An artist’s impression of the Cygnus X-1 system, with the black hole appearing in the center and its companion star to the left.
Credit: JOHN PAICE
Matter is heated to millions of degrees when it is drawn into a black hole, and this hot matter glows in X-rays.
Observations of the stellar-mass black hole Cygnus X-1 reveal new details about the configuration of extremely hot matter in the region immediately surrounding the black hole.
Matter is heated to millions of degrees when it is drawn toward a black hole, and this hot matter glows in X-rays. Researchers use measurements of the polarization of these X-rays to test and refine models that describe how black holes swallow matter, becoming some of the brightest light sources, including X-rays, in the universe.
Published in the journal Science, the new measurements of Cygnus X-1 represent the first observations of a mass-creating black hole made by the Imaging X-Ray Polarimetry Explorer (IXPE) mission, an international collaboration between NASA and the Italian Space Agency. (SO). Cygnus X-1 is one of the brightest X-ray sources in our galaxy, formed by an orbiting 21-solar-mass black hole with a 41-solar-mass companion star.
“Previous observations of X-ray black holes only measured the direction, arrival time and energy of X-rays coming from hot plasma spiraling towards the black holes,” explains lead author Henric Krawczynski, Wayman Crow Professor of Physics in Arts and Sciences at the University of Washington, United States, and a professor at the university’s McDonnell Center for Space Sciences. IXPE also measures its linear polarization, which carries information about how the X-rays were emitted and whether , and where, are scattered from material near the black hole.”
No light, not even X-ray light, can escape from inside a black hole’s event horizon. The X-rays detected with IXPE are emitted by hot matter, or plasma, in a 2,000-km-diameter region surrounding the black hole’s 60-km-diameter event horizon.
Combining the IXPE data with simultaneous observations from NASA’s NICER and NuSTAR X-ray observatories in May and June 2022 allowed the authors to narrow down the geometry, that is, the shape and location, of the plasma.
The researchers found that the plasma extends perpendicular to a two-sided, pencil-shaped plasma flow, or jet, imagined in earlier radio observations. The alignment of the polarization direction of the X-rays and the jet strongly supports the hypothesis that processes in the X-ray bright region near the black hole play a crucial role in jet launch.
The observations are consistent with models that predict that the corona of hot plasma intercalates the disk of matter spiraling toward the black hole or replaces the inner part of that disk. The new polarization data rule out models in which the black hole’s corona is a narrow column or cone of plasma along the axis of the jet.
The scientists noted that a better understanding of the geometry of the plasma around a black hole can reveal a lot about the inner workings of black holes and how they accumulate mass.
“These new insights will improve X-ray studies of how gravity bends space and time near black holes,” says Krawczynski.
For the Cygnus X-1 black hole in particular, “the IXPE observations reveal that the accretion flow is seen more edge-on than previously thought,” explains co-author Michal Dovciak of the Astronomical Institute of the Czech Academy of Sciences. Sciences.
“This may be a signature of a misalignment of the black hole’s equatorial plane and the binary’s orbital plane,” or the paired duo of the black hole and its companion star, says co-author Alexandra Veledina of the University of Turku.
“The system may have become misaligned when the black hole’s parent star exploded,” he adds.
The IXPE mission uses X-ray mirrors manufactured at NASA’s Marshall Space Flight Center and focal plane instrumentation provided by a collaboration of ASI, the National Institute of Astrophysics (INAF) and the National Institute of Nuclear Physics. the co-author Fabio Muleri, from INAF-IAPS.
“Beyond Cygnus X-1, IXPE is being used to study a wide range of extreme X-ray sources, including mass accreting neutron stars, pulsars and pulsar wind nebulae, supernova remnants, our galactic center and active galactic nuclei. We have found many surprises and we are having a lot of fun,” he says.
A second paper in the same issue of ‘Science’ led by Roberto Taverna of the University of Padua (Italy) describes the IXPE detection of highly polarized X-rays from magnetar 4U 0142+61.