Galaxies

M51 Whirlpool Galaxy. Image Credit: NASA, ESA, S. Beckwith (STScI) and the Hubble Heritage Team (STScI/AURA)

M51 Whirlpool Galaxy. Image Credit: NASA, ESA, S. Beckwith (STScI) and the Hubble Heritage Team (STScI/AURA)

Galaxies are enormous collections of stars, gas, dust, dark matter, and solar systems all held together by gravity. They are the major building blocks of the universe. A single galaxy can contain millions to trillions of stars, including stars with planets—like our Sun. 

Galaxies are surrounded by giant halos of dark matter, which provide enough gravity to keep stars bound.

 

Researchers