Colliding Galaxies, X-rays and Dark Matter

Dark matter is one step closer to be identified because new research from the Niels Bohr Institute in Copenhagen presents new information.

Earlier in 2007, scientists mapped the shape of the collected groupings of dark matter using Hubble technology. The universe, made up of visible celestial bodies, stars, planets and galaxies, is mostly comprised of large quantities of invisible--and as yet unidentified--dark matter.

Dark matter is invisible because it does not reflect light. There are theories as to what it might be, including that it might be made up of axions, which are hypothetical elementary particles that are predicted to have no electric charge and a very small mass and that interact minimally with ordinary visible matter.

Dark matter, first discovered in the 1970s, has mass and therefore has gravitation. This gravity can be measured according to Newton's principal of the proportionality of mass and distance. Further, galaxies can be analyzed and weighed to derive mass. From this measurement it is clear that the greatest component of mass in galaxies is invisible dark matter.

Additionally, these galaxies, which can yield revealing measurements, gather into clusters with each cluster containing up to several thousand galaxies. Just as galaxies can collide, galaxy clusters can also collide. Astrophysicist Signe Riemer-Sorensen, a Ph. D. student at the Niels Bohr Institute, has added to the understanding of dark matter through his analysis of two clusters of galaxies that are colliding.

When galaxies collide, it is not the galaxies nor the dark matter of the galaxies that meet in the collision. What meets is the huge clouds of gas and dust which comprise about 12 percent of the mass of galaxy clusters.