Telescope spies on supernova’s heart

Famous explosion left behind a neutron star, infrared data hint

Within the dusty cloud left behind by supernova 1987A, the most famous stellar explosion in modern history, astronomers have found compelling evidence for a long-sought neutron star. NASA’s James Webb Space Telescope has spied indirect hints of a powerful source of light — probably a type of neutron star — coming from the core of the supernova remnant, researchers report in the Feb. 23 Science. The finding could provide insights into how a neutron star behaves mere decades after its birth. “Supernova 1987A is truly a unique laboratory to study supernovas,” astrophysicist Patrick Kavanagh of Maynooth University in Ireland said February 17 in a news conference in Denver at a meeting of the American Association for the Advancement of Science. It’s “the gift that keeps on giving, with new observations continually yielding new discoveries.” On February 23, 1987, telescopes around the world got a front-row seat to a spectacular supernova in the Large Magellanic Cloud, a companion galaxy to the Milky Way (SN: 2/18/17, p. 20). Such explosions occur when a star at least eight times the mass of the sun dies. Located just 160,000 light-years from Earth, supernova 1987A, as it came to be known, was visible with the naked eye for months afterward. The explosion generated tremendous amounts of neutrinos, a handful of which ended up hitting detectors on Earth. It was the first time the ghostly particles had been seen coming from beyond the solar system. Since the discovery of 1987A, scientists have wondered what happened to the iron core of the blue supergiant star that exploded. Did it collapse into an ultradense neutron star or a black hole? The fact that neutrinos escaped the event favors the neutron star possibility, but whatever was left behind has yet to be directly spotted. That’s partly because the original star’s outer layers, now traveling away from the explosion at 10,000 kilometers per second, have created a thick haze of dust that obscures the area. Infrared light travels through dust more easily than other wavelengths, so the infrared eyes of the James Webb Space Telescope, or JWST, are well suited to peering into the cloud surrounding 1987A. With JWST, Kavanagh and colleagues detected photons, or particles of light, in the dusty central region that indicate the presence of argon and sulfur. Tellingly, these elements had been ionized, meaning that some of their electrons had been stripped away. “You need a source of high-energy photons in order to create these ions,” says coauthor Claes Fransson, an astronomer at Stockholm University. “The question is: What is giving rise to this ionization?” The team suggests two possibilities. Supernova 1987A could have left behind a pulsar, a highly magnetized neutron star that generates powerful beams of radiation. Alternatively, the photons could come from an ordinary neutron star whose surface blazes at a million degrees Celsius. “This is some of the strongest indirect evidence suggesting the presence of a neutron star,” says Aravind Pazhayath Ravi, an astrophysicist at the University of California, Davis. Taken together with data gathered by other instruments including the Atacama Large Millimeter/submillimeter Array in Chile, the new observations make the possibility of a black hole even more unlikely. Directly detecting the young neutron star would enable researchers to compare it with older ones elsewhere in the cosmos, providing more insight into the interior structure of such exotic objects. But first, the clouds surrounding 1987A’s remnant will have to thin out more, which is expected in roughly the next decade, Ravi says. When that happens, “we’ll have the photograph of the youngest ever observed neutron star.”