Sam Wormley wrote:
Fred Chen wrote:
Sam Wormley wrote:
Have we seen the first "dark galaxy"? (Feb 24)
http://physicsweb.org/article/news/9/2/14
Radio astronomers may have found the first ever galaxy that is
made
almost entirely of dark matter. The "dark galaxy", which lies
in
the
Virgo cluster about 50 million light years away, rotates in the
same way
as an ordinary galaxy but does not contain any stars (R Minchin
et al.
Astrophysical Journal at press).
What is interesting is their estimate that the invisible mass in
the
galaxy is estimated 1000 times the hydrogen in the galaxy VIRGOHI21
which is 100 million solar masses. That means the dark mass is 100
billion solar masses, way more massive than expected for active
galactic nuclei; it is essentially on the galactic mass scale.
But most visible galaxy rotation indicates 10 times more unseen
matter
than visible matter, so this new observation does not seem unusual
in
terms of total mass.
I see .. so it is considered a typical 'dark halo' without the visible
galactic matter.
Given the widely held belief that there are many more of these than
normal visible galaxies, hopefully there are some gravitational lensing
experiments that are in the process of finding more of these.
.
