Re: Dark matter

In message <1190045107.868790.128830@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>, Bill Hudson <oldgeek61-951@xxxxxxxxx> writes
On Sep 17, 7:24 am, Ye Old One <use...@xxxxxxxxx> wrote:
On Mon, 17 Sep 2007 01:17:39 -0700, spintronic
<spintro...@xxxxxxxxxxx> enriched this group when s/he wrote:

>On 16 Sep, 19:29, Lee Oswald Ving <leeov...@xxxxxxxxx> wrote:
>> > spintronic <spintro...@xxxxxxxxxxx> wrote in
>> >news:1189941467.586354.45840@xxxxxxxxxxxxxxxxxxxxxxxxxxx:
>> >> Question!

>> >> Could you tell me why dark matter is homogenous in *all* galaxies,
>> >> yet missing in globular clusters?

>> And while we're at it - why do you believe this?

>Because it's true!

Cite?

--
Bob.

I don't know that it is true. Since dark matter was only recently
detected in galaxies, it could be that they have not refined the
technique enough to detect it in clusters. As far as I know (but I
certainly could be wrong) dark matter is detected (indirectly) only in
galaxy clusters, not individual galaxies. So far, DM is detectable
only by the gravitational lensing of more distant objects, so you'd
need a lot of it. Clusters need not apply at this point.

One of the observations that supports the existence of dark matter is that galaxies in clusters and stars in (the outer regions of) galaxies would not be bound if the visible matter was all that was there (and our theories of gravity and mechanics are correct). Globular clusters are much denser systems than galaxies and clusters, so, if dark matter is (much) less strongly clumped than visible baryonic matter the effect of dark matter on orbits within globular clusters could be less than the error bars on the observations.

From observations of stellar motions we can at best only put a lower bound on the excess density of dark matter in globular clusters.
--
alias Ernest Major

.

Relevant Pages

  • Dail Report # 4442
    ... filter and chip combinations before WFPC2 is decommissioned in SM4. ... Group galaxies which we recently discovered: ... nature of dark matter by using two, massive, newly-identified merging ... clusters of galaxies. ...
    (sci.astro.hubble)
  • Galaxies are born inside dark matter clumps (Forwarded)
    ... Galaxies are born inside dark matter clumps, ... University research associate Duncan Farrah, the lead author of a paper ... clusters in the early universe. ...
    (sci.space.news)
  • Galaxies are born inside dark matter clumps (Forwarded)
    ... Scientists are finding that galaxies may distribute themselves in similar ways throughout the universe and in places where there is lots of so-called dark matter. ... "Our findings suggest that unseen dark matter -- which emits no light but has mass -- has had a major effect on the formation and evolution of galaxies, and that bright active galaxies are only born within dark matter clumps of a certain size in the young universe," said Cornell University research associate Duncan Farrah, the lead author of a paper on spatial clustering that appeared in the April 10 issue of Astrophysical Journal Letters. ... From this he was able to calculate the amount of bunching in candidate galaxy clusters in the early universe. ...
    (sci.astro)
  • Re: Dark matter
    ... interested in the claim that 'dark matter is missing from globular ... is no dark matter in globular clusters" I'm not sure what point you ... detected in all galaxies. ...
    (talk.origins)
  • Daily #4085
    ... Holes in Globular Clusters ... that globular clusters contain massive black holes. ... selected galaxies exceeds that of optically selected galaxies. ... star formation and AGN activity and the manner in which instabilities ...
    (sci.astro.hubble)