Scientists investigate the origins of the Crab Nebula with the James Webb Space Telescope

A team of scientists used NASA/ESA/CSA’s 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 (Mid-Infared 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 a supernova that collapsed and killed a massive star. The supernova explosion itself was seen on Earth in 1054 CE and was bright enough to see during the day. The much fainter remnant observed today is an expanding shell of gas and dust, and an outflowing wind driven by a pulsar, a rapidly spinning and highly magnetized neutron star.

The Crab Nebula is also highly unusual. The atypical composition and very low explosion energy previously led astronomers to think it was an electron-capture supernova – a rare type of explosion that arises from a star with a less developed core of oxygen, neon and magnesium, instead of a supernova. more typical iron core.

Previous research efforts have calculated the total kinetic energy of the explosion based on the amount and velocities of the current ejecta. Astronomers concluded that the nature of the explosion was one of relatively low energy (less than one-tenth that of a normal supernova), and that the mass of the progenitor star was between eight and ten solar masses, balancing on the thin line between stars . who experience a violent supernova death and those who do not.

However, inconsistencies exist between the electron capture supernova 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 supernovae and now think that this type can also produce low-energy explosions, provided the star’s mass is sufficiently low.

To reduce uncertainty about the Crab’s precursor star and the nature of the explosion, the science team used Webb’s spectroscopic capabilities to examine two regions in the Crab’s inner filaments.

Theories predict that due to the different chemical composition of the core in an electron capture 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 of planets) . stars). 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 would support the scenario of a supernova with seemed to promote electron capture.

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

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

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

Thanks to the images and data collected by MIRI, the team was able to isolate the dust emission in the Crab and map it in high resolution for the first time. By mapping the warm dust emission with Webb and even combining it with the Herschel Space Observatory’s data on cooler dust grains, the team created a well-rounded picture of the dust distribution: the outer filaments contain relatively warmer dust, while cooler ones grains predominate. near the center.

The work has been published in The astrophysical diary letters.