Red giant star Betelgeuse mysteriously shrinks over past 15 years

June 10th, 2009 - 2:13 pm ICT by ANI  

Hubble Space Telescope Washington, June 10 (ANI): In a new research, scientists have determined that the red supergiant star Betelgeuse, the bright reddish star in the constellation Orion, has mysteriously shrunk over the past 15 years.

Long-term monitoring by UC (University of California) Berkeley’s Infrared Spatial Interferometer (ISI) on the top of Mt. Wilson in Southern California shows that Betelgeuse, which is so big that in our solar system it would reach to the orbit of Jupiter, has shrunk in diameter by more than 15 percent since 1993.

Since Betelgeuse’s radius is about five astronomical units, or five times the radius of Earth’s orbit, which means the star’s radius has shrunk by a distance equal to the orbit of Venus.

“To see this change is very striking,” said Charles Townes, a UC Berkeley professor emeritus of physics. “We will be watching it carefully over the next few years to see if it will keep contracting or will go back up in size,” he added.

Despite Betelgeuse’s diminished size, Edward Wishnow, a research physicist at UC Berkeley’s Space Sciences Laboratory, pointed out that its visible brightness, or magnitude, which is monitored regularly by members of the American Association of Variable Star Observers, has shown no significant dimming over the past 15 years.

“The ISI has been focusing on Betelgeuse for more than 15 years in an attempt to learn more about these giant massive stars and to discern features on the star’s surface,” Wishnow said.

He speculated that the measurements may be affected by giant convection cells on the star’s surface that are like convection granules on the sun, but so large that they bulge out of the surface.

Townes and former graduate student Ken Tatebe observed a bright spot on the surface of Betelgeuse in recent years, although at the moment, the star appears spherically symmetrical.

“But, we do not know why the star is shrinking,” Wishnow said. “Considering all that we know about galaxies and the distant universe, there are still lots of things we don’t know about stars, including what happens as red giants near the ends of their lives,” he added.

Betelgeuse was the first star ever to have its size measured, and even today is one of only a handful of stars that appears through the Hubble Space Telescope as a disk rather than a point of light. (ANI)

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