The James Webb Space Telescope has revealed extraordinary new details in the heart of the famous Butterfly Nebula, one of the most striking planetary nebulae in our galaxy.
Located around 3,400 light-years away in the constellation Scorpius, the Butterfly Nebula is one of the best studied planetary nebulae. Its 'wings' of glowing gas were previously captured in by the Hubble Space Telescope but Webb's new observations, published in Monthly Notices of the Royal Astronomical Society today, go even further, uncovering hidden structures and finally pinpointing the nebula's elusive central star.
Planetary nebulae like the Butterfly form when stars heavier than the sun reach the end of their lives, casting off their outer layers of gas and dust. The Butterfly Nebula is what astronomers call a bipolar nebula, meaning that it has two lobes of gas that spread in opposite directions to form the 'wings' of the butterfly. At its centre, a dense band of dusty gas called the torus, which poses as the butterfly's 'body'. This structure energises the nebula and may be responsible for its insect-like shape by preventing gas from flowing evenly in all directions.
Using James Webb's Mid-Infrared Instrument (MIRI), scientists have now been able to see through this dusty torus for the first time, providing an unprecedented view of its complex structure.
By combining images at many different wavelengths with complementary data from the Atacama Large Millimetre/submillimetre Array in Chile, the international team of researchers, including from The University of Manchester, discovered the butterfly's central star, one of the hottest ever found in our galaxy, with a scorching surface temperature of around 220,000 Kelvin.
Although this intense heat powers the nebula's colourful glow, earlier telescopes lacked the sensitivity and resolution needed to see through the thick layer of dust, making the star impossible to detect at visible wavelengths.
Professor Albert Zijlstra, a co-author of the paper from The University of Manchester, said: "This is an extraordinary discovery. We're looking at one of the hottest stars ever found - an object so elusive that even Hubble couldn't detect it for decades. Thanks to JWST, we've finally uncovered it, concealed within its own dense shroud of dust.
"Surrounding the star is a massive dark torus, the heaviest ever observed around such an object, containing more material than our own Sun. Even Webb can't fully pierce through it. Inside, the environment is sheer chaos; powerful radiation and stellar winds tearing into the surrounding cloud. It's unlike anything I've ever seen.
"Most planetary nebulae appear graceful and symmetric, but this one is still at the beginning of its transformation - it's more like a butterfly struggling out of its cocoon than the elegant shapes we're used to seeing."
The Webb data revealed that the torus is composed of crystals similar to quartz as well as unusually large grains of dust, suggesting they have been growing for a long time. Outside the torus, the team observed jets of iron and nickel blasting away from the star in opposite directions, along with a multilayered structure made up of different atoms and molecules.
Perhaps most intriguing was the discovery of carbon-based molecules known as polycyclic aromatic hydrocarbons, or PAHs. On Earth, these molecules are found in smoke from fires or even burnt toast - but they have never before been seen in an oxygen-rich planetary nebula. The team believes the PAHs may form when a bubble of stellar wind bursts into the surrounding gas.
The finding provides an important glimpse into the details of how these molecules form.
