Astronomers have uncovered the most massive pair of black hole jets ever observed, spanning an astonishing 23 million light-years in length. To put that in perspective, this structure, dubbed "Porphyrion" after a giant in Greek mythology, is equivalent to aligning 140 Milky Way galaxies back to back.
"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," said Martijn Oei, a postdoctoral scholar at Caltech and lead author of a paper published in *Nature*. "The Milky Way would be a little dot in these two giant eruptions."
Porphyrion's powerful jets, generated by a supermassive black hole at the heart of a distant galaxy, eject hot plasma far beyond its host galaxy, reaching well into the intergalactic space. These jets existed when the universe was 6.3 billion years old, less than half its current age of 13.8 billion years. Their energy output is equivalent to that of trillions of suns.
Larger Than Ever Before
Before this discovery, the largest confirmed jet system was Alcyoneus, spanning 100 Milky Ways, discovered by the same team in 2022. In comparison, the well-known Centaurus A jets, located relatively close to Earth, span just 10 Milky Ways.
The discovery of Porphyrion suggests that such enormous jet systems may have played a more significant role in galaxy formation in the early universe than previously thought. The system existed during a time when the cosmic web—the vast network of filaments connecting galaxies—was more densely packed than it is today, allowing jets like Porphyrion to influence a greater portion of intergalactic space.
"Jets can spread vast amounts of energy that affect the growth of their host galaxies and those nearby," explained George Djorgovski, co-author and professor of astronomy at Caltech. "This discovery shows that their effects can extend much farther than we previously imagined."
A Sky Survey Unearths Thousands of Giants
Porphyrion is the largest system found during a massive sky survey conducted with the LOFAR (LOw Frequency ARray) radio telescope in Europe. The survey revealed more than 10,000 faint but massive jet systems. Previously, astronomers knew of only a few hundred such systems, which were thought to be much rarer.
"Giant jets were known before we started the campaign, but we had no idea there would be so many," said Martin Hardcastle, co-author and professor of astrophysics at the University of Hertfordshire, England. "Seeing so many of these objects emerge was truly exciting."
The survey covered only 15% of the sky, and the team believes many more colossal jet systems are waiting to be discovered.
A Look Back in Time
To trace the origins of Porphyrion's jets, the team used India’s Giant Metrewave Radio Telescope (GMRT) and additional data from the Dark Energy Spectroscopic Instrument (DESI) in Arizona. Their observations revealed that the jets originated from a galaxy 7.5 billion light-years from Earth, about 10 times more massive than the Milky Way.
Surprisingly, Porphyrion emerged from what astronomers call a "radiative-mode" active black hole, previously not believed to produce jets of such magnitude. This mode was more common in the early universe, suggesting that many more colossal jet systems could be found in the distant cosmos.
"We may be looking at the tip of the iceberg," Oei said. "Many of these giant jets are likely difficult to spot, so there are probably many more of these behemoths out there."
Ongoing Mysteries
How these jets can remain stable over such vast distances is still an unsolved mystery. Theories suggest that an unusually long-lived and stable accretion event around the central black hole might be responsible for the jets' persistence over billions of years.
As the study of these jet systems continues, astronomers are particularly interested in their effects on the surrounding cosmos. Jets like Porphyrion spread cosmic rays, heat, heavy elements, and magnetic fields throughout intergalactic space. Oei is keen to understand how they contribute to spreading magnetism across the universe.
"The magnetism on our planet allows life to thrive, so we want to understand how it came to be," Oei added. "Have these giant jets spread magnetism through the cosmos?"
With this discovery, scientists are poised to learn more about the forces shaping galaxies and the universe itself. Porphyrion represents not just a record-breaking find, but also a window into the powerful processes that shaped the early universe.
California Institute of Technology. “Astronomers Discover Biggest Ever Seen Black Hole Jets, Which Blast Hot Plasma Well beyond Their Own Host Galaxy.” Phys.org, Phys.org, 18 Sept. 2024, phys.org/news/2024-09-astronomers-biggest-black-hole-jets.html. Accessed 19 Sept. 2024.
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