Not so long ago, in a galaxy not that far away, a blue supergiant star – burned out from eons of immense pressure – collapsed at its core and exploded in a bright supernova visible some 170,000 light-years away in Earth’s Southern Hemisphere.
It was there, in the dwarf satellite galaxy known as the Large Magellanic Cloud, that a neutron star was born.
Inside the Large Magellanic Cloud galaxy lies what astronomers believe is a neutron star, the result of a supernova that was seen from Earth in 1987. Scientists have studied the development of the dense stellar body since its creation. (NASA image by Robert Kirshner and Pete Challis, NASA/ESA, and Alex Angelich, NRAO/AUI/NSF. )
Astronomers from around the globe, using the James Webb Space Telescope and other ones, announced Feb. 22 in a published paper they believed they could confirm the formation of the neutron star.
“We knew a neutron star or possibly a black hole – something very, very dense – was there,” said Roger Chevalier, W.H. Vanderbilt Professor of Astronomy at the University of Virginia. “The paper indicates this is a neutron star, and it’s important because it’s the first time we’ve been able to see a newly formed neutron star early in its existence. We’re learning something about typical neutron stars that are made in supernovae.”
Chevalier is a bit of a star himself. He recently was awarded the 2024 Distinguished Career Prize from the High Energy Astrophysics Division of the American Astronomical Society. Although he was not involved in writing the paper that announced the star, known by its supernova designation SN 1987A (the first supernova discovered in 1987), he has studied it. He helped review the paper prior to publication and is thanked by the authors in the acknowledgement section.
Roger Chevalier, UVA’s W.H. Vanderbilt Professor of Astronomy, has studied the supernova known as SN 1987A. He said scientists are learning more about the creation of neutron stars. (Photo by Molly Angevine)
Neutron stars are created when a star’s core collapses and the inward pressure squishes electrons and protons together to form neutrons. The core crash either continues into a black hole or stabilizes, creating an opposite reaction that throws shockwaves through the star’s surface and creates stellar debris known as “ejecta.”
Due to this stellar gas and debris, it was difficult to determine if that neutron star had continued collapsing into a black hole. Luckily, in 1987 astronomers traced neutrino emissions from the explosion, which indicated the immediate creation of a neutron star.
“It’s the only time that’s ever been done and that’s because the star was relatively close, something like 170,000 light-years away,” Chevalier said. “We knew from seeing these neutrinos that something had formed at the center of the supernova. But after this initial explosion, we didn’t see any sign of it at all. We knew it had to be in there because of the neutrinos, but it didn’t show itself up in any way.”
According to the paper, SN 1987A likely has a weaker magnetic field than other studied neutron stars, corresponding to slower rotation. But the ejecta from the supernova can mask measurements.
“It has been difficult to see, so we weren’t sure, but it turns out that the amount of power it’s putting out is really pretty small,” Chevalier said. “This one turns out to be quite faint compared to the observed pulsar population. We’d like to understand better what kind of neutron stars form from what kind of a star that becomes a supernova.”
Investigators said the light and radiation measured by the James Webb Space Telescope and other monitoring devices likely come from a once-hot neutron star that’s cooling off or from a pulsar wind nebula, created by a spinning neutron star dragging charged particles in its wake.
Because the neutron star is young, scientists are watching to see if the star gains momentum or increases its magnetic field as it ages.
Using the James Webb Space Telescope’s near-infrared camera, astronomers got a clearer look at the remnants of the 1987 supernova. Gas spectral analysis of the photo indicates the neutron star is to the right of center in the picture. (NASA image by M. Matsuura, Cardiff University; R. Arendt, Goddard Spaceflight Center and University of Maryland; and C. Fransson, NASA, ESA, CSA.)
“We conclude that the [observations] can be explained by either the cooling neutron star or pulsar wind nebula models, which both require the presence of a neutron star,” the researchers stated in the paper. “A combination of the models is also possible, [but] for the expected parameters, the pulsar wind nebula shock model is less likely.”
Having the Webb Telescope and a known supernova that can be monitored from the time it went off is helping astronomers better understand the impacts of exploding stars. It’s as if they have their own cosmic laboratory for exploration.
“It’s really dependent on having the Webb out there to be able to get the spatial resolution so you can see it – it’s just a little dot near the center,” Chevalier said. “It’s giving us good information about where [the neutron star] is and also how the material is moving along the line of sight.”
Watching the birth and growth of a neutron star is exciting for astronomers, but earthlings need not worry about any nearby stars going supernova, Chevalier said.
“There’s nothing very close to us that’s going to explode, and most of the massive star supernovae we see are from red supergiant stars, like Betelgeuse,” Chevalier said, noting that Betelgeuse was a big topic a few years ago when it began dimming and brightening again.
“Even at 700 light-years, it’s far enough away that it really wouldn’t harm us on Earth,” he said.
Assistant Editor, UVA Today Office of University Communications
bkm4s@virginia.edu 434-924-3778
November 21, 2024
