Using an array of ground and space-based telescopes, including the NASA/ESA/CSA James Webb Space Telescope, NASA’s Fermi Gamma-ray Space Telescope, and NASA’s Neil Gehrels Swift Observatory, astronomers observed GRB 230307A, the second-brightest gamma-ray burst ever seen, which was caused by a neutron star merger. In the aftermath of the explosion, the researchers detected the heavy chemical element tellurium. Other elements such as iodine and thorium are also likely to be amongst the material ejected by the explosion, also known as a kilonova.
This image from Webb’s NIRCam instrument highlights GRB 230307A’s kilonova and its former home galaxy. Image credit: NASA / ESA / CSA / STScI / A. Levan, IMAPP, Warw / A. Pagan, STScI.
First detected by Fermi in March 2023, GRB 230307A is the second brightest gamma-ray burst observed in over 50 years of observations, about 1,000 times brighter than a typical gamma-ray burst that Fermi observes.
The event also lasted for 200 seconds, placing it firmly in the category of long duration gamma-ray bursts, despite its different origin.
“This burst is way into the long category. It’s not near the border. But it seems to be coming from a merging neutron star,” said Fermi team member Dr. Eric Burns, an astronomer at Louisiana State University.
The collaboration of many telescopes on the ground and in space allowed scientists to piece together a wealth of information about this event as soon as the burst was first detected.
It is an example of how satellites and telescopes work together to witness changes in the Universe as they unfold.
After the first detection, an intensive series of observations from the ground and from space, including with Swift, swung into action to pinpoint the source on the sky and track how its brightness changed.
These observations in the gamma-ray, X-ray, optical, infrared, and radio showed that the optical/infrared counterpart was faint, evolved quickly, and became very red — the hallmarks of a kilonova.
“This type of explosion is very rapid, with the material in the explosion also expanding swiftly,” said Dr. Om Sharan Salafia, an astronomer at the INAF – Brera Astronomical Observatory.
“As the whole cloud expands, the material cools off quickly and the peak of its light becomes visible in infrared, and becomes redder on timescales of days to weeks.”
At later times it would have been impossible to study this kilonova from the ground, but these were the perfect conditions for Webb’s NIRCam (Near-Infrared Camera) and NIRSpec (Near-Infrared Spectrograph) instruments to observe this tumultuous environment.
The spectrum has broad lines that show the material is ejected at high speeds, but one feature is clear: light emitted by tellurium, an element rarer than platinum on Earth.
The highly sensitive infrared capabilities of Webb helped scientists identify the home address of the two neutron stars that created the kilonova — a spiral galaxy about 120,000 light-years away from the site of the merger.
Prior to their venture, they were once two normal massive stars that formed a binary system in their home spiral galaxy.
Since the duo was gravitationally bound, both stars were launched together on two separate occasions: when one among the pair exploded as a supernova and became a neutron star, and when the other star followed suit.
In this case, the neutron stars remained as a binary system despite two explosive jolts and were kicked out of their home galaxy.
The pair traveled approximately the equivalent of the Milky Way Galaxy’s diameter before merging several hundred million years later.
“Webb provides a phenomenal boost and may find even heavier elements,” said Dr. Ben Gompertz, an astronomer at the University of Birmingham.
“As we get more frequent observations, the models will improve and the spectrum may evolve more in time.”
“Webb has certainly opened the door to do a lot more, and its abilities will be completely transformative for our understanding of the Universe.”
The team’s paper was published in the journal Nature.
A. Levan et al. Heavy element production in a compact object merger observed by JWST. Nature, published online October 25, 2023; doi: 10.1038/s41586-023-06759-1
Source : Breaking Science News