Astronomers have examined the well-studied Crab Nebula in great detail, and discovered just what a huge oddity it is in space. Chemical signatures around the dead star suggest that the star could have died one of two violent deaths.
The Crab Nebula taken by JWST. (Image courtesy: NASA, ESA, CSA, STScI, T. Temime, Princeton University)
New Delhi: Researchers have turned the James Webb Space Telescope toward the Crab Nebula, a supernova remnant located 6,500 light-years away in the constellation of Taurus. The Crab Nebula was formed by the violent death of a massive star, a core-collapse supernova. The supernova was observed by astronomers on Earth in A.D. 1054, and was bright enough to be visible during the daytime. The extended blanket of gas and dust violently thrown out by the dying star is much dimmer today.
The center of the Crab Nebula is a pulsar, a highly magnetized and rapidly spinning neutron star. Observations made by Webb have allowed astronomers to see detailed features and investigate the structure of the Crab Nebula. The Crab Nebula is unusual, and has an unusual structure that has previously been explained as arising from an electron-capture supernova, a rare type of explosion caused by a star with a less evolved or primitive core composed of oxygen, neon, and magnesium, rather than the more typical core of iron.
The web allows for new interpretations
The observations made by Webb broaden the possible explanations. The nebula's structure no longer requires an electron-capture explosion, and it can also be easily explained by a weak core-collapse supernova of an iron-core star. Previous studies had also indicated that the explosion was relatively low-energy, less than a tenth that of a typical supernova, and that the progenitor star had eight to ten solar masses, which is around the lower limit of stars that can experience violent core-collapse supernovae.
Previous studies in the late 1980s and 1990s indicated a ratio of nickel to iron abundance that favored an electron-capture supernova scenario. However, the new observations by Webb indicate that the ratio is still elevated compared to the Sun, but only modestly so, and much lower than previous estimates. The new observations are consistent with an electron-capture supernova, but also do not rule out the possibility of an iron core-collapse explosion.
A paper describing the findings has been published Astrophysical Journal LettersNathan Smith, a co-author of the paper, says, “Where the dust appears in the Crab is interesting because it's different from other supernova remnants such as Cassiopeia A and Supernova 1987A. In those objects, the dust is right in the middle. In the Crab, the dust is found in the dense filaments of the outer envelope. The Crab Nebula maintains a tradition in astronomy: the nearest, brightest, and best-studied objects tend to be the faintest.”