WASHINGTON, Aug. 15 - Astronomers have discovered that a giant star that has been studied for centuries is streaking across the sky trailing an enormous, cometlike tail.
Scientists said Wednesday that they were stunned to learn that the giant red star, Mira, zipping through the Milky Way galaxy 300 times faster than a speeding bullet, has a turbulent tail stretching trillions of miles across space.
"I was shocked when I first saw this completely unexpected humongous tail trailing behind a well-known star," said Christopher Martin of the California Institute of Technology, principal scientist for the Galaxy Evolution Explorer spacecraft, also known as the Galex, that discovered the tail.
The craft, built and managed by NASA's Jet Propulsion Laboratory in Pasadena, Calif., surveys the sky with an instrument highly sensitive to ultraviolet light.
The craft noticed an unusual glow around Mira, scientists said, and inspection showed the tail and other features surrounding Mira that were visible just in ultraviolet light. That helps explain how other observatories missed them, the team said.
Mira is an old star of a class called a red giant that represents the end stages of stars like our Sun, which will evolve into a red giant in four billion or five billion years, scientists said.
Mira is 400 times the size of the Sun, but with only about the same mass. Dying red giants spew material into space that eventually becomes building material for new stars and planets.
Mark Seibert, a research associate at the Observatories of the Carnegie Institute of Washington in Pasadena, said Mira expanded and contracted every 332 days, making it periodically visible with the naked eye from Earth. Mira, which travels with a distant companion believed to be a compact white dwarf star, is in the constellation Cetus (the whale) 350 light-years from Earth.
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