Death spiral: A black hole spins on its side
Date:
February 25, 2022
Source:
University of Turku
Summary:
Researchers found that the axis of rotation of a 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.
FULL STORY ========================================================================== Researchers from the University of Turku, Finland, found that the axis
of rotation of a 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.
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.
By following these jets, the researchers were able to determine the
direction of the axis of rotation of the black hole very accurately. As
the amount of gas falling from the companion star to the black hole
later began to decrease, the system dimmed, and much of the light in the
system came from the companion star. In this way, the researchers were
able to measure the orbit inclination using spectroscopic techniques,
and it happened to nearly coincide with the inclination of the ejections.
"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," says Juri Poutanen.
The results published in the Science magazine open interesting prospects towards studies of black hole formation and evolution of such systems,
as such extreme misalignment is hard to get in many black hole formation
and binary evolution scenarios.
"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 behavior 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," Poutanen states.
The key finding was made using the in-house built polarimetric instrument DIPol-UF mounted at the Nordic Optical Telescope, which is owned by the University of Turku jointly with the Aarhus University in Denmark.
========================================================================== Story Source: Materials provided by University_of_Turku. Note: Content
may be edited for style and length.
========================================================================== Journal Reference:
1. Juri Poutanen, Alexandra Veledina, Andrei V. Berdyugin, Svetlana V.
Berdyugina, Helen Jermak, Peter G. Jonker, Jari J. E. Kajava,
Ilia A.
Kosenkov, Vadim Kravtsov, Vilppu Piirola, Manisha Shrestha,
Manuel A.
Perez Torres, Sergey S. Tsygankov. Black hole spin-orbit
misalignment in the x-ray binary MAXI J1820 070. Science, 2022;
375 (6583): 874 DOI: 10.1126/science.abl4679 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2022/02/220225100218.htm
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