Q&A: Miscellaneous X-ray Sources

Q:
Is there such a thing as a red dwarf? If so, how is it different from a white or brown dwarf?

A:
A red dwarf is a star that has a mass between approximately 8% and 50% of the mass of the Sun. It is different from a brown dwarf in that its interior is hot enough to sustain hydrogen fusion reactions as a supply of energy. It will eventually (in 20 billion years or so) turn into a white dwarf, a collapsed star in which no nuclear reactions occur in the center. The pressure for support against gravity is supplied by degenerate electron pressure. See the entries in our Field Guide.