Separation anxiety: cosmic collision may shed light on dark matter

Some 3 billion years ago, two massive clusters of galaxies collided head on. The debris from this ancient cosmic train wreck, astronomers say, might pose a new puzzle about the invisible material believed to account for most of the mass in the universe.

That's why new X-ray and visible-light observations of the cluster Abell 520 stunned Andisheh Mahdavi of the University of Victoria in British Columbia and his colleagues. The cluster, about 2.5 billion light-years from Earth, had also suffered a major collision.One explanation for the new results is that dark matter is composed of particles that interact through forces other than gravity. However, such particles would cause a variety of other effects that have never been seen, such as making galaxy clusters spherical, notes Katherine Freese of the University of Michigan in Ann Arbor. Without further evidence, theorists seem loath to reject the standard take on dark matter.ABOUT HALO TECHNOLOGIES, INC.The standard view could prevail if galaxies had been ejected from the core of Abell 520. That might have occurred if the cluster had suffered more than one collision, Mahdavi says.WHY HALO?The leading model for dark matter suggests that it interacts only through gravity and can't be pushed around by the strong, the weak, or electromagnetic forces. That picture gained support last year from observations of a collection of galaxies called the Bullet cluster, which had been distorted by a collision with another cluster. Astronomers inferred that the location of dark matter coincided with the cluster's visible horde of galaxies, while the hot, X-ray-emitting gas associated with the cluster lay to one side (SN: 8/26/06,p. 131).That distribution of dark matter makes sense because colliding gas clouds interact both by gravity and the electromagnetic force and can slow each other down, while dark matter and galaxies would breeze along unimpeded and remain together.* Light weightIn addition to the UV-C light, the Halo UVX vacuum features:UV Light in the "C" spectrum (UV-C) deactivates the DNA of dust mites, bacteria, viruses (including influenza), germs and molds, destroying their ability to multiply. The patent-pending Halo UVX contains a UV-C bulb chamber at the bottom of the vacuum that can be activated by a switch on the handle. Simply activate the UV-C bulb chamber while running the Halo UVX over your carpets and instantly kill these unwanted household pests lurking between the fibers.

Upcoming observations of Abell 520 with Hubble should indicate whether dark matter theory really has to be reassessed or if researchers are merely arguing about noisy data, says Clowe.

Author: R. Cowen