Galaxies

Galaxies are vast systems containing billions or even trillions of stars, along with gas, dust, dark matter, and often a supermassive black hole at their center. They are the largest gravitationally bound structures in the universe. Galaxies exist in a remarkable variety of shapes and sizes, from majestic spiral galaxies to massive ellipticals and irregular galaxies with chaotic appearances. Our home galaxy, the Milky Way, is a barred spiral galaxy about 100,000 light-years across. It is just one member of the Local Group, which also includes the Andromeda Galaxy and dozens of smaller galaxies. Galaxies can be found alone, in pairs, or grouped into massive clusters containing thousands of members.

Galaxies evolve over billions of years, colliding and merging in cosmic dances that shape their structure and trigger bursts of star formation. By observing distant galaxies, astronomers look back in time to study the early universe and the processes that created the cosmic web.