View Single Post
  #8  
Old March 8th 16, 09:17 AM posted to sci.astro.research
Steve Willner
external usenet poster
 
Posts: 1,172
Default Did LIGO Detect Dark Matter? - New paper on arxiv.org

Nature doi:10.1038/nature17140
"The dispersion measure and redshift, in combination, provide a
direct measurement of the cosmic density of ionized baryons in the
intergalactic medium of Omega_IGM = 4.9 +/- 1.3 percent"


which happens to be exactly the Concordance value for the total
baryon density. The uncertainty is fairly large, though.

In article ,
"Richard D. Saam" writes:
It is important to note 4.9 percent refers to ionized baryons and
is not an indicator of non ionized baryons, if they exist,


Neutral gas would show up in the 21 cm hydrogen line. I don't know
whether this particular line of sight has been observed, but all the
H I masses I know of are far smaller than 4.9%, i.e, neutral gas
seems to be a trivial fraction of the "baryon budget." Stars are a
more significant fraction and (based on the quote above -- I haven't
read the paper yet) are also not accounted for in the ionized gas
measurement.

The interesting thing is that this measurement is in agreement with
newer estimates of ionized gas in galaxy clusters, and the "missing
baryon" problem seems to have gone away.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA