This artist's illustration shows Porphyrion, the largest black hole jet system ever observed. Its jets span about 23 million light-years, or 140 Milky Way galaxies lined up end-to-end. Credit: E. Wernquist/D. Nelson (IllustrisTNG Collaboration)/M. Oei
Like a dragon breathing out puffs of fire, a black hole in the distant universe is spewing plumes of energy into the cosmos, forming jets that stretch across 23 million light-years. 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 NatureThe massive jet formation was named Porphyrion, after a mythological Greek giant who battled the gods for control of the cosmos. The astronomical Porphyrion is twice as large as the previous jet formation record holder, which was also named after a Greek giant (Alcyoneus), and which was discovered by the new study's lead author, Martijn Oei of Caltech and Leiden University in the Netherlands, and colleagues in 2022.
The discovery of this enormous energy output could change astronomers' view of how these structures affect the universe at large. By pouring the energy equivalent of many galaxies into the cosmos, heating and stirring the tenuous material found between stars and galaxies and even galaxy clusters, the jets can slow star formation and dictate the evolution of their cosmic neighborhoods — and the boundaries of that “neighborhood” may have just gotten a lot bigger.
Looking back
Porphyrion was discovered from data from a sky survey using the European satellite Lofar (LOw Frequency ARray). Radio waves are the best way to look for massive black hole jets, which form when material 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 primarily by their gravitational manipulation of the stars around them. But if material starts actively falling into a black hole, the turbulent swirl — like water in a drain — can eject some of that material at high speeds. These are the jets that astronomers like Oei are looking for.
Although the LOFAR survey will eventually cover the entire Northern Hemisphere, Oei and his colleagues only had access to about 15 percent of the sky. Even with that comparatively small space, the survey found more than 11,000 jets spanning more than a megaparsec (3.26 million light-years) in length. Before the survey, astronomers knew of only a few hundred.
With so much information, the team had to outsource some of the search. Machine learning algorithms uncovered some of the structures, but many of the jets were discovered by citizen scientists who analyzed the images one by one. Martin Hardcastle of the University of Hertfordshire in the U.K. said during a press conference that they received most of their citizen science contributions during the early days of the pandemic. “It slowed down a bit when people went back to work,” he said. But within three years, the project had received a million views.
Porphyrion was the largest system found. Once identified, Oei and his colleagues needed to determine the source of the enormous streams of energy. Using telescopes in India, Arizona, and Hawaii, they explored Porphyrion's corner of the sky deeper and found a galaxy of about 70 billion solar masses (about the size of M82), seen when the universe was a little over 6 billion years old, about half its current age.
A long road: to what end?
Porphyrion’s extraordinary length is raising questions among astronomers. Until now, all huge megaparsec-scale jet systems had been found closer to Earth — that is, later in the universe’s 13.8-billion-year history. Astronomers saw them mostly in older, “red and dead” elliptical galaxies. While black holes can pour enormous amounts of energy into their jets — more than a hundred star-filled galaxies — it takes hundreds of millions of years for such jets to stretch to record lengths. Younger galaxies, where stars are forming, were thought to be too unstable to sustain jets for that long.
But Porphyrion does exist, and at a much earlier time in the history of the universe, when it was more dynamic 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 not only extends beyond its host galaxy, but encompasses two-thirds of the cosmic void – the space between not just galaxies, but superclusters of galaxies. This means that its reach was truly cosmological, on a scale of the largest structures in the cosmos.
And it is only the largest of 11,000 huge jet systems discovered (there are many tens of thousands more smaller jet systems). If jet systems like Porphyrion turn out to be common, as seems likely, then they may have had a much bigger impact on the evolution of the universe than astronomers previously believed.
Astronomers have come to realize in recent decades how deeply intertwined the evolution of a galaxy and its central black hole are. When jets from such a black hole pass beyond the galaxy itself, their influence doesn’t stop. In addition to heating the thin material inside their host and halting star formation, they can magnetize the even vaporier material between galaxies and galaxy clusters — a phenomenon that astronomers thought might be a relic of the Big Bang itself. But it’s now possible that jets from black holes are the architects of this process, a subtle ordering of the universe’s largest scales.
Discovering the giants
Astronomers now have the task of finding out whether their new hypotheses are true: Are these gigantic systems as common as they suddenly seem? Do they have an equally large, hitherto undiscovered influence on the evolution of the universe? How do they remain stable for so long at such a turbulent time in cosmic history?
LOFAR should reveal tens of thousands more colossal jet systems as it continues to scan the skies. With thousands already identified in the first batch of data, machine learning can be used to speed up the search process in the new radio maps, providing abundant material for these investigations.
One thing is clear: Porphyrion, a leviathan in the depths of space, is no longer hidden.
Leave feedback about this