As seen a couple of postings down, dark matter has been a topic of recent interest on this blog. A few weeks ago, Texas Tech astrophysicist Ron Wilhelm gave a talk on campus about dark matter and his research on visible matter from the stars, which I was able to attend (on Ron's website, you'll notice his self-description as a "stellar astronomer;" whether the pun is intentional or not, I don't know).
An exciting development for Ron is that an article from his research team has just appeared in the prestigious general-science journal, Nature (Texas Tech news release; abstract from Nature). The article is about our Milky Way galaxy's two stellar halos.
This University of Tennessee document provides a nice overview of the visible and invisible components of a galaxy, with the dark-matter halo included among the latter. The dark matter halo is said to be "of unknown composition but [it] makes itself felt by its gravitational influence on the visible matter." This page also notes that:
In our own galaxy, the observed rotation of the stars and gas clouds indicates that the visible matter is surrounded by a halo of this dark matter containing the major portion of the total galaxy mass and extending very far beyond the visible matter.
The Wikipedia provides this page on dark matter halos, whereas this news release from the University of California, Santa Cruz discusses how computer simulation has been used to characterize them.
Also, the January 2008 issue of Discover magazine has awarded dark-matter research the No. 7 slot in the "100 Top Science Stories of 2007." Quoting from the dark-matter article:
In the early universe, astronomers believe, dark matter provided the gravitational scaffolding on which ordinary matter coalesced and grew into galaxies.
In addition to dark-matter halos surrounding visible-matter galaxies, dark matter galaxies also appear to exist. The Discover article notes that "small, dark matter-dominated satellite galaxies," which had been hypothesized but gone undetected, have now been found in greater numbers (this finding is elaborated in this CalTech news release).
As far as future approaches to detecting dark matter, the Discover article cites the following:
Some astrophysicists believe that dark matter particles may occasionally annihilate each other, producing bursts of high-energy gamma rays. If the Milky Way has dark matter satellites, and if they do emit gamma rays, the Gamma-Ray Large Area Space Telescope, scheduled for launch in February, might detect them.
The GLAST search for dark matter, and related topics, are summarized in this University of California, Irvine document.
In conclusion, the various lines of research described herein should help the scientific community become less in the "dark" about this unusual type of matter.