It’s an astronomical rarity—two stars orbiting each other so closely that they’re connected by a gas bridge through which they swap a staggering amount of stellar material. Each burns so bright that their surface temperatures exceed 72,000˚ F.
But their deaths will probably be even more spectacular than their lives. For astronomers, the two possible scenarios—either a rare long-duration gamma ray burst or a flurry of never-before-seen gravitational waves—are equally alluring. Discovering a contact binary in its death throes could shed light on the universe’s hidden workings.
The system, known as VFTS 352, isn’t at the end of its life yet. It’s two stars have a combined mass 57 times larger than our sun. Orbiting just 7.5 million miles apart, the two circle each other in just over 24 hours. Their close proximity means the two stars appear as one misshapen stellar body, a type known as an overcontact binary.
This isn’t the first overcontact binary system discovered, but it is the largest, and the two stars’ equal size makes it that much more unusual. Here Xaq Rzetelny, reporting for Ars Technica:
In other close binary systems, one star might be siphoning material off its neighbor, growing its mass at the expense of the other’s. That’s why they are nicknamed “vampire stars.” But that’s not the case here, since the two stars have almost the same mass and thus nearly equal gravity.
This sharing of material allows the stars to become mixed, their chemical compositions gradually reaching an equilibrium. Due to the strong tidal forces that the stars exert on each other, this mixing process is likely enhanced, and the researchers estimate a full 30 percent of each individual star’s material is being shared.
VFTS 352’s demise could come about one of two ways. First, the two stars could complete their merger, forming one enormous, fast-rotating magnetic star that might flash out of existence in a gamma ray burst that could last as long as two seconds (an eternity by GRB standards).
Or, more intriguingly, the two stars might both supernova and collapse into two orbiting black holes that would throw off gravitational waves at the speed of light as their orbits slowed. When they finally merge, they would form one big black hole, giving off one last, intense blast of gravitational waves.