Scientists have observed the creation of rare chemical elements in the second-brightest gamma-ray burst seen in outer space. The discovery has been described as opening “the door to a transformative understanding of our universe and how it works”.
Researchers, including astrophysicists at University College Cork and Queen’s University Belfast, examined the exceptionally bright gamma-ray burst – known as GRB 230307A – which was caused by a neutron star merger.
The explosion was observed using an array of ground and space-based telescopes, including Nasa’s James Webb Space Telescope (JWST); Fermi Gamma-ray Space Telescope; and Neil Gehrels Swift Observatory.
Publishing their findings in Nature on Wednesday, the international team reveal they found the heavy chemical element tellurium in the aftermath of the explosion. Other elements such as iodine and thorium, needed to sustain life on Earth, are likely to be among material ejected by the explosion, known as a kilonova.
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“Gamma-ray bursts come from powerful jets travelling at almost the speed of light – in this case driven by a collision between two neutron stars. These stars spent several billion years spiralling towards one another before colliding to produce the gamma-ray burst we observed in March this year,” explained Dr Ben Gompertz of the University of Birmingham.
The merger site is the approximate length of the Milky Way (about 120,000 light-years) outside of their home galaxy.
“Colliding neutron stars provide the conditions needed to synthesise very heavy elements and the radioactive glow of these new elements powered the kilonova we detected as the blast faded. Kilonovas are extremely rare and very difficult to observe and study, which is why this discovery is so exciting,” he said.
It was one of the brightest gamma-ray bursts ever observed – over a million times brighter than the entire Milky Way galaxy combined.
Prof Andrew Levan of Radboud University in the Netherlands said: “Just over 150 years since Dmitri Mendeleev wrote down the periodic table of elements, we are now finally in the position to start filling in those last blanks of understanding where everything was made, thanks to the James Webb Telescope.”
The kilonova lasted for 200 seconds. This is unusual as short gamma-ray bursts of less than two seconds are more commonly caused by neutron star mergers. Long gamma-ray bursts like this one are usually caused by the explosive death of a massive star.
Discoveries like this would not have been possible without the ability of the JWST to observe mergers in exquisite detail.
Dr Mark Kennedy, based at UCC’s School of Physics, took data using the European Southern Observatory’s “new technology telescope” in Chile which led to the discovery of an optical counterpart to the kilonova using the JWST.
“Not every gamma-ray burst produces an explosion that we can study with JWST and the light from those that do can fade very rapidly. This means every second – between when Nasa’s Fermi Gamma-ray Space Telescope detects a gamma-ray burst and when we point our telescopes on Earth at where we think the bust occurs – counts,” he said.
“This explosion occurred in the very southern part of the night sky, making it impossible to observe with most of our ground-based facilities. Fortunately, I was observing with a telescope in Chile – remotely from my diningroom in Cork – several hours after the explosion reached us here on Earth, and found a new object had appeared in the night sky right where the burst had come from.
“This excitement rippled out through the astronomical community as we realised we might be witnessing a kilonova. In the following weeks, our group submitted proposals to use JWST to study such an event for the first time, with the results speaking for themselves,” he said.
Another team member, Dr Matt Nicholl of QUB, said: “The Webb [observatory’s] detection of the kilonova and the presence of tellurium tell the incredible story of how the universe manufactures heavy elements.
“Two massive stars grow old together in a close orbit around each other and each eventually undergoes a huge supernova explosion to produce a neutron star or black hole. If they manage to stay together, they emit gravitational waves – ripples in the universe – that shrink the orbit until these remnants collide in one final spectacular explosion that makes a kilonova and a gamma-ray burst.”
