2023-09-01 19:09:35
The James-Webb continues to renew our knowledge of certain celestial bodies formerly observed with Hubble and other telescopes in orbit, such as Spitzer and Chandra. Today, it is towards the remains of the mythical supernova observed on Earth in 1987 that the space telescope has turned its gaze in the near infrared.
It is well known that when we count the supernovae in other galaxies over a year, all types combined (SN II and SN Ia in particular), we are led to estimate that on average three to four supernovae per century should occur in our Milky Way. However, the penultimate known for example, before the recent observations of Chandra, dates from regarding 330 years ago. This is Cassiopeia A, and unlike those of 1572 and 1604, observed in visible light by Tycho Brahe (SN 1572) and Johannes Kepler (SN 1604), it does not seem to have been noted by astronomers. It was only discovered on radio and in 1947.
Astrophysicists believe, however, that such a supernova deficit is apparent. Indeed, our Milky Way contains numerous clouds of dust which strongly absorb visible light over interstellar distances. The fact remains that scientists are quite frustrated that they cannot closely study and even simply cannot observe an example of these cosmic catastrophes with the naked eye.
Since its discovery, telescopes around the world and from space have observed supernova 1987A. This includes NASA’s Chandra X-ray Observatory, which has examined this object many times over its 17 years of scientific operations. From 1999 to 2013, data from Chandra showed an expanding X-ray emission ring that was getting brighter and brighter. This was produced by the shock wave from the original explosion which had erupted and heated the ring of gas surrounding the supernova. To obtain a fairly accurate French translation, click on the white rectangle at the bottom right. The English subtitles should then appear. Then click on the nut to the right of the rectangle, then on “Subtitles” and finally on “Translate automatically”. Choose “French”. © Chandra X-ray Observatory
A blue supergiant of 20 solar masses
Luckily, that’s almost what happened when SN 1987A was detected just 168,000 light-years from our Galaxy in the Large Magellanic Cloud. Since its discovery in February 1987, astrophysicists have continued to study the evolution of the remnant of this gigantic explosion of a star that has been spotted on old images and which has been called Sanduleak -69° 202a, abbreviated SK-69 202. It was a blue supergiant, born 10 million years ago from a stellar collision with fusion and 20 times more massive than the Sun, and which was originally mapped by the Romanian-American astronomer Nicholas Sanduleak in 1970.
For this, researchers have mobilized almost all the bands of wavelengths ranging from gamma rays to radio for almost 40 years. There have thus been observations made with Hubble and Chandra. We will therefore not be surprised that today it is the turn of the James-Webb space telescope, as explained by a NASA communiqué.
The new observations were made with Webb’s NIRCam instrument (Near Infrared Camera). This imaged a central structure of the keyhole-shaped supernova remnant. It’s filled with gas and dust so densely that even near-infrared light detected by Webb can’t pass through it, forming the dark “hole” in the keyhole.
A continuously evolving supernova remnant
There is still a bright equatorial ring formed of material ejected tens of thousands of years before the supernova explosion that contains bright hot spots, which appeared when the supernova shock wave caught up with material from the ring.
The release also explains that Webb’s unparalleled sensitivity and spatial resolution revealed small crescent-shaped structures. These crescents are thought to be part of the outer layers of gas thrown up by the supernova explosion. He concludes by recalling that Despite decades of study since the initial discovery of the supernova, several mysteries remain, including regarding the neutron star that should have formed as a result of the supernova explosion.
Like Spitzer, Webb will continue to observe the supernova over time. Its NIRSpec instruments (Near-Infrared Spectrograph) and Miri (Mid-Infrared Instrument) will provide astronomers with the ability to capture new high-fidelity infrared data over time and gain new insights into newly identified crescent structures. Additionally, Webb will continue to collaborate with Hubble, Chandra and other observatories to provide new insights into the past and future of this legendary supernova. ».
The explosion of very massive stars in gravitational supernovae enriches the interstellar medium with the chemical elements synthesized by nuclear fusion, while giving rise to a neutron star or a black hole by the collapse of the star’s core. The transition between the collapse of the core and the expulsion of the stellar envelope is a challenge for the theoretical understanding of supernovae. A hydraulic experiment designed and carried out at the CEA made it possible to reproduce by analogy one of the phenomena of hydrodynamic instability which facilitates the explosion. This experimental approach is complementary to numerical simulations. Discover this experience in animation. This animated film was produced and co-financed by the CEA and the ERC, and directed by Studio Animea. © T. Foglizzo, J. Guilet, G. Durand (CEA)
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