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.
