Rare Double Star is Hottest, Largest Yet Discovered

October 22, 2015 | Gillian Burrell

Artist's impression of VFTS 352, a binary star system in the Tarantula Nebula
Photo credit: ESO

Astronomers at the European Southern Observatory (ESO) who discovered the recording-breaking stars predict they will meet a cataclysmic end.

ESO astronomers announced today (October 21) the discovery of a rare and record-breaking star system in the Tarantula Nebula. VFTS 352 is a binary star system located about 160,000 light-years from us, and it’s extraordinary in every way, including the way it’s going to die.

Firstly, VFTS 352 is a binary star system, meaning it has not one but two stars at its center. While it is not unheard of for a star system to have two stars, VFTS 352 falls into a very special category because the stars are actually so close that they overlap. With an estimated 12 million kilometers between the two stars, these “overcontact binaries” share an estimated 30 percent of their mass with one another.

SEE ALSO: Twin Supermassive Black Holes on Verge of Collision

Secondly, both stars in VFTS 352 are considered O-type stars. With a combined mass of about 57 times the size of our sun, the double star dwarfs all others in its class, and with a surface temperature of 40,000° C (72,032° F), it is also the hottest contact binary system in existence. O-type stars are so hot they emit white-blue light rather than yellow light like our sun.

The third notable characteristic about VFTS 352 is that both stars are more or less equal in size. In other contact binaries, the smaller star is called a “vampire star” because it sucks matter from the surface of the larger star.

Because of these exceptional qualities, astronomers anticipate a cataclysmic event when the stars finally die. The precarious situation of overlapping stars is generally a brief stage in their life cycle and the proximity of the two stars in VFTS 352 may even shorten their lifespans. What happens next could go one of two ways: either the stars will merge or they’ll collapse into twin black holes.

The first scenario is likely because the two stars are already orbiting each other. Gravitational forces between the stars could cause the rotations to increase in speed until the two merge into one giant, spinning, 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,” explained lead scientist, Hugues Sana in a press release. Gamma ray bursts are the brightest lights in the universe (although invisible to humans) and are thought to be emitted by a star in the seconds to hours before it collapses into a black hole.

Alternatively, the double star could immediately collapse into two black holes. This scenario is likely if the two stars continue to mix thoroughly so that tidal forces counteract the spinning motion. According to the team’s lead theoretical astrophysicist, Selma de Mink, “This would lead the objects down a new evolutionary path that is completely different from classic stellar evolution predictions.”  

Neighboring black holes would be an astronomical event because they are thought to emit significant gravitational waves — ripples in the fabric of space and time — when formed so close together. We still haven’t found direct evidence of gravitational waves, so a potential binary black hole is a very exciting find for the world of astrophysics.


Based on materials provided by the European Southern Observatory.

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