NewScientist (1 September 2018, paywall) reports on a possible natural phenomenon that would wipe us out without a chance of redemption:
Most gravitational waves – ripples in the fabric of the universe caused by the motion of massive objects – are spherical. They propagate outwards like a 3D version of ripples on the surface of a pond after a stone is thrown in. But when a high energy object or particle moves at the speed of light, theory says it creates a different type of gravitational wave: flat, or plane-fronted waves, like a tidal wave.
Frans Pretorius at Princeton University in New Jersey and William East at the Perimeter Institute for Theoretical Physics in Canada simulated what happens if two of these unusual waves collide.
Smaller varieties simply pass through one another and go on to dissipate. But when they get large enough, a pair of colliding waves can collapse into a black hole, Pretorius and East found. “These particles have a lot of energy and produce curvature in space-time, and when the waves collide, that curvature wraps in on itself,” says Pretorius.
The black hole left behind would devour about 85 per cent of the energy in the waves, the pair found. Most of the remaining energy would stream outwards 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 (arxiv.org/abs/1807.11562v1).
I’m just fascinated at both the idea of gravitational waves colliding causing a black hole – and that a gravitational wave is itself affected by gravitation. I suppose it’s inevitable, given how a black hole warps the area around it, but I’m still boggling a bit. A measure of my lack of knowledge about exotic physics.
