Science Gazette

A black hole rotates on its side, creating a death spiral


The axis of rotation of a black hole in a binary system is inclined more than 40 degrees relative to the axis of star orbit, according to researchers from the University of Turku in Finland. The discovery casts doubt on existing theories of black hole genesis.

The astronomers from Finland’s Tuorla Observatory have made the first accurate measurement of a considerable divergence between a black hole’s rotation axis and the axis of a binary system orbit. The researchers found a difference of more than 40 degrees between the axes of a binary star system dubbed MAXI J1820+070.

The rotation axis of the central big body is often aligned with the rotation axis of its satellites in space systems with smaller objects circling around it. This holds true for our solar system as well: the planets circle the Sun on a plane that nearly aligns with the Sun’s equatorial plane. The Sun’s rotation axis is merely seven degrees incline with regard to the Earth’s orbital axis.

“The expectation of alignment does not hold for strange objects like black hole X-ray binaries to a great extent. A cosmic disaster — the fall of a huge star — created the black holes in these systems. We can now see the black hole tugging stuff from its close, lighter partner star. As the final gasp of the infalling material, we detect strong optical and X-ray radiation, as well as radio emission from the relativistic jets blasted from the system “Professor of Astronomy at the University of Turku and the publication’s primary author, Juri Poutanen, explains.

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The researchers were able to precisely pinpoint the direction of the black hole’s axis of spin by tracing these jets. The system darkened as the quantity of gas falling to the black hole from the companion star decreased, and most of the light in the system came from the companion star. The researchers were able to use spectroscopic methods to estimate the orbit inclination, which occurred to be virtually identical to the inclination of the ejections.

“To establish the orbit’s 3D orientation, one must also know the system’s position angle on the sky, or how the system is rotated in relation to the sky’s north direction. This was determined using polarimetric methods “Juri Poutanen agrees.

The findings, which were published in the journal Science, offer up new avenues for research into black hole creation and development, since high misalignment is difficult to achieve in many black hole formation and binary evolution scenarios.

“The orbital axis and black hole spin differed by more than 40 degrees, which was absolutely unexpected. When scientists have studied the behavior of matter in a curved temporal space surrounding a black hole, they have often assumed that this difference is relatively tiny. Current models are already quite complicated, and new results push us to add a new dimension to them “According to Poutanen.

The important discovery was achieved using the DIPol-UF polarimetric equipment, which was manufactured in-house and deployed at the Nordic Optical Telescope, which is jointly owned by the University of Turku and Aarhus University in Denmark.

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