Astronomers may have detected never-before-seen way to destroy a star

Astronomers, using the Gemini South telescope, may have detected a never-before-seen way to annihilate a star. While studying a powerful gamma-ray burst (GRB), they have found evidence of a demolition-derby-like collision of stars or stellar remnants in a densely packed region near an ancient galaxy’s supermassive black hole.

This finding challenges the conventional understanding of stellar deaths and sheds light on a long-hypothesized, yet previously unseen, phenomenon. Traditionally, stars in the universe are known to meet predictable fates based on their mass. Low-mass stars, like our Sun, gradually shed their outer layers and fade away as white dwarf stars. On the other hand, more massive stars burn brighter and end their lives in cataclysmic supernova explosions, leaving behind dense remnants such as neutron stars and black holes. In the case of binary systems consisting of two such remnants, they also can eventually collide.

Cores of ancient galaxies harbour a plethora of ultra-dense stellar remnants like white dwarfs, neutron stars, and black holes. Astronomers have long speculated that the chaotic environment surrounding a supermassive black hole could eventually lead to the collision of two stellar objects, resulting in a GRB. However, until now, concrete evidence of such a merger had remained elusive.

The first indications of this event emerged on October 19, 2019, when NASA's Neil Gehrels Swift Observatory detected a brief but intense burst of gamma rays, lasting just over a minute. Typically, GRBs that last more than two seconds are classified as "long" bursts, primarily originating from the supernova deaths of stars at least ten times the mass of our Sun.

To gather more insights into the origins of this intriguing GRB, the astronomers employed the Gemini South telescope to conduct long-term observations of its fading afterglow. They were able to pinpoint the GRB's location to a region less than 100 light-years from the core of the ancient galaxy, placing it in close proximity to the supermassive black hole. Notably, no evidence of a corresponding supernova was found, which would typically leave distinct imprints on the observed light.

"By pinpointing its location to the center of a previously identified ancient galaxy, we had the first tantalizing evidence of a new pathway for stars to meet their demise," said Andrew Levan, an astronomer with Radboud University in The Netherlands and lead author of a paper appearing in the journal Nature Astronomy.

Typically, the occurrence of long GRBs resulting from colliding stellar remnants like neutron stars and black holes is believed to be exceptionally rare in normal galactic environments. However, ancient galaxy cores defy the norm with their extreme population density, potentially housing a million or more stars within a region just a few light-years across. In such densely packed regions, stellar collisions may occur sporadically, particularly under the gravitational influence of a supermassive black hole, which can perturb the motions of stars and send them hurtling in unpredictable directions. Over time, these wandering stars may intersect and merge, triggering a colossal explosion observable across vast cosmic distances.

The researchers attribute the elusiveness of such events in the past to the abundance of dust and gas prevalent in galactic centers. These materials can obscure the initial burst of the GRB as well as its subsequent afterglow. However, the GRB labelled as GRB 191019A appears to be a rare exception, allowing astronomers to detect the burst and study its aftermath.

The researchers aim to discover more instances of such events in the hope to correlate GRB detections with corresponding gravitational-wave detections, which would unveil further insights into the true nature of these events and confirm their origins.