The faint, flickering distortions of space-time, which we call gravitational waves, are difficult to discover, and we have only succeeded in the last few years. However, scientists have now calculated that these waves may leave more stubborn traces of their passages – traces we may possibly discover.
Such traces are called persistent gravitational wave observables. In a new article, an international research team has refined the mathematical framework for their definition. They give three examples of what these observables might be.
Here are the gravitational waves fast: When two massive objects collide like neutron stars or black holes, they send shockwaves through the universe that bounce all the stuff of space-time itself. This effect was predicted by Einstein in his general theory of relativity of 1
This device is an interferometer that shoots two or more laser beams that are several kilometers long. The wavelengths of these laser beams interfere to cancel each other out, so that normally no light falls on the photodetectors of the instrument.
However, when a gravitational wave strikes, these laser beams will vibrate, shrink and stretch by warping space-time. This means that their interference pattern is broken and they no longer cancel each other out – so the laser strikes the photodetector. The pattern of light that strikes can inform the scientists about the event that created the wave.
But this shrinking and stretching and stretching of space-time could have a much longer-lasting effect, according to astrophysicist Éanna Flanagan of Cornell University and her colleagues.
As the waves propagate in space-time, they can also change the speed, acceleration, trajectories and relative positions of objects and particles on their way – and these properties will not immediately return to normal and make them potentially observable.
Particles, for example, disturbed by a shock of gravitational waves could show up. In its new framework, the research team noted mathematically detailed changes that could occur in the rotational speed of a spinning particle and in its acceleration and velocity.
Another of these persistent gravitational wave observables has a similar effect to time dilation, which causes a strong gravitational field to slow down time.
Since gravitational waves deform both the time and the time between space and two extremely accurate and synchronized clocks in different places, such as atomic clocks, can be affected by gravitational waves that show different times after the waves passed by. Finally, the gravitational waves could actually permanently shift the relative positions in the mirrors of a gravitational wave interferometer – not much, but enough to be detectable.
Between their first discovery in 2015 and last year, LIGO-Virgo's gravitational wave collaboration discovered a handful of events before LIGO was shut down for upgrades.
At the moment, there are not enough discoveries in the bank for a meaningful statistical database to test these observables.
LIGO-Virgo was turned back on April 1st and has since detected at least one gravitational wave event per week.
The field of gravitational-wave astronomy heats up space scientists are itching to test new mathematical calculations and frameworks, and it will not be long before we float positively in data.
This is such an incredibly exciting time for space exploration, really.  The research was published in Physical Review D .