For decades, scientists have believed that nothing can escape the powerful gravity of a black hole. While this is largely true, physicist Stephen Hawking proposed in 1974 that black holes could slowly lose energy by emitting a form of thermal radiation, now known as Hawking radiation.
Now, an international team of physicists has observed a key process linked to Hawking radiation in a laboratory experiment that used light to create a black hole analogue. The research, led by Lorenzo Procopio of Paderborn University in Germany, has been published in the journal Nature.
The scientists say their findings could provide important clues about how black holes gradually lose energy and may even help solve some of the biggest mysteries in modern physics.
Black holes are among the most extreme objects in the Universe. Their gravity is so strong that once anything crosses a boundary called the event horizon, it cannot escape. Not even light can travel fast enough to break free.
According to Hawking's theory, quantum effects near the event horizon allow black holes to emit tiny amounts of radiation. Over extremely long periods, this process could cause black holes to slowly evaporate.
However, scientists have struggled to understand exactly how the energy transfer takes place. This process, known as backreaction, has remained one of the biggest unanswered questions in black hole physics.
Because Hawking radiation from real black holes is expected to be incredibly weak, direct observation is currently impossible. To overcome this challenge, researchers create laboratory systems that mimic the physics of black holes.
In this latest study, the team used ultrafast laser pulses travelling through a specially designed optical fibre. One laser pulse altered the optical properties of the fibre, creating conditions similar to a black hole's event horizon for a second pulse.
Earlier experiments using this setup successfully recreated Hawking radiation. This time, the researchers searched for evidence of backreaction, the tiny loss of energy that occurs when radiation is emitted.
To understand backreaction, scientists compare it to two people standing on roller skates. If one person pushes the other, both move in opposite directions. In a similar way, when Hawking radiation carries energy away, the black hole system must also lose energy.
The researchers detected this effect by measuring a small shift in the laser pulse responsible for creating the analogue black hole.
The discovery also revealed an unexpected result. Scientists had previously believed that Hawking radiation in laboratory systems was produced through a complicated series of interactions. Instead, the new findings suggest that both the radiation and the backreaction arise through a single, direct process.
According to the researchers, it is possible that real black holes may produce Hawking radiation through a similarly simple mechanism. If future experiments confirm this finding in other black hole analogues, it could transform scientists' understanding of black hole evaporation.
The discovery may also help explain the famous black hole information paradox, a problem that Stephen Hawking continued to investigate until his final scientific paper in 2018.
Although observing these processes in actual black holes remains beyond current technology, the new study marks an important step towards understanding some of the Universe's greatest mysteries.
