A black hole can be formed when the core of a massive star is destroyed. As shown here, some of the surrounding matter escapes as powerful jets that travel at nearly the speed of light in opposing directions. Normaly, gamma-rays are produced by jets of collapsing star for several seconds to minutes. Astronomers believe that the jets of GRB 200826A shut down quickly and produced the fastest gamma ray burst (magenta), from a collapsing Star ever seen. Credit: NASAs Goddard Space Flight Center/Chris Smith (KBRwyle)NASA's Fermi Gamma Ray Space Telescope detected a pulse containing high-energy radiation, which had been traveling toward Earth for almost half of the current age of the universe. It lasted only a second and was the shortest gamma radiation burst (GRB), ever caused by the death a large star.GRBs, which are the most powerful events of the universe, can be detected across billions upon billions light-years. Astronomers categorize them as either long or short depending on how long the event lasts. Long bursts are associated with the death of massive stars. Short bursts, however, have been linked to another scenario.Bin-bin Zhang from Nanjing University in China, and the University of Nevada Las Vegas said, "We knew that some GRBs of massive stars could register short GRBs. But we thought this was because of instrumental limitations." This burst is unique because it is a short-duration GRB. However, its other properties indicate that it was created from a collapsing Star. We now know that dying stars can also produce short bursts.Astronomers analyzed data from NASAs Fermi Gamma Ray Space Telescope and other space missions to discover the origin of GRB200826A, a short but powerful radiation burst. This is the shortest known burst of radiation that was powered by a collapsing Star and nearly didn't happen. Credit: NASAs Goddard Space Flight CenterThe burst was named GRB 200826A after the date it occurred. Two papers were published in Nature Astronomy Monday, July 26. Zhang leads the first paper, which examines the gamma radiation data. The second, which is led by Toms Ahumada (a doctoral student at Maryland's College Park and NASA’s Goddard Space Flight Center, Greenbelt), describes the GRB’s fading multiwavelength aftermath glow and the rising light of the supernova explosion.Ahumada stated that the event was "effectively a fizzle", and was very close to not occurring at all. "Even so the burst produced 14 million times more energy than the entire Milky Way galaxy in the same time period, making it one the most energetic GRBs of short duration ever observed."A star that is much larger than the Sun suddenly runs out of fuel will collapse and form a black hole. Some of the matter that swirls towards the black hole is ejected in two powerful jets, which rush outward at the speed of light in opposing directions. Astronomers can only detect a GRB if one of these jets points almost directly towards Earth.Each jet drills through the star producing a pulse gamma radiation, which is the highest-energy form light that can last for up to minutes. The supernova explodes rapidly after the burst.Discovery image of GRB 200826A's fading afterglow (center). Credit: ZTF and T. Ahumada et al., 2021GRBs are short, however, formed when compact objects such as neutron stars collide. These also form during stellar collapsespiral spiral inward over many billions of years. Fermi observations have recently shown that in nearby galaxies giant flares produced by supermagnetized neutron star is also masquerading as short GRBs.GRB 200826A was an extremely short blast of high-energy radiation lasting only 0.65 seconds. The signal traveled for eons in the expanding universe and was only detected by Fermi’s Gammaray Burst Monitor after it had lasted just one second. It was also detected by instruments aboard NASA's Wind mission (which orbits a point approximately 930,000 miles (1 million kilometers) from Earth), and Mars Odyssey (which orbits the Red Planet since 2001). The blast was also observed by the ESA (European Space Agency) INTEGRAL satellite.These missions all participate in the GRB-locating system known as the InterPlanetary network (IPN). The Fermi project provides all U.S. funds. Each detector is able to use the other's data to narrow down the exact location of the burst. The IPN located its position in a small area of sky in the constellation Andromeda about 17 hours after the GRB.The National Science Foundation-funded Zwicky Transient Facility at Palomar Observatory was used by the team to scan the sky for visible light changes that could be related to the GRB's fading glow.Shreya, a Caltech graduate student and co-author of the afterglow papers, said that conducting this search is like trying to find a needle among a haystack. However, the IPN helps shrink it. "Out of over 28,000 ZTF notifications received the first night, we found only one that met our search criteria. It also appeared in the IPN-defined sky region.NASA's Neil Gehrels Swift Observatory found fading Xray emission at the same spot within a day. The National Radio Astronomy Observatory's Karl Jansky Large Array in New Mexico detected variable radio emission a few days later. The team began to observe the afterglow using a variety ground-based equipment.The Gran Telescopio Canarias telescope, a 10.4-meter telescope located at the Roque de los Muchachos Observatory in La Palma, Spain's Canary Islands, was used to observe the bright galaxy associated with the burst. It showed that the light takes 6.6 billion year for it to reach us. This is 48% of the universe’s current age, 13.8 billion years.Researchers had to also capture the supernova emerging to confirm that the brief burst was caused by a collapsing Star.Leo Singer, a Goddard astronomer and Ahumada’s research advisor, stated that if the supernova burst was caused due to a collapsing Star, then the afterglow should fade away. To see the supernova's light at these distances, one needs a large and sensitive telescope.Singer was given time at the Gemini North telescope, 8.1 meters in height, in Hawaii. He also had access to the Gemini Multi-Object Spectrograph, a sensitive instrument that allows him to conduct the search. The astronomers took images of the host galaxy using infrared and red light beginning 28 days after the burst and then repeated the search 45 to 80 days later. The supernova was detected in the first set of observations.Researchers suspect that the burst was caused by jets that just emerged from the star before shutting down. This is not the usual case of long-lasting jets breaking out of the star and traveling a great distance from it. The possibility that there was no GRB could have occurred if weaker jets were fired off by the black hole or if the star had been much larger at the time of its collapse.This discovery solves a long-standing mystery. Long GRBs are required to be coupled with supernovae. Astronomers however detect far more supernovae than long GRBs. Even after taking into account the fact that GRB Jets must be nearly in our line of sight to allow astronomers detect them, this discrepancy continues.Researchers conclude that short GRBs produced by collapsing stars must be marginal cases. This is consistent with the idea that most massive stars do not produce jets or GRBs. This result shows that the duration of a burst does not necessarily indicate its origin.B.-B. has more information. Zhang et. al., A peculiarly short-duration Gamma-ray burst resulting from massive star core collapsing, Nature Astronomy (2021). B.-B. Zhang et. al., A peculiarly short-duration Gamma-ray burst resulting from massive star-core collapse (2021). DOI: 10.1038/s41550-021-01395-z Toms Ahumada et al, Discovery and confirmation of the shortest gamma-ray burst from a collapsar, Nature Astronomy (2021). DOI: 10.1038/s41550-021-01428-7 Journal information: Nature Astronomy
