October 18, 2018

  • Gravitational waves from black hole pairs could act like tractor beams

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    Trapped by a black hole tango. Henze, NASA

    By Leah Crane of NewScientist for Science Daily

    Gravitational waves, the ripples in space-time caused by the motions of massive objects, could act like sci-fi tractor beams.

    We already know that a rotating beam of light can trap tiny particles and move them around – this year’s Nobel prize in physics was awarded for related research.

    This works because particles essentially get stuck between peaks of the light wave as it propagates forward, like a surfer riding a swell. As the wave rotates, it acts like a sort of whirlpool of light, trapping the particle in place.

    Iwo Bialynicki-Birula at the Polish Academy of Sciences and Szymon Charzyński at the University of Warsaw calculated that the same thing could happen with a rotating beam of gravitational waves, and in much the same way. An object could get stuck in a swell of increased gravity and rotation of the wave would trap it there.

    “When something gets trapped, it is like it is in the eye of the gravitational wave hurricane,” says Bialynicki-Birula.

    This sort of gravity vortex is probably produced when a pair of black holes or other enormous objects orbit one another, he says. All of the gravitational waves that we have observed came from systems like this, where orbiting black holes or neutron stars spiralled inwards and smashed together.

    There’s just one problem, says Lionel London at Cardiff University, UK: for a tractor beam to do anything, it needs something to grab hold of, but black holes tend to sweep away or suck in surrounding matter.

    Neutron star systems may host more matter, he says, but then it’s not certain the gravitational waves would be powerful enough to trap anything.

    That said, if a rock passed by a pair of black holes at exactly the right time, it might be able to get trapped in a beam of gravitational waves, leaving it stuck in an eddy in the fabric of space-time.