X-rays reveal details about the matter around the black hole

Madrid, 3 (European press)

Matter is heated to millions of degrees when pulled toward a black hole, and this hot material glows in X-rays. Researchers use measurements of these X-ray polarizations to test and refine models that describe how black holes swallow matter, becoming some of the brightest sources of light, including X-rays, in the universe.

The new measurements of Cygnus X-1 were published in the journal Science, and represent the first observations of a mass-creating black hole 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, and it consists of a black hole orbiting around 21 solar masses with a companion star of 41 solar masses.

Explains lead author Henric Krawczynski, Wyman Crowe Professor of Physics in the Arts and Sciences at the University of Washington, US, and professor at the university’s McDonnell Space Science Center. IXPE also measures its linear polarization, which carries information about how the X-rays are emitted and whether they are scattered by material near black and where the gap is.”

No light, not even X-ray light, can escape the black hole’s event horizon. The X-rays detected by IXPE are emitted by hot matter, or plasma, in a region 2,000 km in diameter surrounding the 60 km in diameter black hole event horizon.

Combining IXPE data with simultaneous observations from NASA’s NICER and NuSTAR X-ray Observatory in May and June 2022 allowed the authors to narrow down the scope of the plasma geometry, that is, the shape and position of the plasma.

The researchers found that the plasma extends perpendicular to the two-sided flow of pencil-shaped plasma, or jet, imagined in previous radio observations. The alignment of the polarization direction of the X-rays and the plane strongly supports the hypothesis that processes in the bright X-ray region near the black hole play an important role in the jet launch.

The observations are consistent with models that predict that the hot plasma halo cuts through the disk of matter spiraling toward the black hole or displaces the interior of that disk. The new polarization data exclude models in which the black hole’s halo is a narrow column or cone of plasma along the flow axis.

Scientists note that a better understanding of the plasma geometry around a black hole can reveal much 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,” Krawczynski says.

En relación con el agujero negro Cygnus X-1 en concreto, “las observaciones de IXPE revelan que el flujo de acreción se ve más de canto de lo que se pensaba”, explica el coautor Michal Dovciak, del Instituto Astronómico de la A Sciences.

“This could be a signature of misalignment of the black hole’s equatorial plane and the black hole’s orbital plane,” says co-author Alexandra Vildina of the University of Turku, or the black hole’s double star and companion pair. “The system may have skewed when the black hole’s original star exploded,” he adds.

The IXPE mission uses X-ray mirrors manufactured at NASA’s Marshall Space Flight Center and focal plane instruments provided by the ASI Collaboration, the National Institute of Astrophysics (INAF), and the National Institute of Nuclear Physics. Co-author Fabio Mullieri, of INAF-IAPS.

“Beyond Cygnus X-1, IXPE is being used to study a wide range of extreme X-ray sources, including neutron accretion stars, pulsars and stellar wind nebulae, supernova remnants, our galactic center and active galactic core. We have found many surprises and are having a lot of fun “.

A second research paper in the same issue of “Science” led by Roberto Taverna of the University of Padova (Italy) describes the IXPE discovery of highly polarized X-rays from Magnetar 4U 0142 + 61.

“We are excited to be part of this new wave of scientific discovery in astrophysics,” Krawczynski says.