Stellar demolition derby births powerful gamma-ray burst

Whereas trying to find the origins of a robust gamma-ray burst (GRB), a global group of astrophysicists might have stumbled upon a brand new method to destroy a star.

Though most GRBs originate from exploding large stars or neutron-star mergers, the researchers concluded that GRB 191019A as a substitute got here from the collision of stars or stellar remnants within the jam-packed surroundings surrounding a supermassive black hole on the core of an historical galaxy. The demolition derby-like surroundings factors to a long-hypothesized—however never-before-seen—method to demolish a star and generate a GRB.

The research was revealed within the journal Nature Astronomy. Led by Radboud College within the Netherlands, the analysis group included astronomers from Northwestern College.

“For each hundred occasions that match into the normal classification scheme of gamma-ray bursts, there’s at the least one oddball that throws us for a loop,” stated Northwestern astrophysicist and research co-author Wen-fai Fong, “Nevertheless, it’s these oddballs that inform us probably the most concerning the spectacular variety of explosions that the universe is able to.”

“The invention of those extraordinary phenomena inside dense stellar programs, particularly these encircling supermassive black holes on the cores of galaxies, is undeniably thrilling,” stated Northwestern astrophysicist and research co-author Giacomo Fragione. “This exceptional discovery grants us a tantalizing glimpse into the intricate dynamics at work inside these cosmic environments, establishing them as factories of occasions that may in any other case be deemed unattainable.”

Fong is an assistant professor of physics and astronomy at Northwestern’s Weinberg School of Arts and Sciences and a member of the Middle for Interdisciplinary Exploration and Analysis in Astrophysics (CIERA). Fragione is a analysis assistant professor in CIERA. Different Northwestern co-authors embrace Anya Nugent and Jillian Rastinejad—each Ph.D. college students in astronomy and members of Fong’s analysis group.

Most stars die, in accordance with their mass, in considered one of three predictable methods. When comparatively low-mass stars like our sun attain previous age, they shed their outer layers, ultimately fading to grow to be white dwarf stars. Extra large stars, however, burn brighter and explode quicker in cataclysmic supernovae explosions, creating ultra-dense objects like neutron stars and black holes. The third state of affairs happens when two such stellar remnants kind a binary system and ultimately collide.

However the brand new research finds there is perhaps a fourth possibility.

“Our outcomes present that stars can meet their demise in a few of the densest areas of the universe, the place they are often pushed to collide,” stated lead writer Andrew Levan, an astronomer with Radboud College. “That is thrilling for understanding how stars die and for answering different questions, comparable to what sudden sources would possibly create gravitational waves that we might detect on Earth.”

Long gone their star-forming prime, historical galaxies have few, if any, remaining massive stars. Their cores, nonetheless, teem with stars and a menagerie of ultra-dense stellar remnants, comparable to white dwarfs, neutron stars and black holes. Astronomers have lengthy suspected that within the turbulent beehive of exercise surrounding a supermassive black hole, it solely could be a matter of time earlier than two stellar objects collided to supply a GRB. However proof for that kind of merger has remained elusive.

On Oct. 19, 2019, astronomers glimpsed the primary hints of such an occasion when NASA’s Neil Gehrels Swift Observatory detected a vivid flash of gamma rays that lasted a little bit over one minute. Any GRB lasting longer than two seconds is taken into account “lengthy.” Such bursts usually come from the collapse of stars at the least 10 occasions the mass of our sun.

The researchers then used the Gemini South telescope in Chile—a part of the Worldwide Gemini Observatory operated by the Nationwide Science Basis’s NOIRLab—to make long-term observations of the GRB’s fading afterglow.

These observations enabled the astronomers to pinpoint the situation of the GRB to a area lower than 100 light-years from the nucleus of an historical galaxy—very close to the galaxy’s supermassive black hole. Curiously, the researchers additionally discovered no proof of a corresponding supernova, which would depart its imprint on the sunshine captured by Gemini South.

“The dearth of a supernova accompanying the lengthy GRB 191019A tells us that this burst just isn’t a typical large star collapse,” stated Rastinejad, who carried out calculations to make sure a supernova was not hiding inside the information. “The situation of GRB 191019A, embedded within the nucleus of the host galaxy, teases a predicted however not but evidenced concept for a way gravitational-wave emitting sources would possibly kind.”

In typical galactic environments, the manufacturing of lengthy GRBs from colliding stellar remnants, comparable to neutron stars and black holes, is extremely uncommon. The cores of historical galaxies, nonetheless, are something however typical, and there could also be one million or extra stars crammed right into a area just some light-years throughout.

Such excessive inhabitants density could also be nice sufficient that occasional stellar collisions can happen, particularly below the titanic gravitational affect of a supermassive black hole, which might perturb the motions of stars and ship them careening in random instructions. Finally, these wayward stars would intersect and merge, triggering a titanic explosion that could possibly be noticed from huge cosmic distances.

“This occasion confounds virtually each expectation we have now for the environments of brief and lengthy GRBs,” stated Nugent, who carried out essential modeling of the host galaxy.

“Whereas lengthy GRBs are by no means present in galaxies as previous and lifeless as GRB 191019A’s host, brief GRBs, with their merger origins, haven’t been noticed to be so related to their hosts’ nuclei. The invention of this occasion within the core of its previous, quiescent galaxy opens the door to promising new avenues for the formation of binary programs which have hardly ever been noticed earlier than.”

It’s doable that such occasions happen routinely in equally crowded areas throughout the universe however have gone unnoticed till this level. A doable purpose for his or her obscurity is that galactic facilities are brimming with dust and gasoline, which might obscure each the preliminary flash of the GRB and the ensuing afterglow. GRB 191019A could also be a uncommon exception, permitting astronomers to detect the burst and research its aftereffects.

“Whereas this occasion is the primary of its form to be found, it is doable there are extra on the market which might be hidden by the massive quantities of dust near their galaxies,” Fong stated. “Certainly, if this long-duration occasion got here from merging compact objects, it contributes to the rising inhabitants of GRBs that defies our conventional classifications.”

By working to find extra of those occasions, the researchers hope to match a GRB detection with a corresponding gravitational-wave detection, which might reveal extra about their true nature and make sure their origins—even within the murkiest of environments. The Vera C. Rubin Observatory, when it comes on-line in 2025, will likely be invaluable in this type of analysis.

The research, “An extended-duration gamma-ray burst of dynamical origin from the nucleus of an historical galaxy,” is revealed in Nature Astronomy.