SPACE/COSMOS
Mysterious iron ‘bar’ discovered in famous nebula
image:
A composite RGB image of the Ring Nebula (also known as Messier 57 and NGC 6720) constructed from four WEAVE/LIFU emission-line images. The bright outer ring is made up of light emitted by three different ions of oxygen, while the ‘bar’ across the middle is due to light emitted by a plasma of four-times-ionised iron atoms. North is up and East is to the left in the image.
RGB key:- Red: the bar-shaped emission from four-times-ionized iron atoms in the [Fe V] spectral line at a wavelength of 4227 Angstrom (422.7 nm). Also shown in red, in the main ring, is emission in the [O I] 6300 Angstrom auroral line produced by neutral oxygen atoms. Green: emission in the [O II] 3727 Angstrom line pair emitted by singly-ionized oxygen atoms. Blue: emission in the [O III] 4959 Angstrom line of doubly-ionized oxygen atoms.
The angular dimensions of the image are 120 x 110 arcseconds on the sky (E-W x N-S), corresponding to physical dimensions of 95,000 x 87,000 Astronomical Units (AU) for the 787 parsec distance to the Ring Nebula. An Astronomical Unit is the mean distance from the Sun to the Earth.
view moreCredit: Roger Wesson et al / MNRAS
A mysterious bar-shaped cloud of iron has been discovered inside the iconic Ring Nebula by a European team led by astronomers at UCL (University College London) and Cardiff University.
The cloud of iron atoms, described for the first time in Monthly Notices of the Royal Astronomical Society, is in the shape of a bar or strip: it just fits inside the inner layer of the elliptically shaped nebula, familiar from many images including those obtained by the James Webb Space Telescope at infrared wavelengths1. The bar’s length is roughly 500 times that of Pluto’s orbit around the Sun and, according to the team, its mass of iron atoms is comparable to the mass of Mars.
The Ring Nebula, first spotted in 1779 in the northern constellation of Lyra by the French astronomer Charles Messier2, is a colourful shell of gas thrown off by a star as it ends the nuclear fuel-burning phase of its life. Our own Sun will expel its outer layers in a similar way in a few billion years’ time.3
The iron cloud was discovered in observations obtained using the Large Integral Field Unit (LIFU) mode of a new instrument, the WHT Enhanced Area Velocity Explorer (WEAVE)4, installed on the Isaac Newton Group’s 4.2-metre William Herschel Telescope5.
The LIFU is a bundle of hundreds of optical fibres. It has enabled the team of astronomers to obtain spectra (where light is separated into its constituent wavelengths) at every point across the entire face of the Ring Nebula, and at all optical wavelengths, for the first time.
Lead author Dr Roger Wesson, based jointly at UCL’s Department of Physics & Astronomy and Cardiff University, said: “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 ionised iron atoms, in the middle of the familiar and iconic ring.”
How the iron bar formed is currently a mystery, the authors say. They will need further, more detailed observations to unravel what is going on. There are two potential scenarios: the iron 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 vaporisation of a rocky planet caught up in the star’s earlier expansion.
Co-author Professor Janet Drew, also based at UCL Physics & Astronomy, said: “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 are working on a follow-up study, and plan to obtain data using WEAVE’s LIFU at higher spectral resolution to better understand how the bar might have formed.
WEAVE is carrying out eight surveys over the next five years, targeting everything from nearby white dwarfs to very distant galaxies. The Stellar, Circumstellar and Interstellar Physics strand of the WEAVE survey, led by Professor Drew, is observing many more ionised nebulae across the northern Milky Way.
Dr Wesson said: “It would be very surprising if the iron bar in the Ring is unique. So hopefully, as we observe and analyse more nebulae created in the same way, we will discover more examples of this phenomenon, which will help us to understand where the iron comes from.”
Professor Scott Trager, WEAVE Project Scientist based at the University of Groningen, added: “The discovery of this fascinating, previously unknown structure in a night-sky jewel, beloved by sky watchers across the Northern Hemisphere, demonstrates the amazing capabilities of WEAVE. We look forward to many more discoveries from this new instrument.”
1 See e.g. https://www.ucl.ac.uk/news/2023/aug/second-james-webb-image-ring-nebula-hints-dying-stars-companion
2 The Ring Nebula is also known as M 57 – the 57th listing in Messier’s catalogue of ‘Nebulae and Star Clusters’. John L E Dreyer also included it in his New General Catalogue, first published in 1888 by the Royal Astronomical Society, where it appears as NGC 6720.
3 Once a star like the Sun runs out of hydrogen fuel, it expands to become an extreme red giant and sheds its outer layers, which then coast out to form a glowing shell. A shell created in this way is known in astronomy as a planetary nebula. The leftover stellar core becomes a white dwarf, which, though no longer burning any fuel, continues to shine as it slowly cools over billions of years. The Ring Nebula is a planetary nebula located 2,600 light years (or 787 parsec) away, that is thought to have formed about 4,000 years ago. Planetary nebula ejection returns matter forged in a star to interstellar space and is the source of much of the Universe’s carbon and nitrogen – key building blocks of life on Earth. Stars more than about eight times the mass of the Sun age differently, ending life abruptly in a powerful explosion called a supernova as they collapse to form a black hole or neutron star.
4Funding for the WEAVE facility has been provided by UKRI STFC, the University of Oxford, NOVA, NWO, Instituto de Astrofísica de Canarias (IAC), the Isaac Newton Group partners (STFC, NWO, and Spain, led by the IAC), INAF, CNRS-INSU, the Observatoire de Paris, Région Île-de-France, CONACYT through INAOE, the Ministry of Education, Science and Sports of the Republic of Lithuania, Konkoly Observatory (CSFK), Max-Planck-Institut für Astronomie (MPIA Heidelberg), Lund University, the Leibniz Institute for Astrophysics Potsdam (AIP), the Swedish Research Council, the European Commission, and the University of Pennsylvania. The WEAVE Survey Consortium consists of the ING, its three partners, represented by UKRI STFC, NWO, and the IAC, NOVA, INAF, GEPI, INAOE, Vilnius University, FTMC – Center for Physical Sciences and Technology (Vilnius), and individual WEAVE Participants. The WEAVE website can be found at https://weave-project.atlassian.net/wiki/display/WEAVE and the full list of granting agencies and grants supporting WEAVE can be found at https://weave-project.atlassian.net/wiki/display/WEAVE/WEAVE+Acknowledgements.
5The William Herschel Telescope is the leading telescope of the Isaac Newton Group (ING), which in turn is part of the Roque de los Muchachos Observatory on La Palma, in the Canary Islands. The ING is jointly operated by the United Kingdom (STFC-UKRI), the Netherlands (NWO) and Spain (IAC, funded by the Spanish Ministry of Science, Innovation and Universities).
An illustrative set of 8 individual WEAVE LIFU emission-line images of the Ring Nebula. The colour in each panel tracks the brightness of emission, with brown-red being the most intense, shading through yellow and green to blue for the faintest emission. North is up and east, left.
The 4 emission line images that are combined in Figure 1 are shown separately in the top row. Left to right, the emission lines are: the [Fe V] 4227 Angstrom (422.7 nm) line due to four-times-ionized iron atoms; the [O I] 6300 Angstrom auroral line due to neutral oxygen atoms; the [O II] 3727 Angstrom line pair due to singly-ionized oxygen atoms; the [O III] 4959 Angstrom line due to twice-ionized oxygen atoms.
Bottom row, from left to right: emission in the 4861-Angstrom line that is produced as ionized hydrogen atoms recombine in the nebula; emission in the [N II] 6548 Angstrom line of singly-ionized nitrogen; emission in the C II 4267 Angstrom line resulting from the recombination of twice-ionized carbon atoms; emission in the [Ar V] 6435 Angstrom line by four-times-ionized argon.
Notice the very different appearance of the emission from four times ionized iron atoms (top left) compared to the emission from four-times-ionized argon atoms (bottom right) – usually, these ions of argon and iron arise in the same volume, as they require the same physical conditions.
The angular dimensions of each of the 8 frames are 120 x 110 arcseconds on the sky (E-W x N-S), corresponding to physical dimensions of 95,000 x 87,000 Astronomical Units (AU) at the 787 parsec distance of the Ring Nebula. An Astronomical Unit is the mean distance from the Sun to the Earth.
Credit
Roger Wesson et al / MNRAS
'Reborn' black hole spotted 'erupting like cosmic volcano'
Royal Astronomical Society
One of the most vivid portraits of “reborn” black hole activity – likened to the eruption of a “cosmic volcano” spreading almost one million light-years across space – has been captured in a gigantic radio galaxy.
The dramatic scene was uncovered when astronomers spotted the supermassive black hole at the heart of J1007+3540 restarting its jet emission after nearly 100 million years of silence.
Radio images revealed the galaxy locked in a messy, chaotic struggle between the black hole's newly ignited jets and the crushing pressure of the massive galaxy cluster in which it resides.
They have been published today in Monthly Notices of the Royal Astronomical Society after being obtained using highly sensitive radio interferometers – the Low Frequency Array (LOFAR) in the Netherlands and India’s upgraded Giant Metrewave Radio Telescope (uGMRT).
Most galaxies host a supermassive black hole, but only a few produce vast jets of radio-emitting magnetised plasma. J1007+3540 is unique, the international team of researchers behind the new study say, because it shows clear evidence of multiple eruptions – proof that its central engine has turned on, shut down, and restarted after long periods of quiet.
The radio images show a compact, bright inner jet, which lead researcher Shobha Kumari, of Midnapore City College in India, said was the unmistakable sign of the black hole’s recent awakening. Just outside it lies a cocoon of older, faded plasma – leftover debris from the black hole’s past eruptions, distorted and squeezed by the hostile environment around it.
“It’s like watching a cosmic volcano erupt again after ages of calm – except this one is big enough to carve out structures stretching nearly a million light-years across space”, Kumari added.
“This dramatic layering of young jets inside older, exhausted lobes is the signature of an episodic AGN – a galaxy whose central engine keeps turning on and off over cosmic timescales.”
The research was carried out by Kumari and co-authors Dr Sabyasachi Pal, of Midnapore City College, Dr Surajit Paul, associate professor at the Manipal Centre for Natural Sciences in India, and Dr Marek Jamrozy, of Jagiellonian University in Poland.
“J1007+3540 is one of the clearest and most spectacular examples of episodic AGN with jet-cluster interaction, where the surrounding hot gas bends, compresses, and distorts the jets,” Dr Pal said.
J1007+3540 lives inside a massive galaxy cluster filled with extremely hot gas. This environment creates enormous external pressure – far higher than what most radio galaxies experience. As the revived jets push outward, they are bent, squeezed, and distorted by the interaction with the dense medium.
The LOFAR image reveals that the northern lobe is compressed and dramatically distorted, the authors say, showing a curved backflow signature of plasma that seems to be shoved sideways by the surrounding gas.
The uGMRT image also shows that this compressed region has an ultra-steep radio spectrum, meaning the particles there are extremely old and have lost much of their energy – another sign of the cluster’s harsh influence.
The long, faint tail of diffuse emission stretching to the southwest tells an equally dramatic story, the researchers say. It shows that magnetised plasma is being dragged in a large extension through the cluster environment, leaving behind a wispy trail millions of years old. This, they add, suggests the galaxy is not just producing jets, it is also being shaped and sculpted by the powerful environment around it.
Systems such as J1007+3540 are extremely valuable to astronomers. They reveal how black holes turn on and off, how jets evolve over millions of years, and how cluster environments can reshape the entire morphological structure of a radio galaxy.
The combination of restarted activity, giant scale, and strong environmental pressure makes J1007+3540 a useful example of galaxy evolution in action. The authors say it shows that the growth of galaxies is not peaceful or gradual but rather a battle between the explosive power of black holes and the crushing pressure of the environments they live in.
By studying this galaxy, astronomers are gaining rare insight into:
- How often black holes switch between active and quiet phases
- How old radio plasma interacts with hot cluster gas
- How repeated eruptions can transform a galaxy’s surroundings over cosmic time
The research team now plans to use more sensitive, high-resolution observations to zoom even deeper into the core of J1007+3540 and track how the restarted jets propagate through this turbulent environment.
Understanding systems like J1007+3540 helps scientists piece together how galaxies grow, shut down, and awaken again, and how huge cosmic environments can shape, bend, distort, and even suffocate the jets that try to escape from their central engine.
ENDS
Media contacts
Sam Tonkin
Royal Astronomical Society
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Science contacts
Shobha Kumari
Midnapore City College in India
Images & captions
J1007+3540 radio image + optical image
Caption: This LOFAR DR2 image of J1007+3540 superimposed over an optical image by Pan-STARRS shows a compact, bright inner jet, indicating the reawakening of what had been a ‘sleeping’ supermassive black hole at the heart of the gigantic radio galaxy.
Credit: LOFAR/Pan-STARRS/S. Kumari et al.
Caption: The same images with labels showing the compressed northern lobe, curved backflow signature of plasma and the inner jet of the black hole.
Credit: LOFAR/Pan-STARRS/S. Kumari et al.
Further information
The paper ‘Probing AGN duty cycle and cluster-driven morphology in a giant episodic radio galaxy’ by S. Kumari et al. has been published in Monthly Notices of the Royal Astronomical Society. DOI: 10.1093/mnras/staf2038.
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Journal
Monthly Notices of the Royal Astronomical Society
Article Title
Probing AGN duty cycle and cluster-driven morphology in a giant episodic radio galaxy
Article Publication Date
15-Jan-2026
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