Webb reveals new details of the Butterfly Nebula
The NASA/ESA/CSA James Webb Space Telescope has revealed new details in the core of the Butterfly Nebula, NGC 6302. From the dense, dusty torus that surrounds the star hidden at the centre of the nebula to its outflowing jets, the Webb observations reveal many new discoveries that paint a never-before-seen portrait of a dynamic and structured planetary nebula. Those new discoveries are published in a Monthly Notices of the Royal Astronomical Society science paper, to which Peter van Hoof from the Royal Observatory of Belgium and Joris Blommaert from the Vrije Universiteit Brussel (VUB) contributed.
Three views of the Butterfly Nebula, also called NGC 6302. The left and middle images shown here highlight the bipolar nature of the Butterfly Nebula in optical and near-infrared light captured by the NASA/ESA Hubble Space Telescope. The new Webb + ALMA image on the right zooms in on the centre of the Butterfly Nebula and its dusty torus, providing an unprecedented view of its complex structure. Credit: ESA/Webb, NASA& CSA, M. Matsuura, J. Kastner, K. Noll, ALMA (ESO/NAOJ/NRAO), M. Zamani (ESA/Webb). Source: https://esawebb.org/images/weic2517a.
The Butterfly Nebula, a bipolar planetary nebula
The Butterfly Nebula, located about 3400 light-years away in the constellation Scorpius, is one of the best-studied planetary nebulae in our galaxy. This stunning nebula was previously imaged by the NASA/ESA Hubble Space Telescope.
Planetary nebulae are among the most beautiful and most elusive creatures in the cosmic zoo. These nebulae form when stars with masses between about 0.8 and 8 times the mass of the Sun shed most of their mass at the end of their lives. The planetary nebula phase is fleeting, lasting only about 20 000 years.
Contrary to the name, planetary nebulae have nothing to do with planets: the naming confusion began several hundred years ago, when astronomers reported that these nebulae appeared round, like planets. The name stuck, even though many planetary nebulae aren’t round at all and the Butterfly Nebula is a prime example of the fantastic shapes that these nebulae can take.
The Butterfly Nebula is a bipolar nebula, meaning that it has two lobes that spread in opposite directions, forming the ‘wings’ of the butterfly. A dark band of dusty gas poses as the butterfly’s ‘body’. This band is actually a doughnut-shaped torus that’s being viewed from the side, hiding the nebula’s central star — the ancient core of a Sun-like star that energises the nebula and causes it to glow. The dusty doughnut may be responsible for the nebula’s insectoid shape by preventing gas from flowing outward from the star equally in all directions.
Picture of the Butterfly Nebula, NGC 6302, taken by the NASA/ESA Hubble Space Telescope. Credit: ESA/Webb, NASA & CSA, K. Noll, M. Zamani (ESA/Webb). Source: https://esawebb.org/images/weic2517d/.
New structures revealed by an international research team
This new Webb image zooms in on the centre of the Butterfly Nebula and its dusty torus, providing an unprecedented view of its complex structure. The image uses data from Webb’s Mid-InfraRed Instrument (MIRI) working in integral field unit mode. This mode combines a camera and a spectrograph to take images at many different wavelengths simultaneously, revealing how an object’s appearance changes with wavelength. The research team supplemented the Webb observations with data from the Atacama Large Millimetre/submillimetre Array (ALMA), a powerful network of radio dishes.
Researchers analysing these Webb data, including Peter van Hoof from the Royal Observatory of Belgium and Joris Blommaert from the VUB, identified nearly 200 spectral lines, each of which holds information about the atoms and molecules in the nebula. These lines reveal nested and interconnected structures traced by different chemical species.
The research team has pinpointed the location of the Butterfly Nebula’s central star, which heats a previously undetected dust cloud around it, making the latter shine brightly at the mid-infrared wavelengths that MIRI is sensitive to. The location of the nebula’s central star had remained elusive until now, because this enshrouding dust renders it invisible at optical wavelengths. Previous searches for the star lacked the combination of infrared sensitivity and resolution necessary to spot its obscuring warm dust cloud. With a temperature of 220 000 Kelvin, this is one of the hottest known central stars of a planetary nebula in our galaxy.
Image of the Butterfly Nebula, NGC 6302, which combined infrared data from the NASA/ESA/CSA James Webb Space Telescope with submillimetre observations from the Atacama Large Millimetre/submillimetre Array (ALMA). Credit: ESA/Webb, NASA & CSA, M. Matsuura, ALMA (ESO/NAOJ/NRAO), M. Zamani (ESA/Webb). Source: https://esawebb.org/images/weic2517b/.
This blazing stellar engine is responsible for the nebula’s gorgeous glow, but its full power is constrained by the dense band of dusty gas that surrounds it: the torus. The new Webb data show that the torus is composed of crystalline silicates like quartz as well as irregularly shaped dust grains. The dust grains have sizes on the order of a millionth of a metre — large, as far as cosmic dust is considered — indicating that they have been growing for a long time.
Outside the torus, the emission from different atoms and molecules takes on a multilayered structure. The ions that require the largest amount of energy to form are concentrated close to the centre, while those that require less energy are found farther from the central star. Iron and nickel are particularly interesting, tracing a pair of jets that blast outward from the star in opposite directions.
Intriguingly, the team also spotted light emitted by carbon-based molecules known as polycyclic aromatic hydrocarbons, or PAHs. They form flat, ring-like structures, much like the honeycomb shapes found in beehives. On Earth, we often find PAHs in smoke from campfires, car exhaust, or burnt toast. Given the location of the PAHs, the research team suspects that these molecules form when a ‘bubble’ of wind from the central star bursts into the gas that surrounds it. This may be the first-ever evidence of PAHs forming in a planetary nebula, providing an important glimpse into the details of how these molecules form.
The results have been published in Monthly Notices of the Royal Astronomical Society.
The complicated structure at the centre of the Butterfly Nebula, NGC 6302. There is a bright source at the centre of the image, labeled ‘dying star’. This is surrounded by greenish nebulosity and several looping lines in cream, orange and pink. One of these lines appears to form a ring oriented vertically and nearly edge-on around the bright source at the centre. This ring is labeled in several different places to indicate the near and far sides of a structure called the torus, a dust lane running along the torus and an area where the torus is ionised. Other lines trace out a figure eight shape. These lines are labeled to indicate the inner bubble as well as where the bubble intersects with the torus. Moving outward from these complex lines and green nebulosity, there is a section of red light on either side of the object, labeled ‘outer bubble’. The upper-right and lower-left corners of this image show a purple streak pointing out of the image. These purple streaks are labeled ‘jet’. Credit: ESA/Webb, NASA & CSA, M. Matsuura, ALMA (ESO/NAOJ/NRAO), M. Zamani (ESA/Webb). Source: https://esawebb.org/images/weic2517c/.
More information
Webb is the largest, most powerful telescope ever launched into space. This telescope is an international partnership between NASA, ESA and the Canadian Space Agency (CSA). Scientists of the Royal Observatory of Belgium are involved in several research projects using the Webb. See for example this news published on August 2023.
The science paper: Matsuura et al., The JWST/MIRI view of the planetary nebula NGC 6302 – I. A UV-irradiated torus and a hot bubble triggering PAH formation. Monthly Notices of the Royal Astronomical Society, Volume 542, Issue 2, September 2025, Pages 1287–1307, https://doi.org/10.1093/mnras/staf1194
This publication is adapted from an ESA press release. Other images of this news can be found on the ESA press release.