Astronomers have just seen the strongest gamma-ray burst ever recorded

Astronomers have just seen the strongest gamma-ray burst ever recorded

Gamma-ray bursts (GRBs) are one of the most mysterious transient phenomena astronomers face today. These incredibly energetic bursts are the most powerful electromagnetic events observed since the Big Bang and can last from a few milliseconds to many hours. While longer outbursts are thought to occur during supernovae, when massive stars gravitationally collapse and shed their outer envelopes to become black holes, shorter events have also been recorded when massive binary objects (black holes and neutron stars) merge.

These bursts are characterized by an initial burst of gamma rays and a longer-lasting “afterglow,” typically emitted in X-rays, ultraviolet, radio, and other longer wavelengths. In the early hours of October 14, 2022, two independent teams of astronomers observed the aftermath of a GRB designated GRB221009A using the Gemini South telescope. This event, located 2.4 billion light-years away in the constellation Sagittarius, was perhaps the last and most powerful explosion ever recorded and was likely triggered by a supernova that spawned a black hole.

Longer-duration GRBs occur when massive stars go supernova, produce a black hole, and blow off their outer layers. The force of this explosion produces powerful jets as ejected material is accelerated to near the speed of light, penetrating debris and emitting X-rays and gamma rays as it advances farther into space. As these jets travel in the general direction of Earth, astronomers will observe them as bright flashes of X-rays and gamma rays. Using data from some of the most powerful telescopes on Earth and in space, astronomers have been able to make unprecedented observations of a nearby GRB.

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GRB221009A was first spotted on the morning of October 9, 2022 by X-ray and gamma-ray space telescopes – including NASA’s Fermi gamma-ray space telescope, Neil Gehrel’s Swift Observatory and the Wind spacecraft. Almost immediately, observatories around the world raced to make follow-up observations and determine what resulted. Using the Gemini South telescope (operated by NOIRLab), two independent teams made fast Target of Opportunity (ToO) observations of the afterglow of the powerful event.

The teams were led by Brendan O’Connor, a graduate observational astronomer from the University of Maryland and George Washington University, and Jillian Rastinejad, a graduate student at Northwestern University’s Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA). The two teams obtained the earliest possible observations of the afterglow, just minutes apart, using Gemini South’s FLAMINGOS-2 near-infrared imaging instrument and the Gemini Multi-Object Spectrograph (GMOS), respectively.

As Rastinejad explained in a recent NOIRLab press release, their combined data sets provided a picture of what could be the brightest GRB ever observed:

“In our research group, we refer to this outburst as ‘BOOT,’ or brightest of all time, because when you look at the thousands of outbursts that gamma-ray telescopes have detected since the 1990s, this one stands out. Gemini’s sensitivity and diverse instrumentation will help us observe GRB221009A’s optical counterparts at much later times than most ground-based telescopes can observe. This will help us understand what made this gamma-ray burst so uniquely bright and energetic.

The speed at which the teams made their observations is a testament to the Gemini Observatory’s infrastructure and data reduction software — including the Fast Initial Reduction Engine (FIRE) and Data Reduction for Astronomy from Gemini Observatory North and South (DRAGONS) platforms. Shortly thereafter, the NASA Gamma-ray Coordinates Network began filling up with reports from observatories around the world. Based on the available data, scientists believe that the GRB was the result of the collapse of a star many times the mass of our Sun, creating a black hole.

Artist’s impression of two merging neutron stars. Photo credit: Dana Berry, SkyWorks Digital, Inc.

In addition, the data from this event may help solve an ongoing mystery related to GRBs. While most gamma-ray bursts have been observed in distant galaxies, some appear as solitary flashes from intergalactic space. This has raised questions about the true origins and distances of GRBs, with many astronomers theorizing that certain brief bursts originated in the intergalactic medium (IGM). However, these results suggest that short GRBs may have historically occurred more frequently than expected.

The research teams came to this conclusion after consulting data on the 120 short GRBs observed by the two main instruments aboard NASA’s Neil Gehrel’s Swift Observatory — the Burst Alert Telescope (BAT) and the Swift X-ray Telescope , detecting flares and the X-ray afterglow. They combined this with additional afterglow studies performed with the Lowell Discovery Telescope (LDT) and found that 43 of the short GRBs were not associated with any known galaxy and appeared in the comparatively empty space between galaxies. As O’Connor explained in a University of Maryland news article:

“Many short GRBs are found in bright galaxies relatively close to us, but some of them do not seem to have a corresponding galactic home. By pinpointing where the short GRBs are forming, we were able to search data banks from observatories like the twin Gemini telescopes to find the faint glow of galaxies that were just too distant to see beforehand.”

These results could also have implications for our understanding of the early Universe. In recent years, astronomers have found evidence that precious metals such as gold and platinum may have come from neutron star mergers that occurred billions of years ago. If these events have occurred more frequently in the past, it could mean that the universe was seeded with precious metals sooner than expected. In the meantime, the energetic nature of this event makes it a unique opportunity for astronomers. As O’Conner explained:

“The extraordinarily long GRB 221009A is the brightest GRB ever recorded and its afterglow breaks all records at all wavelengths. Because this burst is so bright and so close, we think this is a unique opportunity to answer some of the most fundamental questions about these explosions, from black hole formation to testing dark matter models.

Artist’s rendering of the collision of two neutron stars, known as the “Kilonova” event. Credits: Elizabeth Wheatley (STScI)

Because of its relative proximity to Earth, this event is also a unique opportunity to study the origin of the heavier-than-iron elements (forming inside stars) and whether they come from neutron star mergers alone or from collapsing stars as well . Last but not least, this event also led to disturbances in the Earth’s ionosphere, which affected long-wavelength radio transmissions and produced very energetic (18 tera-electron volts) photons, which were detected by China’s Large High Altitude Air Shower Observatory.

How these photons survived the 2.4 billion year journey to Earth is a mystery. Therefore, this data could provide new insights into how the laws of physics behave under extreme circumstances, and allow astrophysics to predict the effects that future GRBs could have on Earth.

The International Gemini Observatory consists of the Gemini North Telescope in Hawaii and the Gemini South Telescope in Chile, operated by the National Optical-Infrared Astronomy Research Laboratory (NOIRLab) – part of the National Science Foundation (NSF). The papers describing the results of the two teams recently appeared in the Monthly Bulletins of the Royal Astronomical Society and The Astrophysical Journal.

Further reading: NOIRLab, UMD, AJL, MNRAS

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