The Protostellar Family

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


Like planets, stars are born, but they do so in considerably more spectacular fashion and at rates highly dependent on their environment. A protostar, sometimes called an embryonic star, is a molecular cloud (S 25) undergoing gravitational contraction and accretion of gas and dust prior to initiating fusion reactions. The end of accretion and the onset of a stellar wind (S 29) is often considered the dividing line between a collapsing protostar and the next stage in stellar evolution, the so-called pre-main sequence stars (S 2 and S 3) such as T Tauri or higher mass Herbig Ae/Be objects, discussed in the next two entries. But the transition is not sharp: some pre-main sequence stars are still accreting matter. Other classes of objects associated with newborn stars are jets (S 20) and Herbig-Haro objects (S 21). Protostars are also called “young stellar objects” (YSOs), but that term sometimes also encompasses pre-main sequence stars. Surprisingly, our Galaxy births only about one star per year, but “starburst” galaxies such as M82 may form stars at a thousand times that rate.

Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

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

Personalised recommendations