James Webb Space Telescope research team, with the cooperation of Vrije Universiteit Brussel, detects radiation from nebula-concealed neutron star in the iconic supernova SN 1987A

Supernovas are the spectacular end result of the collapse of stars with a mass greater than 8-10 times that of the sun. This process creates chemical elements such as carbon, oxygen, silicon and iron that make life possible. However, supernovas are also responsible for the creation of neutron stars and black holes, the most exotic objects in the universe.

Supernova 1987A (or SN 1987A for short) exploded on 23 February 1987 in the Large Magellanic Cloud in the southern skies at a distance of 160,000 light years. Visible to the naked eye, it was the closest supernova to be seen in more than 400 years. Modern observatories gave astronomers an unprecedented close-up view of the supernova blast. Despite being one of the most studied objects in the sky, SN 1987A still holds its mysteries. One of the most intriguing questions is, “What was left over from the exploded star?” The detection of neutrinos, incredibly tiny subatomic particles produced in the supernova, indicated that a neutron star must have formed. What remained unknown, however, was whether the neutron star survived or collapsed to form a black hole. Even after three-and-a-half decades of intense monitoring by highly advanced world-class observatories, convincing proof of the presence of a neutron star in the centre of SN 1987A remained elusive. Until now.

In a new publication in the journal Science, an international team of astronomers announce new discoveries made using the powerful James Webb Space Telescope (JWST). Observations using the JWST’s Mid-Infrared Instrument (MIRI) and Near-Infrared Spectrometer (NIRSpec) have revealed light emitted by ionised argon and sulphur in the centre of the supernova remnant (see Figs. 1 and 2). Thanks to the spatial resolution of the JWST and the ability to precisely determine the speed of the emission source, we know that the source is located close to the centre of the 1987 explosion. This is exactly what is expected from a compact central stellar remnant, given that most of the exploding star was blown out at up to 10,000 km/second and is now already far away from the centre. Ionisation of argon and sulphur indicates the emission of energetic photons, such as UV or X-rays, from a compact source at the centre. We thus see the unique signature of a newly created neutron star, as was predicted in 1992. According to the researchers, the radiation comes either from the million-degree heat of the neutron star itself or from energetic particles in the strong magnetic field of a very rapidly rotating neutron star, known as a pulsar wind nebula.

“Although there’s too much material swarming around the neutron star for us to see it directly, we can detect it indirectly using the JWST’s spectrometers,” says Professor Joris Blommaert of the Astronomy and Astrophysics Research Group of Vrije Universiteit Brussel, co-author of the publication. “We can form a picture, and for every pixel in that picture, we get a spectrum of electromagnetic radiation. That enables us to create a precise map of the radiation and localise its source,” adds Prof. Blommaert. Blommaert worked from the early 2000s onwards on the development of MIRI, which was crucial to detecting the spectra. “Thanks to our contribution to MIRI, we obtained observation time to study SN 1987A on the JWST, which ultimately enabled us to gather strong evidence for the existence of the central neutron star.”

Fig. 1. Combination of a Hubble Space Telescope image of SN 1987A and the argon light source in Fig. 2. The faint blue spot in the center is the radiation from the compact source detected with the JWST/NIRSpec instrument. Surrounding it is the debris expanding at thousands of km/second. The bright "string of pearls" on the inside, is the gas originating from the outer layers of the star, emitted approximately 20,000 years before the final explosion. The rapidly receding debris is now colliding with the ring, explaining the bright spots. Outside the inner ring, there are two more rings, presumably formed by a similar process that created the inner ring. The bright stars to the left and right of the inner ring are unrelated to the supernova.

Fig. 2. Image from a video depicting the appearance of the compact ionized argon light source (at a wavelength of 7 micrometers) with the MIRI instrument. (mpeg4 file available separately)

Fig. 3. Top row: on the left, the Argon light source image of SN1987A, in the middle, the Argon light source of the gas ring. On the right is the difference between the left and middle, showing only the argon light source of the compact object in the center. Bottom row: the same for another emission line in the spectrum of Argon.

Fig. 4. The star that exploded before the event on February 23, 1987 (left) and after the explosion (right). This illustrates the tremendous increase in the brightness of the supernova. Credit: David Malin AAT.

The study is the work of 34 authors from 12 European countries and the United States.

Reference: C. Fransson et al., Emission lines due to ionizing radiation from a compact object in the remnant of Supernova 1987A. Science 383, 898-903(2024). DOI:10.1126/science.adj5796

Contact:

Joris Blommaert

Joris.blommaert@vub.be

Tel: +32 (0)498 126422

NIRSpec was constructed for the European Space Agency by Airbus Industries; the micro-shutter assembly and detector subsystems were supplied by NASA. The development of MIRI was a joint collaboration between European and US partners.

The MIRI optical system was built by a consortium of European partners from Belgium, Denmark, France, Germany, Ireland, the Netherlands, Spain, Sweden, Switzerland and the United Kingdom. EADS-Astrium (now Airbus Defence and Space) provided the project office and management, and the full instrument test was conducted at Rutherford Appleton Laboratory. The Jet Propulsion Laboratory (JPL) supplied the core instrument flight software and the detector system, including infrared detectors from Raytheon Vision Systems, collaborated with Northrop Grumman Aerospace Systems on the development and testing of the cooler, and managed the US effort.

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