Astronomy: Galaxies

Galaxies are conglomerations of millions to trillions of stars, gas, dust, stellar remnants, and dark matter. For more information, see:

https://science.nasa.gov/astrophysics/focus-areas/what-are-galaxies

https://www.nasa.gov/subject/6894/galaxies/

For more information on galaxy classification, see: 

https://www.spacetelescope.org/images/heic9902o/

https://www.britannica.com/science/galaxy/Types-of-galaxies

For more information about dark matter:

https://www.britannica.com/science/dark-matter

https://www.nasa.gov/audience/forstudents/9-12/features/what-is-dark-matter.html

https://home.cern/science/physics/dark-matter