Gravitational-Wave Detector Could Sense Merging Primordial Black Holes With the Mass of a Planet, Millions of Light-Years Away

Since the early days of astronomy, gravitational-wave detectors have been part of the field. They provide a wealth information about black holes as well as what happens to them when they combine. Gravitational-wave Astronomy is still in its infancy and the types of gravitational wave we can see are limited. However, this could soon change.The mergers of stellar-mass black hole are detected by current gravitational wave observatories. Although we have seen a few mergers between neutron stars, most of these were between black holes with tens to thousands of solar masses. We are unable to observe the gravitational waves from supermassive black hole in galaxies. Proposed detectors like eLISA will enable us to observe the former but we will need a new idea to detect it.Different gravitational wave detectors have different sensitivities. Credit: Christopher Moore. Robert Cole. Christopher BerryGravitational waves from planet-mass body are difficult to observe because they are very faint and extremely high in frequency. These waves are difficult to see with current laser interferometry designs. We can only see the gravitational waves barely above background noise. A team recently proposed a gravitational-wave detector that uses resonance, rather than lasers.It is not a new idea to use resonance to detect gravitational wave. Joseph Weber attempted to detect them with a large aluminum tube in the 1960s. The cylinder would ring at a specific frequency as gravitational waves passed through it. This was due to their pulling and squeezing. Weber believed that gravitational waves would produce a stronger ring than background noise or heat. Weber's experiment was unsuccessful, and astronomers began to look for other methods like the laser interferometry we use today.Joseph Weber with one of his gravitational-wave detectors. Credit: University Archives and Special Collections, University of Maryland LibrariesWeber's design is a model for this new design, but it uses modern technology. Webers' design had a limitation in that he needed to use piezoelectric sensor to measure vibrations of the cylinder. This limited his experiment's sensitivity. Instead, the team suggests using a hollow cylindrical placed in strong magnetic fields. The cylinder should be subject to gravitational waves that pass through it. This would cause electromagnetic waves inside the cylinder which could be detected. The team believes they should detect faint gravitational waves based on their design.The most intriguing aspect of the detector's idea is its ability to detect high-frequency gravitational wave, such as those produced by merging primordial dark holes. Primordial blackholes are hypothetical objects that measure about the same size as a tennis ball and were formed in the early moments of the universe's history. They might be able to explain dark matter if they are indeed real. This new detector is perfect for finding them.This new design is still in its design phase and it's a little speculative. To test it, the team will need to create one. It remains to be determined if they can distinguish between signal and noise. If they succeed, it could reveal more about dark matter, black holes, and other things.Reference: Herman and Nicolas. Detecting Planetary-mass Primordial black Holes using Resonant Electromagnetic Wave Detectors. arXiv preprint arXiv.12189 (2020).