Black hole caught shooting jets into cosmic void

Like a dragon spitting jets of fire, a black hole in the distant universe is spewing plumes of energy into the cosmos, forming jets that stretch 23 million light-years across. That’s 140 times the width of the Milky Way, enough to influence the evolution of the universe on scales never before seen.

An international team of astronomers announced the discovery today in the journal NatureThey named the massive jet formation Porphyrion, after a mythological Greek giant who warred with the gods for control of the cosmos. The astronomical Porphyrion is twice as large as the previous record-holder for jet formations, which was also named after a Greek giant (Alcyoneus), and was discovered by the new study’s lead author, Martijn Oei of Caltech and Leiden University in the Netherlands, and his colleagues in 2022.

The discovery of this massive flow of energy could change astronomers’ view of how these structures affect the universe as a whole. By pouring the energy of several galaxies into the cosmos, heating and stirring the vaporous matter between stars and galaxies, or even galaxy clusters, jets can stifle star formation and dictate the evolution of their cosmic neighborhoods—and the boundaries of that “neighborhood” may have just expanded dramatically.

Looking to the past

Porphyrion was discovered in data from a sky survey conducted using Europe’s LOFAR (LOw Frequency ARray) radio telescope. Radio waves are the best way to look for massive jets from black holes, which form when matter falls into a black hole. Most, if not all, massive galaxies contain supermassive black holes at their centers. But black holes are typically dark and invisible, observable mainly through the gravitational manipulation of the stars around them. But if matter begins to actively fall into a black hole, the turbulent swirl, like water in a sewer, can fling some of that matter back out at high speeds. It’s these jets that astronomers like Oei are tracking.

The LOFAR survey will eventually cover the entire Northern Hemisphere, but Oei and his colleagues only had access to about 15 percent of the sky. Even with this relatively small area, the survey found more than 11,000 jets longer than a megaparsec (3.26 million light-years). Before the survey, astronomers knew of only a few hundred.

With so much data, the team had to outsource some of the research. Machine learning algorithms helped to uncover some structures. But many jets were discovered by citizen scientists who pored over the images one by one. Martin Hardcastle of the University of Hertfordshire in the United Kingdom said at a news conference that most of the citizen science contributions came in early in the pandemic. “It slowed down a bit when people went back to work,” he said. But in three years, the project has been viewed a million times.

Porphyrion was the largest system yet discovered. Once identified, Oei and his colleagues had to figure out the source of the enormous energy outflows. Using telescopes in India, Arizona, and Hawaii, they probed deeper into Porphyrion’s corner of the sky and discovered a galaxy about 70 billion solar masses (about the size of M82), observed when the universe was just over 6 billion years old, about half its current age.

A long road ahead – to what end?

Porphyrion’s impressive length has astronomers wondering. So far, all of these huge jet systems on the order of megaparsecs have been discovered closer to Earth, that is, later in the 13.8 billion-year history of the Universe. Astronomers have mostly observed them in older, “red and dead” elliptical galaxies. While black holes can pour enormous amounts of energy into their jets (the equivalent of more than 100 galaxies in stars), it takes hundreds of millions of years for these jets to reach record lengths. Younger, star-producing galaxies were thought to be too unstable to sustain jets for such long periods.

But Porphyrion does exist, and at a much earlier time in the universe’s history, when it was more vibrant and compact than it is today. The relentless expansion of the universe means that 140 times the length of the Milky Way was an even more impressive distance 8 billion years ago, when the universe was smaller. Porphyrion’s long reach extends not only beyond its host galaxy, but two-thirds of the way into the cosmic void, the space between not just galaxies but superclusters of galaxies. That means its reach was truly cosmological, on the scale of the largest structures in the cosmos.

And this is just the largest of the 11,000 giant jet systems discovered (there are tens of thousands of other smaller jet systems). If jet systems like Porphyrion turn out to be common, as seems likely, they could have had a much bigger impact on the evolution of the universe than astronomers thought.

Astronomers have only realized in recent decades how closely linked the evolution of a galaxy and its central black hole are. When jets from such a black hole extend beyond the galaxy itself, their influence doesn’t stop. In addition to heating the fine matter of their host and stopping star formation, they can magnetize even finer matter between galaxies and galaxy clusters, a phenomenon that astronomers thought was a remnant of the Big Bang itself. But it’s now possible that black hole jets are the architects of this process, a subtle arrangement of the largest scales in the universe.

Discovering the giants

Astronomers must now determine whether their new hypotheses are true: Are these gigantic systems as common as they seem? Do they have such a large, hitherto unknown influence on the evolution of the universe? How do they manage to remain stable for so long in such a busy period of cosmic history?

LOFAR is expected to reveal tens of thousands more colossal jet systems as it continues to scan the sky. With thousands of them already identified in the first batch of data, machine learning can be used to speed up the search process on the new radio maps, providing many more clues for these investigations.

One thing is clear: Porphyrion, a leviathan in the depths of space, is no longer hidden.