It may look like the Eye of Sauron, but the tiny blue purple sphere in the image above is actually an incredibly dense neutron star surrounded by stellar debris. The image is combination of photos from the James Webb Space Telescope (JWST) and the Hubble Space Telescope, and it marks the moment an international team of astronomers found a tiny neutron star hidden inside a giant supernova that exploded 37 years ago.
Designated Supernova 1987A, the star explosion is the most studied supernova – and the brightest one in 400 years. For a few months before it faded, it could even be seen with the naked eye.
But what remained hiding at its centre has been the source of mystery for almost four decades.
Supernovae form when a star over 8-10 times more massive than our Sun collapse, forming a spectacular explosion. The collapsed core often turns into a smaller neutron star (which are made of the densest matter in the Universe). That, or a black hole.
However, no compact object had ever been found within Supernova 1987A – despite signs that a neutron star may have formed. The most significant sign was that, the day before the explosion on 23 Feb 1987, neutrinos (unimaginably small sub-atomic particles) were detected from Earth.
A large dust cloud blocked out visible light from its centre, leading to the biggest unsolved problem in the study of this supernova.
New research, published in the journal Science, may have finally seen through this dust cloud by observing it at infrared wavelengths. Using the JWST, the researchers discovered heavy argon and sulphur atoms whose outer electrons had been ionised – literally stripped away – close to where the supernova had taken place.
This effect, the researchers say, could only have been caused by a neutron star. Ionisation would have happened either as the star rapidly rotated and dragged the particles around it, or by its ultraviolet and X-ray radiation as it cooled (from a whopping 100 billion to 1 million °C).
Study co-author Prof Josefin Larsson said: “This supernova keeps offering us surprises. Nobody had predicted that the compact object would be detected through a super strong emission line from argon, so it's kind of amusing that that’s how we found it in the JWST.”
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