Galaxies
Islands of Stars in the Cosmos
Galaxies are massive collections of stars, gas, dust, and dark matter bound together by gravity. Our Milky Way is just one of hundreds of billions of galaxies in the observable universe. Galaxies come in various shapes and sizes.
Types of Galaxies
- Spiral Galaxies: Flat, rotating discs with spiral arms (e.g., Milky Way, Andromeda)
- Elliptical Galaxies: Round or oval shapes, ranging from small to giant
- Irregular Galaxies: No distinct shape, often due to gravitational interactions
- Lenticular Galaxies: Disc-shaped with no visible spiral arms
Andromeda Galaxy
The Andromeda Galaxy (M31) is the nearest large galaxy to the Milky Way, located about 2.5 million light-years away. It is on a collision course with our galaxy and will merge with it in about 4.5 billion years.
Supermassive Black Holes
Most galaxies contain a supermassive black hole at their center. The Milky Way's central black hole, Sagittarius A*, has a mass of about 4 million times that of the Sun.