Gravitational waves: wrinkles in spacetime

Colliding blackholes produce intense gravitational waves that permanently alter the properties of particles in their wake, researchers claim.

The detection of gravitational waves by laser interferometers like Virgo and LIGO rely on the stretching of one “arm” of the detector relative to the other, as measured by a laser bouncing back and forth along each. Current measurements suggest that the arms return to their normal length after such a ripple in spacetime has passed. 

Now an international team of mathematicians and astrophysicists, led by Éanna Flanagan of Cornell University, New York, has produced a robust mathematical framework that suggest several effects remain after the wave has passed. 

The work, published in the journal Physical Review D, explains how to measure the impact of passing waves on a particle’s properties. 

Flanagan’s team used the new framework to detail changes in a particle’s acceleration, velocity and rotation, as well as a modification of the rotation rate of its spin. The researchers also recovered a previously known permanent change in the separation between two nearby particles, or, in the case of LIGO mirrors, at each end of the four-kilometre-long arms.

Critically, the particles do not return to their original state after the wave, meaning that these “persistent gravitational wave observables” can be measured. 

Detecting such persistent effects may also have become easier because recent measurements of the collision of dense objects such black holes and neutron stars suggest the universe is a far more violent place than previously thought.

“Yet again the LIGO and Virgo detectors have surpassed expectations,” says Mark Hannam, director of Cardiff University’s Gravity Exploration Institute, in Wales.

“Our most optimistic estimates were for a detection every week, and the first month of the run gave us five candidates.”

Having more sources of intense gravitational waves provides a greater signal to try and tease out of the background noise of future experiments to measure the lasting impact of the roiling wake of spacetime.

Related reading: ‘The success is very sweet’: gravitational wave triumph in quotes

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