Argon emission in SN1987A

The NASA/ESA/CSA James Webb Space Telescope has observed the best evidence yet for emission from a neutron star at the site of a well-known and recently-observed supernova. The supernova, known as SN 1987A, occurred 168 000 light-years from Earth in the Large Magellanic Cloud.

Left: Webb’s 2023 NIRCam (Near-Infrared Camera) image of SN 1987A that highlights the object’s central structure, expanding with several thousands km/s. The blue region is the densest part of the clumpy ejecta, containing heavy elements like carbon, oxygen, magnesium and iron, as well as dust. The bright ‘ring of pearls’ is the result of the collision of the ejecta with a ring of gas ejected about 20 000 years before the explosion. Now spots are found even exterior to the ring, with diffuse emission surrounding it. These are the locations of supernova shocks hitting more exterior material from the progenitor star. The outer ejecta is now illuminated by X-rays from the collision, while the inner ejecta is powered mainly by radioactivity and a putative compact object.

Right: An international team of astronomers has now used two of Webb’s instruments to study the emissions from the core of SN 1987A. The top image features the data from Webb’s MRS (Medium Resolution Spectrograph) mode of the MIRI instrument (Mid-InfraRed Instrument). The bottom image depicts data from Webb’s NIRSpec (Near Infrared Spectrograph) at shorter wavelengths. Spectral analysis of the MIRI results showed a strong signal due to ionised argon from the centre of the ejected material that surrounds the original site of SN 1987A. The NIRSpec data found even more heavily ionised chemical species, particularly five times ionised argon (meaning argon atoms that have lost five of their 18 electrons). Weak lines of ionised sulphur were also detected with MIRI. This indicated to the science team that there is a source of high-energy radiation in the centre of the SN 1987A remnant, illuminating an almost point-like region in the centre. The most likely source is believed to be a newly born neutron star.