The Circumgalactic Family

  • Steven J. Dick
Part of the Astronomers' Universe book series (ASTRONOM)


Just as satellites orbit planets and planets orbit stars, so do galaxies have their own satellites and circumgalactic material orbiting them, notably in the form of smaller galaxies or their shredded debris known as rings or stellar streams. At least 59 of these galaxies orbit our Milky Way Galaxy out to about 1.5 million light years, believed to be the edge of the dark matter halo (G 12). These are dominated by irregular, elliptical, and spheroidal dwarf galaxies, although several larger irregular galaxies also orbit, including the Large and Small Magellanic Clouds. The preponderance of dwarf galaxies may be due to their origin as pieces of larger spirals pulled out by tidal interactions when galaxies collide. Stellar streams are related to these satellite galaxies because they are their shredded remains torn apart by the gravity of the Milky Way, sometimes colloquially referred to as “sky rivers” or more poetically as “gravity’s rainbow.”

Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  • Steven J. Dick
    • 1
  1. 1.AshburnUSA

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