Dwarf galaxy Andromeda 29 311.
(photo credit: Gemini Observstory/AURA/Eric Bell )
ANN ARBOR, Mich. - In work that could help advance astronomers' understanding of dark matter, University of Michigan researchers have discovered two additional dwarf galaxies that appear to be satellites of Andromeda, the closest spiral galaxy to Earth.
Eric Bell, an associate professor in astronomy, and Colin Slater, an astronomy Ph.D. student, found Andromeda XXVIII and XXIX - that's 28 and 29. They did it by using a tested star-counting technique on the newest data from the Sloan Digital Sky Survey, which has mapped more than a third of the night sky. They also used follow-up data from the Gemini North Telescope in Hawaii.
At 1.1 million and 600,000 light years from Andromeda, these are two of the furthest satellite galaxies ever detected. Invisible to the naked eye, the galaxies are 100,000 times fainter than Andromeda, and can barely be seen even with large telescopes.
The findings are published in the current Nov. 20 edition of Astrophysical Journal
These astronomers set out looking for dwarf galaxies around Andromeda to
help them understand how matter relates to dark matter, an invisible
substance that doesn't emit or reflect light, but is believed to make up
most of the universe's mass. Astronomers believe it exists because they
can detect its gravitational effects on visible matter. With its
gravity, dark matter is believed to be responsible for organizing
visible matter into galaxies.
"These faint, dwarf, relatively nearby galaxies are a real battleground
in trying to understand how dark matter acts at small scales," Bell
said. "The stakes are high."
The prevailing hypothesis is that visible galaxies are all nestled in
beds of dark matter, and each bed of dark matter has a galaxy in it. For
a given volume of universe, the predictions match observations of large
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"But it seems to break down when we get to smaller galaxies," Slater
said. "The models predict far more dark matter halos than we observe
galaxies. We don't know if it's because we're not seeing all of the
galaxies or because our predictions are wrong."
"The exciting answer," Bell said, "would be that there just aren't that
many dark matter halos." Bell said. "This is part of the grand effort to
test that paradigm."
The papers are titled, "Andromeda XXIX: A New Dwarf Spheroidal Galaxy
200 kpc from Andromeda," and Andromeda XXVIII: A Dwarf Galaxy more than
350 kpc from Andromeda."This article was first published on www.newswise.com.
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