Nasa’s Neil Gehrels Swift Observatory, which has spent two decades studying the most powerful explosions in the cosmos, is expected to re-enter the Earth’s atmosphere on Wednesday, burning up in the process. The satellite, which was designed to operate with its three telescopes for just two years, is no longer able to steer or observe, and its re-entry is uncontrolled. The US Space Force predicts the 3,200lb spacecraft will hit the atmosphere at about 3.30am EST on 4 November.
Nasa says most of the spacecraft is set to burn up, but some components are expected to survive. The agency continued: “The risk of harm coming to anyone on Earth is unlikely – approximately 1 in 2,100. NASA and Space Force will continue to monitor the re-entry and update predictions.” The observatory was launched in 2004 to explore the universe’s most powerful explosions, called cosmic gamma-ray bursts, and quickly return its observations of location and strength to Earth.
Over the course of its operational life, the observatory detected and tracked more than 2,000 gamma-ray bursts ( GRBs) that are considered the most powerful explosions the universe has seen since the big bang. Nasa says these bursts of energy occur approximately once per day and are brief, but intense, flashes of gamma radiation and come from all different directions, and can last from a few milliseconds to a few hundred seconds. But scientists do not know what causes them – theorizing that they may be the birth of a black hole in a massive stellar explosion or produced by the collision of two neutron stars, or some other phenomenon.
Swift was launched as part of Nasa’s medium explorer, or Midex, program. In July, it observed a wandering mega black hole shredding star, which occurs when a star passes fatally close to a supermassive black hole. The black hole, described as an “orphan”, lit up as it devoured the star on the outskirts of a galaxy, in what scientists call a “tidal disruption event”.
Nearly every galaxy has a supermassive black hole at its center, and a tidal disruption occurs about once every 100,000 years. The star-shedding event occurred 2,600 light-years from the center of the host galaxy, but the Swift team observed one more than 30,000 light-years away. A paper describing the results published in The Astrophysical Journal Letters, said “the tidal disruption event outshone its entire host galaxy in ultraviolet wavelengths, temporarily radiating with the light of about 10 billion suns.” Still unknown is how the black hole came to drift so far.
Stein said it could have started off in a small galaxy that merged with the big one, but the key question was how common are wandering black holes. Nasa attempted to push Swift into a higher orbit last year using a private space contractor but the mission did not succeed after they failed to rendezvous. Last month, Swift was estimated to be orbiting 171 miles above the Earth and it was commanded to end operations to prepare for re-entry.
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