European astronomers have detected a massive iron structure hidden within the iconic Ring Nebula, using a new instrument on the William Herschel Telescope. The bar-shaped cloud spans about 500 times the size of Pluto's orbit and holds iron equivalent to Mars's mass. Its origins remain unclear, prompting further investigation.
The Ring Nebula, a glowing shell of gas in the constellation Lyra first observed by Charles Messier in 1779, has revealed an unexpected feature. Located 2,600 light-years away and formed around 4,000 years ago, this planetary nebula results from a dying star ejecting its outer layers, much like the Sun is expected to do in billions of years.
A team from University College London and Cardiff University identified a narrow, bar-shaped cloud of iron deep inside the nebula's inner elliptical region. The structure, detailed in the Monthly Notices of the Royal Astronomical Society, measures roughly 500 times the length of Pluto's orbit around the Sun and contains iron mass comparable to Mars.
The discovery came through observations with the WEAVE instrument's Large Integral Field Unit (LIFU) mode on the 4.2-meter William Herschel Telescope at the Roque de los Muchachos Observatory. This setup, comprising hundreds of optical fibers, enabled detailed spectra across the entire nebula for the first time, mapping its composition at every point.
Lead author Dr. Roger Wesson, based at UCL's Department of Physics & Astronomy and Cardiff University, explained: "Even though the Ring Nebula has been studied using many different telescopes and instruments, WEAVE has allowed us to observe it in a new way, providing so much more detail than before. By obtaining a spectrum continuously across the whole nebula, we can create images of the nebula at any wavelength and determine its chemical composition at any position. When we processed the data and scrolled through the images, one thing popped out as clear as anything -- this previously unknown 'bar' of ionized iron atoms, in the middle of the familiar and iconic ring."
The iron bar's origin is mysterious. It might preserve details of the star's material ejection or represent remnants of a vaporized rocky planet from the star's earlier expansion phase. Co-author Professor Janet Drew of UCL emphasized: "We definitely need to know more -- particularly whether any other chemical elements co-exist with the newly-detected iron, as this would probably tell us the right class of model to pursue. Right now, we are missing this important information."
The team plans follow-up observations with WEAVE at higher resolution to detect co-existing elements and clarify formation. Dr. Wesson suggested similar structures may be common in other nebulae, while WEAVE Project Scientist Professor Scott Trager highlighted the instrument's potential for more discoveries. WEAVE will conduct eight major surveys over five years, including studies of ionized nebulae across the northern Milky Way.