The Bridge V Learning 2(clone) - Page 4

A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter.

Galaxies are categorized according to their visual appearance.

Many galaxies are thought to have black holes at their active centers.

The Milky Way's central black hole, known as Sagittarius A*

has a mass four million times greater than the  Sun.