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Using the James Webb Space Telescope (JWST), astronomers have put an end to a nearly decade-long game of celestial hide-and-seek after they discovered a neutron star among the remains of a stellar explosion.
Supernova 1987A represents the remains of an exploded star that once had a mass between 8 and 10 times that of the sun. It is located about 170,000 light years away, in the Large Magellanic Cloud, a dwarf galaxy neighboring the Milky Way. Supernova 1987A was first detected by astronomers 37 years ago, in 1987, hence the numerical aspect of its name. When it exploded, Supernova 1987A first covered Earth with ghostly particles called neutrinos and then became visible in bright light. This made it the closest and brightest supernova seen in Earth’s night sky in about 400 years.
Supernova explosions like this one are responsible for seeding the cosmos with elements like carbon, oxygen, silicon and iron. These elements ultimately become the building blocks of the next generation of stars and planets, and may even form molecules that could one day become an integral part of life as we know it. These explosions also generate compact stellar debris, either in the form of neutron stars or black holes; For 37 years, astronomers have not known which of them may be hiding 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 4 decades?
Neutron stars are born when massive stars exhaust their fuel supplies needed for the nuclear fusion that occurs in their cores. This cuts off the outgoing energy flowing from the cores of these stars that protects them from collapsing under their own gravity.
When the core of a star collapses, tremendous supernova explosions tear away the star’s outer layers and destroy them. This leaves behind a “dead” star as wide as the average city here on Earth, but with a mass about one or two times that of the sun; the star ends up composed of a fluid of neutron particles, which is the densest known matter in the universe.
However, neutron stars are saved from total collapse thanks to the quantum effects that occur between the neutrons inside them. These effects prevent neutrons from crowding together. This so-called “neutron degeneracy pressure” can be overcome if a stellar core has sufficient mass, or if a neutron star, after its creation, accumulates more mass. This would result in the birth of a black hole (although if the minimum mass is not reached, it will not happen).
Scientists were fairly certain that the object of Supernova 1987A is a neutron star, but they could not rule out the possibility that this recently deceased star, at least as we see it about 170,000 years ago, had not gathered the mass necessary to transform into a black hole.
“Another possibility was that infalling matter could have accumulated in the neutron star and caused it to collapse into a black hole. Therefore, a black hole was a possible alternative scenario,” Barlow said. “However, the spectrum produced by the falling material is not the right type of spectrum to explain the emission we see.”
You’re getting hot…
The newly identified neutron star had avoided detection for 37 years due to the fact that, as a newborn, it was still surrounded by a thick layer of gas and dust released during the supernova explosion that marked the death throes of its parent star.
“Detection has been hampered by the fact that the supernova condensed about half a solar mass of dust in the years following the explosion,” Barlow said. “This dust acted as a radioon obscuring 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 through this deadly shroud and the heart of Supernova 1987A, Barlow and his colleagues turned to JWST’s highly sensitive infrared eye, particularly the telescope’s mid-infrared instrument and near-infrared spectrograph.
The irrefutable evidence of this hidden neutron star had to do with emissions of the elements argon and sulfur from the center of Supernova 1987A. These elements are ionized, meaning they have had electrons removed from their atoms. Barlow said that this ionization could only have occurred due to radiation emitted by a neutron star.
The emissions allowed the team to put a limit on the brightness or luminosity of the once-hidden neutron star. They determined that it was about one-tenth the brightness of the sun.
The team may have determined that Supernova 1987A gave rise to a neutron star, but not all of the mysteries of this neutron star are solved yet.
This is because the ionization of argon and sulfur that served as their smoking gun could have been caused by a neutron star in two ways. Winds of charged particles entrained and accelerated to near the speed of light by a rapidly spinning neutron star could have interacted with surrounding supernova material, causing ionization. Or, ultraviolet and
If the first scenario is correct, then the neutron star at the heart of Supernova 1987A is actually a pulsar surrounded by a pulsar wind nebula. Pulsars are practically spinning neutron stars. However, if the latter scenario is the correct recipe for these emissions, this nearby supernova gave rise to a “naked” neutron star, whose surface would be directly exposed to space.
Barlow suggested that researchers could distinguish between a naked neutron star and one encased by a pulsar wind nebula by conducting more infrared observations of the heart of Supernova 1987A with JWST’s NIRSpec instrument.
“We have a program that is collecting data now, which will get data with 3 or 4 times higher resolution in the near infrared,” he concluded. “So by obtaining this new data, we will be able to distinguish the two models that have been proposed to explain neutron star-driven emission.”
The team’s research was published Thursday (February 22) in the journal. Science.