On February 24, 1987, a star exploded in a bright supernova in our neighboring galaxy, the Large Magellanic Cloud. Since then, astronomers have been searching for the rest of the star’s core that should have been left with it. Now they could have found this neutron star. Because several telescopes, including NASA’s Chandra X-ray telescope, have detected high-energy radiation signatures in the supernova remnant. Their pattern suggests that a rapidly rotating neutron star – a young pulsar – is hidden in the dust-shrouded center of this supernova relic.
When a massive star has reached the end of its life cycle, the radiation pressure from its nuclear fusion is no longer sufficient to counteract the tremendous gravity of its matter. The result is a core collapse and the star explodes in a supernova. The outer shells of the star are ejected far into space, while either only an extremely compressed remnant remains of the core, a neutron star, or a black hole. When a star 168,000 light-years away exploded in the Large Magellanic Cloud on February 24, 1987, it was the first supernova that could even be seen in the night sky with the naked eye. Accordingly, astronomers have studied this supernova 1987A and its remains intensively since then.
Where is the remnant of the stars?
But precisely the center of this supernova relic is covered by dust and gas clouds, so that it has not yet been possible to locate the relic of the star core. “For 34 years, astronomers have been searching the stellar rubble for the neutron star we are expecting there,” explains first author Emanuele Greco from the University of Palermo. “There was also a lot of evidence that later turned out to be dead ends. But our latest results are different. ”Several new observations corroborate the assumption that a rapidly rotating neutron star – a pulsar – is hidden in the heart of Supernova 1987A. As early as 2020, astronomers discovered a noticeably hot spot in the center of the dust cloud with the help of the Atacama Large Millimeter / submillimeter Array (ALMA). It is several million degrees hot and its features and position match a hot, young neutron star.
Greco and his team have now detected X-rays in the supernova relic that come from its center and also fit well with the expected emissions of a young neutron star. Your data comes from images that the two orbital NASA X-ray telescopes Chandra and NuSTAR (Nuclear Spectroscopic Telescope Array) made of the supernova remnant between 2012 and 2014. The changes in radiation during this time allowed the researchers to compare this with two possible sources of such radiation using an astrophysical model. X-rays in a supernova relic can come from a neutron star, but they can also come from the shock wave of the explosion colliding with gas and star debris.
Telltale X-rays
As the astronomers discovered, X-rays are made up of two components, a lower-energy part of “soft” X-ray radiation and a higher-energy part. According to the models, these two parts must have different origins. “We found that the soft X-rays of 0.5 to 8 kiloelectron volts originate from thermal radiation from the shocked circumstellar matter,” report Greco and his team. “But we also found strong proportions of more than ten kiloelectronvolts of energy in all NuSTAR spectra. This clearly shows that there has to be another component. ”The characteristics of this more energetic component match the radiation that one would expect from a young, rapidly rotating neutron star. In addition, it would take 400 years to accelerate electrons from the shock wave to such high speeds that they emit X-rays of this energy, as the researchers explain. Since the supernova was only 34 years ago, this is ruled out.
The astronomers consider it much more likely that behind the dust of Supernova Relic 1987A is a young pulsar that emits strong streams of particles and rays, the so-called pulsar wind nebulae. You (?) Could be the originator of the hot spot that ALMA had already found in the center of the cloud. Whether a pulsar actually formed during the star explosion could be clarified in the next ten years or so. Because the astronomers expect that the central dust cloud of the supernova relic will slowly spread and dissolve by then. “This could give us the once-in-a-lifetime opportunity to study the evolution of a baby pulsar,” says co-author Salvatore Orlando of the Astronomical Observatory.
Source: Emanuele Greco (University of Palermo) et al., The Astrophysical Journal