Astronomers using the James Webb Space Telescope (JWST) have ended nearly a decade of celestial hide-and-seek after discovering a neutron star in the debris of a star explosion.
Supernova 1987A represents the remains of an exploded star that once had a mass 8 to 10 times that of the Sun. It is located about 170,000 light-years away in the Large Magellanic Cloud, a dwarf galaxy neighbor of the Milky Way. Supernova 1987A was first detected by astronomers 37 years ago in 1987, hence the numerical aspect of its name. When supernova 1987A exploded, it first showered the Earth with ghostly particles called neutrinos that then became visible in bright light. This made it the closest and brightest supernova seen in the night sky on Earth for nearly 400 years.
Supernova explosions like this are responsible for seeding the cosmos with elements such as carbon, oxygen, silicon and iron. These elements eventually become the building blocks of future generations of stars and planets, and may even form molecules that may one day become an integral part of life as we know it. These explosions also give rise to compact stellar remnants in the form of neutron stars or black holes; For 37 years, astronomers didn’t know which of these was lurking at the heart of Supernova 1987A.
“For a long time, we have been looking for evidence of a neutron star in the gas and dust of Supernova 1987A,” Mike Barlow, professor emeritus of physics and astronomy and part of the team behind this discovery, told Space.com. . “We finally have the evidence we were looking for.”
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How does a neutron star hide for 40 years?
Neutron stars are born when massive stars exhaust the fuel resources needed for nuclear fusion occurring in their cores. This cuts off the energy flowing outward from the stars’ cores, keeping them from collapsing under their own gravity.
When a star’s core collapses, massive supernova explosions tear apart the star’s outer layers, destroying them. This leaves behind a “dead” star that is about the size of an average city on Earth but has a mass of one or two times that of the Sun; The star consists of a liquid of neutron particles, the densest known matter in the universe.
However, neutron stars are supported against complete collapse by quantum effects occurring between the neutrons within them. These effects prevent neutrons from being squeezed together. This so-called “neutron decay pressure” can be overcome if a stellar core has sufficient mass or if a neutron star accumulates more mass after creation. This will result in the birth of a black hole (if the minimum mass is not reached, this will not occur).
Scientists were pretty sure that the object in Supernova 1987A was a neutron star, but they couldn’t rule out the possibility that this newly deceased star had not accumulated mass, at least as we saw it some 170,000 years ago. turns itself into a black hole.
“Another possibility was that the falling material accumulated on the neutron star, causing it to turn into a black hole. So a black hole was a possible alternative scenario,” Barlow said. “But the spectrum produced by the falling material is not the right type of spectrum to explain the emission we see.”
You’re getting hotter…
The newly identified neutron star had evaded detection for 37 years because, as a newborn, it was surrounded by a thick blanket of gas and dust ejected during the supernova explosion that signaled the death throes of its progenitor star.
“Detection was hampered by the fact that the supernova concentrated about half the solar mass in the years after the explosion,” Barlow said. “This dust acted like a radion blocking the screen from the center of Supernova 1987A.”
Dust is much less effective at blocking infrared light than it is at blocking visible light. So to see beyond this shroud of death and into the heart of Supernova 1987A, Barlow and his colleagues turned to JWST’s highly sensitive infrared eye, specifically the telescope’s Mid-Infrared Instrument and Near-Infrared Spectrograph.
Conclusive evidence of this hidden neutron star was related to emissions of the elements argon and sulfur from the center of Supernova 1987A. These elements are ionized, meaning their electrons have been removed from their atoms. Barlow said that this ionization could only have occurred due to the radiation emitted by a neutron star.
The emissions enabled the team to place a limit on the luminosity, or luminosity, of the once-hidden neutron star. They determined that it was around one-tenth the luminosity of the Sun.
The team may have detected that a neutron star was born by Supernova 1987A, but not all the mysteries of this neutron star have been solved yet.
This is because a neutron star could have caused the ionization of argon and sulfur, which acted as a smoking gun, in one of two ways. Winds of charged particles dragged by a rapidly rotating neutron star and accelerated to near the speed of light may have interacted with surrounding supernova material, causing ionization. Or ultraviolet and X-ray light emitted from the million-degree surface of a hot neutron star may have stripped electrons from atoms at the heart of this stellar debris.
If the first scenario is correct, the neutron star at the heart of Supernova 1987A is actually a pulsar surrounded by a pulsar wind nebula. Pulsars are nearly rotating neutron stars. But if the second scenario is the correct recipe for these emissions, this nearby supernova gave birth to a “naked” or “naked” neutron star whose surface would be directly exposed to space.
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Barlow suggested that by making more infrared observations of the heart of Supernova 1987A with JWST’s NIRSpec instrument, researchers could distinguish between a bare neutron star and a star covered by a pulsar wind nebula.
“We currently have a program that collects data and will receive data at 3 or 4 times higher resolution in the near infrared,” he concluded. “So by obtaining these new data, we can distinguish 2 models proposed to explain the emission supported by a neutron star.”
The team’s research was published Thursday, February 22, in the journal Science.