The Luminous Short Gamma-ray Burst

Gamma-ray bursts (GRBs) are short-lived, with the longest ones lasting only a few minutes. Some are as short as a few milliseconds. But what they lack in lifespans, these showy bursts of gamma-ray light make up for in luminosity. They are incredibly bright phenomena –  the most luminous in the universe and a quintillion times as bright as the sun. Short gamma-ray bursts are those that last less than two seconds. These shorter bursts are distinct from their longer counterparts, and there’s a mystery surrounding their creation.

Scientists believe these bursts occur when neutron stars collide. Elias Most, assistant professor of Theoretical Astrophysics at Caltech, is working with a team to help dispel some of the mystery around why these bursts occur. Utilizing NCSA’s Delta supercomputer through an allocation from the National Science Foundation-funded ACCESS program, his research team is creating simulations to help prove their theories.

“With the co-incident detection of gravitational waves and a short gamma-ray burst from colliding neutron stars (some of the most extreme objects in the universe, subject to Einstein’s theory of general relativity),” Most said,  “we now have firm evidence that many of [the short gamma-ray bursts] originate in such collisions. However, it remained unclear whether they were ultimately sourced from a massive neutron star remnant or a black hole formed in the collision.”

Most goes on to explain the importance of investigating these burst formations. “This has strong implications for our understanding of nuclear physics governing the structure of the star if it were to collapse under its own weight to form a black hole in the collision process,” he said. 

With supercomputers like Delta, scientists don’t need to wait until two neutron stars collide to observe and study the reaction. Instead, they can run hundreds of simulations in a short time. Utilizing cyberinfrastructure resources can speed up studies like this, giving results in a far shorter time than using observation of real events when they happen.

“Using numerical relativity simulations on NCSA’s Delta supercomputer,” Most said, “we clarified the launching mechanism of relativistic outflows from neutron star remnants that can ultimately power short gamma-ray bursts. Our findings show that part of the motion of the star can potentially be imprinted in these bursts, although the precise details will need further simulations. This also has implications for certain quasi-periodic oscillations in gamma-ray bursts discovered by NASA scientists earlier this year.”

Most’s simulation code is built on top of the Einstein Toolkit simulation framework, co-developed by NCSA Delta Support team member Roland Haas. This combination of compute resource availability and domain-expert support staff accessibility makes Delta an attractive destination for relativistic astrophysics simulations.

Studies like Most’s have been instrumental in understanding astronomical phenomena like GRBs. “This question had been around for a bit,” he said, “with numerical relativity simulations struggling to numerically investigate this process. Just this year, there were two more studies finding similar evidence, greatly moving this subfield forward.” Supercomputers like Delta have made this kind of research possible, advancing the science of the stars by allowing researchers to take one observation and turn it into thousands.

“These findings will help us to better understand the relativistic universe, as well as connections of physics on the smallest microscales to those of Einstein’s theory of relativity,” Most said. “With the currently ongoing observing run of the LIGO-Virgo-KAGRA gravitational wave detectors we hope to observe more multi-messenger gravitational wave events with GRB counterparts. Simulations on high-performance computers, such as this one,  will be crucial for the interpretation of such events.

“Running these simulations on a workstation (if at all possible) would likely have taken up to a year.  In light of the current gravitational-wave observing campaign by the LIGO-Virgo-KAGRA collaboration and the discovery of quasi-periodic oscillations in gamma-ray bursts by NASA scientists earlier this year, access to supercomputer time enabled a rapid investigation that would otherwise not have been possible.”

Most’s original study has been published in the Astrophysical Journal Letters, with a recent follow-up work on physics aspects of these results available here. 

San Diego Supercomputing Center’s Kimberly Mann Bruch (science writer) contributed to this story.