A binary black hole, or a single giant star. Those are the two options that await a pair of stars in the double star system VFTS 352. The star pair sits about 160,000 light-years away from Earth in the Tarantula Nebula. What makes this pair so strange is how close they are to each other. They touch each other.
The centers of each star are separated by just 7.4 million miles. Scientists say the stars are so close their surfaces overlap and are connected.
The two stars are known as O-type stars. They are usually between 15 and 80 times more massive than our Sun and shine up to a million times brighter.
Each star is roughly the same size. And instead of one star ‘sucking’ material from the other, they appear to be sharing. Observations with the ESO’s Very Large Telescope estimate about 30 percent of the stars’ material is being mixed. Astronomers believe incredibly strong tidal forces are responsible for this mixing.
“The VFTS 352 is the best case yet found for a hot and massive double star that may show this kind of internal mixing,” explains lead author Leonardo A. Almeida of the University of São Paulo, Brazil. “As such it’s a fascinating and important discovery.”
VFTS 352’s Fate
Astronomers predict VFTS 352 will go out with a bang. A very large bang. The study’s authors describe how this will happen in two ways. The first? A massive fast-spinning, possibly magnetic star.
“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,” says the lead scientist of the project, Hugues Sana.
The second option is even more destructive. It involves a pair of supernova explosions leading to a close binary system of black holes.
“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,” says Selma de Mink, lead theoretical astrophysicist on the team.
The Tarantula Nebula
Tarantula Nebula via the Hubble Space Telescope
Now this is an interesting region of space. The Tarantula Nebula is described as one of the most active regions for new stars in the nearby Universe. The European Southern Observatory even have a dedicated survey for it – the VLT FLAMES Tarantula Survey.
Other discoveries made by this survey include VFTS 102, the fastest rotating star (found so far), and VFTS 682, a massive but lonely star.
In 2011, astronomers announced the discovery of VFTS 102. It’s size and brightness isn’t unusual, but it’s rotating speed sure is. VFTS 102 rotates at 2 million kilometers per hour. That’s more than 300 times faster than our Sun.
VFTS 682’s discovery was also announced in 2011. It’s about 150 times larger than the Sun, but what surprised astronomers was that the star sits by itself. “We were very surprised to find such a massive star on its own, and not in a rich star cluster,” said Joachim Bestenlehner, lead author of the study at the time.
The VLT-FLAMES Tarantula Survey looked at more than 900 stars. Today, astronomers continue to pour over the data to see what other discoveries the ESO’s Very Large Telescope can yield.