A galaxy is a loose formation of between 1 million and 1 trillion stars, dust, and gases.
These stars, dust, and gases are drawn together in clusters by their forces of gravity, much in the same way as our solar system is held together by the gravity of the Sun and the planets.
It is believed that dark matter accounts for around 90% of the mass of most galaxies.
Recent data also suggests that super massive black holes may exist at the center of many large galaxies.
