A powerful gamma-ray burst has been detected, which may represent a never-before-seen way of destroying a star

A powerful gamma-ray burst (GRB) detected by astronomers using the Gemini South telescope, operated by the NOIRLab of the US National Science Foundation (NSF), may have revealed a never-before-seen way of destroying a star, according to a study published in the journal 'Nature Astronomy'.

Unlike most GRBs caused by the explosion of massive stars or the chance merger of neutron stars, astronomers have concluded that this GRB occurred due to the collision of stars or stellar remains in the crowded environment surrounding a supermassive black hole at the core of an ancient galaxy.

Most stars in the universe die predictably depending on their mass. Relatively low-mass stars, like our Sun, shed their outer layers as they age and eventually fade away into white dwarfs. More massive stars burn brighter and die earlier in cataclysmic supernova explosions, creating ultradense objects like neutron stars and black holes. If two of these stellar remains form a binary system, they may also end up colliding. However, a new study points to a fourth option, long hypothesized but never seen before.

While searching for the origins of a long-duration gamma-ray burst (GRB), astronomers using the Gemini South telescope in Chile, part of the International Gemini Observatory operated by NSF's NOIRLab, and other telescopes, have found evidence of a collision of stars or stellar remains similar to a demolition in the chaotic and dense region near the supermassive black hole of an ancient galaxy.

According to Andrew Levan, an astronomer at Radboud University (Netherlands) and lead author, "these new results demonstrate that stars can meet their end in some of the densest regions of the Universe, where they can be pushed to collide. This is exciting for understanding how stars die and for answering other questions such as what unexpected sources could create gravitational waves that we could detect on Earth," he adds.

Ancient galaxies have long since left their star-forming stage and would have few, if any, giant stars, which are the main source of long GRBs. However, their cores are filled with stars and ultradense stellar remains such as white dwarfs, neutron stars, and black holes.

Astronomers have long suspected that in the turbulent hive of activity surrounding a supermassive black hole, it would only be a matter of time before two stellar objects collided to produce a GRB. However, evidence of this type of merger has been elusive.

The first indications that such an event had occurred were observed on October 19, 2019, when NASA's Neil Gehrels Swift Observatory detected a bright gamma-ray burst that lasted just over a minute. Any GRB that lasts more than two seconds is considered "long." Such bursts typically come from the supernova death of stars at least 10 times the mass of our Sun - but not always.

The researchers then used Gemini South to make long-term observations of the GRB's afterglow to better understand its origins. The observations allowed astronomers to locate the GRB in a region less than 100 light-years from the core of an ancient galaxy, placing it very close to the galaxy's supermassive black hole. The researchers also found no signs of a corresponding supernova, which would leave its signature in the light studied by Gemini South.

"Our follow-up observation indicated that, rather than being the collapse of a massive star, the most likely explanation for the burst was the merger of two compact objects," explains Levan. "By determining its location at the center of a previously identified ancient galaxy, we obtained the first tantalizing evidence for a new pathway of star disappearance."

In normal galactic environments, the production of long GRBs from colliding stellar remains such as neutron stars and black holes is believed to be extremely rare. However, the cores of ancient galaxies are anything but normal and may have a million or more stars crammed into an area just a few light-years in diameter.

Next Post Previous Post
No Comment
Add Comment
comment url