The Coma Cluster of Galaxies
Click on image for full size
Courtesy of NASA.
Elliptical Galaxies
Elliptical galaxies are generally egg-shaped. If you have the chance
to see one through a small telescope, it will probably look just like
a fuzzy smudge to you, a piece of lint. But it is really formed of
many billions of stars orbitting the center of the galaxy.
Each elliptical galaxy is assigned a number ranging from 0 to 7 which
represents how elliptical it is. The most elliptical galaxies are a
7, while a galaxy which appears circular is a 0. Their shape may tell
us something about how the galaxies formed and evolved. Elliptical
galaxies also come in a range of sizes from giants, which are very
massive and bright, to dwarfs, which are small but which may be very
numerous. In fact, ellipticals are both the largest and smallest
galaxies known!
We think of ellipticals as old because they have not formed any new
stars recently, unlike spiral
galaxies which are forming new stars even now. They appear not to
have very much cool gas or dust from which to form stars.
Elliptical galaxies are the dominant type of galaxy in most clusters
and groups of galaxies. In our own Local Group, for example, there
are no large ellipticals, but many dwarf ellipticals orbiting both the
Milky Way and the Andromeda galaxy.
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