Researchers have created a “black hole bomb” in the lab for the first time.
In 1972, physicists William Press and Saul Teukolsky described a theoretical phenomenon called a black hole bomb, in which mirrors enclose, reflect and exponentially amplify waves emanating from a rotating black hole.
Now, in a new study, physicists from the University of Southampton, the University of Glasgow, and the Institute for Photonics and Nanotechnologies at Italy’s National Research Council experimentally verified the theoretical black hole bomb. This breakthrough will help astrophysicists better understand how black holes spin. The paper was published to the preprint server Arxiv on March 31 and has not yet been peer-reviewed.
The ideas underpinning this and the original 1972 paper trace back to foundational work laid by two other physicists. In 1969, British mathematical physicist and Nobel laureate Sir Roger Penrose proposed a way to extract energy from a rotating black hole, which became known as black hole superradiance. Then, in 1971, Belarussian physicist Yakov Zel’dovich sought to better understand the phenomenon. In the process, he realized that under the right conditions, a rotating object can amplify electromagnetic waves. This phenomenon is known as the Zel’dovich effect.
‘Components exploded’
In their new research, the scientists harnessed the Zel’dovich effect to create their experiment. They took an aluminum cylinder rotated by an electric motor and surrounded it with three layers of metal coils. The coils created and reflected a magnetic field back to the cylinder, acting as a mirror.
As the team directed a weak magnetic field at the cylinder, they observed that the field the cylinder reflected was even stronger, demonstrating superradiance.
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Next, they removed the coils’ initial weak magnetic field. The circuit, however, generated its own waves, which the spinning cylinder amplified, causing the coils to amass energy. Between the cylinder’s rotational speed and amplified magnetic field, the Zel’dovich effect was in full swing. Zel’dovich had also predicted that a rotating absorber — like the cylinder — would change from absorption to amplification if its surface moves faster than the incoming wave, which the experiment verified.
“Our work brings this prediction fully into the lab, demonstrating not only amplification but also the transition to instability and spontaneous wave generation,” study co-author Maria Chiara Braidotti, a physics research associate at the University of Glasgow, told Live Science in an email.
“We sometimes pushed the system so hard that circuit components exploded,” study co-author Marion Cromb, a researcher at the University of Southampton, told Live Science in an email. “That was both thrilling and a real experimental challenge!”
While the team didn’t create a real black hole, this analog demonstrates the crucial idea that rotational superradiance and exponential amplification are universal and don’t only apply to black holes. This model will also help physicists understand black hole rotation as well as concepts at the intersection of astrophysics, thermodynamics and quantum theory, Braidotti said. Their research is being reviewed for publication in a peer-reviewed journal.
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