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Galaxies and Black Holes

March 8, 2011

Black holes can lurk in the centers of even the smallest galaxies. An example is a galaxy known as Henize 2-10. It's just three percent the diameter of our own galaxy, the Milky Way. Yet astronomers recently discovered a black hole in its core that's about a quarter of the mass of the one in the heart of the Milky Way.

The discovery's greatest importance isn't the black hole itself, but what it may tell us about the birth of black holes and galaxies in the early universe.

In big galaxies like the Milky Way, there's a relationship between the mass of the black hole at the galaxy's center and the "bulge" of stars around it. That suggests that the black holes and the surrounding galaxies were born together.

In fact, black holes may help control the growth of their home galaxies. The idea is that a black hole first pulls gas and dust toward the galaxy's center, helping give birth to stars. The black hole then eats some of the stars, producing radiation that blows away the material needed to give birth to more stars.

The relationship doesn't hold in Henize 2-10, or in a few other tiny galaxies that have black holes. These galaxies are a lot like the earliest galaxies, which clumped together to form the big galaxies we see today. They're small puffs of stars, with no regular shape and no bulge of stars in the middle.

And that suggests that perhaps the black holes came first, with the galaxies building up around them later on.

Script by Damond Benningfield, Copyright 2011

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