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Closest Known Star, Proxima Centauri, Measured, Theories Hold Up
By SPACE.com Staff
posted: 07:31 am ET
04 December 2002
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Quick quiz: What is the closest star to our Sun? A lot of people think it is Alpha Centauri. Actually, Proxima Centauri is closest. But Proxima Centauri is so small that astronomers have not been able to accurately measure it. Proxima Centauri is a very-low-mass star, in fact barely massive enough to burn hydrogen to helium in its interior. It is about seven times smaller than the Sun, and the surface temperature is "only" about 3000 degrees, about half of that of our own star. Consequently, it is also much fainter -- the intrinsic brightness is only 1/150th of that of our Sun. New software, however, along with detailed observations from the European Southern Observatory's VLT Interferometer, has allowed some calculations. The star has a mass and diameter about 1/7 of those of the Sun. Yet while it is 150 times more massive than Jupiter, it is only about 1.5 times larger than that planet. Low-mass stars are very interesting objects, also because the physical conditions in their interiors have much in common with those of giant planets, like Jupiter. A determination of the sizes of the smallest stars has been impossible until now because of their general faintness and lack of adequate instrumentation. In astronomical terms, the newly measured angular diameter of Proxima Centauri is 1.02 + 0.08 milliarcsec, or about the size of an astronaut on the surface of the Moon as seen from the Earth, astronomers said, or a head of a pin on the surface of the Earth, as seen from the International Space Station."The measured sizes agree well with theoretical predictions, based on numerical models of planets and low-mass stars," said Didier Queloz of the Geneva Observatory. "The same holds for the sizes of a number of more massive stars that were measured at the same time. This gives us new confidence in the models of these extreme objects."Proxima Centauri is barely massive enough to produce thethermonuclear fusion that powers a star. Slightly less massive objects fail togenerate the reaction and are called browndwarfs.More Deep SpaceNews | Astronotes | | | |
