Astronomers consider they’ve discovered the rest of the neutron star that was left behind by Supernova 1987A

It was the brightest supernova in nearly 400 years when it lit the skies of the southern hemisphere in February 1987. Supernova 1987A – the explosion of a blue supergiant star in the nearby mini-galaxy known as the Great Magellanic Cloud – took the astronomical community by surprise. It gave them an unprecedented opportunity to observe an exploding star in real time using modern instruments and telescopes. But something was missing. After the supernova faded, astronomers expected to find a neutron star (a hyperdense, collapsed star core made mostly of neutrons) at the heart of the explosion. They didn’t see anything.

In the 34 years since then, astronomers have searched unsuccessfully for the missing neutron star. Various theories arose. Perhaps it hadn’t had time to form yet. Or maybe the mass of the blue supergiant was greater than expected, and the supernova created a black hole instead of a neutron star. Perhaps the neutron star was hidden and obscured by the dust from the explosion. If the missing star was there at all, it was really hard to see.

But persistence pays off. Astronomers may have finally found it.

The first clue came from the Atacama Large Millimeter / Submillimeter Array (ALMA) in Chile last summer. The radio telescope observed a hot “spot” in the core of the supernova. The ‘blob’ itself is not a neutron star, but a heated mass of dust and gas that can hide the neutron star behind it: after all, something supplies the heat. However, further observations would be required to confirm the presence of a neutron star.

Using the promising radio signal results from ALMA, a team of researchers then observed the supernova in X-ray wavelengths using data from two different NASA spacecraft: the Chandra X-ray Observatory and the Nuclear Spectroscopic Telescope Array (NuSTAR). Their results will be published in the Astrophysical Journal this month. What they found is an X-ray emission near the core of the supernova explosion, with two possible explanations.

Supernova 1987A with a pulsar wind nebula in the middle. Photo credit: Chandra (X-ray): NASA / CXC / Univ. di Palermo / E. Greco; Illustration: INAF-Osservatorio
Palermo astronomer / Salvatore Orlando

First, the emission could be the result of particles being accelerated by the shock wave of the explosion. This shock wave theory cannot be completely ruled out, but the evidence seems to point to a second, more likely explanation – a pulsar wind nebula.

Pulsars are a type of energetic neutron star that rotates quickly and the radiation flashes outwards like a lighthouse when it rotates. Pulsars can sometimes create fast winds that blow outward, creating fog that is shaped by charged particles and magnetic fields. The researchers believe they can see that.

The Chandra and NuSTAR data support last year’s ALMA detection. Somewhere in the center of Supernova 1987A lies a young pulsar. It may take a decade or more for the supernova’s core to be clear enough to see the pulsar directly, but for the first time in 30 years, astronomers can be pretty sure it’s there.

Supernova 1987A as seen by NuSTAR and Chandra. Photo credit: Chandra (X-ray): NASA / CXC / Univ. from Palermo / E. Greek; Image: INAF-Palermo Astronomical Observatory / Salvatore Orlando; NuSTAR (X-ray): NASA / JPL-CalTech

The discovery is exciting. “It would be unprecedented to be able to observe a pulsar essentially since birth,” said Salvatore Orlando, one of the researchers involved in the discovery. “It could be a golden opportunity to study the evolution of a baby pulsar.”

After a 30 year old mystery is solved and there is much new science to be done in the years and decades to come, Supernova 1987A promises to keep our attention. After all, it’s the closest and brightest supernova we’ll ever see.

Unless Betelgeuse explodes …

(Betelgeuse probably won’t explode anytime soon)

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