On Sunday, October 9, Judith Racusin was 35,000 feet in the air, en route to a high-energy astrophysics conference, when the largest cosmic explosion in history took place. “I landed, looked at my phone, and got dozens of messages,” said Racusin, an astrophysicist at NASA’s Goddard Space Flight Center in Maryland. “It was truly exceptional.”
The explosion was a long burst of gamma rays, a cosmic event where a dying massive star releases powerful jets of energy as it collapses into a black hole or neutron star. This particular burst was so bright that it supersaturated the Fermi Space Gamma-Ray Telescope, an orbiting NASA telescope designed in part to observe such events. “There were so many photons per second that they couldn’t keep up,” said Andrew Levan, an astrophysicist at Radboud University in the Netherlands. The burst even appears to have inflated Earth’s ionosphere, the upper layer of Earth’s atmosphere, for several hours. “The fact that you can change Earth’s ionosphere from an object halfway through the universe is pretty amazing,” said Doug Welch, an astronomer at McMaster University in Canada.
Astronomers cheekily called it the BOAT – “the brightest of all time” – and began squeezing it for information about gamma-ray bursts and the cosmos in general. “Even 10 years from now, there will be new insights from this dataset,” said Eric Burns, an astrophysicist at Louisiana State University. “It still hasn’t quite struck me that it really happened.”
Initial analysis suggests that there are two reasons the BOAT was so brilliant. First, it happened about 2.4 billion light-years from Earth, which is close enough for gamma-ray bursts (although well outside our galaxy). It is also likely that the BOAT’s powerful jet was pointed towards us. The two factors combined to make this the kind of event that only happens once every few hundred years.
Perhaps the most consequential sighting occurred in China. There, in Sichuan province, the Large High Altitude Air Shower Observatory (LHAASO) tracks high-energy particles from space. In the astronomy history of gamma-ray bursts, researchers have only seen a few hundred high-energy photons from these objects. LHAASO saw 5,000 from this event alone. “The gamma-ray burst basically erupted in the sky right above them,” said Sylvia Zhu, an astrophysicist at the German Electronic Synchrotron (DESY) in Hamburg.
Among those detections was a suspected high-energy photon at 18 teraelectron volts (TeV), four times higher than anything seen before in a gamma-ray burst and more energetic than the highest energies attainable by the Large Hadron Collider. A photon of such energy should have been lost on the way to Earth, absorbed by interactions with the background light of the universe.
So how did he get here? One possibility is that, following the gamma-ray burst, a high-energy photon was converted into an axion-like particle. Axions are hypothesized light particles that may explain dark matter; axion-like particles are thought to be slightly heavier. High-energy photons could be converted into such particles by strong magnetic fields, like those surrounding an imploding star. The axion-like particle would then move through the vastness of space unhindered. When it arrives in our galaxy, the magnetic fields would convert it back into a photon, which would then make its way to Earth.
Within a week of the initial detection, several teams of astrophysicists suggested this mechanism in papers uploaded to the preprint science site arxiv.org. “It would be a very incredible discovery,” said Giorgio Galanti, an astrophysicist at the National Institute of Astrophysics (INAF) in Italy, who co-authored one of the first of these papers.
Still, other researchers wonder if the detection of LHAASO could be a case of mistaken identity. Maybe the high-energy photon came from somewhere else and its exact time of arrival was just a coincidence. “I’m very skeptical,” said Milena Crnogorčević, an astrophysicist at the University of Maryland. “I’m currently leaning toward it being a background event.” (To complicate matters further, a Russian observatory reported a hit by an even higher energy 251 TeV photon from the burst. I’m a bit skeptical.”)
So far, the LHAASO team has not released the detailed results of their observations. Burns, who is coordinating a global collaboration to study BOAT, hopes they will. “I’m very curious to see what they have,” he said. But he understands why some mistrust may be justified. “If I was sitting on data that had even a few percent chance of defining dark matter evidence, I would be extremely cautious at this time,” Burns said. If the photon can be linked to BOAT, “it would most likely be evidence for new physics and potentially dark matter,” Crnogorčević said. The LHAASO team did not respond to a request for comment.
Even without the LHAASO data, the amount of light seen by the event could allow scientists to answer some of the biggest questions about gamma-ray bursts, including major puzzles about the jet itself. “How is the jet launched? What happens in the jet as it shoots through space? said Tyler Parsotan, an astrophysicist at Goddard. “These are really big questions.”
Other astrophysicists hope to use the BOAT to determine why only certain stars produce gamma-ray bursts when they go supernova. “It’s one of the big mysteries,” said Yvette Cendes, an astronomer at the Harvard-Smithsonian Center for Astrophysics. “He must be a very massive star. A galaxy like ours may produce a gamma-ray burst every million years. Why does such a rare population produce gamma-ray bursts? »
Whether the gamma-ray bursts result in a black hole or a neutron star at the core of the collapsed star is also an open question. Preliminary BOAT analysis suggests that the first occurred in this case. “There’s so much energy in the jet that it must essentially be a black hole,” Burns said.
What is certain is that this is a cosmic incident that will not be eclipsed for many, many lifetimes. “We will all be long dead before we have the chance to start again,” Burns said.
Main image: The rings around the burst, seen here in colorized data from NASA’s Swift Observatory, formed when X-rays dispersed dust hidden in our Milky Way galaxy. Credit: NASA Swift Observatory; Processing: Jon Miller.
This article was originally published on the Quantum Abstractions Blog.
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