Elliptical Galaxies
M87 is one of the most impressive galaxies in the universe. It's wider than our home galaxy, the Milky Way, but it's also much thicker, because it's shaped like a fat football. That extra volume is filled with a lot of stars -- a trillion or more. And the biggest known black hole inhabits the galaxy's heart.
Because of its shape, M87 is classified as an elliptical galaxy. It's a member of one of two classes of ellipticals.
M87 and the other giant ellipticals are fatter then the other class. They rotate slowly, and their stars zip around at random speeds and in random directions. Most important, stars in a small volume near the center of the galaxy -- known as the core -- are fairly evenly spaced.
The second class of ellipticals is more flattened, and rotates faster.
Texas astronomer John Kormendy and his colleagues have studied M87 and all the other known ellipticals in the Virgo Cluster -- a collection of thousands of galaxies.
They found that the second class of ellipticals doesn't have what astronomers describe as a "core." Instead, these galaxies have dense clusters of stars in their centers. The clusters were born in "starbursts" when the galaxies were made. Galaxies like M87 don't have starburst centers.
This suggests that the two types of galaxies formed in different ways -- both of them involving smaller galaxies and big black holes. More about that tomorrow.
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