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| Image credit: Pixabay |
The researchers at the University of Turku, Finland, have found that the rotation axis of a black hole in a binary star system is tilted more than 40 degrees relative to the stellar orbit axis (stars’ rotation axis).
A binary star system consists of two stars held together by gravitational force. This force makes the stars orbit around each other at a common center. When a black hole passes through a binary system, a force of attraction is established that tilts the rotation axis of the black hole. This observation by the researchers is the first reliable evidence that shows a huge difference between the axis of a binary system orbit and the axis of rotation of a black hole. This discovery can challenge current black hole formation theories and models.
“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 sign of the infalling material, and also radio emission from the relativistic jets expelled from the system,” said Juri Poutanen, Professor of Astronomy at the University of Turku and the lead author of the study.
Relativistic jets
A relativistic jet is an astronomical phenomenon where charged particles or matter are emitted from a binary system (two-star system) as an extended beam of light along the axis of rotation. Researchers followed the relativistic jets to determine the direction of the rotation axis of the black hole. A companion star to the black hole, MAXI J1820+070 threw light on it that helped the scientists measure the angle of inclination of the stellar orbit to the black hole’s rotation axis. They used a polarimetric instrument- DIPol-UF fixed at the Nordic Optical Telescope and spectroscopic techniques for this purpose. As a result, they found that the difference between the rotation axis of the star MAXI J1820+070 and the black hole was more than 40 degrees.
“To determine the 3D orientation of the orbit, one additionally needs to know the position angle of the system on the sky, meaning how the system is turned with respect to the direction to the North on the sky. This was measured using polarimetric techniques,” said Juri Poutanen.
“The difference of more than 40 degrees between the orbital axis and the black hole spin was completely unexpected. Scientists have often assumed this difference to be very small when they have modeled the behaviour of matter in a curved time-space around a black hole. The current models are already really complex, and now the new findings force us to add a new dimension to them,” stated Poutanen.
The study results showed the evolutions in the black hole and binary system formations, such as misalignment in rotation axes. However, more such space phenomenona are yet to be discovered.
The detailed study was published in the Science magazine.
Contributed by: Simran Dolwani
