NASA’s NuSTAR Observes Shocking Events in the Most Intense Cosmic Burst on Record

Astronomers believe that GRB 221009A could be the result of a new black hole forming in the collapsing core of a star. The newly formed black hole ejected powerful jets of particles traveling near the speed of light that pierced through the star and emitted X-rays and gamma rays. This exceptional phenomenon was observed by NASA's NuSTAR X-ray telescope, which provided new pieces of evidence about the brightest and most energetic gamma-ray burst detected to date.

The burst, named GRB 221009A or BOAT, had a unique jet structure that differed from previous gamma-ray bursts. The jet had a narrow core with wider sides and had a variation in energy that depended on the distance from the core. The burst was 70 times brighter and far more energetic than its predecessor, and scientists are still studying its unusual characteristics to learn more about the mechanisms that launch such jets into space and the properties of progenitor stars that lead to the uniqueness of the burst.

The most energetic kind of explosion in the universe, gamma-ray bursts can be seen billions of light-years away. Gamma rays are the most energetic form of light in the universe, although they are invisible to human eyes. This explosion was so bright that it blinded most gamma-ray instruments in space, making it difficult to study in detail. Scientists reconstructed the event using data from several telescopes, including NASA's Fermi Gamma Ray Space Telescope, Hubble and James Webb space telescopes, the agency's Wind and Voyager 1 spacecraft, and the ESA's Solar Orbiter.

Based on their observations, scientists believe that the source of the distinctions seen in the jets could be the physical properties of the progenitor star. It is also possible that entirely different mechanisms launch very bright jets into space.

Similar to other gamma-ray bursts, GRB 221009A had a jet that erupted from the collapsing star like it was shot into space from a fire hose, with gamma rays radiating from the hot gas and particles at the jet’s core. But GRB 221009A’s jet stood out in a few ways. In just about every previously observed gamma-ray burst, the jet remained remarkably compact and there was little to no stray light or material outside the narrow beam. (In fact, gamma-ray bursts are so compact, the gamma rays can only be observed when their jets are pointed almost directly at Earth.)

The Fermi Gamma-ray Space Telescope observes the cosmos using the highest-energy form of light, providing an important window into the most extreme phenomena of the universe, from gamma-ray bursts and black-hole jets to pulsars, supernova remnants, and the origin of cosmic rays. Credit: © Daniëlle Futselaar/MPIfR (artsource.nl)

By contrast, in GRB 221009A the jet had a narrow core with wider, sloping sides. Some of the most energetic gamma-ray jets have shown similar properties, but the jet from the BOAT was unique in one important way: The energy of the material in GRB 221009A also varied, meaning that instead of all the material in the jet having the same energy – like a single bullet shot from a gun – the energy of the of the material changed with distance from the jet’s core. This has never been observed in a long gamma-ray burst jet before.

“The only way to produce a different jet structure and vary the energy is to vary some property of the star that exploded, like its size, mass, density, or magnetic field,” said Eleonora Troja, a professor of physics at the University of Rome, who led NuSTAR the observations of the event. “That’s because the jet has to basically force its way out of the star. So, for example, the amount of resistance it meets would potentially influence the features of the jet.”

Artist’s concept of NuSTAR on orbit. Credit: NASA/JPL-Caltech

Astronomers can see the light from gamma-ray jets, but the distance means they can’t resolve images of the jets directly. Researchers have to interpret the light from these events to learn about the physical characteristics of faraway objects. It’s sort of like looking at footprints in the snow and inferring something about the physical traits of the person who left them.

In many cases, there may be more than one possible explanation for the light from a cosmic event. More than one X-ray telescope observed GRB 221009A, including NASA’s Neil Gehrels Swift Observatory and Neutron star Interior Composition Explorer (NICER), as well as ESA’s XMM-Newton telescope. The NuSTAR data helped narrow down those possibilities. It shows that as the jet traveled into space, it collided with the interstellar medium, or the sparse sea of atoms and particles that fills the space between stars. This collision created X-rays – particles of light slightly less energetic than gamma rays.

“There are multiple X-ray telescopes operating in space, each with different strengths that can help astronomers understand these cosmic objects better,” said Daniel Stern, NuSTAR project scientist at NASA’s Jet Propulsion Laboratory in Southern California.

Reference: “A structured jet explains the extreme GRB 221009A” by Brendan O’Connor, Eleonora Troja, Geoffrey Ryan, Paz Beniamini, Hendrik van Eerten, Jonathan Granot, Simone Dichiara, Roberto Ricci, Vladimir Lipunov, James H. Gillanders, Ramandeep Gill, Michael Moss, Shreya Anand, Igor Andreoni, Rosa L. Becerra, David A. H. Buckley, Nathaniel R. Butler, Stephen B. Cenko, Aristarkh Chasovnikov, Joseph Durbak, Carlos Francile, Erica Hammerstein, Alexander J. van der Horst, Mansi M. Kasliwal, Chryssa Kouveliotou, Alexander S. Kutyrev, William H. Lee, Gokul P. Srinivasaragavan, Vladislav Topolev, Alan M. Watson, Yuhan Yang and Kirill Zhirkov, 7 June 2023, Science Advances.DOI: 10.1126/sciadv.adi1405

More About the Mission

A Small Explorer mission led by Caltech and managed by the Jet Propulsion Laboratory (JPL) for NASA’s Science Mission Directorate in Washington, NuSTAR was developed in partnership with the Danish Technical University and the Italian Space Agency (ASI). The spacecraft was built by Orbital Sciences Corp. in Dulles, Virginia. NuSTAR’s mission operations center is at the University of California, Berkeley, and the official data archive is at NASA’s High Energy Astrophysics Science Archive Research Center at the agency’s Goddard Space Flight Center in Greenbelt, Maryland. ASI provides the mission’s ground station and a mirror data archive. Caltech manages JPL for NASA.