New type of supernova detected as stellar corpse kills companion star
Astronomers have spotted a new type of supernova for the very first time. An unlucky star seems to have prematurely exploded after colliding with an extremely dense object, perhaps a black hole or a neutron star, creating a unique signature in the sky.
The story starts in 2017, when Caltech astronomer Dillon Dong spotted a strange signal in data gathered by the Very Large Array (VLA) Sky Survey, which constantly scans the cosmos looking for radio sources. This particular signal, designated VT 1210+4956, was an extremely bright pulse of radio waves.
Dong calculated that the most likely cause of the flare was a star in the process of going supernova, producing a radio signal when ejected material interacted with a gas envelope that the star had shed a few hundred years ago. But that didn’t feel like the whole story.
Another Caltech astronomer, Anna Ho, suggested that clues could lie in a different type of signal besides radio. So the team searched a separate catalog of short-lived X-ray events, and found one that lined up with the radio source VT 1210+4956 in space, but years earlier.
“These two events have never been associated with each other, and on their own they're very rare,” says Dong.
So what kind of event could have produced both radio and X-ray emissions like this? After extensive modeling, the team eventually settled on an intriguing scenario.
The astronomers hypothesize that the star was being orbited by an extremely compact stellar corpse, most likely a black hole but potentially a neutron star. The extreme gravitational pull of this object would have slurped gas off of the star over time, throwing some of it out into space to form a “donut” shape around the star.
Eventually, the stellar corpse would have been pulled into the star, causing it to suddenly explode in a supernova long before its time. A jet of material would have been ejected from the core of the star as it collapsed, producing the X-ray signal. Years later, the blast from the exploding star would have reached the gassy donut surrounding it, producing a burst of radio waves that the VLA Sky Survey picked up.
This kind of merger-triggered supernova has long been predicted to exist, but none have ever been detected before.
"Massive stars usually explode as supernovae when they run out of nuclear fuel," says Gregg Hallinan, professor of astronomy at Caltech. “But in this case, an invading black hole or neutron star has prematurely triggered its companion star to explode.”
The research will be published in the journal Science.