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Mercredi, 07 Décembre 2011 19:00

Blue Vampire Star Caught Sucking Red Giant's Gas

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Blue Vampire Star Caught Sucking Red Giant's Gas

Astronomers have captured the best-ever image of a star sucking the gas away from its bloated, dying companion.

The mechanics of stellar vampirism, however, proved less dramatic than astronomers anticipated. They expected to see hot gas funneling from a cool red giant star into a hot, dense blue star. Instead they saw mostly nothing.

The binary star system, called SS Leporis, likely uses a lesser-known method to send gas from one star to the other.

“For a long time this system was suspected as a typical example of star vampirism, but it’s more light and friendly than we would have loved to see,” said astronomer Jean-Philippe Berger of the European Southern Observatory and co-author of an upcoming study on SS Leporis in Astronomy & Astrophysics.

Binary systems contain two stars orbiting a common center of mass. If the stars orbit close enough to each other, they can share gas to become “symbiotic binaries” like SS Leporis, which is located about 910 light-years from Earth.

In that system, two stars complete an orbit around one another every 260 days, and it’s a tight one. They are separated by a distance similar to the Earth’s distance to the Sun.

SS Leporis’ dense blue star is about 2.7 times the mass of our sun and feeds on a dying red giant star that’s about 1.3 times the sun’s mass. As the red giant’s hot gas pushes outward, the conventional thinking goes, it passes a point where the blue companion pulls the material into a funnel using its gravitational tug.

But it doesn’t.

“The red giant is losing a lot of mass, as the blue star is much more massive than we expected,” Berger said. “But we did not see vampirism. The stars must be doing something more peaceful and lengthy.”

Berger and his colleagues suspect the red giant is politely donating its mass through solar wind, an outward spray of particles. After the particles waft into space, the blue star could corral them.

“It’s named the CRAP mechanism,” Berger said. “I don’t know who came up with the term, but that’s what it is called.”

The CRAP-y stellar vampirism has been ongoing for 500,000 years and should continue for another 200,000. Within a few million years, the red giant will end its life as a white dwarf. A few million years after that, the blue star should follow suit.

Berger said the most exciting part of the study was how it was done: Astronomers photographed the stars using four 6-foot-wide telescopes in Chile’s high-altitude Atacama Desert. A technique called interferometry then allowed the researchers to combine the images and, in effect, simulate the resolution of telescope 426 feet wide.

Such a resolution is 50 times better than the Hubble Space Telescope. It’s so powerful that an astronaut on the moon could be seen from Earth.

In the future, Berger and his colleagues plan to use interferometry on other stellar vampire candidates to see if they have hot, gassy funnels. But they aren’t done probing SS Leporis yet. The team wants to zoom in 10 times further with another instrument and look for signs of the system’s hot accretion disk.

“We know the blue star is acquiring matter,” Berger said. “The question now is, how is that matter organized?”

Image: Three snapshots of SS Leporis show the double-star system’s clockwise orbit. Although a fuzzy stream of blue gas seems to connect the two objects in the first frame, Berger said it is probably an artifact of the interferometry technique used to create the image. (ESO/PIONIER/IPAG)


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