Bizarre Gamma-ray Burst Reveals Undetected Neutron-Star Mergers That May Shed Light on the Production of Heavy Elements in the Universe

The standard view of the origin of a gamma-ray burst (GRB) as a signature of dying stars might need to be revised due to recent astronomical observations that reveal a new observational fingerprint of neutron star mergers, shedding light on how heavy metals are produced in the universe.

Astrophysicist Chris Fryer, the co-author and lead researcher of the paper, said that astronomers believed gamma-ray bursts are either long-duration bursts from dying stars or short-duration bursts from merging compact stellar objects. But the recent observation found a kilonova along with a long-duration GRB, changing previous beliefs on these events.

Long- and Short-duration Gamma-ray Bursts

According to SciTech Daily, a long-duration GRB is usually linked to a supernova and a short-duration GRB is linked to neutron star mergers. It is a long-duration GRB if it lasts for more than two seconds, while a short-duration GRB only lasts for less than two seconds.

These forms of observable gamma-ray bursts are all known as transients and neutron star mergers form some of the heavy elements in the universe.

Last year, on December 11, 2021, observatories and satellites detected very bright, 50-second GRB and optical, infrared, and X-ray emissions that are linked to the burst. Scientists said that its source is relatively nearby, about a billion light-years away from Earth, and is located in a different galaxy.

The burst has characteristics that do not fit that of a long-duration GRB. Instead, researchers picked up evidence that it may come from a compact-object merger as described in a theorized but unobserved hybrid event that produces a kilonova.

study co-author Ryan Wollaeger said that their modeling team from Los Alamos compared the observation to different supernova and kilonova simulations and found that it match the signal to a supernova model, while the kilonova model is a good match of the optical infrared data points.

Challenging Previous Models

Study co-author Eve chase said that the detection breaks the current standard idea of gamma-ray bursts and scientists can no longer assume that all short-duration GRBs came from neutron star mergers as well as all long-duration GRBs are from a supernova. The observation shed light on how complex it is to classify GRBs and pushes the understanding of the bursts to limits.

EurekAlert! reported that the observation, called GRB211211A, is the first evidence of a hybrid event. Fryer said that a merger explains all the other observed features of the GRB211211A, which differed from the accepted understanding of compact-binary-merger models.

In 1999, Fryer and his Ph.D. advisor coined and developed the term black hole accretion disk paradigm that explains the two classes of gamma-ray burst events, wherein merging compact objects would produce short-duration gamma-ray bursts and supernovae produce longer bursts. There are growing observations that supported these two classes and the stellar types associated with them.

Now, the team developed the supernova and kilonova models to run on supercomputers and apply these codes to the observational data, which was crucial to interpreting the observations of GRB211211A.