海角社区

BATON ROUGE 鈥� On Sunday, Oct. 9, 2022, a pulse of intense radiation swept through the solar system so exceptional that astronomers quickly dubbed it the BOAT 鈥� the brightest of all time.

The source was a gamma-ray burst, or GRB, the most powerful class of explosions in the universe.

The burst triggered detectors on numerous spacecraft, and observatories around the globe followed up. After combing through all of this data, astronomers can now characterize just how bright it was and better understand its scientific impact.

鈥淕RB 221009A was likely the brightest burst at X-ray and gamma-ray energies to occur since human civilization began,鈥� said Eric Burns, 海角社区 Department of Physics and Astronomy assistant professor.

鈥淕RB 221009A was likely the brightest burst at X-ray and gamma-ray energies to occur since human civilization began.鈥� 

Eric Burns, 海角社区 Department of Physics and Astronomy assistant professor

Burns led an analysis of some 7,000 GRBs 鈥� mostly detected by 狈础厂础鈥檚 and the Russian Konus instrument on 狈础厂础鈥檚 spacecraft 鈥� to establish how frequently events this bright may occur. Their answer: once in every 10,000 years.

The burst was so bright it effectively blinded most gamma-ray instruments in space, which means they could not directly record the real intensity of the emission. U.S. scientists were able to reconstruct this from the Fermi data. They then compared the results with those from the Russian team working on data and Chinese teams analyzing observations from the GECAM-C detector on their SATech-01 satellite and instruments on their Insight-HXMT observatory. Together, they prove the burst was 70 times brighter than any yet seen.

Burns and other scientists presented new findings about the BOAT at the High Energy Astrophysics Division meeting of the American Astronomical Society in Waikoloa, Hawaii. Observations of the burst span the spectrum, from radio waves to gamma rays, and include data from many NASA and partner missions, including the X-ray telescope on the , 狈础厂础鈥檚 observatory, and even in interstellar space. Papers describing the results presented will appear in a .

The signal from GRB 221009A had been traveling for about 1.9 billion years before it reached Earth, making it among the closest-known 鈥渓ong鈥� GRBs, whose initial, or prompt, emission lasts more than two seconds. Astronomers think these bursts represent the birth cry of a black hole that formed when the core of a massive star collapsed under its own weight. As it quickly ingests the surrounding matter, the black hole blasts out jets in opposite directions containing particles accelerated to near the speed of light. These jets pierce through the star, emitting X-rays and gamma rays as they stream into space.

With this type of GRB, astronomers expect to find a brightening supernova a few weeks later, but so far it has proven elusive. One reason is that the GRB appeared in a part of the sky that鈥檚 just a few degrees above the plane of our own galaxy, where thick dust clouds can greatly dim incoming light.

鈥淲e cannot say conclusively that there is a supernova, which is surprising given the burst鈥檚 brightness,鈥� said Andrew Levan, a professor of astrophysics at in Nijmegen, Netherlands. Since dust clouds become more transparent at infrared wavelengths, Levan led near- and mid-infrared observations using 狈础厂础鈥檚 鈥� its first use for this kind of study 鈥� as well as the to spot the supernova. 鈥淚f it鈥檚 there, it鈥檚 very faint. We plan to keep looking,鈥� he added, 鈥渂ut it鈥檚 possible the entire star collapsed straight into the black hole instead of exploding.鈥� Additional Webb and Hubble observations are planned over the next few months.

As the jets continue to expand into material surrounding the doomed star, they produce a multiwavelength afterglow that gradually fades away.

鈥淏eing so close and so bright, this burst offered us an unprecedented opportunity to gather observations of the afterglow across the electromagnetic spectrum and to test how well our models reflect what鈥檚 really happening in GRB jets,鈥� said Kate Alexander, an assistant professor in the department of astronomy at the in Tucson. 鈥淭wenty-five years of afterglow models that have worked very well cannot completely explain this jet,鈥� she said. 鈥淚n particular, we found a new radio component we don鈥檛 fully understand. This may indicate additional structure within the jet or suggest the need to revise our models of how GRB jets interact with their surroundings.鈥�

The jets themselves were not unusually powerful, but they were exceptionally narrow 鈥搈uch like the jet setting of a garden hose 鈥� and one was pointed directly at us, Alexander explained. The closer to head-on we view a jet, the brighter it appears. Although the afterglow was unexpectedly dim at radio energies, it鈥檚 likely that GRB 221009A will remain detectable for years, providing a novel opportunity to track the full life cycle of a powerful jet.

The burst also enabled astronomers to probe distant dust clouds in our own galaxy. As the prompt X-rays traveled toward us, some of them reflected off of dust layers, creating extended 鈥渓ight echoes鈥� of the initial blast in the form of X-ray rings expanding from the burst鈥檚 location. The X-ray Telescope on 狈础厂础鈥檚 discovered the presence of a series of echoes. Detailed follow-up by 鈥檚 (the European Space Agency鈥檚) telescope, together with Swift data, revealed these extraordinary rings were produced by 21 distinct dust clouds.  

鈥淗ow dust clouds scatter X-rays depends on their distances, the sizes of the dust grains, and the X-ray energies,鈥� explained Sergio Campana, research director at and the in Merate, Italy. 鈥淲e were able to use the rings to reconstruct part of the burst鈥檚 prompt X-ray emission, and also to determine where in our galaxy the dust clouds are located.鈥�

GRB 221009A is only the seventh gamma-ray burst to display X-ray rings, and it triples the number previously seen around one. The echoes came from dust located between 700 and 61,000 light-years away. The most distant echoes  鈥� clear on the other side of our Milky Way galaxy 鈥� were also 4,600 light-years above the galaxy鈥檚 central plane, where the solar system resides.

Lastly, the burst offers an opportunity to explore a big cosmic question. 鈥淲e think of black holes as all-consuming things, but do they also return power back to the universe?鈥� asked Michela Negro, an astrophysicist at the , and 狈础厂础鈥檚 in Greenbelt.

Her team was able to probe the dust rings with 狈础厂础鈥檚 to glimpse how the prompt emission was organized, which can give insights into how the jets form. In addition, a small degree of polarization observed in the afterglow phase confirms that we viewed the jet almost directly head-on.

Together with similar measurements now being studied by a team using data from ESA鈥檚 observatory, scientists say it may be possible to prove that the BOAT鈥檚 jets were powered by tapping into the energy of a magnetic field amplified by the black hole鈥檚 spin. Predictions based on such models have already successfully explained other aspects of this burst.