Spiral of Death: Black Hole Spinning Sideways
Researchers at the University of Turku in Finland discovered that the axis of rotation of a black hole in a binary star system is tilted more than 40 degrees relative to the star’s orbital axis. The findings challenge existing theoretical models of black hole formation.
The new observation by researchers at Tuorla Observatory in Finland is the first reliable measurement to show that there is a large discrepancy between the spin axis of a black hole and the orbital axis of a binary star system. This difference, which the researchers measured between axes in a binary star system called MAXI J1820+070, is more than 40 degrees.
Generally, in space systems with smaller objects revolving around a central giant object, the axis of rotation of the central body corresponds to a high degree with the axes of rotation of its satellites. This is also true in our own solar system: The planets revolve around the Sun in a plane that almost coincides with the Sun’s equatorial plane. This curve in the Sun’s axis of rotation is only seven degrees from Earth’s orbital axis.
Juri Poutanen, professor of astronomy at the University of Turku and lead author of the new study, explains: “The alignment expectation often doesn’t hold true for strange objects like black hole X-ray binaries. Black holes in these systems are the result of a cosmic disaster; formed by the collapse of a giant star. Near the black hole; that is, we can see that it is pulling matter from the lighter star orbiting around it. For the last time, we see matter falling into the black hole in the form of bright optics and X-ray radiation. We can see the radio waves emitted by the relativistic jets ejected from the system.”
Researchers following these jets were able to very precisely determine the direction of the black hole’s axis of rotation. As the amount of gas falling into the black hole from the companion star subsequently began to decrease, the star’s light dimmed and most of the light in the system began to come from the companion star. In this way, scientists were able to measure the orbital inclination using spectral measurement methods. Moreover, this measurement almost coincided with the slope of the launched jets.
“In order to determine the 3-dimensional direction of the orbit, the angle of the system’s position in the sky must also be known; that is, it is necessary to know how the system rotates relative to the North direction in the sky. We measured this using polarimetric methods,” says Juri Poutanen.
Since such extraordinary misalignments are hardly seen in the scenarios of the formation of many black holes and the evolution of binary stars; The results, published in Science, open the door to interesting possibilities for studies of black hole formation and the evolution of such systems.