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Investigating the origins of the Crab Nebula with Webb

New data revise our view of this unusual supernova explosion.

The Crab Nebula is a nearby example of the debris left behind when a star undergoes a violent death in a supernova explosion. However, despite decades of study, this supernova remnant continues to maintain a degree of mystery: what type of star was responsible for the creation of the Crab Nebula, and what was the nature of the explosion? The NASA/ESA/CSA James Webb Space Telescope has provided a new view of the Crab, including the highest-quality infrared data yet available to aid scientists as they explore the detailed structure and chemical composition of the remnant. These clues are helping to unravel the unusual way that the star exploded about 1000 years ago.

Image of the Crab Nebula captured by Webb’s NIRCam and MIRI, with compass arrows, scale bar, and colour key for reference.The north and east compass arrows show the orientation of the image on the sky. Note that the relationship between north and east on the sky (as seen from below) is flipped relative to direction arrows on a map of the ground (as seen from above). The scale bar is labelled in light-years, which is the distance that light travels in one Earth-year. (It takes two years for light to travel a distance equal to the length of the bar.) One light-year is equal to about 9.46 trillion kilometres or 5.88 trillion miles. The field of view shown in this image is approximately 10 light-years across. This image shows invisible near-infrared and mid-infrared wavelengths of light that have been translated into visible-light colours. The colour key shows which components were observed by NIRCam and MIRI, and which visible-light colour is assigned to each feature. Credit: NASA, ESA, CSA, STScI, T. Temim (Princeton University) — Image of the Crab Nebula captured by Webb’s NIRCam and MIRI, with compass arrows, scale bar, and colour key for reference.
The north and east compass arrows show the orientation of the image on the sky. Note that the relationship between north and east on the sky (as seen from below) is flipped relative to direction arrows on a map of the ground (as seen from above).
The scale bar is labelled in light-years, which is the distance that light travels in one Earth-year. (It takes two years for light to travel a distance equal to the length of the bar.) One light-year is equal to about 9.46 trillion kilometres or 5.88 trillion miles. The field of view shown in this image is approximately 10 light-years across.
This image shows invisible near-infrared and mid-infrared wavelengths of light that have been translated into visible-light colours. The colour key shows which components were observed by NIRCam and MIRI, and which visible-light colour is assigned to each feature.
Credit: NASA, ESA, CSA, STScI, T. Temim (Princeton University)

A team of scientists used the NASA/ESA/CSA James Webb Space Telescope to parse the composition of the Crab Nebula, a supernova remnant located 6500 light-years away in the constellation Taurus. With the telescope’s MIRI (Mid-Infared Instrument) and NIRCam (Near-Infrared Camera), the team gathered data that are helping to clarify the Crab Nebula’s history.

The Crab Nebula is the result of a core-collapse supernova that was the death of a massive star. The supernova explosion itself was seen on Earth in 1054 CE and was bright enough to view during the daytime. The much fainter remnant observed today is an expanding shell of gas and dust, and an outflowing wind powered by a pulsar, a rapidly spinning and highly magnetised neutron star.

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

Past research efforts have calculated the total kinetic energy of the explosion based on the quantity and velocities of the present-day ejecta. Astronomers deduced that the nature of the explosion was one of relatively low energy (less than one-tenth that of a normal supernova), and the progenitor star’s mass was in the range of eight to 10 solar masses — teetering on the thin line between stars that experience a violent supernova death and those that do not.

However, inconsistencies exist between the electron-capture supernova theory and observations of the Crab, particularly the observed rapid motion of the pulsar. In recent years, astronomers have also improved their understanding of iron-core-collapse supernovae and now think that this type can also produce low-energy explosions, providing the stellar mass is adequately low.

To lower the level of uncertainty about the Crab’s progenitor star and the nature of the explosion, the science team used Webb’s spectroscopic capabilities to home in on two areas located within the Crab’s inner filaments.

Theories predict that because of the different chemical composition of the core in an electron-capture supernova, the nickel to iron (Ni/Fe) abundance ratio should be much higher than the ratio measured in our Sun (which contains these elements from previous generations of stars). Studies in the late 1980s and early 1990s measured the Ni/Fe ratio within the Crab using optical and near-infrared data and noted a high Ni/Fe abundance ratio that seemed to favour the electron-capture supernova scenario.

The Webb telescope, with its sensitive infrared capabilities, is now advancing Crab Nebula research. The team used MIRI’s spectroscopic abilities 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 elevated compared to the Sun, but only modestly so and much lower in comparison to 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 higher-mass 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.

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

The Crab Nebula seen in new light by Webb

The images and data collected by MIRI enabled the team to isolate the dust emission within 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 outermost filaments contain relatively warmer dust, while cooler grains are prevalent near the centre.

These findings have been accepted for publication in The Astrophysical Journal Letters.

The observations were taken as part of the Webb General Observer programme 1714.

The NASA/ESA/CSA James Webb Space Telescope dissected the Crab Nebula’s structure, aiding astronomers as they continue to evaluate leading theories about the supernova remnant’s origins. With the data collected by Webb’s NIRCam (Near-Infrared Camera) and MIRI (Mid-Infrared Instrument), a team of scientists were able to closely inspect some of the Crab Nebula’s major components.For the first time ever, astronomers mapped the warm dust emission throughout this supernova remnant. Represented here as fluffy magenta material, the dust grains form a cage-like structure that is most apparent toward the lower left and upper right portions of the remnant. Filaments of dust are also threaded throughout the Crab’s interior and sometimes coincide with regions of doubly ionised sulphur (sulphur III), coloured in green. Yellow-white mottled filaments, which form large loop-like structures around the supernova remnant’s centre, represent areas where dust and doubly ionised sulphur overlap. The dust’s cage-like structure helps constrain some, but not all of the ghostly synchrotron emission represented in blue. The emission resembles wisps of smoke, most notable toward the Crab’s centre. The thin blue ribbons follow the magnetic field lines created by the Crab’s pulsar heart — a rapidly rotating neutron star. Credit: NASA, ESA, CSA, STScI, T. Temim (Princeton University) — The NASA/ESA/CSA James Webb Space Telescope dissected the Crab Nebula’s structure, aiding astronomers as they continue to evaluate leading theories about the supernova remnant’s origins. With the data collected by Webb’s NIRCam (Near-Infrared Camera) and MIRI (Mid-Infrared Instrument), a team of scientists were able to closely inspect some of the Crab Nebula’s major components.
For the first time ever, astronomers mapped the warm dust emission throughout this supernova remnant. Represented here as fluffy magenta material, the dust grains form a cage-like structure that is most apparent toward the lower left and upper right portions of the remnant. Filaments of dust are also threaded throughout the Crab’s interior and sometimes coincide with regions of doubly ionised sulphur (sulphur III), coloured in green. Yellow-white mottled filaments, which form large loop-like structures around the supernova remnant’s centre, represent areas where dust and doubly ionised sulphur overlap.
The dust’s cage-like structure helps constrain some, but not all of the ghostly synchrotron emission represented in blue. The emission resembles wisps of smoke, most notable toward the Crab’s centre. The thin blue ribbons follow the magnetic field lines created by the Crab’s pulsar heart — a rapidly rotating neutron star.
Credit: NASA, ESA, CSA, STScI, T. Temim (Princeton University)

Press release from ESA Webb.

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The Crab Nebula – in the constellation Taurus – is seen in new light by James Webb Space Telescope as new details are uncovered

Although the Crab Nebula is one of the best-studied supernova remnants, questions about its progenitor, the nature of the explosion that created it still remain unanswered. The NASA/ESA/CSA James Webb Space Telescope is on the case as it sleuths for any clues that remain within the supernova remnant. Webb’s infrared sensitivity and spatial resolution are offering astronomers a more comprehensive understanding of the still-expanding scene.

The NASA/ESA/CSA James Webb Space Telescope has gazed at the Crab Nebula in the search for answers about the supernova remnant’s origins. Webb’s NIRCam (Near-Infrared Camera) and MIRI (Mid-Infrared Instrument) have revealed new details in infrared light.Similar to the Hubble optical wavelength image released in 2005, with Webb the remnant appears to consist of a crisp, cage-like structure of fluffy red-orange filaments of gas that trace doubly ionised sulphur (sulphur III). Within the remnant’s interior, yellow-white and green fluffy ridges form large-scale loop-like structures, which represent areas where dust particles reside. The area is composed of translucent, milky material. This material is emitting synchrotron radiation, which is emitted across the electromagnetic spectrum but becomes particularly vibrant thanks to Webb’s sensitivity and spatial resolution. It is generated by particles accelerated to extremely high speeds as they wind around magnetic field lines. The the synchrotron radiation can be traced throughout the majority of the Crab Nebula’s interior. Locate the wisps that follow a ripple-like pattern in the middle. In the centre of this ring-like structure is a bright white dot: a rapidly rotating neutron star. Further out from the core, follow the thin white ribbons of the radiation. The curvy wisps are closely grouped together, following different directions that mimic the structure of the pulsar’s magnetic field. Note how certain gas filaments are bluer in colour. These areas contain singly ionised iron (iron II). Credit: NASA, ESA, CSA, STScI, T. Temim (Princeton University) — The NASA/ESA/CSA James Webb Space Telescope has gazed at the Crab Nebula in the search for answers about the supernova remnant’s origins. Webb’s NIRCam (Near-Infrared Camera) and MIRI (Mid-Infrared Instrument) have revealed new details in infrared light.
Similar to the Hubble optical wavelength image released in 2005, with Webb the remnant appears to consist of a crisp, cage-like structure of fluffy red-orange filaments of gas that trace doubly ionised sulphur (sulphur III). Within the remnant’s interior, yellow-white and green fluffy ridges form large-scale loop-like structures, which represent areas where dust particles reside.
The area is composed of translucent, milky material. This material is emitting synchrotron radiation, which is emitted across the electromagnetic spectrum but becomes particularly vibrant thanks to Webb’s sensitivity and spatial resolution. It is generated by particles accelerated to extremely high speeds as they wind around magnetic field lines. The the synchrotron radiation can be traced throughout the majority of the Crab Nebula’s interior.
Locate the wisps that follow a ripple-like pattern in the middle. In the centre of this ring-like structure is a bright white dot: a rapidly rotating neutron star. Further out from the core, follow the thin white ribbons of the radiation. The curvy wisps are closely grouped together, following different directions that mimic the structure of the pulsar’s magnetic field. Note how certain gas filaments are bluer in colour. These areas contain singly ionised iron (iron II).
Credit: NASA, ESA, CSA, STScI, T. Temim (Princeton University)

The NASA/ESA/CSA James Webb Space Telescope has gazed at the Crab Nebula, a supernova remnant located 6500 light-years away in the constellation Taurus. Since this energetic event was recorded in 1054 CE by 11th-century astronomers, the Crab Nebula has continued to draw attention and additional study as scientists seek to understand the conditions, behaviour, and after-effects of supernovae by carefully studying this relatively close example.

With Webb’s NIRCam (Near-Infrared Camera) and MIRI (Mid-Infrared Instrument), the game is afoot as new details are uncovered—including the first complete map of dust distribution—in the search for answers about the Crab Nebula’s origins.

At first glance the general shape of the nebula is reminiscent of the 2005 optical wavelength image from the NASA/ESA Hubble Space Telescope. In Webb’s infrared observation, a crisp, cage-like structure of fluffy gaseous filaments are shown in red and orang. However, in the central regions, emission from dust grains (yellow-white and green) is mapped out by Webb for the first time. The Hubble and Webb images of this object can be contrasted here.

On the left is the 2005 Hubble optical wavelength image of the Crab Nebula. On the right is a new image of the object from the James Webb Space Telescope’s NIRCam (Near-Infrared Camera) and MIRI (Mid-Infrared Instrument) instruments that has revealed new details in infrared light.
In Webb’s infrared observation, a crisp, cage-like structure of fluffy red-orange filaments and knots of dust surround the object’s central area. However, some aspects of the inner workings of the Crab Nebula become more prominent and increase in detail in infrared light. In particular, Webb highlights what is known as synchrotron emission, seen here with a milky smoke-like appearance throughout the majority of the Crab Nebula’s interior.
Credit: NASA, ESA, CSA, STScI, T. Temim (Princeton University)

Additional aspects of the inner workings of the Crab Nebula become more prominent and are seen in greater detail in the infrared light captured by Webb. In particular, Webb highlights what is known as synchrotron radiation: emission produced from charged particles, like electrons, moving around magnetic field lines at relativistic speeds. The radiation appears here as milky smoke-like material throughout the majority of the Crab Nebula’s interior.

This feature is a product of the nebula’s pulsar, a rapidly rotating neutron star. The pulsar’s strong magnetic fields accelerate particles to extremely high speeds and cause them to emit radiation as they wind around magnetic field lines. Though emitted across the electromagnetic spectrum, the synchrotron radiation becomes particularly vibrant in the infrared with Webb’s NIRCam instrument.

To locate the Crab Nebula’s pulsar heart, trace the wisps that follow a circular ripple-like pattern in the middle to the bright white dot in the centre. Further out from the core, follow the thin white ribbons of the radiation. The curvy wisps are closely grouped together, outlining the structure of the pulsar’s magnetic fields, which sculpt and shape the nebula.

At centre left and right, the white material curves sharply inward from the filamentary dust cage’s edges and goes toward the neutron star’s location, as if the waist of the nebula is pinched. This abrupt slimming may be caused by the confinement of the supernova wind’s expansion by a belt of dense gas.

The wind produced by the pulsar heart continues to push the shell of gas and dust outward at a rapid pace. Notice how the filaments tend to be longer toward the upper right side of the nebula, in the same direction the pulsar is moving – not restricted by the belt of gas. Among the remnant’s interior, yellow-white and green mottled filaments form large-scale loop-like structures, which represent areas where dust grains reside.

The search for answers about the Crab Nebula’s past continues as astronomers further analyse the Webb data and consult previous observations of the nebula taken by other telescopes. Scientists will have newer Hubble data to review within the next year or so from the telescope’s reimaging of the supernova remnant. This will mark Hubble’s first look at the Crab Nebula in over 20 years, and will enable astronomers to more accurately compare Webb and Hubble’s findings.

Press release from ESA Webb.

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