In a first for science, astronomers have observed the speed and power of matter that erupts from a black hole, shedding light on how this process shapes the structure of the universe.
Hungry black holes are the hidden architects of the cosmos. Nothing can escape their depths, but as matter funnels into them, a small fraction of it can rebel at the brink of oblivion and form twin jets of terrifying power near the black hole’s poles that beam out into space. Bigger black holes make bigger jets, and the biggest—supermassive black holes—can generate jets so immense that they influence entire groups of galaxies.
No direct hits are required; shock waves from a jet can ripple across hundreds of thousands of light-years to churn galactic gas into stars or to extinguish star formation entirely by expelling those gas reservoirs into intergalactic space. Even a glancing blow can make the difference between a galaxy filled with stars and no galaxy at all.
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Until now, no one had ever managed to directly measure the might of these jets. Using data from two international networks of radio telescopes, researchers pinned down the energetics of jets erupting from a black hole in a system called Cygnus X-1, some 7,200 light-years from Earth. Their results, published today in Nature Astronomy, show that the black hole’s jets move at about half the speed of light and carry about 10 percent of the total energy released by infalling matter—equivalent to the power output of 10,000 suns.
“Cygnus X-1 is a particularly special system. It’s one of the best laboratories for studying how black holes behave,” says the study’s lead author Steve Prabu, an astrophysicist at the University of Oxford. The system holds the first confirmed black hole, a roughly 20-solar-mass object that blasts out jets as it orbits and siphons gas from a supergiant star.
By combining observations gathered across nearly two decades by the U.S. Very Long Baseline Array (VLBA) and the European VLBI Network (EVN), Prabu and his colleagues were able to reconstruct high-resolution images of the jets over time, watching as they were buffeted to and fro by intense stellar winds from the nearby star. “By combining all of these observations, we were able to piece together the ‘dancing’ motion of the jet and measure its properties in a way that hadn’t been possible before,” Prabu says. The team’s discovery of “black hole jet bending,” he says, “gave us a unique way to measure the jets’ power directly.”
James Miller-Jones, a co-author of the study and an astrophysicist at the Curtin Institute of Radio Astronomy in Australia, notes that the result likely applies to black holes of all sizes. “Because our theories suggest that the physics around [all] black holes is very similar, we can now use this measurement to anchor our understanding of jets, whether they are from black holes 10 or 10 million times the mass of the sun,” he said in a statement.
Previously, researchers inferred the strength of a black hole’s jets by observing how they affected their surroundings over thousands or even millions of years. These more piecemeal estimates have informed large-scale cosmic simulations that model the growth and evolution of galaxies.
“It’s a really cool result,” says Rob Fender, a University of Oxford astrophysicist, who was not involved with the study. “Calibrating the power in black hole jets is really the key measurement for understanding how these objects have helped shape the cosmos, near and far. This is notoriously hard to do, and the results depend on assumptions about the matter content of the jets, how fast they’re moving (harder to measure than you might think) and the density of the environment into which they’re plowing.”
All those assumptions, Fender adds, are minimized in the case of Cygnus X-1 because of just how much is already known about the black hole’s companion star and its winds. In fact, the team’s measurement “really isn’t possible for any other system we know in the entire universe,” he says.