This light comes from stars that formed when the universe was only a tenth of its present age, several billion years before Earth existed.
American astronomer Edwin P. Hubble used a larger telescope starting in the 1920s and saw a wide variety of galaxy shapes. He classified them intoelliptical, with a smooth texture; disk-like with spirals; and everything else, which he called irregular.
Elliptical Galaxies.
Elliptical galaxies are three-dimensional objects that range from spheres to elongated spheroids like footballs. Some may have developed from slowly rotating hydrogen clouds that formed stars in their first billion years. Others may have formed from the merger of two or more smaller galaxies. Most ellipticals have very little gas left that can form new stars, although in some there is a small amount of star formation within gas acquired during recent mergers with other galaxies.
Spiral Galaxies.
Spiral galaxies, which include the Milky Way, formed from faster-spinning clouds of hydrogen gas. Theoretical models suggest they got this spin by interacting with neighboring galaxies early in the universe. Thecenter of a spiral galaxy is a three-dimensional bulge of old stars, surrounded by a spinning disk flattened to a pancake shape.
This is a free page. This page contains 187 words. This
article contains 2,401 words (approx. 8 pages at 300
words per page).
Read the rest of this Article with our Galaxies Access Pass.
