After its “birth” in the Big Bang, the Universe mainly consisted of hydrogen and a few helium atoms. These are the lightest elements in the periodic table. Over the past 13.8 billion years, stars have produced many heavier elements through nuclear fusion. However, fusion in stars only produces elements as heavy as iron. Creating heavier elements requires energy instead of releasing it, posing a significant mystery for scientists.
One promising candidate for producing these heavier elements is gamma-ray bursts (GRBs), the most powerful explosions in the Universe. GRBs can emit a quintillion (10 followed by 18 zeros) times the luminosity of our Sun and are thought to originate from various catastrophic events.
GRBs are divided into two categories: long bursts and short bursts. Long GRBs are associated with the deaths of massive, fast-rotating stars. During the collapse of these stars, material is ejected into narrow jets that move at extremely high speeds. Short bursts, on the other hand, last only a few seconds and are believed to result from the collision of two neutron stars – incredibly dense remnants of dead stars.
In August 2017, a pivotal event supported this theory. The LIGO and Virgo gravitational wave detectors in the US detected a signal from two neutron stars moving towards a collision. Shortly after, a short gamma-ray burst, GRB 170817A, was observed from the same direction. This led to an unprecedented global effort to study the event’s aftermath, revealing a kilonova explosion. A kilonova is a fainter cousin of a supernova, and this one showed evidence of heavy element production.
A study in Nature analyzing this kilonova identified two types of debris: one composed of light elements and another of heavy elements. While nuclear fusion in stars can only produce elements up to iron, the rapid neutron-capture process, or r-process, can create heavier elements. This process requires high density, high temperature, and many free neutrons – conditions present in gamma-ray bursts.
However, mergers of two neutron stars, like the kilonova GRB 170817A, are rare. This rarity makes them unlikely sources for the Universe’s abundant heavy elements. This led scientists to explore long GRBs further.
A recent study focused on GRB 221009, dubbed the BOAT (Brightest of All Time). Detected on October 9, 2022, this GRB was 10 times more energetic than the previous record holder and had measurable effects on Earth’s atmosphere. Among the telescopes studying the BOAT was the James Webb Space Telescope (JWST), which observed the GRB six months after the explosion to avoid the initial afterglow.
JWST’s data revealed that, despite its extraordinary brightness, the BOAT was caused by an average supernova explosion. Surprisingly, the observations showed no indication of elements produced by the r-process. This finding challenges the assumption that the brightness of a long GRB correlates with the conditions in its core, which were expected to favor the r-process.
These results suggest that gamma-ray bursts may not be the crucial source of the Universe’s heavy elements as previously hoped. The search for the true sources of these elements continues, pointing to other, yet-to-be-discovered phenomena in the cosmos.
As scientists delve deeper into the mysteries of the Universe, understanding the origins of heavy elements remains a tantalizing frontier, promising new discoveries and insights into the fundamental processes that shape our cosmic environment.
Edited by Dr. Brijendra Kumar Mishra, (Disaster Risk Reduction Expert)