() – Astronomers have observed a pair of enormous jets spewing out from a supermassive black hole 7.5 billion light-years from Earth. The megastructure spans 23 million light-years in length, making these black hole jets the largest ever seen, according to new research.
Black holes are seen as the garbage dumps of the universe, devouring almost everything that comes near them. But a fraction of material is ejected before an object falls in, forming a jet on either side of the black hole, said Martijn Oei, a postdoctoral researcher at the California Institute of Technology and lead author of a new study describing the discovery.
The findings were published on September 18 in the journal Nature.
Black hole jets can accelerate radiation and particles to close to the speed of light, causing them to glow in wavelengths visible to radio telescopes. Such a glow caught the attention of the astronomers responsible for the new study while they were observing the sky with Europe’s LOFAR (LOw Frequency ARray) radio telescope in 2018.
The newly described jets have an output power equivalent to that of trillions of suns and are so enormous that researchers have nicknamed the megastructure Porphyrion after a giant from Greek mythology.
The discovery has caused astronomers to reconsider their understanding of how large black hole jets can be, as well as how these giant features may affect their surroundings and the structure of the universe.
“This pair is not just the size of a solar system or a Milky Way — we’re talking about 140 Milky Way diameters in total,” Oei said. “The Milky Way would be a tiny dot in these two giant flares.”
Researchers were initially looking for something else with LOFAR: the wispy filaments of the cosmic web.
The cosmic web is the large-scale structure of the universe, a network of matter that permeates all the space between galaxies, Oei explained.
However, while looking to peer into the cosmic web, the team discovered large jets coming from galaxies. In total, the team detected 10,000 new pairs of black hole jets. A paper describing the pairs has been accepted for publication in another journal, Astronomy & Astrophysics.
“When we first found the giant jets, we were quite surprised,” Oei said. “We had no idea there were so many.”
Supermassive black holes are found at the centers of large galaxies. The team’s observations highlighted that an increasing number of galaxies have jets of black holes that reach far beyond their boundaries, Oei said.
A researcher in a different field, study co-author Aivin Gast, was the first to spot the larger pair of jets.
At the time, Gast was an undergraduate studying classical archaeology and ancient history at Oxford University. But due to the pandemic, his main academic work was put on hold, so he offered to help Oei with a visual inspection of the radio images captured by LOFAR.
“After finding Porphyrion, we were both very excited, and after talking about it I felt the thrill of seeing and co-discovering something special that no one had appreciated before,” Oei said via email.
Once the team confirmed the galaxy where the jets originated, “Aivin took advantage of its classical formation and proposed giving the system the beautiful name ‘Porphyrion,’ which it now bears,” Oei added.
Prior to the LOFAR observations, large jet systems were thought to be rare and expected to be smaller in size. Before Porphyrion was detected, the largest confirmed black hole jet system was Alcyoneus.
The same team found Alcyoneus, also named after a mythical Greek giant, in 2022, and this jet system is equivalent to about 100 Milky Way galaxies.
The Milky Way is estimated to have a diameter of 100,000 light years. One light year is the distance that light travels in one year, that is, 9.46 trillion kilometers.
However, the study’s authors took a broader approach, considering the Milky Way to be 163,078 light-years in diameter to account for all the stars and invisible matter within the galaxy, Oei said.
They therefore decided that Porphyrion is equivalent to 140 diameters of the Milky Way.
Now, the authors said they believe it may be possible to find jets larger than Porphyrion as radio telescope technology improves.
To uncover more details about the jets’ origin, the team conducted follow-up observations using the Giant Metal-Wave Radio Telescope in India and the W.M. Keck Observatory in Hawaii. The observations pointed to a distant galaxy about 10 times larger than the Milky Way.
Data collected by the Keck Observatory also revealed that the structures came from a black hole active in radiative mode, rather than the type known to produce larger jets, which surprised researchers.
As supermassive black holes flare, their gravitational pull heats up surrounding material, which releases energy in the form of radiation or jets. Radiative-mode black holes are more common in the distant universe, while jet-mode black holes are more common in the nearby universe, according to researchers.
“Our study suggests that radiatively active black holes might be just as capable of generating giant jets as jet-mode active black holes in the nearby universe,” Oei said in an email. “We found that giant jets may be a very old phenomenon: we now know that they have existed for most of the lifetime of the universe. Our LOFAR survey only covered 15 percent of the sky. And most of these giant jets are probably hard to detect, so we think there are many more of these behemoths out there.”
Understanding how long giant jets from black holes have existed over the 13.8 billion years of the universe could help astronomers figure out how the jets have influenced their environment.
Two big questions facing astronomers are how the universe became magnetized and how the large-scale structures of the cosmic web between galaxies formed. Black holes’ massive jets could help answer both.
If sustained for millions of years, powerful jets from black holes can affect the flow of matter through intergalactic space by releasing charged particles and magnetic fields into space, the study’s authors say.
“Whenever jets reach intergalactic space, we think they have a strong influence on heating the space between galaxies and on their magnetization,” Oei said. “One of the unexpected conclusions of finding this system of giant jets is that jets from black holes can reach the scale of the cosmic web. They are so large that they can reach, in principle, everywhere.”
The team’s research shows that Porphyrion was capable of heating its surroundings in intergalactic space by about a million degrees.
“If that warming occurred early enough in cosmic time,” Oei said, “it may have slowed the formation of galaxies, which require relatively cold intergalactic plasma or gas to collapse and form.”
The team continues to investigate how black hole jets can extend so far beyond their host galaxy without becoming unstable.
“Martijn’s work has shown us that there is nothing particularly special about the environments of these giant sources that makes them reach such large sizes,” said study co-author Martin Hardcastle, a professor of astrophysics at the University of Hertfordshire in England, in a statement.
The study reveals an exciting discovery, a “fossil record” of supermassive black hole activity that can show how the jets and the black hole have evolved over time, said Sasha Tchekhovskoy, an associate professor in the Department of Physics and Astronomy at Northwestern University.
“The remarkable longevity of the jets can also help us test physical models of the jets, in particular their stability in the face of low probabilities of successfully punching their way through (intergalactic space),” said Tchekhovskoy, who was not involved in the new study.
Porphyrion may also have magnetized its local environment, and Oei wants to understand how massive jets could spread magnetism through the cosmic web. The origin of magnetism is key because magnetic fields, like the one surrounding Earth, can protect and shield a life-supporting atmosphere.
“Our planet’s magnetism allows life to thrive, so we want to understand how it originated,” Oei said. “We know that magnetism permeates the cosmic web, then makes its way to galaxies and stars, and eventually to planets, but the question is: Where does it start? Have these giant jets spread magnetism throughout the cosmos?”
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