According to a famous theory by Stephen Hawking, black holes evaporate over time, gradually losing mass in the form of a strange type of radiation as the event horizon wreaks havoc with surrounding quantum fields. But it turns out that the dramatic precipice of an event horizon might not be so critical to this process after all. According to new research by astrophysicists Michael Wondrak, Walter van Suijlekom, and Heino Falcke of Radboud University in the Netherlands, a steep enough slope in the curvature of spacetime could do the same. This means that Hawking radiation, or something very similar to it, may not be limited to black holes. It could be everywhere, which means that the Universe is very slowly evaporating before our eyes.
“We proved it” Wondrak says”In addition to the well-known Hawking radiation, there is also a new form of radiation.”
Hawking radiation is something we’ve never been able to observe, but theory and experiment suggest it’s plausible. Here is a very simplified explanation of how it works. If you know anything about black holes, chances are they’re cosmic vacuum cleaners, gravitationally sucking in everything around them with relentless finality, right? Well, that’s all, but black holes have no more gravity than any other body of equivalent mass. What they have is density: a lot of mass packed into a very, very small space. Within a certain proximity of this dense object, the gravitational pull becomes so strong that escape velocity, the speed needed to escape, is impossible. Not even the speed of light in a vacuum, the fastest in the Universe, is enough. This proximity is known as the event horizon.
Hawking demonstrated mathematically that event horizons can interfere with the complex mix of fluctuations rippling through the chaos of quantum fields. Waves that would normally cancel no longer do, leading to an imbalance in the chances of producing new particles. The energy within these spontaneously generated particles is tied directly to the black hole. Tiny black holes would see high-energy particles form near the event horizon, quickly taking large amounts of energy from the black hole and causing the dense object to quickly disappear.
Large black holes would shine cold light in ways that are difficult to detect, causing the black hole to gradually lose its energy as a mass over a much longer time.
AA very similar phenomenon hypothetically occurs in electric fields. Known as the Schwinger effect, strong enough fluctuations in a quantum electric field can upset the balance of virtual particles of electrons and positrons, causing some to appear. Unlike Hawking radiation, however, the Schwinger effect would not need a horizon, just an incredibly powerful field. Wondering if there was a way for particles to appear in curved spacetime that was analogous to the Schwinger effect, Wondrak and his colleagues mathematically reproduced the same effect under a variety of gravitational conditions.
“We show that well beyond a black hole, the curvature of space-time plays an important role in creating radiation,” he said. van Suijlekom explains. “The particles are already separated there by the tidal forces of the gravitational field.”
Anything suitably massive or dense can cause significant curvature of space-time. Basically, the gravitational field of these objects causes space-time to warp around them. Black holes are the most extreme example, but spacetime also curves around other dense dead stars, such as neutron stars and white dwarfs, as well as extremely massive objects, such as galaxy clusters. In these scenarios, the researchers found that gravity can still affect fluctuations in quantum fields enough to give rise to new particles very similar to Hawking radiation, without requiring the catalyst of an event horizon. “This means that objects without an event horizon, such as the remnants of dead stars and other large objects in the Universe, also have this type of radiation,” he said. Falcke says.