Raging storms of hot and cold gas

New observations with the Space Telescope Imaging Spectrograph (STIS), Hubble’s high-precision and ultra-sensitive spectrometer, show that the warm chromosphere of Betelgeuse extends out to more than 50 times its radius in visible light, a size five times larger than the orbit of Neptune. (The chromosphere is an inner layer of a star’s atmosphere, between the photosphere and the corona. The Sun’s chromosphere is visible as a thin reddish line during a total solar eclipse, and extends outward for only a fraction of a solar radius.) STIS detected the spectral signatures of tenuous hot gas in cold, remote, and dusty places of Betelgeuse’s mammoth atmosphere. The observations help to determine the mechanisms that form and sustain warm gaseous envelopes in many other red and yellow stars, including the Sun. The team investigated the atmosphere of Betelgeuse, the brightest star in the constellation Orion, over the past five years with the STIS instrument aboard Hubble. They found that the bubbling action of the chromosphere tosses gas out one side of the star, while it falls inward at the other side, similar to the slow-motion churning of a lava lamp. A team led by Alex Lobel of the Harvard-Smithsonian Center for Astrophysics announced the findings at the American Astronomical Society meeting on Jan. 6, 2004.