Cosmic monster: 23 million light-years-wide black hole jets discovered by Caltech

Astronomers have discovered the largest known black hole jets, stretching an astonishing 23 million light-years. To put it in perspective, that’s the length of 140 Milky Way galaxies aligned end-to-end.

Dubbed “Porphyrion” after a mythological Greek giant, this immense structure originates from a period when the universe was just 6.3 billion years old, roughly half its current age of 13.8 billion years. The powerful jets emerge from a supermassive black hole located at the core of a distant galaxy, projecting in opposite directions.

“Black hole jets like Porphyrion’s are very powerful: in this case, the two jets have a combined power of 10^39 watts! That is equivalent to the energy output of trillions of stars, or about 100 galaxies combined,” Martijn Oei, a Caltech postdoctoral scholar and lead author of a new paper reporting the findings, told Interesting Engineering .

“This pair is not just the size of a solar system, or a Milky Way; we are talking about 140 Milky Way diameters in total,” he says. “The Milky Way would be a little dot in these two giant eruptions.”

Black hole jets shaping the early universe

This new discovery indicates that massive jet systems like Porphyrion may have played a more significant role in shaping galaxies in the early universe than once thought. Porphyrion formed during a period when the cosmic web — the delicate network of filaments that link and nourish galaxies — was more tightly packed than it is today.

As a result, colossal jets like Porphyrion spanned a larger portion of this interconnected structure, influencing a wider area compared to similar jets in our present universe.

Oei explains, “In the last few decades, astronomers have done numerous observations and numerical simulations that show that the heat dissipated by black hole jets warms the interstellar medium (ISM). This increases the pressure of the ISM, and prevents gas clouds from collapsing into stars.”

“So, black hole jets slow down the formation of new stars. This ’stellar birth control’ makes sure that galaxies don’t evolve too quickly, causing them to remain more youthful than if black hole jets wouldn’t exist.”

He explains further: “You can quantify how energetic jets are through their power—equivalent to the energy released during the most cataclysmic cosmic collisions: i.e. those that occur when two galaxy clusters (each sometimes containing thousands of galaxies!) merge together.”

“So jet systems like Porphyrion appear to be among the most energetic ’spectacles’ that have occurred in the Universe post-Big Bang.”

Identifying Porphyrion’s parent galaxy

To identify the galaxy responsible for Porphyrion, researchers utilized the Giant Metrewave Radio Telescope (GMRT) in India, supplemented by data from the Dark Energy Spectroscopic Instrument (DESI) project at Kitt Peak National Observatory in Arizona.

Their observations traced the origin of these jets to a massive galaxy, about 10 times the size of the Milky Way. Further analysis with the W. M. Keck Observatory in Hawai‘i revealed that Porphyrion lies a staggering 7.5 billion light-years away from Earth.

“Up to now, giant jets have been seen mostly in the more recent or ’nearby’ Universe. In the nearby Universe, most active black holes are of the ‘jet-mode’ type: of all the energy they send off to the outer parts of their galaxy (and beyond), most is in the form of jets,” says Oei.

“As we are building more sensitive instruments, as we have done with the International LOFAR Telescope over the last two decades or so, we are starting to see giant jet systems in the more distant Universe.”

“Porphyrion is one such example. The surprising thing is that we see that Porphyrion does not come from a jet-mode active black hole, but from a radiative-mode black hole — like the quasars of the young Universe.”

Spreading magnetism

How the jets can extend so far beyond their host galaxies without destabilizing is still unclear. “My interpretation is that we need an unusually long-lived and stable accretion event around the central, supermassive black hole to allow it to be active for so long—about a billion years—and to ensure that the jets keep pointing in the same direction over all of that time,” says Martin Hardcastle, second author of the study.

Next, Oei aims to delve deeper into how these colossal jet systems affect their environment. The jets distribute cosmic rays, heat, heavy elements, and magnetic fields across the regions between galaxies .

Oei’s main focus is to explore how extensively these massive jets contribute to the spread of magnetism in the surrounding space. “Up to now, because giant jets appeared to be so rare, the possibility that giant jets may have created the cosmic seed field from which modern magnetic fields arose, had not been considered.

“That is why I now want to investigate in more detail whether, and precisely how, giant jets produced the cosmic seed fields.”

The study has been published in the journal Nature.