According to a famous theory by Stephen Hawking, black holes evaporate over time, gradually losing mass in the form of a strange kind of radiation as the event horizon plays havoc with surrounding quantum fields.
But it turns out that the dramatic cliff of an event horizon may not be as 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 space-time could do the same thing.
This means Hawking radiation, or something very similar to it, may not be limited to black holes. It could be everywhere, meaning that the Universe is very slowly evaporating before our very eyes.
"We demonstrate that," Wondrak says, "in addition to the well-known Hawking radiation, there is also a new form of radiation."
Hawking radiation is something we have never been able to observe, but theory and experiments suggest it's plausible.
Here's a very simplified explanation of how it works. If you know anything about black holes, it's probably that they're cosmic hoovers, gravitationally slurping up everything in their vicinity, with an inexorable finality, right?
Well, that's more or less the case, but black holes don't have 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 that 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 thing in the Universe, is sufficient. That proximity is known as the event horizon.
Hawking showed mathematically that event horizons could interfere with the complex mix of fluctuations rippling through the chaos of quantum fields. Waves that would normally cancel out no longer do so, leading to an imbalance in probabilities that produces new particles.
The energy within these spontaneously generated particles is linked directly to the black hole. Tiny black holes would see high energy particles form near the event horizon, which would carry away large amounts of the black hole's energy quickly and cause the dense object to vanish rapidly.
Big black holes would glow with a cool light in ways that would be hard to detect, causing the black hole to gradually lose its energy as mass over a much longer time.
A very similar phenomenon hypothetically occurs in electric fields. Known as the Schwinger effect, strong enough fluctuations in an electric quantum field can disrupt the balance of virtual electron-positron particles, causing some to pop into existence. Unlike Hawking radiation, however, the Schwinger effect wouldn't need a horizon – just a mind-blowingly powerful field.
Wondering if there was a way for particles to appear in curved space-time that was analogous to the Schwinger effect, Wondrak and his colleagues mathematically reproduced the same effect under a range of gravitational conditions.
"We show that far beyond a black hole the curvature of space-time plays a big role in creating radiation," van Suijlekom explains. "The particles are already separated there by the tidal forces of the gravitational field."
Anything suitably massive or dense can produce a 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 space-time 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, 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.
"That means that objects without an event horizon, such as the remnants of dead stars and other large objects in the Universe, also have this sort of radiation," Falcke says.
"And, after a very long period, that would lead to everything in the Universe eventually evaporating, just like black holes. This changes not only our understanding of Hawking radiation but also our view of the Universe and its future."
You don't have anything to worry about in the imminent future, though. It would take a black hole the mass of the Sun (with an event horizon diameter of just 6 kilometers or 3.7 miles, by the way) 1064 years to evaporate.
We've got time to kill before we all vanish in a cold puff of light.
The research has been published in Physical Review Letters, and is available on arXiv.