It started with a homework assignment: A University of Texas astronomy class run jointly by its Austin and San Antonio campuses has led to students making a discovery that has landed in the pages of a scientific journal.

Researchers have believed that Segue 1, a puny galaxy orbiting the Milky Way just 75,000 light-years away, was packed with dark matter , a substance in space that doesn't shine or interact with light. Some scientists have recommended it as a key place in the local universe to study this mysterious material.

But a new study indicates that the dim dwarf galaxy gets most of its mass from a previously unknown supermassive black hole , which is also invisible, not dark matter. The black hole is estimated to weigh upward of 450,000 suns . Nathaniel Lujan, a

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