By Ken Croswell
The Milky Way’s core harbors two giants: the galaxy’s largest black hole and a cluster of tens of millions of stars around the black hole that is denser and more massive than any other star cluster in the galaxy.
Most of the cluster’s many stars shine within just 20 light-years of the galactic center and all together weigh about 25 million times as much as the sun. New observations suggest that this “nuclear star cluster” owes some of its brilliance to another big group of stars, or even a small galaxy, that the main cluster swallowed.
Nuclear star clusters exist in many galaxies and are the densest star clusters in the universe. Astronomers are trying to figure out how these gatherings get so jam-packed and how they feed the giant black holes at the centers of galaxies.
To get a look at the Milky Way’s core, Tuan Do, an astronomer at UCLA, and colleagues observed about 700 red giant stars within five light-years of the galaxy’s heart. Because dust between Earth and the galactic center blocks the stars’ visible light, the astronomers studied infrared wavelengths, which better penetrate the dust.