SGU Science Picture Of The Week: Extraordinary Binary Stars
What you see here is an artist’s impression of the hottest most massive binary stars discovered to-date.
These conjoined stars (called VFTS 352) are 160 000 light-years away in the Tarantula Nebula. They were spotted by the European Space Organization’s descriptively-named “Very Large Telescope”.
Look up at the night sky. About 80% of those singular points of light you see are actually double or multiple stars orbiting a common center of gravity (barycenter). When you look at the more common (dimmer and less massive) stars that are not easy to see, the incidence of double stars goes way down to 20%. The big strapping stars though (4-10 solar masses) are almost always found in a binary or multiple star systems. These two stars in the VFTS system are especially extraordinary since their combined mass is 57 times that of the sun and they are quite hot with a surface temperature of 40,000 degrees celsius.
The orbits of binary stars can be slow and stately if they are far apart. The orbital periods of such stars can be as long as centuries or millennia if they are exceptionally distant. The closer the twins are however, the less time it takes them to orbit each other. The binaries pictured here are so close that their orbital period is little more than a single earth day. As is obvious from this image, the word “close” doesn’t even do their separation justice. Their stellar centers are so close (12 million kilometres) that a bridge has formed between the two causing them to actually share the gasses that comprise them. Since their masses are so similar, one star doesn’t simply consume the other; instead they share as much as 30% of their resources fairly back and forth.
This kind of twin-star system is often called a contact or over-contact binary and it’s ultimate fate is at least as interesting as this relatively brief period of intimate coupling.
One possibility is that these two stars will merge to create a single massive (57 solar mass) star that would likely rotate very very fast and even possibly be intensely magnetic. Regarding its subsequent fate, lead scientist Hugues Sana, of the University of Leuven in Belgium has said:
“If it keeps spinning rapidly it might end its life in one of the most energetic explosions in the Universe, known as a long-duration gamma-ray burst,”
Yet another possibility is even more exciting since it would essentially cover new ground for star evolution. Lead theoretical astrophysicist Selma de Mink of University of Amsterdam has said:
“If the stars are mixed well enough, they both remain compact and the VFTS 352 system may avoid merging. This would lead the objects down a new evolutionary path that is completely different from classic stellar evolution predictions. In the case of VFTS 352, the components would likely end their lives in supernova explosions, forming a close binary system of black holes. Such a remarkable object would be an intense source of gravitational waves.”
I would love to see which fate comes to fruition (or if another yet unanticipated one comes to pass). If a far future astronomer witnesses this event, please use your tachyon gmail service to tell me what happens 🙂
Image Credit: http://www.eso.org/public/news/eso1540/