A supermassive black hole in a distant galaxy cluster has erupted after approximately 100 million years of complete silence, unleashing a jet of magnetised plasma across nearly a million light-years of space in what the astronomers who observed it have described as a cosmic volcano coming back to life after ages of calm

Every large galaxy in the observable universe is thought to host a supermassive black hole at its centre. Most of the time, on the available observational evidence, these black holes are dormant. They accrete only tiny amounts of matter from their immediate surroundings, emit only faint radiation, and produce no visible jets. From cosmic distances, they are effectively invisible.

Occasionally, and for reasons that remain incompletely understood, a supermassive black hole enters an active phase. Matter falls onto its accretion disk in substantially greater quantities. The disk heats. Intense magnetic fields channel charged particles from the poles of the black hole into two focused beams that stream outward at relativistic speeds. The beams, when they encounter the diffuse gas of the surrounding intergalactic medium, produce enormous lobes of radio-emitting plasma that can extend for hundreds of thousands or millions of light-years from the galaxy.

An active supermassive black hole is one of the most powerful engines in the universe. It is also, on the observational record, a temporary phenomenon. The active phase lasts for a period, and then, on timescales that vary from tens of millions to hundreds of millions of years, the black hole shuts down again.

Whether an individual black hole ever restarts, and if it does, how frequently, and what conditions produce the restart, are questions astronomers have been trying to resolve for approximately half a century.

The galaxy that woke up

The galaxy is called J1007+3540. It lies at the centre of a galaxy cluster called WHL 100706.4+354041, at a distance of several hundred million light-years from Earth. The host galaxy itself is an evolved elliptical, with a stellar population approximately 12 billion years old and a total stellar mass of approximately 100 billion solar masses. The supermassive black hole at its centre is substantially larger than the one at the centre of the Milky Way.

In January 2026, a research team led by Shobha Kumari at Midnapore City College in India, with collaborators Sabyasachi Pal, Surajit Paul, and Marek Jamrozy, published a paper in Monthly Notices of the Royal Astronomical Society reporting the detailed radio-frequency observations of the galaxy and its central black hole. The observations, which combined data from two of the world’s most sensitive radio telescopes, revealed a specific and unusual configuration of features at the galaxy’s centre.

The most striking feature was the presence of two distinct plasma structures in the same image. The outer structure was a pair of large, diffuse lobes extending for approximately 1.45 megaparsecs, or roughly 4.7 million light-years, across the surrounding intergalactic space. The plasma in the outer lobes was faded and low-frequency, with a radiative age of approximately 240 million years, indicating that the lobes had been produced by an active phase of the black hole that had ended a very long time ago.

Inside the outer lobes, and clearly separate from them, was a second, brighter, more compact plasma structure. This inner structure was substantially younger, with a radiative age of approximately 140 million years, and its bright, compressed morphology was consistent with the signature of a fresh, active jet still being produced by the black hole.

The interpretation of the combined data was direct. The black hole at the centre of J1007+3540 had been active in the distant past, had gone completely dormant for approximately 100 million years, and had then restarted. The old faded lobes and the new active jets were both visible in a single image of the same galaxy, capturing a supermassive black hole caught mid-cycle in the act of restarting itself.

The environmental struggle

The freshly launched jets are not, on the available observations, propagating in the smooth outward pattern that would be expected in an empty medium. They are being bent, compressed, and distorted by the crushing external pressure of the hot gas that fills the surrounding galaxy cluster.

The intracluster medium, as this hot gas is called, exerts substantially higher pressure on the plasma of the emerging jets than most radio galaxies experience. On the Kumari team’s imaging, the northern lobe of the fresh jet is visibly compressed and curved sideways rather than expanding freely outward. Its plasma appears to be curling back toward the source rather than continuing to stream away. The southern jet is distorted into an elongated S-shape, extends outward for approximately 250 kiloparsecs, then dissipates into an offset diffuse tail that reaches approximately 600 kiloparsecs from the host galaxy.

Co-author Dr Sabyasachi Pal described J1007+3540 as one of the clearest and most spectacular examples of episodic active galactic nuclei with jet-cluster interaction currently known. The Royal Astronomical Society, in its announcement of the finding, quoted lead researcher Shobha Kumari describing the event as “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.”

How the observations were made

The observations combined data from two of the world’s most sensitive low-frequency radio telescopes. The first was the Low Frequency Array, or LOFAR, a distributed network of radio antennas centred in the Netherlands and extending across Europe, which observed J1007+3540 as part of the LOFAR Two-metre Sky Survey second data release (LoTSS DR2) at 144 megahertz. The second was the upgraded Giant Metrewave Radio Telescope, or uGMRT, in Maharashtra, India, which observed the same source at 400 megahertz.

The two frequencies together allowed the Kumari team to distinguish between the older and newer plasma populations in the galaxy. The older, more distant lobes emit predominantly at low frequencies, because the electrons that produce their radiation have lost energy through synchrotron radiation over the intervening 240 million years. The younger, brighter inner jets emit at both frequencies more strongly. The frequency-dependent contrast between the two structures was the specific observational signature that allowed the team to separate the two cycles of activity and to estimate their respective ages.

What it means

The J1007+3540 observations resolve a specific and long-standing question about supermassive black hole activity. Whether individual black holes cycle between active and dormant phases had been debated for decades, and the evidence for episodic activity had been largely circumstantial. The presence of both old dead lobes and new active jets in a single galaxy, imaged simultaneously in the same observation, provides direct visual confirmation that at least some supermassive black holes are episodic engines that can cycle between dormancy and activity over timescales of hundreds of millions of years.

The specific timescale of J1007+3540’s dormancy is also informative. Approximately 100 million years is substantially longer than the timescales over which most other observed black hole reactivations have been documented. It suggests that the mechanisms driving the shutdown and restart of these central engines operate over intervals comparable to the evolution of species on Earth, and that any single supermassive black hole may experience multiple such cycles across the age of its host galaxy.

The environmental interaction is a second finding that extends beyond the specific case. The jets emerging from J1007+3540 are being visibly bent and compressed by their surroundings, which means that the shape of a galaxy’s radio structure is not determined solely by its central black hole. The pressure, temperature, and density of the surrounding intergalactic medium can, on the available observations, substantially reshape the jets that a black hole produces, and any complete model of black hole jet evolution must include the effects of the environment through which the jets propagate.

The black hole at the centre of J1007+3540 has been silent for longer than modern humans have existed as a species.

It has now started erupting again.

The astronomers watching it are seeing, in a single image, both the fresh eruption and the fossilised wreckage of the eruption that came before it.