The largest-ever pair of radiation jets has been discovered bursting out of a distant supermassive black hole, burning brighter than 100 galaxies, or over a trillion stars.
From the end of one jet to the end of the other, the pair measures roughly 7 megaparsecs or about 23 million light-years, making them the longest jets ever found, according to a new paper in the journal Nature.
Before these jets—nicknamed Porphyrion after a giant in ancient Greek myth—were discovered, it was thought that supermassive black hole jets couldn't get larger than 5 megaparsecs, or about 16 million light-years.
"The key finding is that jets from black holes can, if circumstances are right, become as large as the universe's major cosmic structures (galaxy clusters, cosmic filaments, cosmic voids)," Martijn Oei, a researcher at the California Institute of Technology, Pasadena, told Newsweek. "This means that individual black holes can have a sphere of influence that extends way beyond the galaxy in which they reside. In the case of Porphyrion (our newly found jet pair), the jets reach places 140 Milky Way galaxies apart."
"The two jets combined have a jet power of 1039 watts! That's equivalent to the energy output of trillions of suns, or ~100 galaxies," Oei said.
Supermassive black hole jets are powerful streams of matter and energy ejected from the regions around the black hole. These jets are thought to arise when material falling into the black hole gets trapped in the accretion disk, heating up and moving at near-light speeds because of the immense gravitational forces and rotation (spin) of the black hole. The black hole's magnetic field focuses this energy into two narrow beams, which shoot out along the black hole's rotational axis.
"The rough picture is that material (e.g. gas, dust, stars) that comes close to the black hole dissolves into a magnetic plasma. The infalling (and therefore moving) magnetic field creates a strong electric field (as in a dynamo!), that accelerates electrons and positrons. More electrons and positrons are made through collisions with photons (light) from the brightly shining accretion disk around the black hole. In an 'avalanche' effect, electrons and positrons are created and accelerated due to the electric field into a jet pointing towards the north pole of rotation of the black hole, and into a jet pointing towards the south pole of rotation of the black hole," Oei said.
The Porphyrion jets, which come from a supermassive black hole about 7.5 billion light-years from Earth, were found thanks to radio images from the International LOFAR Telescope, which revealed them to be between 6.8–7.3 megaparsecs in total length (22 million to 24 million light-years). The telescope also spotted around 10,000 other large jet structures, but none quite as large as Porphyrion.
Before Porphyrion was found, the previous largest jet system was Alcyoneus, which measures around 100 Milky Ways across.
The type of black hole that the jets are being shot out from indicates that it is very old, and the jets themselves are thought to have been burning since the universe was 6.3 billion years old, less than half its current age of 13.8 billion years.
"Another key finding is that such very long jets can apparently thrive in the first half of the universe's existence, whereas most of the long jets known so far have been found in the last few billion years of the universe's life," Oei said. "Porphyrion emerged from a so-called 'radiatively efficient' active black hole: a type of active black hole that was much more common in the young universe than it is now. Most giant jets known so far instead come from 'radiatively inefficient' active black holes.
"Very long black hole jets, like Porphyrion, could be more common than previously thought in the young universe. If so, those large spheres of influence might overlap, and energy and magnetism from active black holes might have been spread through most of the cosmos."
Exactly how these jets became so long remains a mystery to the researchers, but is likely connected to the jets' age and power.
"We know from simulations that jets of higher power have more stability. The higher the jet power, not only the more stable are the jets, but they can also reach further in the same amount of time. And Porphyrion's jets are not only powerful, they also have been 'on' for a billion years or so," Oei said. "The fact that the jets are really powerful and that the jets have been (roughly) continuously produced for a billion years or so are two major factors that have made Porphyrion's jets so large."
The researchers hope to study the black hole and its jets more closely to try and determine exactly how they got so long.
"We might find that the circumstances are less special than we thought, and more Porphyrion-like jet systems lie waiting to be discovered in the more distant universe," Oei said.
They also plan to study the night sky to try and spot other huge jets like Porphyrion that may be lurking out in the cosmos.
"The LOFAR Two-metre Sky Survey, in which we found these jets, is currently expanding its northern sky coverage from about 30 percent to most of the northern sky," Oei said. "I would like to continue to develop methodology (chiefly automated methodology, including machine learning steps) to search the newly imaged sky for giant jets."
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References
Oei, M. S. S. L., Hardcastle, M. J., Timmerman, R., Gast, A. R. D. J. G. I. B., Botteon, A., Rodriguez, A. C., Stern, D., Calistro Rivera, G., van Weeren, R. J., Röttgering, H. J. A., Intema, H. T., de Gasperin, F., & Djorgovski, S. G. (2024). Black hole jets on the scale of the cosmic web. Nature. https://doi.org/10.1038/s41586-024-07879-y
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