💫 This black hole's jets dance through space

An extreme cosmic dance is unfolding in the binary system Cygnus X-1, 7,000 light-years away from us. There, a stellar black hole of 21 solar masses is slowly devouring a blue supergiant star. But that's not the only activity: jets of matter erupt from the black hole at dizzying speeds, and they don't stay straight.

Astronomers have discovered that these jets are pushed back by the powerful stellar wind of the companion star, and appear to dance through space depending on its orbital position.


Using the Square Kilometre Array Observatory (SKA) radio telescope, scientists have been able to measure the power of these jets for the first time. They carry about 10% of the energy released by matter falling into the black hole. This is important information, because models simulating the Universe assumed this value without being able to verify it. The jets travel at half the speed of light, i.e. about 93,000 miles per second (150,000 km/s), and their power is equivalent to that of 10,000 Suns.

The Cygnus X-1 system is particularly tight: the black hole and its star are separated by only 18.6 million miles (30 million kilometers), or 20% of the Earth-Sun distance. The star loses matter through an intense stellar wind, which feeds an accretion disk around the black hole. This disk heats up and emits X-rays, making Cygnus X-1 one of the brightest sources in this domain.

This discovery now makes it possible to calibrate the power of jets from other black holes, including the supermassive ones that sit at the hearts of galaxies. Since the laws of physics are the same everywhere in the Universe, measuring the energy of Cygnus X-1's jets helps us understand how black holes influence their environment, even on much larger scales. Future projects will be able to detect millions of jets thanks to this reference.


The research team, led by Steve Prabu of the University of Oxford, observed that the jets appeared to "dance" in the SKA images. This movement comes from the stellar wind pushing the jets, deflecting them over the course of the orbit. This phenomenon had never been observed with such precision.

This study, published in the journal Nature Astronomy, paves the way for future observations. Researchers estimate that millions of galaxies host active black holes, and jets play an important role in the evolution of galaxies.