They find an unexpected black hole that turns on its side

A black hole  is rotated 40° in the binary star system called MAXI J1820+070.


The axis of rotation of a black hole  in a binary system is tilted more than 40 degrees with respect to the axis of the stellar orbit. The finding challenges models of black hole formation .

The observation by researchers at the Tuorla Observatory in Finland is the first reliable measurement to show 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 the researchers in a binary star system called MAXI J1820+070 was more than 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 true for the solar system: the planets orbit the sun in a plane that roughly 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 alignment expectation, to a large extent, does not hold for strange objects, such as X-ray binaries of black holes . The black holes in these systems formed as a result of a cosmic cataclysm: the collapse of a massive star. Now, we see the black hole pulling in matter from the nearby, lighter companion star that orbits it We see bright optical and X-ray radiation as the last gasp of infalling material, and also radio emission from relativistic jets ejected of the system,” Juri Poutanen, professor of astronomy at the University of Turku and lead author of the publication, says in a statement.

By following these jets, the researchers were able to pinpoint the direction of the black hole’s axis of rotation.As the amount of gas falling from the companion star into the black hole began to decrease, the system dimmed, with much of the system’s light coming from the companion star. In this way, the researchers were able to measure the inclination of the orbit using spectroscopic techniques, and it almost coincided with the inclination of the ejecta.

“To determine the 3D orientation of the orbit, one also needs to know the position angle of the system in the sky, that is, how the system rotates with respect to the direction of north in the sky. This was measured using polarimetric techniques,” Juri Poutanen says.

New postulates

The results, published in Science, open up interesting perspectives towards studies of black hole formation and the evolution of such systems, since such extreme misalignment is difficult to achieve in many binary formation and evolution scenarios.

“The difference of more than 40 degrees between the orbital axis and the spin of the black hole was completely unexpected. Scientists often assumed that this difference was very small when they modeled the behavior of matter in a curved time space around a black hole . black . Current models are already really complex, and now new findings force us to add a new dimension to them,” says Poutanen.

The key finding was made using the in-house built DIPol-UF polarimetric instrument mounted on the Nordic Optical Telescope, which is owned by the University of Turku together with Aarhus University in Denmark.