A black hole, a disc and an equator

In 1975, Nobel Prize-winning physicist John Bardeen and astrophysicist Jacobus Petterson proposed that the inner-most region of a matter-filled accretion disc would be drawn into an alignment with the equator of the black hole it surrounds.

All black holes are surrounded by such discs, which comprise orbiting matter that is eventually, and inevitably, drawn inside.

Previous research suggested that the discs were tilted in relation to the black hole, but the two physicists predicted that part of it, at least, would lose its tilt and line up. The suggestion became known as the Bardeen-Petterson effect and, ever since, scientists have been looking to confirm it.

And now, at last, the matter has been settled. Sort of. A team of researchers from Northwestern University in the US, the University of Amsterdam in the Netherlands, and the UK’s University of Oxford constructed the most detailed, highest resolution simulations of a black hole to date – and found that the 1975 predictions played out.

“This ground-breaking discovery of Bardeen-Petterson alignment brings closure to a problem that has haunted the astrophysics community for more than four decades,” says co-lead author Alexander Tchekhovskoy. 

“These details around the black hole may seem small, but they enormously impact what happens in the galaxy as a whole. They control how fast the black holes spin and, as a result, what effect black holes have on their entire galaxies.”

The research is published in the journal Monthly Notices of the Royal Astronomical Society, and is available in full on the pre-print server arXiv.

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