Images of Galaxies
The Andromeda Galaxy
Today’s post will focus on images of galaxies. As we’ve discussed before, galaxies are collections of stars, dust, gas, pulsars, quasars, magnatars, and other cosmic bodies all bound together by their common gravity. The image above is the Andromeda Galaxy.
The Andromeda Galaxy is also known as Messier Object 31 or M31. It is a spiral galaxy located about 2.5 million light years away from Earth. It gets it’s name from the constellation Andromeda, which coincidentally enough, is where it is located.
The Sombrero Galaxy
Another favorite galaxy image of mine is the Sombrero Galaxy. This galaxy is also known as M104 and can be found in the constellation Virgo. The interesting thing about the Sombrero Galaxy is that it is an unbarred galaxy – meaning that it does not have the spiral arms found in spiral galaxies.
A Ring Galaxy
A ring galaxy is a bit of an oddity because it does not have much luminous material in the center of the galaxy as you see in other types of galaxies. Scientists speculate that ring galaxies may have been formed by two galaxies colliding leaving the ring galaxy without it’s central mass.
A Spiral Galaxy
And what of the other types of Galaxy’s?
Lenticular (S0):
These are, in short, “spiral galaxies without spiral structure”, i.e. smooth disk galaxies, where stellar formation has stopped long ago, because the interstellar matter was used up. Therefore, they consist of old population II stars only, or at least chiefly. From their appearance and stellar contents, they can often hardly be distinguished from ellipticals observationally.
Elliptical:
Elliptical galaxies are actually of ellipsoidal shape, and it is now quite safe from observation that they are usually triaxial (cosmic footballs, as Paul Murdin, David Allen, and David Malin put it). They have little or no global angular momentum, i.e. do not rotate as a whole (of course, the stars still orbit the centers of these galaxies, but the orbits are statistically oriented so that only little net orbital angular momentum sums up). Normally, elliptical galaxies contain very little or no interstellar matter, and consist of old population II stars only: They appear like luminous bulges of spirals, without a disk component.
However, for some ellipticals, small disk components have been discovered, so that they may be representatives of one end of a common scheme of galaxy forms which includes the disk galaxies.
Irregular:
Often due to distortion by the gravitation of their intergalactic neighbors, these galaxies do not fit well into the scheme of disks and ellipsoids, but exhibit peculiar shapes. A subclass of distorted disks is however frequently occuring.
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