Radiation drives stellar winds.

University of Wisconsin-Madison astronomers, using a NASA satellite to explore an elusive, but information-rich, type of starlight, have found the first direct evidence of the forces that drive the stellar winds scientists believe play a key role in the evolution of stars. The finding is important because it underpins ideas about how stars age and provides clear insights into the forces responsible for ejecting massive amounts of material into interstellar space.

Using the Extreme Ultraviolet Explorer (EUVE) satellite, an orbiting observatory launched by NASA in 1992, astronomer Joseph P. Cassinelli and colleagues at Wisconsin, the University of California at Berkeley, and Oxford University observed the relatively young, hot star Epsilon Canis Majoris in an attempt to uncover the energetic forces that drive stellar winds. Such winds exist on the sun and are responsible for phenomena like the northern lights.

Cassinelli discovered that the winds associated with the star appear to be generated by the extremely short-wave ultraviolet radiation from the star pushing on atoms of stellar gas. "All early type stars seem to have radiation driven winds. This has been known for a long time, but we've never seen before the radiation that essentially drives the wind machine."

Epsilon Canis Majoris, a star about 600 light-years from Earth in the constellation Canis Major is much hotter than the sun and about 30,000 times as bright, seems to lose mass as atoms are blown off the top of its atmosphere by 600 mile-per-second gales, Cassinelli indicates. The radiation that drives the powerful winds also produces what astronomers call H II regions--the spectacular fluorescent cocoons of dust and gas that surround hot, young stars. These act as stellar maternity wards, where stars are born and grow as they feed on the atoms of dust and gas, he...