First evidence of a neutron star in a supernova

Astronomers have confirmed what’s at the centre of a supernovae, the violent explosive deaths of massive stars.

They say they found conclusive evidence that a neutron star exists at the centre of Supernova 1987A.

A stellar explosion was first observed 37 years ago and neutrinos –subatomic particles travelling near the speed of light – were detected on 23 February 1987. The next day, the supernova itself was observed.

Although the neutrino burst lasted only a few seconds it provided important clues to develop the theory of what happens in supernovae. The theory suggests this type of supernova should lead to a neutron star or a black hole.

Neutron stars are usually only tens of kilometres across but super dense, often weighting more than the Sun. Black holes are even more dense – their gravitational pull is so great that not even light can escape.

For nearly 4 decades, astronomers have been unable to say for certain which of these compact objects formed at the centre of the supernova.

SN 1987A was the first supernova that could be seen with the naked eye since Kepler’s Supernova which was spotted by the German astronomer in 1604.

Supernovae are the explosive deaths of stars about 8–10 times the size of our Sun.

The 1987 supernova is the most studied supernova. It is located in the Large Magellanic Cloud, about 160,000 light-years away.

In a study published in the journal Science, astronomers have answered the question saying they used two of the instruments aboard the James Webb Space Telescope to peer through the supernova’s dusty veil to reveal the nature of its centre.

Supernova composite image yellow orange swirls with blue star dot
Combination of a Hubble Space Telescope image of SN 1987A and the compact argon source. The faint blue source in the centre is the emission from the compact source detected with the JWST/NIRSpec instrument. Outside this is the stellar debris, containing most of the mass. The inner bright “string of pearls” is the gas from the outer layers of the star. Credit: Hubble Space Telescope WFPC-3/James Webb Space Telescope NIRSpec/J. Larsson.

They observed the supernova at infrared wavelengths, finding evidence of heavy argon and sulphur atoms whose outer-shell electrons had been stripped away due to intense ionising radiation during the explosion.

Models show that such ionisation could only have occurred in one of two ways: Either UV radiation or X-rays emanating from a cooling (but still hot) neutron star; or winds of near-light speed particles accelerated by a rapidly rotating neutron star.

“Our data can only be fitted with a neutron star as the power source of that ionising radiation,” says co-author Professor Mike Barlow from University College London.

If the first scenario is true, the neutron star’s surface is about a million degrees Celsius. This scorching temperature compares to the 100 billion degrees it would have been at the moment of the core collapse, seen more than 30 years ago.

“Supernovae are the main sources of chemical elements that make life possible – so we want to get our models of them right,” Barlow adds. “There is no other object like the neutron star in Supernova 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.”

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