Astronomy

Looking for Missing Matter

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Science  14 Sep 2012:
Vol. 337, Issue 6100, pp. 1274
DOI: 10.1126/science.337.6100.1274-a
CREDIT: CEN & OSTRICKER, ASTROPHYS. J. 650 560 (2006) REPRODUCED BY PERMISSION OF THE AAS

In the present-day universe, galaxies account for only 10% of baryonic matter (the protons and neutrons that constitute ordinary matter). The rest is expected to be found in the intergalactic medium, mostly in the form of diffuse gas at temperatures ranging from 100,000 to 10 million K. To look for this gas around our galaxy, Gupta et al. searched for absorption lines from highly ionized gas in spectra of bright extragalactic sources obtained with the Chandra X-ray Observatory. The detection of both O VII and O VIII absorption lines implies the presence of gas at temperatures around 1 million degrees. Column density measurements combined with emission measurements from the literature indicate that the gas extends over a large region around the Milky Way and is 10 billion times as massive as the Sun. This gas could be just outside the galaxy, in the circumgalactic medium, or anywhere in the space between our galaxy and its closest neighbors.

Astrophys. J. 756, L8 (2012).

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