February 23, 2024
5 1 minute read
JWST solves decades-old mystery of nearby supernova
Scientists finally discovered the compact object at the heart of the famous supernova in 1987, and it is not a black hole
Nearly forty years ago, Earth’s inhabitants witnessed a rare cosmic spectacle: an exploding star in our sky that was visible to the naked eye. The event is called Supernova 1987A (SN 1987A), and it was the closest such event in the past four centuries. Since then, astronomers have sought to observe the stellar remnant that they knew must be lurking near the supernova’s center, surrounded by an expanding nebula of radioactive ash and glowing gas. Now, thanks to the power of the James Webb Space Telescope (JWST), a team of scientists has finally discovered this elusive quarry, confirming suspicions that the explosion created an extremely dense neutron star rather than a black hole swallowing starlight.
discovery, Published on Thursday in sciencesThe James Webb Space Telescope used its unprecedented infrared capabilities to pierce the veil surrounding Supernova 1987A, allowing it to be seen in literally a new light. By looking into the core of debris left by the star’s demise, astronomers led by Claes Fransson of Stockholm University in Sweden have discovered hints of ionized argon and sulfur — that is, evidence of elements that had been so shocked by some external force that their electrons had been compromised. He was stripped. These energetic elements are not expected to be found so close to SN 1987A’s “zero point”, unless they formed from intense bombardment of ultraviolet and X-ray radiation from a nearby neutron star. A feeding black hole spewing out bursts of radiation could also explain the result, but more than three decades of observations have failed to reveal any other signs of such an object inside SN 1987A, making the James Webb Space Telescope result compelling evidence of the existence of the neutron star.
“It’s very exciting,” says astrophysicist Mikako Matsuura of Cardiff University in Wales, who was not involved in the study and previously suggested in 2019 that a neutron star would be found in this supernova. “This is perhaps the strongest evidence for the presence of a neutron star in Supernova 1987A.”
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SN 1987A exploded on February 23, 1987, in the Large Magellanic Cloud, a dwarf satellite galaxy of the Milky Way about 160,000 light-years from Earth. No supernova has been seen so close to our planet since the Kepler supernova in 1604, when a star exploded within our galaxy at a distance of about 20,000 light-years. Although SN 1987A was initially detected by its sudden brightness in the sky, it has been proven that the first sign of a supernova came from a burst of neutrinos that swept across the Earth a few hours before the flash of light. This explosion was recorded at neutrino observatories spread across the planet, and was clear evidence of the formation of a neutron star somewhere within the star’s scattered remains. The neutron star issue grew stronger when additional analyzes revealed that the predecessor of SN 1987A was likely a blue giant star about 18 times the mass of our Sun, which is heavy but still too light to easily form a black hole.
Supernovas occur in two main ways: The first is when a star pulls too much material from a smaller companion star and explodes, resulting in a Type Ia supernova like a Kepler supernova. The other type of supernova — a Type II supernova like SN 1987A — occurs when a star runs out of fuel in the core of an extremely massive star that has been prevented from collapsing under its own weight by the external pressure of light emanating from its depths. . With no excess starlight to support them, the star’s outer layers fall inward and then bounce back to explode outward, sending shock waves rippling through the surrounding material. This process can emit light faster than the equivalent of an entire galaxy of stars, crushing the solar mass’s core into an ultra-dense ball the size of a city—a neutron star. In cases where the protostar is particularly massive — 20 solar masses or more — the resulting heavier neutron star then collapses into a black hole.
Having a neutron star relatively close by is scientifically fascinating, says Joan Pledger of the University of Central Lancashire in England, who was not involved in the study. “The physics is different for a neutron star,” she says, noting that the intense gravitational fields of these objects squeeze their insides to create strange states of matter, dramatically distorting the fabric of space-time surrounding them. “If we can discover neutron stars, especially nearby neutron stars that we can study well, we can begin to understand the laws of physics in regions that we cannot recreate in the laboratory.”
Although astronomers already suspected that SN 1987A did not leave behind a black hole, they wanted to be sure. Franson and his colleagues observed distinct signs of argon and ionized sulfur near the supernova’s center in July 2022, when the James Webb Space Telescope first began science operations. “[SN 1987A] “It was one of the first objects to be observed,” says Franson, with the James Webb Space Telescope studying the supernova’s aftermath for about 10 hours.
“The only energy source capable of producing those things [signs] “It’s a neutron star,” says study co-author Patrick Kavanagh of Maynooth University in Ireland. For a black hole to do the same, it would need to feed voraciously on matter from a source – such as another star – for which there is no evidence. “We’re confident we’ve evaluated all the different possibilities,” Kavanagh says. “We’ve ruled out everything except the presence of a neutron star.”
Careful analysis of the light emitted by the ionized matter shows that the neutron star is not exactly in the middle of SN 1987A; It’s even a little isolated because it got a “kick” from the supernova. When the star exploded, any slight imbalance would displace more of the outflowing matter to one side or the other, causing the neutron star to bounce in the opposite direction like an egg being squeezed from a balloon. Observations indicate that the neutron star is moving slightly towards us, having traveled about 500 billion kilometers from the site of its catastrophic birth. “The speed of the kick is about 400 kilometers per second,” Kavanagh says, which is unimaginable to us here on Earth, but still very slow compared to the immensity of light years.
What’s not clear is whether remnants of SN 1987A exist only Neutron star. Instead it might be a pulsar, a neutron star rotating so fast that it releases streams of energy from its poles that sweep across a large area of the sky like the beams of a cosmic lighthouse. “If there is a pulsar, its beam is not directed towards us, so we cannot detect it,” says Yvette Sindis of the Center for Astrophysics. Harvard and Smithsonian, who were not involved in the study. But there may be another way to find out. In the standard neutron star scenario, the enormous heat generated by the stellar remnant is so intense that it forms a beacon of ionized silicon that spreads away into the expanding cloud. In the pulsar model — where the emission is not dominated by heat, but rather by winds of electrons and other particles impacting the deeper debris — ionized silicon should be much rarer. So, if silicon can be observed and mapped around SN 1987A, “we can distinguish between the two,” Cavanagh says. As yet unpublished James Webb Space Telescope follow-up observations, taken by the team in the fall of 2023 and earlier this week, may contain that answer.
These observations provide new insights into the first moments after a Type II supernova. “We’ve never seen a neutron star form before,” says Fransson. Now that we know that, further studies of this tiny cosmic body using the James Webb Space Telescope and other telescopes should allow astronomers to learn more about these puzzling stellar events. “Until we see a supernova in our galaxy, this will be the best-studied supernova we will ever have,” Sindis says.