Galaxies: Types, Structure, and Formation

Our planet is part of the solar system, and the solar system is a small part of the Milky Way

galaxy. A galaxy is huge collection of gas, dust, and billion of the

stars, and their solar systems all held together by gravity. Also,

the Milky Way has a super massive black hole in the middle. Galaxies are normally

classified for their shapes and structures. The most common classification is called the Hubble

sequence. These are the seven most common galaxies. Spiral galaxies. This class of galaxy

is defined by the presence of the spiral arms and a central bulge. The arms host much

of the gas and dust, making them fertile regions for new stars. An example of a