• Death spiral: A black hole spins on its

    From ScienceDaily@1:317/3 to All on Fri Feb 25 21:30:42 2022
    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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