Glow Between Clusters Could Be Missing Mass
(From the July/August 1998 issue of StarDate magazine)
A contender for the missing mass that binds the cosmos has been discovered with the detection of an extreme ultraviolet glow in five galaxy clusters, including the Virgo Cluster, which counts our galaxy among its members.
Particles that have not otherwise been detected revealed themselves in observations by Richard Lieu of the University of Alabama and his colleagues using NASA's Extreme Ultraviolet Explorer satellite.
Astronomers have long sought a solution to account for a puzzling imbalance in the galaxies and other large structure of the universe: Their apparent cumulative mass is only about 10 percent of what's needed to hold them together.
In an article in Astrophysical Journal Letters, Lieu, Jonathan Mittaz of Mullard Space Science Laboratory and Felix Lockman of the National Radio Astronomy Observatory propose that the mass of the glowing particles may keep the largest structures in the universe from flying apart. The astronomers' observations would confirm a theory developed recently by Princeton University scientists.
Lieu's team looked at the trillions of cubic light-years of seemingly empty space that separates galaxies. They found the space is permeated by a glowing gas that, while less dense than the best vacuums that can be created on Earth, outweighs hundreds of galaxies. The gas could account for some or even all of the missing mass in the universe.
The theory proposed by Lieu and his colleagues joins others that seek to explain the missing-mass problem. Further observation will be required before any of them will be accepted by most astronomers. -- Doug Addison
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