GalaxiesGALAXIES

Stars are not randomly sprinkled throughout the universe. Most astronomers agree that there are about 100 billion galaxies in the universe, each of which contain about 100 billion stars. Our Solar System forms a tiny part of a galaxy called the Milky Way. Galaxies form in different shapes. Four of the most common shapes are listed. 1/3 of all known galaxies are spiral.

Galaxies

Spiral Galaxy. It has a bright middle and two or more curved arms of stars.

Barred Spiral Galaxy. It has a central bar with an arm at each end.

Elliptical Galaxy. It has masses of old, red stars that contain little gas or dust.

Irregular Galaxy. It has no fixed shape. It is just like clouds of stars.

Andromeda Galaxy M31

The Andromeda Galaxy, or M 31, a spiral galaxy similar to our Milky Way galaxy, is the object farthest from earth still visible with the naked eye. It can be seen from the northern hemisphere in the constellation Andromeda.

The Milky Way and Andromeda galaxies are both part of a group of galaxies called the Local Group, which in turn is part of the Virgo Cluster of groups.

Like the Milky Way, M31 is a giant spiral-shaped disk of stars, with a bulbous central hub of older stars. M31 has long been known to have a bright and extremely dense grouping of a few million stars clustered at the very center of its spherical hub.

MILKY WAY GALAXYOur own solar system exists within one of the spiral arms of the disk-shaped galaxy called the Milky Way. This false-color image looks toward the center of the Milky Way, located 30,000 light-years away. Bright star clusters are visible along with darker areas of dust and gas. The Milky Way Galaxy is a pinwheel-shaped flattened disk about 75,000 light-years in diameter.

The Sun is located on a spiral arm about two-thirds of the way out fromthe center. The galaxy spins, but the center spins faster than thearms. At Earth’s position,the galaxy makes acomplete rotation aboutevery 200 million years.

This never-before-seen view shows the Milky Way from an edge-on perspective with the galactic north pole at the top, the south pole at the bottom and the galactic center at the center. The picture combines images obtained at several near-infrared wavelengths.

Stars within our galaxy are the dominant source of light at these wavelengths. Even though our solar system is part of the Milky Way, the view looks distant because most of the light comes from the population of stars that are closer to the galactic center than our own Sun.

Elliptical Galaxies

These elliptical galaxies are members of the Virgo cluster of galaxies, located about 50 million light-years away from our smaller cluster, the Local Group.

Elliptical galaxies are populated by older stars and contain little interstellar matter. They are usually the brightest galaxies.

Banded Spiral Galaxy

The Hubble Space Telescope captured the core of M100, which is located between 35 and 80 million light years from earth.

Irregular GalaxyMAGELLANIC CLOUD

The colors in this image correspond to radio wave intensity. Black is least intense, and red is most intense.

Details of the structure of irregular galaxies can be learned from studying electromagnetic waves (radio waves).