Spots Like the Sun's Revealed on Giant Star
This infrared view of the red supergiant star Betelgeuse in the constellation Orion reveals two bright spots suggesting the presence of convection, similar to that seen on the sun. Data from 3 telescopes was combined for this image.
Credit: Copyright 2010 Haubois/Perrin (LESIA, Paris Observatory).

A snapshot taken of a giant star hundreds of light-years from Earth has revealed two enormous bright spots - the first direct evidence of sun-like heat transportation on another star, scientists say.

The new infrared view shows the behemoth star Betelgeuse with two bright blotches near its center. The bright spots are hotter than the surrounding area, indicating regions of convection where heat rises from the interior of the star to its surface, just like on the sun.

The convection may play a role in Betelgeuse's known and prolific weight loss, researchers said. The star is shedding the equivalent of one sun's worth of mass every 10,000 to 100,000 years. It is also expelling a gigantic plume of hot gas that may be related to the convection, researchers said.

Betelgeuse is a red supergiant star 600 light-years away and easy to spot in the night sky. It forms the right shoulder of the "hunter" in the constellation Orion. The star is enormous, about 600 times the size of the sun and 20 times as massive.

?The situation on Betelgeuse seems pretty much different than in the case of the sun,? said astronomer Guy Perrin, a co-leader of the research team at the Paris Observatory. ?The convective cells are far much larger.?

The bright spots, like the star itself, are also vast, with the larger of the two spanning of more than 139 million miles ? 1 1/2 times the distance between the Earth and our sun, researchers said. This larger spot is about one-quarter the star's diameter, they added. Similar spots on the sun are about one-twentieth the width of the star.

An international team of astronomers led by Paris Observatory astronomer Xavier Haubois and Perrin observed the Betelgeuse bright spots using three telescopes in Arizona and a method called interferometry ? which combines observations from different telescopes into a cohesive whole to provide greater sensitivity. The spots, researchers said, indicate that in supergiants there is active convection, which is the process of heat moving through matter currents.

?The star has a patchy surface produced by a few convective cells,? Perrin told in an e-mail. ?Now we need to better understand the physical properties of these cells to go further: their temperature, their lifetime, their connection to magnetic fields, etcetera.?

Convection is the process that brings bubbles to the surface of boiling water in your kitchen.

On the sun, bright convection hotspots and darker lulls (cooler areas) can easily be observed from Earth and are well-known. But that's not the case with supergiant stars like Betelgeuse, where the size, longevity and dynamics of convection structures remain a mystery.

The surface of Betelgeuse is typically about 3,600 Kelvin (6,020 degrees Fahrenheit), with the bright spots burning about 500 degrees Kelvin (440 degrees F) hotter, researchers said. The surface of the sun, for comparison, is about 5,810 degrees Kelvin (10,000 degrees F).

Researchers plan to study other layers of Betelgeuse to better understand the interaction between its surface, atmosphere and interior, as well as how they compare to other supergiant stars.

?Betelgeuse may not be an isolated case and is not necessarily peculiar with respect to other stars of the same class,? Perrin said. ?So we may anticipate similar cells on other red supergiants.?

The research, announced Tuesday, is detailed in an October 2009 edition of the journal Astronomy & Astrophysics.

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