Researchers at the University of Turku in Finland found that the axis of rotation of a[{“ attribute=““>black hole in a binary system is tilted more than 40 degrees relative to the axis of stellar orbit. The finding challenges current theoretical models of black hole formation.
The observation by the researchers from Tuorla Observatory in Finland is the first reliable measurement that shows a large difference between the axis of rotation of a black hole and the axis of a binary system orbit. The difference between the axes measured by the researchers in a binary star system called MAXI J1820+070 was more than 40 degrees.
Artist impression of the X-ray binary system MAXI J1820+070 containing a black hole (small black dot at the center of the gaseous disk) and a companion star. A narrow jet is directed along the black hole spin axis, which is strongly misaligned from the rotation axis of the orbit. Image produced with Binsim. Credit: R. Hynes
Often for the space systems with smaller objects orbiting around the central massive body, the own rotation axis of this body is to a high degree aligned with the rotation axis of its satellites. This is true also for our solar system: the planets orbit around the Sun in a plane, which roughly coincides with the equatorial plane of the Sun. The inclination of the Sun rotation axis with respect to orbital axis of the Earth is only seven degrees.
“The expectation of alignment, to a large degree, does not hold for the bizarre objects such as black hole X-ray binaries. The black holes in these systems were formed as a result of a cosmic cataclysm – the collapse of a massive star. Now we see the black hole dragging matter from the nearby, lighter companion star orbiting around it. We see bright optical and X-ray radiation as the last sigh of the infalling material, and also radio emission from the relativistic jets expelled from the system,” says Juri Poutanen, Professor of Astronomy at the University of Turku and the lead author of the publication.
An artist’s rendering of the X-ray binary system MAXI J1820+070, containing a black hole (a small black dot at the center of the gas disk) and a companion star. A narrow beam is directed along the black hole’s spin axis, which differs greatly from the spin axis of the orbit. The picture was created in no time. Photo credit: R Hynes
By tracking these jets, the researchers were able to determine the direction of the black hole’s spin axis very precisely. Later, when the amount of gas falling into the black hole from the companion star began to decrease, the temperature of the system cooled and much of the light in the system came from the companion star. This allowed the researchers to use spectroscopic techniques to measure the orbital inclination, which roughly matched the inclination of the ballistics.
“To determine the 3D orientation of the orbit, one also needs to know the position angle of the system in the sky, ie how the system rotates with respect to the north direction in the sky. This was measured using polarimetry techniques,” says Yuri Potanin.
The results, published in Science, open interesting perspectives for studies of black hole formation and the evolution of such systems, as it is difficult to achieve such extreme imbalance in many scenarios of black hole formation and binary evolution.
The difference of more than 40 degrees between the orbital axis and the black hole’s rotation was completely unexpected. Scientists often assumed this difference to be very small when modeling the behavior of matter in a curved period around a black hole. Existing models are already complex, and now new insights are forcing us to add a new dimension to them,” says Potanin.
Reference: “Orbit-Orbit Black Hole Rotation Imbalance in X-ray-Binary MAXI J1820+070” by Guri Potanin, Alexandra Veledina, Andrei V. Berdyugina, Svetlana V. Berdyugina, Helen Germak, Peter J. Juncker, Gary JE Kagava, Ilya Kozenkov, Vadim Kravtsov Filippo Perola, Manisha Shrestha, Manuel A. Perez-Torres and Serge S. Zygankow February 24, 2022 Available here. to know.
DOI: 10.1126 / science.abl4679
The most important discovery was made with the in-house built DIPol UF polarimeter installed on the Northern Optical Telescope, co-owned by the University of Turku
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