Scientists have detected key ingredients for life in the fallout of one of the biggest and most inexplicable space explosions ever seen, reports a new study.
The discovery offers a rare glimpse of cosmic processes that may forge substances essential to many lifeforms on Earth, such as iodine and thorium, while also raising new mysteries about the sources of radiant bursts known as kilonovas.
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On March 7 of this year, a NASA space telescope detected an enormous explosion in deep space known as a gamma ray burst (GRB) that blazed brightly for about 200 seconds. In the days and weeks that followed, astronomers observed the aftermath of the burst, known as GRB 230307A, with a number of different facilities including the James Webb Space Telescope (JWST), the most powerful space observatory ever launched.
Scientists soon realized that GRB 230307A was more than a million times brighter than all the stars of the Milky Way combined, making it the second most luminous GRB ever observed. The signatures of the burst suggested it was caused by a so-called “kilonova” collision between two hyper-dense objects, known as neutron stars, located about eight million light years from Earth. But whereas most kilonova bursts last only a few seconds, this strange event blazed on for more than three whole minutes, baffling scientists.
Now, a team led by Radboud University astrophysicist Andrew Levan have discovered that this puzzling long-lived explosion created a host of heavy elements, including materials that are essential to life on Earth, through a process known as nucleosynthesis. By observing the burst with JWST, the researchers were able to show that “GRB 230307A belongs to the class of long-duration gamma-ray bursts associated with compact object mergers” and demonstrate that these events “play a central role in heavy element nucleosynthesis across the Universe,” according to a study published on Wednesday in Nature.
“This has been a fast moving, sometimes challenging and also utterly fantastic experience to work on,” Levan told Motherboard in an email. “It has been a little bit like a cosmic murder mystery—a whodunnit of what caused this gamma-ray burst. It has taken a lot of piecing together by an amazing group of people working on the various bits of data, and of course on building models that can explain it. Although it was very bright, it hasn’t been a simple thing to understand. For example, it took us a day and half to really locate where the burst was on the sky, another few days to see a color change that told us it was probably a kilonova, and then we had to wait for it to move into the bit of the sky where JWST could see it.”
“In the end it all came together, but there was a lot of work, and a bit of luck, in that happening,” he added. “To give a bit of a handle on the discussion and the collaboration, we have a dedicated Slack channel, and from the first observations to the paper submission ~3 months later there were about 9,000 messages on it.”
Gamma ray bursts are the most energetic explosions in space, and they can be produced by different pyrotechnic phenomena, such as the deaths of massive stars or interactions between compact dead stars, such as neutron stars or black holes. Since 2008, astronomers have observed a handful of kilonova GRBs, which they believe erupt out of mergers between two neutron stars, or between a neutron star and a black hole.
Most of the heavy elements that are essential for life—such as carbon, phosphorus, or oxygen—are created in the bellies of stars. When stars die, they spew these materials out into space where they coalesce into new planetary systems. And when the remnants of dead stars collide in kilonova events, they produce their own suite of elemental materials, such as gold, platinum, and uranium. In this way, the materials that make up stars, planets, and all life on Earth is primarily made of the remains of our ancient stellar elders, in one way or another.
JWST’s observations of GRB 230307A have now revealed that kilonova can produce heavy chemical elements such as tellurium, as well as iodine and thorium, which are critical for many lifeforms on Earth. This discovery provides a tantalizing hint about the potential origins of life on our world, and perhaps elsewhere in the universe.
“Iodine is vital for mammals, where it controls thyroid function but also has anti-oxidant effects in other places,” Levan explained. “Indeed, in the literature, there are even some suggestions that it was needed in the so-called Last Universal Common Ancestor—the single-celled organism from which all life on Earth evolved. Now, I don’t think we know that for sure, but it raises the question of whether some heavy elements are required for life as we know it, if they make the various evolutionary paths easier, or if there are workarounds that don’t require iodine at all.”
“While supernovas explode in young stars while lower-mass stars (like the Sun) still form around them, neutron star mergers happen on much longer timescales, often in more remote places in the Universe,” he added. “This means the timescales on which these heavy elements can be incorporated into stars, planets, and even life might be much longer. If the delays for making some elements critical to life are long (and it is still very much an open question if it is), then it may make a difference to where and when in the Universe complex life is possible.”
In addition to its interesting elemental output, the long duration of GRB 230307A challenges models of these epic collisions, and motivates scientists to come up with new explanations for their strange spectral signatures.
“The big surprise is that bursts so bright and long as this one can be formed by the merger of two compact stars,” Levan said. “Established wisdom in the field is that collapsing massive stars form bright, long bursts, and the coalescence of two compact stars creates fainter, shorter bursts. Last year, there was the first evidence that this wasn’t the case, but I certainly didn’t expect to see the second brightest burst of all time turn out to be from a merger.”
Levan and his colleagues hope to explain these long-lived events by exploring mergers involving black holes or very massive neutron stars, or perhaps even invoking new physics. There is also much more work to be done before scientists can pin down any clear insights about the role of kilonova in the emergence of life. In the meantime, astronomers have plenty of other questions that they hope to resolve or constrain about these incredibly beautiful and enigmatic mergers between dead stars.
“One of the fundamental challenges in this work is that the mergers of neutron stars and their kilonovae are very rare,” Levan said. “This means that we have studied few of them, and this is only the second case where anyone has taken a spectrum (and the first where it has been in the wavelength range of JWST). There is a vast discovery space still out there because there may be a lot of variation between the different events.”
“In the future, we need more targets and to study them with JWST and other facilities from right after they happen for hundreds of days,” he concluded, noting that there are many missions along these lines currently in the works. “Ultimately, we would like to dissect the kilonovae in enough detail to pick apart all the different elements that form there and how much of each element there is. If we can do this, we can test if they make some, most, or all of the heavy elements we see around us, and we will finally be able to say where every element in the periodic table is made.”
