A team of astronomers led by Northwestern University has developed the most comprehensive inventory to date of the galaxies from which short gamma-ray bursts (SGRBs) originate.
Using several highly sensitive instruments and sophisticated galaxy modeling, the researchers identified the galactic foci of 84 SGRBs and probed the characteristics of 69 of the identified host galaxies. Among their findings, they discovered that about 85% of the SGRBs studied come from young galaxies in active star formation.
Astronomers also discovered that more SGRBs occurred in earlier times, when the universe was much younger – and at greater distances from the centers of their host galaxies – than previously known. Surprisingly, several SGRBs have been spotted well outside their host galaxies – as if they’ve been “expelled,” a finding that raises questions as to how they could have traveled so far.
“This is the largest catalog of SGRB host galaxies to ever exist, so we expect it to be the gold standard for many years to come,” said Anya Nugent, a graduate student from the Northwest who led the study focused on modeling host galaxies. “Building this catalog and finally having enough host galaxies to see patterns and draw meaningful conclusions is exactly what the field needed to push our understanding of these fantastical events and what happens to stars after they die.”
The team published two articles detailing the new catalog today (21 November) in The Astrophysical Journal. Because SGRBs are among the brightest bursts in the universe, the team calls their catalog BRIGHT (Broadband Repository for Investigating Gamma-ray burst Host Traits). All BRIGHT data and modeling 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 Exploration and Research in Astrophysics (CIERA). She is advised by Wen-fai Fong, an assistant professor of physics and astronomy at Weinberg and a key member of CIERA, who led a second study focused on observations of SGRB hosts.
Reference for future comparisons
When two neutron stars collide, they generate momentary flashes of intense gamma light, called SGRBs. While gamma rays only last a few seconds, optical light can continue for hours before fading below detection levels (an event called afterglow). SGRBs are among the brightest explosions in the universe with, at most, a dozen detected and spotted each year. They currently represent the only way to study and understand a large population of merging neutron star systems.
Since NASA’s Neil Gehrels Swift Observatory first discovered an SGRB afterglow in 2005, astronomers have spent the past 17 years trying to figure out which galaxies produce these powerful bursts. A galaxy’s stars can provide insight into the environmental conditions needed to produce SGRBs and can link mysterious bursts to their neutron star merger origins. 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 binary neutron star merger (GW170817).
number of gamma-ray bursts in a new record catalog
“A decade from now, the next generation of gravitational wave observatories will be able to detect neutron star mergers at the same distances as we do today with SGRBs,” Fong said. “Thus, our catalog will serve as a reference for comparison with future detections of neutron star mergers.”
“The catalog can really have impacts beyond a single class of transients like SGRBs,” said Yuxin “Vic” Dong, study co-author and PhD in astrophysics. student at Northwestern. “With the wealth of data and results presented in the catalog, I think a variety of research projects will make use of it, perhaps even in ways we haven’t yet thought of.”
Overview of neutron star systems
To create the catalog, the researchers used several highly sensitive instruments from the WM Keck Observatory, Gemini Observatories, MMT Observatory, Large Binocular Telescope Observatory, and Magellan Telescopes from Las Campanas Observatory to capture deep imaging and spectroscopy of some of the fainter galaxies. identified in the survey of SGRB hosts. The team also used data from two of NASA’s major observatories, the Hubble Space Telescope and the Spitzer Space Telescope.
“This is the largest catalog of SGRB host galaxies to ever exist, so we expect it to be the gold standard for many years to come.” — Anya Nugent, graduate student in astrophysics
Prior to these new studies, astronomers characterized host galaxies from just a few dozen SGRBs. The new catalog is four times the number of existing samples. With the benefit of a much larger dataset, the catalog shows that SGRB host galaxies can be young and star-forming Where old and near death. This means that neutron star systems form in a wide range of environments and many of them have rapid fusion formation time scales. Because neutron star mergers create heavy elements like gold and platinum, the catalog data will also help scientists better understand when precious metals were first created in the universe.
“We suspect that the younger SGRBs we have found in younger host galaxies are from binary star systems that formed during a ‘burst’ of star formation and are so tightly bound that they can merge very quickly,” Nugent said. “Longstanding theories suggest that there must be ways to quickly merge neutron stars, but, so far, we haven’t been able to witness this. We find evidence of older SGRBs in galaxies that are much older and believe that stars in these galaxies took longer to form a binary system or were a more separate binary system. Therefore, these took longer to merge.
Potential of JWST
With the ability to detect the faintest host galaxies since the very earliest times of the universe, NASA’s new flagship infrared observatory, the James Webb Space Telescope (JWST), is poised to advance understanding of mergers. neutron stars and how far back in time they go. began.
“I’m very excited to use JWST to probe deeper into the hotbeds of these rare explosive events,” Nugent said. “JWST’s ability to observe faint galaxies in the universe could uncover more SGRB host galaxies that currently escape detection, perhaps even revealing a missing population and a connection to the early universe.”
“I started observations for this project 10 years ago, and it was so rewarding to be able to pass the torch to the next generation of researchers,” Fong said. “It’s been one of the greatest joys of my career to see years of work come to life in this catalog, thanks to the young researchers who have really taken this study to the next level.”
The studies, “Short GRB host galaxies I” and “Short GRB host galaxies II”, were supported by the National Science Foundation (award numbers AST-1814782 and AST-2047919), the David and Lucile Packard Foundation, the Alfred P. Sloan Foundation and Research Society for Scientific Advancement.
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