A tiny nearby galaxy is home to a shockingly enormous black hole

A nearby galaxy once thought to be dominated by dark matter appears to have an unexpected supermassive black hole at its center. Segue 1 is just a galaxy with only about 1,000 stars compared to the hundreds of billions in the Milky Way, and yet it appears to harbor a black hole about 10 times more massive than all its stars combined.

Seg 1 and others similar dwarf galaxies they don't have enough stars to provide the gravity needed to hold them all together. To solve this problem, physicists have long theorized that they are filled with a mysterious substance called dark matterwhich we do not see, but which can create additional gravity.

So when Nathaniel Lujan at the University of Texas at San Antonio and his colleagues began testing computer models of Segue 1. They expected that the best-fitting model would be one dominated by dark matter. “I tried hundreds of thousands of models and couldn’t find anything that worked,” Lujan says. “And then finally I decided to play with the mass of the black hole, and suddenly it started working.”

The model that best fit our observations of Segue 1 included a black hole with a mass of about 450,000 times the mass of the Sun. This was especially surprising not only because of the galaxy's lack of stars, but also because of its age: the few stars it does contain indicate that it formed only about 400 million years after the universe began to form stars. This doesn't leave much time to create one colossal black holeespecially since the much larger Milky Way siphons off most of the gas that would have powered it from Segment 1 shortly after its birth.

“This probably means there are more supermassive black holes than we thought,” Luján says. If so, they could explain some of the gravity so far attributed to dark matter – but we don't yet know whether Segue 1 is representative of all dwarf galaxies, so the hunt for more massive black holes continues.