Posted on 01/11/2005 5:23:38 PM PST by neverdem
SAN DIEGO, Jan. 10 - KW Sagitarii is not the brightest star in the Milky Way, or the heaviest or densest. Neither are two other stars, KY Cygni and V354 Cephei.
But these three red supergiant stars have caught the attention of astronomers because they appear to be the biggest stars known, and possibly the biggest possible for a normal star. (Another supergiant, VV Cephei, may be even larger, but that one has been distorted by the gravity of a companion star.)
Each of the three stars is more than a billion miles wide, filling as much space as 3.4 billion Suns. Placed at the center of the solar system, one of these stars would extend to halfway between Jupiter and Saturn. The stars are more than twice as wide as Betelgeuse in the constellation Orion, a red supergiant familiar to amateur astronomers.
"We actually know, both observationally and theoretically, how big a star can get," said Dr. Philip Massey of the Lowell Observatory in Flagstaff, Ariz., who led an international team of astronomers that conducted the research. "These are right at the limit of what solar evolutionary theory says we should get by the way of red supergiants."
Emily Levesque, a Massachusetts Institute of Technology undergraduate on the research team, presented the findings on Monday at a meeting of the American Astronomical Society here. A scientific paper describing the results has been submitted to The Astrophysical Journal.
As stars near the end of their lives, they exhaust the hydrogen fuel at their cores. The fusion process that creates light and energy then spreads outward from the core, and the increased pressure pushes the outer layers. When the Sun reaches this stage four billion to five billion years from now, it will probably swell beyond Venus's orbit, becoming a red giant.
KW Sagitarii, KY Cygni and V354 Cephei are much larger, about 25 times as massive as the Sun, and thus swelled far more.
Astronomers do not have celestial rulers to measure the stars, which appear only as points of light to even the most powerful telescopes. Rather, the colors of light emitted by molecules in the outer layers tell the surface temperatures, and models of how a star works produce estimates of the diameters. But observations of red supergiants conflicted with the models.
In the new research, Dr. Massey and his collaborators took new measurements of 74 red supergiants and found that the coolest, and thus largest, had surface temperatures of about 5,750 degrees Fahrenheit, about 10 percent warmer than earlier measurements. "I think everything is now in agreement," he said.
While KW Sagitarii, KY Cygni and V354 Cephei are most likely the largest possible stars in the Milky Way, Dr. Massey said, they may not be the largest in the universe. Stellar models, he said, predict that even larger stars could evolve in galaxies with lower concentrations of elements heavier than helium, like the nearby Magellanic Clouds.
ping
Thanks. I'll ping the list.
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Yo momma's so fat she retards the earth's rotation when she walks to the welfare office.
...When the Sun reaches this stage four billion to five billion years from now, it will probably swell beyond Venus's orbit, becoming a red giant. ....
proof that global warming exists and it is all Bush's fault.
Thanks for the ping!
Dead thread ping.
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