Physicists say a kind of freakish gravitational wave would be so powerful they could tangle space-time, form a black hole and destroy the Earth. But don鈥檛 worry, they probably won鈥檛.
Most gravitational waves 鈥� ripples in the fabric of the universe caused by the motion of massive objects 鈥� are spherical. They propagate outward like ripples from a stone dropped in a pond. But when an object or particle moves at the speed of light, it creates flat, or plane-fronted, gravitational waves that move forward like a tidal wave.
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Frans Pretorius at Princeton University and William East at the Perimeter Institute for Theoretical Physics in Canada simulated what would happen when two of these waves collide.
Black hole collapse
Smaller varieties of these waves simply pass through one another and eventually dissipate. But Pretorius and East found that when they get large enough, a pair of colliding waves can collapse into a black hole.
鈥淭hese particles have a lot of energy and produce curvature in space-time, and when the waves collide, that curvature wraps in on itself,鈥� says Pretorius. 鈥淪pace-time is sort of sucking itself into a black hole.鈥�
The black hole left behind would devour about 85 per cent of the energy in the original waves, the researchers found. Most of the remaining 15 per cent would stream outward in a shell of slightly weaker gravitational waves, while a small proportion of the waves would be essentially caught in orbit, circling the black hole forever.
This is the same sort of black hole that caused worries when the Large Hadron Collider (LHC) was switched on. The LHC accelerates beams of particles to speeds close to the speed of light and crashes them together 鈥� the same process that could create plane-fronted gravitational waves and then black holes. But those beams don鈥檛 have nearly enough energy.
鈥淵ou would need an accelerator bigger than the size of the solar system to be able to do this,鈥� says David Garfinkle at Oakland University in Michigan. 鈥淭here鈥檚 nothing that we know of in our universe that could cause plane-fronted waves of high enough energy to form a black hole.鈥�
To create a black hole, these gravitational waves would have to be incredibly powerful. The gravitational waves that the Laser Interferometer Gravitational-Wave Observatory (LIGO) has detected stretched and squeezed the four-kilometre-long detectors by about one thousandth of the width of a proton. In contrast, these waves would warp the LIGO detectors by a kilometre or more, Pretorius says.
鈥淵ou wouldn鈥檛 want it to be nearby, and if it were it would stretch Earth by thousands of kilometres and everything would be destroyed,鈥� says Vitor Cardoso at the University of Lisbon in Portugal. 鈥淎s soon as we learned about it, we would die.鈥�
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