Science & Technology (Commonwealth Union) – A previously unknown, bar-like cloud of iron has been identified within the famous Ring Nebula by a European research group led by astronomers from UCL and Cardiff University.
The structure, composed of iron atoms and reported for the first time in Monthly Notices of the Royal Astronomical Society, appears as a narrow strip that sits neatly inside the nebula’s inner elliptical shell—well known from numerous images, including infrared observations captured by the James Webb Space Telescope. The feature stretches to a length around 500 times the size of Pluto’s orbit, and the researchers estimate that the total iron mass is roughly equivalent to that of Mars.
The Ring Nebula was first observed in 1779 by French astronomer Charles Messier in the northern constellation of Lyra. It is a vivid envelope of gas expelled by a star as it reaches the end of its nuclear fuel-burning lifetime—a process our own Sun is expected to undergo several billion years from now.
The iron structure was revealed through observations made with the Large Integral Field Unit (LIFU) mode of the recently commissioned WHT Enhanced Area Velocity Explorer (WEAVE), an instrument mounted on the Isaac Newton Group’s 4.2-metre William Herschel Telescope.
The LIFU consists of hundreds of tightly packed optical fibres, allowing astronomers to capture spectra—by splitting light into its component wavelengths—at every location across the full surface of the Ring Nebula and across the entire optical range for the first time.
Dr Roger Wesson, the study’s lead author from UCL’s Department of Physics & Astronomy and Cardiff University, indicated that although the Ring Nebula has been examined with numerous telescopes and instruments over the years, WEAVE has given us a completely new perspective, revealing far greater detail than ever before. Dr Wesson further indicated that by recording a continuous spectrum across the entire nebula, they can generate images at any chosen wavelength and pinpoint the chemical makeup at each point within it.
“When we processed the data and scrolled through the images, one thing popped out as clear as anything – this previously unknown ‘bar’ of ionised iron atoms, in the middle of the familiar and iconic ring.”
The researchers say the origin of the iron bar remains unclear. More precise and detailed observations will be required to determine how it formed. They outline two main possibilities: the structure could offer fresh insight into how material was expelled from the nebula by its central star, or—more provocatively—it may represent an extremely elongated arc of plasma created when a rocky planet was vaporised during an earlier phase of the star’s expansion.
Co-author Professor Janet Drew of UCL indicated that there is still much they do not know—especially whether other chemical elements are present alongside the newly identified iron and that information would likely point them toward the correct theoretical model. Professor Drew further indicated that at the moment, this crucial evidence is missing.
The team is now preparing a follow-up investigation and intends to collect higher-resolution spectral data using WEAVE’s LIFU instrument to shed more light on the possible formation of the bar.
Over the next five years, WEAVE will conduct eight major surveys, studying objects ranging from nearby white dwarfs to galaxies at extreme distances. One of these programmes—the Stellar, Circumstellar and Interstellar Physics survey, led by Professor Drew—is examining numerous ionised nebulae throughout the northern Milky Way.
Dr Wesson further indicated that it would be remarkable if the iron bar observed in the Ring Nebula were a one-off as they continue to observe and analyse other nebulae formed through similar processes, they expect to find additional examples, helping us to uncover the true origin of the iron.
