The Face of Another Sun

Most stars are so distant that even the largest telescopes resolve them only as pinpoints of light. But then most stars are not Betelgeuse, a red supergiant 500 light-years away, familiar as the star marking the shoulder of Orion the hunter. And most telescopes don’t float above Earth’s blurring atmosphere as does the Hubble Space Telescope. In this, the first direct, detailed image of a star other than the sun, the hot outer atmosphere of Betelgeuse is shown to stretch nearly a billion miles across--if it were our sun it would have swallowed Jupiter. Most of this outer atmosphere has a temperature of around 9,000 degrees Fahrenheit, which is 1,000 to 2,000 degrees cooler than the sun’s surface temperature. But whereas the sun radiates more or less evenly across its entire surface, Betelgeuse has a 12,000-degree hot spot that occupies about 10 to 20 percent of the star’s disk--and baffles astronomers. The dominance of this one very hot spot, from which most of the radiation is emerging, is totally different from what we see in the sun, says Andrea Dupree of the Harvard- Smithsonian Center for Astrophysics. The spot may be connected to Betelgeuse’s 420-day pulsation cycle or to some unknown magnetic field effect.