Astronomers using the WHT Enhanced Area Velocity Explorer (WEAVE), a powerful new instrument mounted on the William Herschel Telescope on La Palma, have detected an unexpected, elongated structure of ionized iron inside the famous Ring Nebula.
A composite image of the Ring Nebula constructed from four WEAVE/LIFU emission-line images. Image credit: Wesson et al., doi: 10.1093/mnras/staf2139.
The Ring Nebula is an archetypal planetary nebula about 2,000 light-years away in the constellation of Lyra.
Otherwise known as Messier 57, M57 or NGC 6720, this nebula was discovered by the French astronomer Charles Messier while searching for comets in January 1779.
Messier’s report of his independent discovery of Comet Bode reached the French astronomer Antoine Darquier de Pellepoix two weeks later, who then independently rediscovered the Ring Nebula while following the comet.
The newly-discovered bar-shaped cloud of iron atoms fits inside the inner layer of the elliptically shaped nebula.
The cloud’s length is roughly 500 times that of Pluto’s orbit around the Sun and its mass of iron atoms is comparable to the mass of Mars.
The cloud was discovered in observations obtained using the Large Integral Field Unit (LIFU) mode of the new WEAVE instrument on the Isaac Newton Group’s 4.2-m William Herschel Telescope.
“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,” said Dr. Roger Wesson, an astronomer at University College London and Cardiff University.
“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 nature of the iron ‘bar’ in the Ring Nebula is unclear.
There are two potential scenarios: the bar may reveal something new about how the ejection of the nebula by the parent star progressed, or (more intriguingly) the iron might be an arc of plasma resulting from the vaporization of a rocky planet caught up in the star’s earlier expansion.
“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,” said Professor Janet Drew, an astronomer at University College London.
“Right now, we are missing this important information.”
The findings were published today in the Monthly Notices of the Royal Astronomical Society.
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R. Wesson et al. 2026. WEAVE imaging spectroscopy of NGC 6720: an iron bar in the Ring. MNRAS 546 (1): staf2139; doi: 10.1093/mnras/staf2139
