A team of scientists used the NASA/ESA/CSA James Webb Space Telescope to analyze the composition of the Crab Nebula, a supernova remnant located 6,500 light-years away in the constellation Taurus. Using the telescope’s MIRI (Infrared Instrument) and NIRCam (Near Infrared Camera), the team collected data that will help clarify the history of the Crab Nebula.

The Crab Nebula is the result of the collapse of a supernova, the death of a massive star. The supernova explosion itself was seen on Earth in 1054 AD and was bright enough to be observed during the day. The much fainter remnant seen today is an outward-flowing wind fed by a pulsar, a rapidly rotating and highly magnetized neutron star with an expanding envelope of gas and dust.

The Crab Nebula is also quite unusual. Its unusual composition and very low explosion energy had previously led astronomers to believe it was an electron-capturing supernova; This is a rare type of explosion that occurs in a star with a less developed core of oxygen, neon and magnesium, rather than in a star. a more typical iron core.

Past studies have calculated the total kinetic energy of the eruption based on the amount and speed of the current eruption. Astronomers concluded that the nature of the explosion was relatively low energy (less than a tenth of a normal supernova) and that the mass of the progenitor star was in the range of eight to ten solar masses oscillating in the thin line. among the stars. those who suffered a violent supernova death and those who did not.

However, there are discrepancies between the electron-captured supernova theory and the Crabb observations, especially the observed rapid motion of the pulsar. Astronomers have also improved their understanding of iron-core collapsing supernovae in recent years and now believe that this type can also produce low-energy explosions if the mass of the star is low enough.

To reduce uncertainty about the Crab’s progenitor star and the nature of the explosion, the research team used Webb’s spectroscopic capabilities to identify two regions located in the Crab’s inner filaments.

Theories predict that, due to the different chemical composition of the nucleus of an electron-capturing supernova, the ratio of nickel to iron (Ni/Fe) should be much higher than the ratio measured in our Sun (which contains these elements from previous generations). Star). Studies in the late 1980s and early 1990s measured the Ni/Fe ratio at Krabi using optical and near-infrared data and noted a high Ni/Fe ratio supporting the electron capture supernova scenario.

The Webb Telescope is currently advancing research into the Crab Nebula with its sensitive infrared capabilities. The team used MIRI’s spectroscopic capabilities to measure the emission lines of nickel and iron, leading to a more reliable estimate of the Ni/Fe ratio. They found that the ratio was still high compared to the Sun, but only modest and much lower than previous estimates.

The revised values ​​are consistent with electron capture but do not exclude the collapse of the iron core of a star with the same low mass. (Higher-energy explosions from more massive stars are expected to produce Ni/Fe ratios closer to solar abundance.) More observations and theoretical work will be required to distinguish between these two possibilities.

In addition to obtaining spectral data from two small regions in the interior of the Crab Nebula to measure its mass ratio, the telescope also observed the remnant’s broader environment to understand details of synchrotron radiation and dust distribution.

The images and data collected by MIRI allowed the team to isolate dust emissions inside the Crab and map them at high resolution for the first time. By mapping the hot dust emission using Webb and even combining it with Herschel Space Observatory data on cooler dust grains, the team created a clear picture of the dust distribution: The outermost filaments contain relatively hot dust, while cooler grains predominate. not far from the centre.