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Tweak to dark matter may explain Milky Way mystery

Radiation in early universe might illuminate problem of missing satellite galaxies

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4:00pm, September 16, 2014
galaxy simulations with dark matter

BLINDED BY THE LIGHT  Dark matter envelops a galaxy similar in size to the Milky Way in this computer simulation, where red indicates high densities of dark matter and blue shows low densities. On the left, traditional dark matter creates many satellite galaxies. At right, dark matter that interacts with light produces far fewer.

Dozens of tiny galaxies known as satellite galaxies orbit the Milky Way, but theorists predict there should be hundreds.  Now a team of astronomers offers a new resolution to this conflict between observation and theory: Maybe dark matter, the mysterious substance thought to bind galaxies together, isn’t quite so dark. The researchers propose that radiation might have stirred up dark matter in the early universe, preventing the formation of satellites.

The mystery of the missing satellite galaxies has bedeviled astronomers for more than a decade. While dark matter has proven to be exceptionally good at explaining the formation of large galaxies and clusters, it routinely runs into trouble when attempting to describe tiny structures such as satellite galaxies.

Physicist Celine Bœhm of Durham University in England and colleagues sought to reconcile this discrepancy by tweaking dark matter theory. They propose that dark matter, long thought to be oblivious to

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