Credit: ESA/XMM-Newton; J-T. Li (University of Michigan, USA); Sloan Digital Sky Survey (SDSS)
The material Universe is made up of normal matter (which scientists call baryons, from the Greek word for "heavy") and mysterious "dark" matter, whose nature and origin is unknown. The nature of dark matter is a critical issue, since most of the matter in the Universe is of the "dark" variety, and dark matter is believed to drive the development of structure in the Universe. Baryonic matter is the well-understood stuff we see around us every day which makes up our houses, planets, stars, and bodies. The amount of baryonic matter created at the origin of the Universe is constrained by modeling the cosmic microwave radiation observed by the COBE, WMAP and Planck microwave background space observatories. But, when astronomers took a census of the amount of baryonic matter that can be seen in the visible Universe, they found that the amount of baryonic matter they could see was about three times less than expected. Perhaps the missing baryons are hiding as hot gas around galaxies, which would not show up in optical studies. Now a new study with the XMM-Newton X-ray observatory has put more stringent limits on the amount of baryons that may be hiding in hot haloes around normal galaxies. The image above is an XMM-Newton X-ray image made by combining individual X-ray images of six similar spiral galaxies in order to bring out the faint X-ray emitting galactic haloes. However, analysis of the combined images failed to find all the missing baryons that were expected to reside in the haloes; about three quarters of the expected baryons are still missing. Where could they be?
Published: June 18, 2018
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Page Author: Dr. Michael F. Corcoran
Last modified Monday, 25-Jun-2018 08:42:01 EDT