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Supergiant Star Seems To Be Shrinking

June 10, 2009

A study released on Tuesday showed that a massive bright reddish star in the Orion constellation has mysteriously shrunk by over 15 percent in the last 15 years and astronomers have not yet determined the cause, AFP reported.

The supergiant star Betelgeuse, which is among the eight brightest stars in our sky, is so large that it would reach to Jupiter’s orbit in our solar system. But the star has shrunk at a radius of about five astronomical units in size since 1993 by a distance equivalent to Venus’s orbit.

Professor Charles Townes from the University of California, Berkeley, who won the 1964 Nobel Prize in physics for inventing the laser, said the change is very striking to see.

“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 said.

In fact, the star’s size diminished smoothly, but faster as the years progressed, according to Townes.

The discovery was based on readings collected at UC Berkeley’s Infrared Spatial Interferometer (ISI) atop Mount Wilson in Southern California and the findings were presented Tuesday at a meeting of the American Astronomical Society in Pasadena, California.

The researchers did not know why the star was shrinking, according to Edward Wishnow, a UC Berkeley research physicist who worked with Townes on the study.

Wishnow said with all that is known about galaxies and the distant universe, there are still lots of things astronomers don’t know about stars, including what happens as red giants near the ends of their lives.

Experts suspect that red supergiant stars likely explode into type-II supernovas, or cosmic explosions due to a massive star’s internal collapse.

A bright spot on the star’s surface had been observed in recent years, but Townes said the star appears spherically symmetrical for now.

Betelgeuse was the first star to ever be measured and is one of the few stars that shows up on the Hubble Space Telescope as a disk rather than a point of light.

Wishnow noted that Betelgeuse’s visible brightness had showed no signs of significant dimming over the past 15 years.

Image Caption: This is the first direct image of a star other than the Sun. Called Alpha Orionis, or Betelgeuse, the star is a red supergiant. The Hubble picture reveals a huge ultraviolet atmosphere with a mysterious hot spot on the stellar behemoth’s surface. The enormous bright spot is at least 2,000 degrees Kelvin hotter than the star’s surface. (NASA)

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