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On the Trail of the Missing Galaxies: The Oldest Stars in the Neighborhood

Presented by: Tom Brown (Space Telescope Science Institute)
Category: Education and Outreach   Duration: 1 hour and 45 minutes   Broadcast date: September 06, 2016
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In the past decade, wide-field surveys have revealed a new class of ultra-faint dwarf galaxies orbiting the Milky Way and Andromeda. They are the least luminous, most dark-matter dominated, and least chemically-evolved galaxies known. These faint galaxies offer a new front in efforts to understand the missing satellite problem - the discrepancy that theory predicts many more satellite galaxies than the number of dwarf galaxies observed. As the best candidates for fossils from the early universe, the ultra-faint dwarfs are ideal places to test the physics of galaxy formation from that era. New data from the Keck Observatory and the Hubble Space Telescope provide evidence that reionization in the early universe suppressed star formation in the smallest seeds of galaxy formation, thus providing a possible explanation for the missing satellite problem.