Saturday, July 28, 2012
'Vampire' Stars Violent, Suck Gas From Neighbors; Population Larger Than Thought, Study Finds

'Vampire' Stars Violent, Suck Gas From Neighbors; Population Larger Than Thought, Study Finds

"Vampire stars," which suck gas from their companion stars giving them a longer life, are surprisingly much more common than previously thought, a new study finds.

Technically, the "vampire stars" are called Type O stars and are important to astronomers and scientists because they are the hottest and extremely bright, being bluish in color, and have a big effect on galaxy evolution. When they die there is a violent explosion that can be seen throughout most of the universe. During the explosion they produce heavy elements that are essential for life.

Recently astronomers studying massive O-type stars discovered that over 70 percent of them have a companion star, according to a new study published in the July 27 issue of the journal "Science." These "vampire" O-type stars suck hydrogen gas from its close neighbor star allowing it to live longer than it normally would. The companion star that played victim will have an exposed core and look like a significantly younger star. Sometimes, the O-type star and its companion star merge and become one star.

"These stars are absolute behemoths," said Huges Sana of the University of Amsterdam, who is the lead author of the study, in a statement posted on the website of fellow research Selma de Mink. "They have 15 or more times the mass of our sun and can be up to a million times brighter. These stars are so hot that they shine with a brilliant blue-white light and have surface temperatures over 30,000 degrees Celsius."

These latest findings came from researchers using the European Southern Observatory's Very Large Telescope in Chile. Astronomers studied 71 O-type single stars and stars in pairs (binaries) in the Milky Way. Researchers were surprised to find that nearly 75 percent of all O-type stars studied were in a binary system, and even more so to learn that they closely interact with their companion star. About 20 to 30 percent of O-type stars end up merging with their companion star.

"We already knew that massive stars are very often in binaries," de Mink told "What is very surprising to us is that they're so close, and such a large fraction is interacting. If a star has a companion so close next to it, it will have a very different evolutionary path. Before, this was very complicated for us to model, so we were hoping it was a minority of stars. But, if 70 percent of massive stars are behaving like this, we really need to change how we view these stars."

Less than 1 percent of the stars in the universe are Type O stars.


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