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

Mon May 23 23:33:19 UTC 2016

On Mon, May 23, 2016 at 2:57 PM, Anders Sandberg <anders at aleph.se> wrote:

O
>  
> n 2016-05-23 19:19, John Clark wrote:
>
>> >> 
>> We know from the percentage of the  elements Hydrogen, Deuterium, Helium
>> and  Lithium  how much regular matter was around one minute after the Big
>> Bang when nucleosynthesis cooked up these elements, and there is no room
>> for Dark Matter.
>
>

> 
> Huh? Can you unfold how the nucleosynthesis data doesn't fit dark matter?
> Last time I checked the literature (fall last year) there was a fairly
> decent parameter window of the nuclei/DM parameter space, where lithium
> abundance was used as a sensitive constraint on the properties of DM.
>

The present

lithium
and Helium 
abundance

gives a tight constraint on the amount of normal baryonic matter (matter
made from electrons neutrons and protons) that
could have 
existed at the time of  nucleosynthesis
, and there is not nearly enough of it to account for
Dark Matter. So whatever Dark Matter is it can not be normal 
baryonic matter
,
 and it can't be made of Stellar Black Holes that came from burnt out
stars either because stars are made
baryonic matter
,
 and there was never enough
baryonic matter
. But Dark Matter
might be made of Primordial Black Holes that were made of stuff that was
never baryonic and formed not one minute after the Big Bang as
Helium and 
Lithium w
ere
but less than a thousandth of a second after the Big Bang.

Primordial Black Holes
could solve another
mystery too. Astronomers have found a 12 billion solar mass
supermassive Black Hole that existed just 900 million years after the Big
Bang, and they've had a very hard time explaining how a Black Hole could
get that big so quickly from the merger of much smaller Stellar Black Holes
that were produced from dead stars. But if you had 100 solar mass Black
Holes around since day one, and if they were very very common, in fact if
85% of all matter was in that form, then the creation of a 12 billion solar
mass Black Hole 900 million years later is much easier to explain.

> 
> I thought the gravitational lensing studies ruled out black hole halos
> fairly strongly.
>

The number of 
gravitational lensing
 events that have been observed has ruled out Dark Matter being made of
Black Holes larger than 100 solar masses, but not smaller. And the fact
that we don't see a lot of widely spaced binary stars moving in strange
orbits rules out Dark Matter made of Black Holes smaller than 10 solar
masses but not larger. Nothing has ruled out Dark Matter being in the 10 to
100 solar mass range and LIGO found Black Holes right smack in the middle
of that range.

 John K Clark
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