September 2022, Southern California: Through telescopes, astronomers watch a sudden flash of intense blue light, about ten billion times stronger than the light from the Sun, in a galaxy a billion light-years away.
After pointing several different telescopes at the area to observe the explosion, researchers found that it was similar to other recent events, known as Fast Blue Luminous Optics, or LFBOT). Three months after the new LFBOT faded, astronomers repositioned their telescopes in the same location to capture five three-minute exposures. That's when they noticed a very rapid flash of light in the images.
“We looked at them and asked ourselves if we weren't dreaming,” he says. it's me, an astronomer at Cornell University. Never before have we seen such a quick and bright flash in space, let alone the aftermath of another event.
Discovered in 2018, LFBOTs are characterized by recurring flashes of light, each lasting a few tens of seconds, that occur months after the initial explosion. Using a high-speed optical camera, the researchers were able to obtain basic data on the event, which not only confirmed the intensity of the recurring explosions, but also provided information about their short and unprecedented time scale.
“At first we thought it was an alien satellite or something,” Anna Ho recalls. “We tried to verify what we saw with other telescopes… Over the course of a few months, we observed 14 explosions in total. There was no longer room for doubt: so it was a very real phenomenon.” “The explosion of what remains of a celestial event.”
This discovery has caused a sensation in the scientific community, leaving researchers around the world fascinated and excited. “The most exciting thing about this discovery is how unprecedented it is,” he says. Daniel Burley, an astrophysicist at Liverpool John Moores University in the United Kingdom, and co-author of the new study. No one had noticed anything like this before. It enhances our knowledge of how violent phenomena work.
In recent years, astronomers have been able to “make movies” of the night sky using longer exposures that capture more light than still images. Anna Hu and other researchers from Zwicky Transit FacilityA group of telescopes used to monitor the night sky and find celestial objects that change in brightness analyzed images taken of the entire northern hemisphere's sky every two days. While LFBOTs are about ten times brighter than supernovas, the speed at which they occur is such that most telescopes miss the flashes.
“Something that only lasts a few minutes goes completely unnoticed if you watch it once a night. In this case, we were very lucky,” confirms Anna Ho.
Producing something as powerful, fast, and bright as LFBOTs, which eject matter at close to the speed of light, requires a high-energy source. According to astronomers, it could be a neutron star or a black hole.
When a massive star goes supernova at the end of its life, it leaves behind a dense core, known as a neutron star. If its density is sufficient, it collapses and turns into a black hole. “It's very difficult to get jets approaching the speed of light from anything other than black holes or neutron stars,” he says. Brian Metzger, a physicist at Columbia University and reviewer of the new study. This is a really wonderful discovery. These flashes really allow us to understand their geometry better. “Until now we did not know specifically whether we were observing events from the side or from the front.”
But the exact causes of these explosions remain a mystery. Are LFBOTs emitted during the birth of a compact body? When a star explodes and leaves its dense core behind? Or does it correspond to the regeneration of a compact object, such as a black hole disrupting another star? How could something that has been exploding for months produce such rapid and intense flashes of energy?
According to Daniel Byerly, lightning can come from jets erupting from the source, such as a beam of light from a lighthouse sweeping across the Earth as the object rotates. The sudden explosions could also be caused by the neutron star's magnetic fields, a phenomenon observed in young, highly magnetic neutron stars. Another possible cause: variations in the dense accretion disk of matter surrounding the black hole, known as the lightning flashes it causes.
“We're not sure yet exactly who she is,” says Anna Ho. If these flashes interest us so much, it is because all the good ideas about their nature can lead to the discovery of a certain type of important phenomenon that has been studied for a long time.
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