The Czechs participated in the revelation of the shape and orientation of the extremely hot matter around the black hole

When matter falls into a black hole, it heats up to millions of degrees, this hot gas emits X-rays.

Scientists use measurements of the polarization of these X-rays to test and improve existing models that describe how black holes engulf matter and become some of the brightest X-ray sources in the universe.

New measurements of Cygnus X-1, published Thursday in the journal Science, represent the first such observations of a matter-sucking black hole. It was taken by the Imaging X-Ray Polarimetry Explorer (IXPE), an international mission of NASA and the Italian space agency ASI.

The Cygnus X-1 system is one of the brightest X-ray sources in our Galaxy, NASA recalls. It consists of a black hole with a mass of 21 times the mass of the Sun, orbiting a companion star with a mass of 41 times the mass of the Sun.

“Previous X-ray observations of black holes have only measured the energy, direction and time of arrival of X-rays from the hot plasma turning into a black hole,” said study lead author Henric Krawczynski. physics professor at Washington University in St. Louis is a member of the university’s McDonnell Center for Space Sciences.

“IXPE also measures their linear polarization, which contains information on how the X-rays were emitted, what they looked like and where they bounced off the material near the black hole,” he added.

No light, not even X-rays, escapes from under the so-called event horizon of a black hole. The X-ray emission detected by IXPE is emitted by hot matter, or plasma, in a region of two thousand kilometers in diameter around the 60-kilometer event horizon of the black hole.

Combining the IXPE data with simultaneous X-ray observations from NASA’s NICER and NuSTAR probes in May and June of this year allowed the authors to determine the arrangement, i.e. shape and position, of the plasma around the black hole. in Cygnus X-1.

The researchers found that the plasma expands perpendicular to the narrow two-sided plasma jet, the so-called jet. The alignment of the polarization direction of the X-rays with the direction of the jet strongly supports the hypothesis that processes in the bright region of the X-rays near the black hole play a substantial role in triggering these jets.

The observations agree with models that predict that the so-called hot plasma corona either replaces the inner part of the disc of matter spiraling towards the black hole, or surrounds the disc “like a sandwich”.

A better understanding of the plasma structure around a black hole can reveal a lot about how black holes bring matter together. “These new views will allow for better X-ray studies of how gravity curves space and time around black holes,” noted Krawczynski.

“The IXPE observations reveal that the flow of matter enveloping the black hole is seen more sideways than previously thought,” explained study co-author Michal Dociak of the Astronomical Institute of the Czech Academy of Sciences. .

“This could be a sign of a mismatch between the black hole’s rotation orientation and the entire binary system,” added study co-author Alexandra Veledinová of the University of Turku, Finland. “This different orientation may have been acquired by the system when the stellar progenitor of the current black hole exploded.”

The contribution of the Czech team to the discovery:

• creation of unique models for polarimetric X-ray data
• analysis and interpretation of the measured spectral and polarization data
• planning of observations with the IXPE, NICER and NuSTAR satellites
• simulation of the observation to estimate the duration of the exposure time during its preparation