Free Astronomy Magazine September-October 2023

35 SEPTEMBER-OCTOBER 2023 ASTRO PUBLISHING Swift Observatory detected a bright flash of gamma rays that lasted for a little more than one minute. Any GRB lasting 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 observa- tions of the GRB’s fading afterglow to learn more about its origins. The observations allowed the as- tronomers to pinpoint the location of the GRB to a region less than 100 light-years from the nucleus of an ancient galaxy, which placed it very near the galaxy’s supermassive black hole. The researchers also found no evidence of a corresponding super- nova, which would leave its imprint on the light studied by Gemini South. “Our follow-up ob- servation told us that rather than being a massive star collaps- ing, the burst was most likely caused by the merger of two compact objects,” said Levan. “By pin- pointing its location to the center of a previously identified ancient galaxy, we had the first tantaliz- ing evidence of a new pathway for stars to meet their demise.” In normal galactic environ- ments, the production of long GRBs from colliding stellar remnants such as neutron stars and black holes is thought to be vanishingly rare. The cores of ancient galaxies, how- ever, are anything but normal and there may be a million or more stars crammed into a region just a few light-years across. Such extreme population density may be great enough that occasional stellar colli- sions can occur, especially under the titanic gravitational influence of a supermassive black hole, which would perturb the motions of stars and send them careening in random directions. Eventually, these way- ward stars would intersect and merge, triggering a titanic explosion that could be observed from vast cosmic distances. It is possible that such events occur routinely in simi- larly crowded regions across the Uni- verse but have gone unnoticed until this point. A possible reason for their obscurity is that galactic centers are brimming with dust and gas, which could ob- scure both the initial flash of the GRB and the resulting afterglow. This particular GRB, identified as GRB 191019A, may be a rare excep- tion, allowing astronomers to detect the burst and study its after effects. The researchers would like to dis- cover more of these events. Their hope is to match a GRB detection with a corresponding gravitational- wave detection, which would reveal more about their true nature and confirm their origins, even in the murkiest of environments. The Vera C. Rubin Observatory, when it comes online in 2025, will be invaluable in this kind of research. “Studying gamma-ray bursts like these is a great example of how the field is really advanced by many facilities working together, from the detection of the GRB, to the dis- coveries of afterglows and distances with telescopes like Gemini, through to detailed dissection of events with observations across the electromagnetic spectrum,” said Levan. “These observations add to Gemini’s rich heritage developing our understanding of stellar evolu- tion,” says Martin Still, NSF’s pro- gram director for the International Gemini Observatory. “The time sen- sitive observations are a testament to Gemini’s nimble operations and sensitivity to distant, dynamic events across the Universe.” ! A stronomers studying a powerful gamma-ray burst (GRB) with the International Gemini Observatory, oper- ated by NSF’s NOIR- Lab, may have observed a never-be- fore-seen way to de- stroy a star. Unlike most GRBs, which are caused by exploding massive stars or the chance mergers of neutron stars, as- tronomers have con- cluded that this GRB came instead from the collision of stars or stellar remnants in the jam-packed envi- ronment surrounding a supermassive black hole at the core of an ancient galaxy. [Inter- national Gemini Ob- servatory/NOIRLab/ NSF/AURA/M. Gar- lick/M. Zamani] T his video illustrates how astronomers studying a powerful gamma-ray burst (GRB)may have de- tected a never-before-seen way to destroy a star. [In- ternational Gemini Observatory/NOIRLab/NSF/AURA, M. Garlick, M. Zamani, K. O Chul, ESO/L. Calçada, NASA’s Goddard Space Flight Center/CI Lab, N. Bartmann]