Earlier this year, a powerful gamma-ray burst traveled through space from a very distant source in the cosmos. The explosion was traced back to the early universe, just millions of years after the Big Bang, but its origin remained unknown. By pointing the Webb telescope toward the ancient mystery, astronomers were able to identify the earliest known aftermath of a star’s tragic death.
The Webb space telescope observed a supernova that took place when the universe was 730 million years old, setting a new record for the oldest stellar explosion detected to date. With this new observation, Webb beat its own record of a star that exploded 1.8 billion years after the Big Bang.
The telescope’s recent observations confirmed the source of a highly energetic flash of light known as a gamma-ray burst, verifying data that had been collected by a fleet of telescopes around the world.
“Only Webb could directly show that this light is from a supernova,” Andrew Levan, an astrophysics professor at Radboud University in the Netherlands and lead author of a paper published in Astronomy and Astrophysics Letters, said in a statement. “This observation also demonstrates that we can use Webb to find individual stars when the Universe was only 5% of its current age.”
Straight to the source
On March 14, the SVOM mission (Space-based multi-band astronomical Variable Objects Monitor) was the first to detect a gamma-ray burst from a distant source in the universe. Within a few hours, three other telescopes were used to pinpoint the source’s location in the skies and estimate when it took place during the cosmic timeline.
“There are only a handful of gamma-ray bursts in the last 50 years that have been detected in the first billion years of the Universe,” Levan said. “This particular event is very rare and very exciting.”
Gamma-ray bursts typically last a few seconds and may be caused by the collision of two neutron stars or a neutron star and a black hole. This particular one, however, lasted for 10 seconds, suggesting it likely was the result of the explosive death of a massive star.
Webb’s observations took place on July 1, roughly three months after the gamma-ray burst was first observed. That allowed time for the supernova to increase in brightness, making it easier for the telescope to spot. Supernovae usually brighten rapidly over the course of a few weeks. Since this one took place so early in the universe, however, its light was stretched as the universe expanded over time. As light stretches, it takes more time for the event to unfold.
Once astronomers honed in on the ancient supernova, they compared it to more recent ones that have taken place closer to us. To their surprise, they were very much alike.
Stars in the early universe contained fewer heavy elements compared to their modern counterparts; they were also more massive and lived for shorter periods of time. Therefore, the astronomers behind the recent findings expected the oldest known supernova to look a little different. “We went in with open minds,” Nial Tanvir, a professor at the University of Leicester and co-author of the paper, said in a statement. “And lo and behold, Webb showed that this supernova looks exactly like modern supernovae.”
The team of astronomers behind the study plan on enlisting Webb to observe the afterglow of distant gamma-ray bursts to learn more about galaxies and how they evolved over time. “That glow will help Webb see more and give us a ‘fingerprint’ of the galaxy,” said Levan.
Passant Rabie
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