The supermassive black hole at the heart of galaxy M87, made famous by the first picture of a black hole shadow, has yielded another first: the jet shooting out from the black hole has been confirmed to wobble, providing direct proof that the black hole is spinning.
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Super massive black holes, monsters up to billions of times heavier than the Sun that eat everything around them including light, are difficult to study because no information can escape from within. Theoretically, there are very few properties that we can even hope to measure. One property that might possibly be observed is spin, but due to the difficulties involved there have been no direct observations of black hole spin.
Searching for evidence for black hole spin, an international team analyzed over two decades of observational data for the galaxy M87. This galaxy located 55 million light-years away in the direction of the constellation Virgo harbors a black hole 6.5 billion times more massive than the Sun, the same black hole which yielded the first image of a black hole shadow by the Event Horizon Telescope (EHT) in 2019. The supermassive black hole in M87 is known to have an accretion disk, which feeds matter into the black hole, and a jet, in which matter is ejected from near the black hole at close to the speed of light.
The team analyzed data for 170 time frames collected by the East Asian VLBI Network (EAVN), the Very Long Baseline Array (VLBA), the joint array of KVN and VERA (KaVA), and the East Asia to Italy Nearly Global (EATING) VLBI network. In total, more than 20 radio telescopes across the globe contributed to this study.
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The results show that gravitational interactions between the accretion disk and the black hole’s spin cause the base of the jet to wobble, or precess, much the same way that gravitational interactions within the Solar System cause the Earth to precess. The team successfully linked the dynamics of the jet with the central supermassive black hole, providing direct evidence that the black hole does in fact spin. The jet’s direction changes by about 10 degrees with a precession period of 11 years, matching theoretical supercomputer simulations conducted by ATERUI II at the National Astronomical Observatory of Japan (NAOJ).
"We are thrilled by this significant finding," says Yuzhu Cui, lead author on the paper summarizing the research she started as a graduate student at NAOJ before moving to Zhejiang Lab as a postdoctoral researcher. "Since the misalignment between the black hole and the disk is relatively small and the precession period is around 11 years, accumulating high-resolution data tracing M87 structure over two decades and thorough analysis are essential to obtain this achievement.”
Initially, the jet is oriented diagonally from upper right to lower left. The precessional motion starts at about simulation timestamp 14000 as shown at the top left, and the jet rotates to the upper-left/lower-right oblique direction at about timestamp 20000. Furthermore, at the end of the movie (around timestamp 26000), the position of the jet returns to a direction close to the initial one.
In the simulation an elapsed time of “10000” corresponds to about 10 years, so it can be seen that precessional motion occurs with a cycle of about 10 years. (Credit: Tomohisa Kawashima, Hiroyuki R. Takahashi, Ken Ohsuga)
“The precession is caused by the force exerted by the black hole's rotation on the tilted accretion disk,” says Dr. Tomoshisa Kawashima, a research fellow at the Institute for Cosmic Ray Research, the University of Tokyo, who led the numerical simulations in this research. “The simulation using ATERUI II reproduces the accretion disk precessing in a circle with a period that matches what was actually observed.”
"After the success of black hole imaging in this galaxy with the EHT, whether this black hole is spinning or not has been a central concern among scientists," explains Dr. Kazuhiro Hada from NAOJ. "Now anticipation has turned into certainty. This monster black hole is indeed spinning."
“This is an exciting scientific milestone that was finally revealed through years of joint observations by the international researchers team from 45 institutions around the world, working together as one,” says Dr. Motoki Kino at Kogakuin University, the coordinator of the East Asian VLBI Network Active Galactic Nuclei Science Working Group. “Our observational data beautifully fitted to the simple sinusoidal curve bring us new advances in our understanding of black hole and jet system.”
This research was presented as Cui et al. "Precessing jet nozzle connecting to a spinning black hole in M87" in Nature on September 27, 2023.
(September 28, 2023 Press Release)
[Publication information]
Title: "Precessing jet nozzle connecting to a spinning black hole in M87"
Authors: Yuzhu Cui, Kazuhiro Hada, Tomohisa Kawashima, Motoki Kino et al.
Journal: Nature
DOI: 10.1038/s41586-023-06479-6
[Supercomputer used in this research]
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[Related Links]
NAOJ Press Release: New Proof for Black Hole Spin
EHT-Japan Press release: Two-decade monitoring of M87 unveils a precessing jet connecting to a spinning black hole