Scientists are investigating the origin of the Crab Nebula using the James Webb Space Telescope

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 MIRI (Mid-Infrared Instrument) and NIRCam (Near-Infrared Camera), the team collected data that helps clarify the history of the Crab Nebula.

The Crab Nebula is the result of a supernova core collapse that was 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 observed today is an expanding envelope of gas and dust and a streaming wind driven by a pulsar, a rapidly rotating and highly magnetized neutron star.

The Crab Nebula is also very unusual. Its atypical composition and very low explosion energy previously led astronomers to believe it was an electron-capture supernova — a rare type of explosion that originates from a star with a less developed core made of oxygen, neon and magnesium, rather than a star. a more typical iron core.

Past research efforts have calculated the total kinetic energy of an explosion based on the amount and velocity of the current ejecta. Astronomers deduced that the nature of the explosion was relatively low-energy (less than one-tenth the mass of a normal supernova) and that the mass of the progenitor star was in the range of 8 to 10 solar masses – balancing on the thin line between stars. which experience a violent supernova death and those which do not.

However, there are discrepancies between the supernova electron capture theory and the crab observations, particularly the observed rapid motion of the pulsar. In recent years, astronomers have also improved their understanding of iron-core-collapsed supernovae, and now think that this type can also produce low-energy explosions, provided the stellar mass is sufficiently low.

To reduce uncertainty about the crab’s progenitor star and the nature of the explosion, the science team used Webb’s spectroscopic capabilities to focus on two regions located in the crab’s inner filaments.

Theories predict that due to the different chemical composition of the core in an electron-capturing supernova, the abundance 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 of the star). Studies in the late 1980s and early 1990s measured the Ni/Fe ratio in the crab using optical and near-infrared data and noted a high Ni/Fe abundance ratio that appeared to favor an electron-capturing supernova scenario.

The Webb Telescope, with its sensitive infrared capabilities, has now advanced research into the Crab Nebula. 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 abundance ratio. They found that the ratio was still elevated compared to the sun, but only slightly and much lower than earlier estimates.

The revised values ​​are consistent with electron capture, but do not rule out an iron core collapse explosion from a similarly low-mass star. (Higher-energy explosions from more massive stars are expected to produce Ni/Fe ratios closer to solar abundances.) Further observational and theoretical work will be needed to distinguish between these two possibilities.

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

The images and data collected by MIRI allowed the team to isolate the dust emissions inside the crab for the first time and map them in high resolution. By mapping the warm dust emission using Webb and even combining it with Herschel Space Observatory data on cooler dust grains, the team created a well-rounded picture of the dust distribution: the outermost filaments contain relatively warmer dust, while cooler grains predominate. near the centre.

The work is published in The Astrophysical Journal Letters.