
> this, but it will be interesting to see how it turns out.

Ethan Siegel discusses why black holes = dark matter is unlikely.

As soon as this idea was first suggested, it was recognized that there
were a number of restrictions on this possibility. Whenever a mass
passes between your line-of-sight and a distant object, that mass acts
like a gravitational lens, thanks to Einstein’s relativity. The effect
of a transiting dense, dark object — known as microlensing — has been
searched for at some length. While there is some microlensing seen due
to these compact masses in our galactic halo, they’ve been more useful
as far as constraining what fraction of the matter could be at the
larger end of these primordial black holes. In addition, if the black
holes are too small in mass, they’ll evaporate due to Hawking

All told, observations of

the lack of Hawking radiation,
gamma-ray-burst microlensing,
neutron star capture in globular clusters,
traditional microlensing,
and the cosmic infrared and microwave backgrounds,

tell us that we can’t have primordial black holes make up the majority
of dark matter over a wide variety of mass ranges.


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