Universe goes on diet of electrons, weight may stay off

William Atkins
Tuesday, 13 November 2007 18:43

Science - Space

Astronomers at the University of Alabama (Huntsville, U.S.A.) and the Helsinki Observatory (Finland) found that X-rays coming from galaxy cluster Abell 3112 originate from electrons and photons. If this conclusion holds with other galaxy clusters, it will considerably reduce the mass of the universe.             

Their results are written up in the October 20, 2007 issue of the Astrophysical Journal—within the article “Soft and Hard X-Ray Excess Emission in Abell 3112 Observed with Chandra.”

Within the article, the UAH team states that X-rays were earlier thought to emanate from intergalactic clouds of dust and gas. However, the Chandra X-ray Observatory did not observe evidence of such interactions located between galaxies. Instead, the team found that the X-rays were created from collisions between lighter-weight electrons and photons. Consequently, their finding indicates that the universe contains less normal “baryonic” matter and dark “non-baryonic” matter than previously thought.

Their abstract states, “Chandra ACIS-S observations of the galaxy cluster Abell 3112 feature the presence of an excess of X-ray emission above the contribution from the diffuse hot gas, which can be equally well modeled with an additional nonthermal power-law model or with a low-temperature thermal model of low metal abundance. We show that the excess emission cannot be due to uncertainties in the background subtraction or in the Galactic H I column density. Calibration uncertainties in the ACIS detector that may affect our results are addressed by comparing the Chandra data to XMM-Newton MOS and PN spectra. While differences between the three instruments remain, all detect the excess in similar amounts, providing evidence against an instrumental nature of the excess."

They go on to say, "Given the presence of nonthermal radio emission near the center of Abell 3112, we argue that the excess X-ray emission is of nonthermal nature and distributed throughout the entire X-ray bandpass, from soft to hard X-rays. The excess can be explained with the presence of a population of relativistic electrons with  7% of the cluster's gas pressure. We also discuss a possible thermal nature of the excess and examine the problems associated with such interpretation.”

Preliminary estimates are that the universe lost ten to twenty percent of its total mass from this discovery.