University of Virginia, College and Graduate School of Arts and Sciences

Spinning black hole has rapidly pivoting jets

April 29, 2019

Astronomers, including Craig Sarazin from U.Va., have discovered jets shooting out at nearly the speed of light from the regions around a black hole, and which are changing their direction rapidly (minutes to hours).  This reorientation of the jets is due to the Lense-Thirring Precession, an effect predicted by Einstein's Theory of General Relativity.  This effect is expected to occur near a rotating black hole, and is caused by the rotating black hole dragging space and time around with it as it rotates.  This is believed to be the first direct observation of the Lense-Thirring Precession occurring around a black hole.  The black hole is surrounded by a disk of material (an accretion disk).   The rotation of this accretion disk and the spin of the black hole are misaligned.  The inner part of the accretion disk is wobbling (“precessing”) as a result of the very strong gravity of the black hole.  This wobble is similar to that of a spinning top as it slows down, but in this case it is due to the distortions of space and time from the rotating black hole, as predicted by Einstein’s theory.

The black hole is part of a binary star system with the rather unromantic name V404 Cygni.  The precessing jets were observed in radio emission with the Very Long Baseline Array (VLBA), a network of ten radio telescopes spread across the United States, from the Virgin Islands in the Caribbean to Hawaii. The VLBA is operated by the National Radio Astronomy Observatory (NRAO), whose headquarters are on the U.Va. grounds.

This research was published on Monday, April 29 in the journal Nature.  The research is part of a project originally conceived in Charlottesville by James Miller-Jones (originally a scientist at NRAO, now a professor at Curtin University in Perth, Australia), Greg Sivakoff (originally a graduate student and post-doc at U.Va., now a professor at the University of Alberta in Edmonton, Canada), and Sarazin.

The figure shows radio emission from the black hole V404 Cygni superposed on a model for the binary system, accretion disk, and precessing jets.

Video from the observations and simulations of the system are available at. https://vimeo.com/icrar/Cygni-animation

You can read more about the discovery in the article at UVAToday.

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