The most thorough list yet of the galaxies from which short gamma-ray bursts (SGRBs) originate has been created by a team of astronomers led by Northwestern University. Researchers used a variety of sensitive instruments and advanced galaxy modelling to find the host galaxies for 84 SGRBs. They then looked at the properties of 69 of the host galaxies they found.
They found, among other things, that roughly 85% of the SGRBs under study originate from young, star-forming galaxies. The astronomers also discovered that more short gamma-ray bursts occurred at earlier times when the universe was much younger — and at greater distances from the centers of their host galaxies — than previously thought.
Several SGRBs were unexpectedly discovered outside the host galaxies as if they had been “kicked out,” which begs the question of how they were able to travel so far.
Advancing Short Gamma-ray Bursts Knowledge
The research team anticipates that since this is the largest catalog of SGRB host galaxies to have ever existed, it will serve as the gold standard for a very long time.
“Building this catalog and finally having enough host galaxies to see patterns and draw significant conclusions is exactly what the field needed to push our understanding of these fantastic events and what happens to stars after they die,”
said Anya Nugent, a Northwestern graduate student who led the study. The team will publish two papers that will go over the new catalog in detail. Both will appear in The Astrophysical Journal.
Broadband Repository for Investigating Gamma-ray burst Host Traits
Due to the fact that short gamma-ray bursts are among the brightest explosions in the universe, the team has dubbed its catalog BRIGHT (Broadband Repository for Investigating Gamma-ray burst Host Traits). All of BRIGHT’s data and modelling products are available for public use online.
When two neutron stars collide, they produce brief bursts of intense gamma-ray light called short gamma-ray bursts. While gamma rays last only a few seconds, optical light can last for hours before fading below detection levels -an event called an afterglow.
SGRBs are some of the brightest explosions in the universe, with only a few dozen detected and pinpointed each year. At the moment, they are the only way to study and understand a large number of neutron star systems merging.
GRB 170817A Neutron Star Merger Link
Astronomers have spent the last 17 years trying to figure out which galaxies produce these powerful bursts since NASA’s Neil Gehrels Swift Observatory first discovered an SGRB afterglow in 2005. Stars within a galaxy can provide information about the environmental conditions required to generate short gamma-ray bursts, as well as link the mysterious bursts to their neutron-star merger origins.
So far, only one SGRB (GRB 170817A) has been identified as having a confirmed neutron-star merger origin, as it was discovered just seconds after gravitational wave detectors observed the binary neutron-star merger (GW170817).
“In a decade, the next generation of gravitational wave observatories will be able to detect neutron star mergers out to the same distances as we do SGRBs today. Thus, our catalog will serve as a benchmark for comparison to future detections of neutron star mergers,”
said Wen-fai Fong, an assistant professor of physics and astronomy at Weinberg and a key member of CIERA, who led the second study.
“The catalog can really make impacts beyond just a single class of transients like SGRBs. With the wealth of data and results presented in the catalog, I believe a variety of research projects will make use of it, maybe even in ways we have yet not thought of,”
said co-author Yuxin Dong, astrophysics Ph.D. student at Northwestern.
Fast Merging Neutron Stars
The researchers used several highly sensitive instruments at W.M. Keck Observatory, Gemini Observatories, MMT Observatory, Large Binocular Telescope Observatory, and Las Campanas Observatory to capture deep imaging and spectroscopy of some of the faintest galaxies identified in the survey of SGRB hosts. Data from two of NASA’s Great Observatories, the Hubble Space Telescope and the Spitzer Space Telescope, were also used by the team.
Before these new studies, astronomers had only identified host galaxies from a few dozen short gamma-ray bursts. The new catalog contains four times as many samples as the previous one.
With the benefit of a much larger dataset, the catalog demonstrates that SGRB host galaxies can be either young and star-forming or old and dying.
This indicates that neutron-star systems can form in a variety of settings, and many of them have quick formation to merger times. Because neutron-star mergers produce heavy elements such as gold and platinum, the catalog’s data will also help scientists understand when precious metals first appeared in the universe.
“We suspect that the younger SGRBs we found in younger host galaxies come from binary stellar systems that formed in a star formation ‘burst’ and are so tightly bound that they can merge very fast,”
Astronomers have not been able to observe neutron star mergers until now, despite the fact that theories have suggested for a long time that such events must be possible. Researchers find evidence of older SGRBs in much older galaxies and conclude that the stars in those galaxies either took a longer time to form a binary or were a more distant binary system. Therefore, those required more time to merge.
James Webb Space Telescope Potential
James Webb Space Telescope (JWST), NASA’s new infrared flagship observatory, will be able to detect the faintest host galaxies from very early times in the universe, thereby advancing our understanding of neutron star mergers and how far back they began.
“I’m most excited about the possibility of using JWST to probe deeper into the homes of these rare, explosive events,”
JWST’s capacity to observe faint galaxies in the universe could reveal more SGRB host galaxies that are currently evading detection, possibly revealing a missing population and a connection to the early universe.
Wen-fai Fong et al. Short GRB Host Galaxies I: Photometric and Spectroscopic Catalogs, Host Associations, and Galactocentric Offsets, Astrophysical Journal. 940 56DOI 10.3847/1538-4357/ac91d0
Anya E. Nugent et al. Short GRB Host Galaxies II: A Legacy Sample of Redshifts, Stellar Population Properties, and Implications for their Neutron Star Merger Origins, Astrophysical Journal. 940 57
The Milky Way Stellar Halo Is Actually Tilted And Oblong
The actual shape of the stellar halo that envelops the disk of our galaxy has been revealed by a recent study. For many years, astronomers believed that the stellar halo, a cloud of stars, was mostly spherical, like a basketball.