Scientists Valerie Domcke from CERN and Camilo Garcia-Cely from DESY have devised a new technique to search for gravitational waves. Their method is published in Physical Review Letters.
What are gravitational waves?
Celestial objects with mass cause curvature in spacetime. In certain cases, when these objects accelerate through spacetime, the change in spacetime’s curvature propagates at the speed of light in a wave-like manner. These are called gravitational waves and were first observed in 2015 by the LIGO and Virgo detectors.
The new method devised by Domcke and Garcia-Cely is based on the conversion of high-frequency gravitational waves into radio waves. The conversion takes place in the presence of magnetic fields, and it distorts the cosmic microwave background. Cosmic Microwave Background (CMB), also known as relic radiation, is an electromagnetic radiation remnant from an early stage of the universe, and it permeates the universe.
The researchers show that this distortion can be used to search for gravitational waves from various cosmic sources, even from the very early ages of the dark universe when hydrogen atoms formed. According to the researchers, the odds of conversion of high-frequency gravitational waves into radio waves are slim; however, the odds are counterbalanced by the enormous detector, the cosmos. The CMB provides an upper bound on the amplitude of the gravitational waves that convert into radio waves. The researchers derived two such upper bounds using CMB measurements from two radio telescopes.
For the weakest possible cosmic magnetic ?elds, determined from current astronomical data, measurements from the EDGES telescope located at the Murchison Radio-Astronomy Observatory in Western Australia resulted in a maximum amplitude of one part in 1012 for a gravitational wave with a frequency of around 78 MHz. For the same weakest cosmic magnetic field, measurements from the balloon-borne ARCADE 2 instrument yielded a maximum amplitude of one part in 1014 at a frequency of 3?30 GHz.
Whereas, for the strongest possible cosmic magnetic fields, these bounds were tighter. EDGES: one part in 1021 and ARCADE 2: one part in 1024. These are about seven orders of magnitude more stringent than lab-based experiments.
The researchers believe that the next generation radio telescopes like the Square Kilometer Array combined with improved data analysis should further tighten these bounds. This could help detect gravitational waves even from the early universe.
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