First-Ever Measurement of a Black Hole's Instantaneous Jet Power

An international research team has reported the first measurement of the instantaneous power and speed of jets emanating from a black hole. The measurements were taken from the Cygnus X-1 binary system, located 7,200 light-years away in the constellation Cygnus.

The team calculated the jet power to be equivalent to the energy output of 10,000 suns and measured the jet speed at approximately 355 million mph (540 million kph), which is about half the speed of light.

The findings, based on 18 years of high-resolution radio imaging data, were published in the journal Nature Astronomy.

The Cygnus X-1 System

Cygnus X-1 is a binary system consisting of a black hole and a blue supergiant star. The black hole, discovered in the 1960s, was the first ever identified. It has a mass approximately 21 times that of the Sun and orbits its companion star every 5.6 days. The companion star is a massive blue supergiant, estimated to be about 40 times the mass of the Sun.

• Stellar Wind: The companion star loses mass through a powerful stellar wind, a stream of particles propelled from its surface. This wind is approximately 100 million times more massive than the solar wind from our Sun and accelerates particles to about three times the speed of the solar wind.
• Accretion: The black hole continually pulls gases from this stellar wind, a process that has been ongoing for an estimated 20,000 years. Some of this accreted material forms an accretion disk around the black hole.

Research Methodology and Key Findings

The research was led by Steve Prabu, who conducted the work while at Curtin University in Australia and is now at the University of Oxford. The team used a global network of telescopes to obtain very high-resolution radio images over 18 years, employing techniques similar to those used by the Event Horizon Telescope.

The study found that the powerful stellar wind from the companion star is strong enough to bend and redirect the narrow beams of plasma, or jets, launched from near the black hole's poles. As the black hole orbits, the stellar wind pushes against the jets, causing them to change direction in correlation with the 5.6-day orbital period.

By modeling this interaction—specifically, by calculating how much the jets were bent by the stellar wind—the researchers were able to measure the instantaneous power of the jets for the first time. Previous methods could only estimate a black hole's jet power by averaging it over tens of thousands of years.

A key quantitative finding, according to the research team, is that approximately 10% of the total energy released as matter falls toward the black hole is carried away by these jets.

Scientific Context and Implications

The jets from Cygnus X-1 travel at nearly the speed of light and have inflated a bubble of hot gas extending approximately 16 light-years into the surrounding interstellar space over millennia.

• Environmental Interaction: The findings demonstrate that even highly energetic phenomena like black hole jets can be shaped by their local environment, in this case, the stellar wind from a companion star.
• Modeling Cosmic Evolution: Researchers state that the new method for measuring instantaneous jet power allows for a more complete "energy budget" calculation for black holes, enabling direct comparison between the rate of accretion and the energy carried away by jets. This information can be used to refine computer simulations of the universe.
• Galaxy Evolution: Understanding how black holes distribute energy is relevant to models of galaxy evolution, as jets from supermassive black holes at galactic centers are theorized to influence star formation and the structure of their host galaxies.

Future Research

Steve Prabu stated plans to apply similar measurement techniques to other black hole systems. He noted that it would be "exciting to measure jet power in many more systems" to better understand the behavior and impact of black hole jets across different environments.

Related Research on Black Hole Outflows

A separate study, also published in Nature Astronomy and led by researchers at the University of Warwick, examined a different black hole system, 4U 1630−472. This research presented observational evidence that black holes can alternate between two primary types of outflows:

1. Relativistic Jets: Narrow beams of plasma launched from the black hole's poles at near-light speed.
2. X-ray Winds: Broader streams of ionized gas ejected from the surface of the accretion disk.

The study of 4U 1630−472 found that these two outflow modes appear to be mutually exclusive. When strong jets were detected, powerful winds were not present, and vice versa, even while the accretion of matter from a companion star remained consistent.

The researchers theorize this "switching" behavior may be driven by changes in the magnetic field configuration within the accretion disk, representing a self-regulating mechanism for how black holes manage their energy output.