Webb Detects Emission from Neutron Star in Supernova 1987A Remnant

SN 1987A is the only supernova visible to the naked eye in the last 400 years and the most studied supernova in history. The event was a core-collapse supernova, meaning the compacted remains at its core formed either a neutron star or a black hole. Evidence for such a compact object has long been sought, and while indirect evidence for the presence of a neutron star has previously been found, this is the first time that the effects of high-energy emission from the probable young neutron star have been detected.

SN 1987A was first observed on February 23, 1987 at the edge of the Large Magellanic Cloud, some 163,000 light-years away.

It was the first naked-eye supernova to be observed since Johannes Kepler witnessed a supernova over 400 years ago.

About two hours prior to the first visible-light observation of SN 1987A, three observatories around the world detected a burst of neutrinos lasting only a few seconds.

The two different types of observations were linked to the same supernova event, and provided important evidence to inform the theory of how core-collapse supernovae take place.

This theory included the expectation that this type of supernova would form a neutron star or a black hole.

Astronomers have searched for evidence for one or the other of these compact objects at the center of the expanding remnant material ever since.

Indirect evidence for the presence of a neutron star at the center of the remnant has been found in the past few years, and observations of much older supernova remnants — such as the Crab Nebula — confirm that neutron stars are found in many supernova remnants.

However, no direct evidence of a neutron star in the aftermath of SN 1987A had been observed, until now.

“From theoretical models of SN 1987A, the 10-second burst of neutrinos observed just before the supernova implied that a neutron star or black hole was formed in the explosion,” said Stockholm University astronomer Claes Fransson, lead author of the study.

“But we have not observed any compelling signature of such a newborn object from any supernova explosion.”

“With this observatory, we have now found direct evidence for emission triggered by the newborn compact object, most likely a neutron star.”

In the study, Dr. Fransson and colleagues used the MIRI and NIRSpec instruments on the NASA/ESA/CSA James Webb Space Telescope to observe SN 1987A at infrared wavelengths and found evidence of heavy argon and sulfur atoms whose outer electrons had been stripped off (i.e. the atoms had been ionized) close to where the star explosion occurred.

They modeled various scenarios and found that these atoms could only have been ionized by ultraviolet and X-ray radiation from a hot cooling neutron star or, alternatively, from the winds of relativistic particles accelerated by a rapidly rotating neutron star and interacting with surrounding supernova material (pulsar wind nebula).

If the former scenario is true, the surface of the neutron star would be about a million degrees, having cooled down from 100 billion degrees or so at the moment of formation at the core of the collapse more than 30 years earlier.

“Our detection with Webb’s MIRI and NIRSpec spectrometers of strong ionized argon and sulfur emission lines from the very center of the nebula that surrounds SN 1987A is direct evidence of the presence of a central source of ionizing radiation,” said University College London’s Professor Mike Barlow.

“Our data can only be fitted with a neutron star as the power source of that ionizing radiation.”

“This radiation can be emitted from the million degree surface of the hot neutron star, as well as by a pulsar wind nebula that could have been created if the neutron star is rapidly spinning and dragging charged particles around it.”

“The mystery over whether a neutron star is hiding in the dust has lasted for more than 30 years and it is exciting that we have solved it.”

“Supernovae are the main sources of chemical elements that make life possible — so we want to get our models of them right.”

“There is no other object like the neutron star in SN 1987A, so close to us and having formed so recently. Because the material surrounding it is expanding, we will see more of it as time goes on.”

“To create the ions that we observed in the ejecta, it was clear that there had to be a source of high-energy radiation in the center of the SN 1987A remnant,” Dr. Fransson said.

“In the paper, we discuss different possibilities, finding that only a few scenarios are likely, and all of these involve a newly born neutron star.”

The paper was published in the February 22, 2024 edition of the journal Science.

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C. Fransson et al. 2024. Emission lines due to ionizing radiation from a compact object in the remnant of Supernova 1987A. Science 383 (6685): 898-903; doi: 10.1126/science.adj5796