Astrophysical plasmas

The plasmas of our solar system are but a small subset of the astrophysical plasmas that constitute what is commonly referred to as the "plasma universe." Stellar jets, such as the one shown in this image acquired with the Hubble Space Telescope's Wide Field Planetary Camera 2, are one example of the rich variety of astrophysical plasmas that exist outside our solar system and that range from the tenuous, partially ionized plasmas of the interstellar medium to the dense plasmas of stellar interiors. Stellar jets are narrow plumes of ionized gas travelling at speeds of a few hundred kilometers per second and extending as far as several trillion miles from newly formed stars. (The jet in this image, known as HH47, extends three trillion miles from the star hidden in the illuminated dust cloud to the left. HH47 is located at the edge of the Gum Nebula, an ionized mass of hydrogen 1500 light years from Earth.) Even larger jets (many times the size of the Milky Way galaxy) emanate from galaxies and are possibly powered by black holes.

Although they occupy only a small niche in the plasma universe, solar system plasmas, unlike other astrophysical plasmas, have the advantage of being accessible to in-situ measurement and thus afford a natural laboratory for the investigation of fundamental plasma processes such as magnetic reconnection, particle acceleration, and shock formation.

(Image courtesy of J. Morse/STScI. On stellar and extragalactic jets, see De Young, D. S., Astrophysical jets, Science, 252, 389, 1991.)