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Venice Update

News of Venice, CA and Marina del Rey CA

Watching a Volatile Stellar Relationship

raqr_w11
 (Photo courtesy of Chandra X-Ray Center.)

Note: This is a press release from Chandra X-Ray Center and NASA/Marshall Space Flight Center.

Bob Eklund Looking Up Column

Bob Eklund
Looking Up Column

 

In biology, “symbiosis” refers to two organisms that live close to and interact with one another. Astronomers have long studied a class of stars—called symbiotic stars—that co-exist in a similar way. Using data from NASA’s Chandra X-ray Observatory and other telescopes, astronomers are gaining a better understanding of how volatile this close stellar relationship can be.

R Aquarii (R Aqr, for short) is one of the best known of the symbiotic stars. Located at a distance of about 710 light-years from Earth, its changes in brightness were first noticed with the naked eye almost a thousand years ago. Since then, astronomers have studied this object and determined that R Aqr is not one star, but two: a small, dense white dwarf and a cool red, giant star.

The red giant star has its own interesting properties. In billions of years, our Sun will turn into a red giant once it exhausts the hydrogen nuclear fuel in its core and begins to expand and cool. Most red giants are placid and calm, but some pulsate with periods between 80 and 1,000 days like the star Mira and undergo large changes in brightness. This subset of red giants is called “Mira variables.”

The red giant in R Aqr is a Mira variable and undergoes steady changes in brightness by a factor of 250 as it pulsates, unlike its white dwarf companion that does not pulsate. There are other striking differences between the two stars. The white dwarf is about ten thousand times brighter than the red giant. The white dwarf has a surface temperature o.

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