More than 60 years after astronomers first detected its X-ray glow, Cygnus X-1 — the first black hole ever confirmed — is still revealing secrets. Researchers have now measured something that long eluded observation: the raw power and speed of the plasma jets this black hole fires into space.
The findings are substantial. Those jets shine with the equivalent energy of around 10,000 suns and travel at roughly half the speed of light. The method that made the measurement possible was unexpectedly elegant — scientists watched the jets dance.
A measurement decades in the making
Cygnus X-1 has a long history. Astronomers first detected its X-ray glow in 1964, when black holes were still theoretical constructs. It was officially confirmed in 1971, making it the first black hole ever verified. Located roughly 7,000 light-years away in the constellation Cygnus, it’s a stellar-mass black hole about 21 times more massive than the sun.
The black hole is locked in a tight binary orbit with HDE 226868, a blue supergiant of comparable mass. The two objects circle each other every 5.6 days at a distance roughly one-fifth that between Earth and the sun. As they orbit, Cygnus X-1 continuously strips away the outer layers of its companion, feeding a superheated accretion disk that blazes in X-ray light.
Like most black holes, Cygnus X-1 fires twin jets of plasma accelerated outward by its rapidly spinning magnetic field. Despite decades of study, accurately measuring those jets remained stubbornly out of reach — their constant motion made precise readings nearly impossible, until researchers found a way to turn that motion to their advantage.
Stellar winds that make jets ‘dance’
HDE 226868 emits powerful stellar winds — streams of charged particles driven outward by intense magnetic fields. Those winds don’t simply dissipate into space. They continuously buffet Cygnus X-1’s jets, bending them away from the star.
Because the two objects orbit a shared center of mass, the direction of that bending shifts constantly. From Earth’s perspective, the jets appear to sway back and forth in a rhythmic wobble.
Steve Prabu, a radio astronomer at the University of Oxford and lead author of the new study, gave this phenomenon a fitting name: “dancing jets.” The term captures the continuous, fluid swaying that historically made these jets so difficult to pin down — and that ultimately became the key to measuring them.
Capturing the uncapturable
The challenge with dancing jets isn’t just that they move. Their movement has historically blurred any attempt to measure their shape or energy. To get around this, the research team combined images from radio telescopes positioned across the globe, building a composite picture precise enough to capture the jets’ true form despite their constant motion.
The results, published April 16 in Nature Astronomy, are significant. The jets from Cygnus X-1 shine with the equivalent energy of roughly 10,000 suns and travel at approximately 335 million mph — about half the speed of light.
No single observatory could have resolved the jets clearly enough on its own. By pooling observations from multiple radio telescopes, the team achieved a level of detail previously out of reach, effectively converting an obstacle — the jets’ movement — into the mechanism that revealed their properties.
A missing puzzle piece for cosmology
Beyond the headline numbers, the study’s findings carry real weight for how scientists model the universe at large.
“A key finding from this research is that about 10 per cent of the energy released as matter falls in towards the black hole is carried away by the jets,” Prabu said in a statement. “This is what scientists usually assume in large-scale simulated models of the universe, but it has been hard to confirm by observation until now.”
That confirmation matters more than it might first appear. Cosmological simulations have long relied on this 10% figure as a built-in assumption — a reasonable estimate embedded in models of how galaxies form and evolve. It now has observational grounding for the first time.
The measurement also has implications well beyond Cygnus X-1 itself. According to Einstein’s general relativity, the physics around black holes is scale-invariant, meaning the same principles governing a stellar-mass black hole should apply to one millions of times more massive. Co-author James Miller-Jones, a radio astronomer at Curtin University in Australia, explained that this measurement can now “anchor our understanding of jets, whether they are from black holes 10 or 10 million times the mass of the sun.”
Jets don’t just shoot energy into the void — they shape surrounding environments, influencing how gas cools, how stars form, and how galaxies like the Milky Way develop over billions of years. “Black hole jets provide an important source of feedback to the surrounding environment and are critical to understanding the evolution of galaxies,” Miller-Jones added.
With confirmed energy output and speed now in hand, researchers have a new baseline for studying jets across the full spectrum of black hole masses. The logical next step involves applying similar techniques to other black hole systems, testing whether this 10% figure holds as broadly as the models have long assumed.