Three main types of galaxies exist in our universe: spiral galaxies, elliptical galaxies and irregular galaxies. Spiral galaxies, such as the Milky Way, consist of a rotating flat disk made up of stars, gas and dust, a bulge containing older stars, and a halo made up of dark matter that cannot be seen by us, but like normal matter, is still affected by gravity. Elliptical galaxies are "triaxial," meaning they have three axes, and consist mainly of old stars that rotate constantly with no order or direction. These galaxies vary the most in size. Irregular galaxies are typically smaller and have no identifiable form and consist of mainly stars and gas.
The Milky Way's neighboring spiral galaxy Andromeda is perhaps the most well-known. Andromeda, or M31, is even larger than the Milky Way, and has a bright yellow nucleus at its center, with bluish spiral arms. Although it is the closest spiral galaxy, it is still approximately 2.52 million light years from the Milky Way solar system. Astronomers predict that Andromeda and the Milky Way will merge in about 2.2 billion years. This galaxy is visible without a telescope and usually appears as a small cloud in the sky.
Hoag's Object, discovered and named by astronomer Art Hoag in 1950, is an extremely rare type of galaxy known as a ring galaxy. Since then, this mysterious galaxy has sparked numerous theories as to how it got its unusual shape. Most astronomers believe it to be the result of multiple small galaxies colliding billions of years ago. Hoag's Object consists of older red stars surrounded by brighter, newer blue stars, and is approximately 600 million light years from the Milky Way.
The Magellanic Clouds, often simply known as the Large Magellanic Cloud and the Small Magellanic Cloud, are two irregular galaxies named after Ferdinand Magellan, who believed that they were small, perpetually visible clouds. They are considered satellite galaxies, or galaxies that are subject to the gravitational pull of the Milky Way galaxy. The Large Magellanic Cloud is 160,000 light years away from the Milky Way system, and the Small Magellanic Cloud is about 200,000 light years away.