Marrakesh, 25 Feb. (Morocco-News) –
The axis of rotation of a black hole in a binary system is tilted more than 40 degrees relative to the axis of stellar orbit. This discovery challenges models of black hole formation.
The observation made by the researchers of the Tuorla Observatory in Finland is the first reliable measurement showing a large difference between the axis of rotation of a black hole and the axis of the orbit of a binary system. The difference between the axes measured by researchers in a binary star system called MAXI J1820+070 was over 40 degrees.
Often, the axis of rotation of a central massive body is largely aligned with the axis of rotation of its satellites. This is the case of the solar system: the planets orbit around the sun in a plane which approximately coincides with the equatorial plane of the sun. The tilt of the sun’s axis of rotation relative to the earth’s orbital axis is only 7 degrees.
“The expectation of alignment, to a large extent, does not hold true for strange objects, such as black hole X-ray binaries. The black holes in these systems were formed following a cosmic cataclysm: the collapse of a massive star. Now we see that the black hole is attracting matter from the nearby, lighter companion star, which orbits around it. We see bright optical and X-rays like the last gasp of falling matter, as well as radio emissions from the relativistic jets ejected from the system,” he explains. in a statement Juri Poutanen, professor of astronomy at the University of Turku and main author of the publication.
By tracking these jets, the researchers were able to accurately determine the direction of the black hole’s spin axis. When the amount of gas falling from the companion star into the black hole began to decrease, the system darkened and much of the light in the system came from the companion star. Thereby, The researchers were able to measure the inclination of the orbit using spectroscopic techniques, and it almost coincided with the inclination of the ejections.
“To determine the 3D orientation of the orbit, it is also necessary to know the angle of position of the system in the sky, that is to say the way the system rotates with respect to the direction of North in the sky. . We measured it using polarimetric techniques,” explains Juri Poutanen.
The results, published in Scienceopen interesting perspectives for studies on the formation of black holes and the evolution of these systems, since it is difficult to obtain such an extreme misalignment in many scenarios of black hole formation and binary evolution.
« The difference of more than 40 degrees between the orbital axis and the rotation of the black hole was totally unexpected.. Scientists have often assumed this difference to be very small when modeling the behavior of matter in curved spacetime around a black hole, and now, new discoveries compel us to add a new dimension to them. »Dit Poutanen.
The main discovery was made using the DIPol-UF polarimetric instrument, built in-house and mounted on the Nordic Optical Telescope, which is owned by the University of Turku and Aarhus University in Denmark.
