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The most reliable inventory to date catalogs the main SGRB galaxies, characteristics — ScienceDaily


A team of astronomers led by Northwestern University has developed the most extensive list of galaxies that produce short gamma-ray bursts (SGRBs) to date.

Using several highly sensitive instruments and sophisticated galaxy simulations, the researchers pinpointed the galactic homes of 84 SGRBs and analyzed the characteristics of the 69 identified host galaxies. Among their findings, they found that about 85% of SGRBs studied come from young galaxies that are actively star-forming.

Astronomers also found that more SGRBs occurred at earlier times, when the universe was much younger – and at a greater distance from the centers of their host galaxies – than previously known. Surprisingly, several SGRBs have been seen far outside their galaxies – as if they had been ‘kicked out’ – and this finding raises questions about how they were able to travel so far.

“This is the largest catalog of SGRB galaxies ever, so we expect it to be the gold standard for many years to come,” said Anya Nugent, a graduate student at Northwestern University who led the study, which focused on galaxy modeling. “Building this catalog and finally having enough host galaxies to see patterns and draw meaningful conclusions is exactly what the field needs to push our understanding of these fantastic events and what happens to stars after they die.”

The team will publish two papers detailing the new catalog. Both newspapers will be published on Monday, November 21 at Astrophysical magazine. Because SGRBs are among the brightest bursts in the universe, the team calls their catalog BRIGHT (Broadband Repository for the Study of Characteristic Properties of Gamma-ray Bursts). All BRIGHT data and simulation products are publicly available online for community use.

Nugent is a graduate student in physics and astronomy at Northwestern’s Weinberg College of Arts and Sciences and a member of the Center for Interdisciplinary Studies and Research in Astrophysics (CIERA). She is advised by Wen-Fai Fong, Weinberg Associate Professor of Physics and Astronomy and a key member of CIERA, who led the second study focusing on SGRB observations.

A benchmark for future comparisons

When two neutron stars collide, they produce instantaneous bursts of intense gamma-ray light known as SGRBs. While gamma rays last only a few seconds, optical light can last for hours before fading below detection (an event called the afterglow). SGRBs are some of the brightest bursts in the universe, with no more than a dozen detected and determined each year. They currently represent the only way to study and understand the large population of merging neutron star systems.

Since the SGRB afterglow was first detected by NASA’s Neil Gehrels Swift Observatory in 2005, astronomers have spent the past 17 years trying to understand which galaxies are producing these powerful bursts. The stars in the galaxy can provide insight into the environmental conditions needed to produce SGRBs, and can link the mysterious bursts to their neutron star merger origin. So far, only one SGRB (GRB 170817A) has a confirmed neutron star merger origin, as it was detected just seconds after gravitational wave detectors observed the neutron star binary merger (GW170817).

“Ten years from now, the next generation of gravitational wave observatories will be able to detect merging neutron stars at the same distances as SGRBs today,” Fong said. “Thus, our catalog will serve as a benchmark against which to compare future detections of neutron star mergers.”

“The catalog may indeed have an impact on more than just one class of transients, such as SGRBs,” said Yuxin “Vic” Dong, study co-author and astrophysics Ph.D. student at Northwestern. “With the large amount of data and results presented in the catalog, I believe that a variety of research projects will use it, perhaps even in ways that we haven’t thought of yet.”

Understanding neutron star systems

To create the catalog, researchers used several highly sensitive instruments at the WM Keck Observatory, the Gemini Observatory, the MMT Observatory, the Large Binocular Telescope Observatory, and the Magellan Telescopes at the Las Campanas Observatory to obtain deep images and spectroscopy of some of the faintest galaxies. revealed in a survey of owners of the SGRB. The team also used data from two of NASA’s Great Observatories, the Hubble Space Telescope and the Spitzer Space Telescope.

Before these new studies, astronomers had characterized the main galaxies from only a few dozen SGRBs. The new catalog is four times the number of existing samples. With the benefit of a much larger data set, the catalog shows that SGRB-hosting galaxies can be young and star-forming or old and nearing death. This means that neutron star systems form in a wide range of environments, and many have rapid formation-to-merger times. Because the fusion of neutron stars creates heavy elements like gold and platinum, the catalog data will also deepen scientists’ understanding of when the precious metals were first created in the universe.

“We suspect that the young SGRBs we detect in young host galaxies come from binary star systems that formed during the star’s ‘explosion’ and are so tightly bound that they can merge very quickly,” Nugent said. “Old theories say that there must be ways for neutron stars to merge rapidly, but until now we have not been able to observe them. We find evidence of old SGRBs in galaxies that are much older, and we believe that the stars in them either took longer to form a binary system or were a binary system that was still broken up. So the galaxies took longer to merge.”

The potential of JWST

NASA’s new flagship infrared observatory, the James Webb Space Telescope (JWST), is poised to further advance understanding of neutron star mergers and how far back in time they began, thanks to its ability to detect the faintest host galaxies from the earliest times of the universe.

“I am very excited about the opportunity to use JWST to study these rare explosive events in houses in greater depth,” Nugent said. “JWST’s ability to observe faint galaxies in the Universe could reveal more galaxies hosting SGRBs that currently elude detection, perhaps even revealing a missing population and connection to the early Universe.”

“I started overseeing this project 10 years ago, and it’s been great to pass the torch to the next generation of researchers,” Fong said. “It is one of the greatest joys of my career to see years of work come to life in this catalog, thanks to young researchers who have really taken this research to the next level.”

Research was supported by the National Science Foundation (award numbers AST-1814782 and AST-2047919), the David and Lucille Packard Foundation, the Alfred P. Sloan Foundation, and the Research Corporation for the Advancement of Science.

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