James Webb Telescope discovers new details in ‘Necklace of Pearls’ supernova

About 168,000 years ago, a blue giant about 17 solar masses collapsed into the Large Magellanic Cloud, a satellite galaxy of our Milky Way. The dying star, Sanduleak −69° 20, was part of a triple system in the constellation Swordfish. It was not until February 1987 that light from the explosion reached Earth. Since then, the remnants of this supernova – the closest to Earth since Kepler’s supernova of 1604 – have been among the most studied astronomical objects.

SN 1987A, as the supernova is called in astronomical jargon, has already been closely examined by numerous telescopes, including the Hubble Space Telescope. Now its powerful successor, the James Webb Space Telescope, has also focused on the fascinating remains of the cosmic catastrophe. And the James Web Telescope wouldn’t be the James Webb Telescope if it hadn’t found something that had never been observed before.

The new Webb NIRCam (near-infrared camera) observations, NASA writes, provide “a crucial clue about how a supernova evolves over time and shapes its remnant.”

The bluish central region resembles a keyhole and consists of agglomerated gas and dust particles expelled by the supernova explosion. The dust here is so dense that not even the Webb telescope with its infrared camera can penetrate it – hence the dark “hole” in the keyhole.

The bright equatorial ring around the blue area is striking and contains warm white spots that resemble a string of pearls. The ring is made of material that was ejected about 20,000 years before the explosion. The white spots — the “pearls” — were created when the supernova’s shock wave passed through the ring. The “string of pearls” is bordered by two reddish arms that extend outward in the shape of an hourglass.

These structures are already known – they have already been observed by the Hubble and Spitzer space telescopes. However, what the Webb telescope has made visible for the first time are also white spots outside the ring, from which diffuse emissions arise. They, too, were created by the effect of the shock wave on the material ejected before the explosion. On the other hand – and this is the most important discovery – there are the two vaguely pronounced ‘crescents’ that can be seen to the left and right of the ‘keyhole’.

The “crescents” are believed to be part of the outer layers of gas ejected by the supernova explosion. However, the astronomers don’t yet know exactly what they actually see. However, they believe our view of SN 1987A gives the illusion that there is more material in these crescent regions than there really is.

These observations are due to the unprecedented resolution of the Webb telescope. The now decommissioned Spitzer telescope observed SN 1987A in infrared for most of its operational life (2003–2020) and provided valuable insights, but with its main mirror 60 times smaller, it could never match the precision and detail of the Webb telescope. The Hubble telescope, on the other hand, has a high resolution, but in the visible light range, which is often obscured by a veil of dust and gas.

Although SN 1987A has been observed for nearly four decades, all of its mysteries are far from being revealed. The astrophysicists assume that a neutron star was created after the collapse of the precursor star Sanduleak −69° 202. However, a corresponding radiation source at the location of the precursor star could not be detected in the range of X-rays or radio emissions, and this is true also for the range of visible light.

There are several hypotheses that try to explain this missing source of radiation – for example, the hypothesis that receded matter has given the neutron star enough mass to turn into a black hole. Another states that a cold dust cloud absorbs the neutron star’s radiation, preventing its detection. The Webb telescope will continue to observe SN 1987A – and may be able to solve the mystery of the strange “crescents” it has now discovered. (i.e)