Decades-long quest ends as the landmark observatory detects signs of the 1987 blast’s central neutron star.

The James Webb Space Telescope (JWST) has solved a decades-old mystery about one of the most famous explosions of a star in history.

Astronomers used the observatory to finally spot signs of an ultradense ‘neutron star’ lurking in the explosion’s core in a galaxy that orbits the Milky Way. Light from the explosion reached Earth 37 years ago this week, in a supernova that revolutionized modern astrophysics by providing an up-close look at how stars die.

But despite years of studying this blast, known as supernova (SN) 1987A, astronomers had not been able to detect what was left behind: maybe a black hole, which can sometimes be formed, or perhaps a neutron star, as many predicted?

“It’s something that’s been searched for ever since the explosion,” says Patrick Kavanagh, an astrophysicist at Maynooth University in Ireland, and a member of the team reporting the discovery today in Science1. “And now we’ve found it.”

JWST did not observe the neutron star directly, because it remains obscured behind a veil of dust from the explosion. But the telescope detected light coming from argon and sulfur atoms that had been ionized, or electrically charged, by radiation blazing from the long-sought neutron star...

... One outcome of such a supernova is to leave behind a black hole. But early observations of SN 1987A, such as the wave of neutrinos, suggested that it should have given rise to a neutron star, which can be just 20 kilometres across but is so dense that a teaspoonful weighs millions of tonnes. Astronomers have found several tantalizing hints of this outcome using other telescopes, but none have yielded a solid conclusion, meaning that other possibilities were still on the table2,3.

Enter JWST, which launched in late 2021 and can observe celestial bodies at different wavelengths and higher resolution than can many other telescopes. In July 2022, in some of its first scientific observations, the powerful space telescope observed SN 1987A for nine hours. Two of its cutting-edge instruments provided unprecedented insights into what was happening at the heart of the exploded star...