A Stellar Collision Triggers a Supernova Explosion

Astronomers have found remarkable evidence that a black hole or neutron star spiraled its way right into the center of a companion star as well as triggered that star to explode as a supernova. The astronomers were alerted by information from the Very Large Array Sky Survey (VLASS), a multi-year project utilizing the National Science Foundation’s Karl G. Jansky Very Large Array (VLA).

“Theorists had forecasted that this might happen, yet this is the very first time we have seen such an occurrence,” said Dillon Dong, a graduate student at Caltech as well as lead author on a paper reporting this discovery in the journal Science.

The first clue came when the researchers analyzed images from VLASS, which started observations in 2017 and discovered an object brightly sending radio waves. However, it had not appeared in an earlier VLA sky survey, called Faint Images of the Radio Sky at Twenty centimeters (FIRST). They made succeeding observations of the object, marked VT 1210 +4956, utilizing VLA and Hawaii’s Keck telescope. They concluded that the bright radio emission was coming from the borders of a dwarf, star-forming galaxy some 480 million light-years from the Planet. They later located that a tool aboard the International Space station had detected a burst of X-rays coming from the item in 2014.

The data from these monitorings allowed the astronomers to assemble the remarkable history of a centuries-long death dance between two colossal stars. Like many stars much larger than our Sun, these two were birthed as a binary pair, closely orbiting each other. Among them was bigger than the other and advanced through its regular, nuclear fusion-powered lifetime quicker exploded like a supernova, leaving behind either a black hole or a superdense neutron star.

The black hole or neutron star’s orbit expanded steadily closer to its companion, and around 300 years ago, it got in the companion’s atmosphere, beginning the death dance. At this time, the interaction started spreading gas away from the companion into the space. The expelled gas, spiraling externally, created an increasing, donut-shaped ring, called a torus, around both.

Ultimately, the black hole or neutron star headed inwards to the companion star’s core, disrupting the nuclear fusion generating the power that kept the core from collapsing of its gravity. As the core fell, it quickly formed a disk of material very closely orbiting the invader and pushed a jet of material outside from the disk at speeds coming close to that of light, drilling a path through the star.

“That jet is what generated the X-rays seen by the MAXI instrument aboard the International Space Station, and also this checks the date of this occurrence in 2014,” Dong said.

Star’s core collapse caused it to explode like a supernova following its sibling’s earlier explosion.

“The companion star would eventually explode, but this merging accelerated the phenomenon,” Dong claimed.

The material expelled by the 2014 supernova explosion moved a lot faster than the material thrown off earlier from the companion star. By the time VLASS observed the item, the supernova blast and that material were colliding, creating potent shocks that generated the bright radio emission seen by the VLA.

“All puzzle pieces fit together to tell this fantastic story,” claimed Gregg Hallinan of Caltech. “The remnant of a star that exploded a very long time ago plunged into its companion, leading it, as well, to blow up,” he included.

Hallinan stated that the secret to the exploration was VLASS, which is imaging the whole skies visible at the VLA’s latitude – about 80 percent of the sky – 3 times over seven years. One of the purposes of doing VLASS is to uncover transient objects, such as supernova explosions, that shine brightly at radio-waves. This supernova, caused by a stellar merger, nevertheless, was a surprise.

“Of all things we believed we would certainly discover with VLASS, this was not one of them,” Hallinan said.

Originally published on Sciencedaily.com. Read the original article.

Reference: D. Z. Dong et al, A transient radio source consistent with a merger-triggered core collapse supernova, Science (2021). DOI: 10.1126/science.abg6037