Electromagnetic (EM) waves and gravitational waves are the only available means to study the Universe on a large scale. For millennia, only the former could be used, in naked-eye astronomical observations by the ancients based on the reception of visible light, or present-day super telescopes operating in various bands of the EM spectrum, from radio waves to gamma rays.
Examples of coherent sources of GWs. Credit: Nancy AggarwalGravitational effects can be inferred from the relative movements of celestial bodies. The first direct measurement of gravitational waves occurred only in 2015. It was effected by the Laser Interferometer Gravitational-Wave Observatory (LIGO in the United States and by the Virgo detector in Italy. As the media emphasized at the time, the feat opened up a totally new window for investigation of the Universe.The window has so far been explored only in a relatively narrow band of frequencies ranging from 10 hertz (10 Hz) to 10 kilohertz (104 Hz). The challenges and opportunities of detecting gravitational waves at much higher frequencies, from megahertz (106 Hz) to gigahertz (109 Hz), were the focus for an in-person meeting held at Trieste, Italy, in 2019, before the pandemic.A commentary on the workshop discussion there and a review of the literature on the topic have now been published in an article in the journal Living Reviews in Relativity.One of the authors is Odylio Denys de Aguiar, a senior researcher at the National Space Research Institute (INPE) in Brazil.The initiative was supported by FAPESP via a Regular Research Grant and a Thematic Project for which Aguiar was principal investigator."To emit in the spectrum band considered, highly compact matter must oscillate at extremely high frequencies. This could happen, for example, with mini black holes, with diameters of less than a kilometer, and masses smaller than the mass of the Sun or even the mass of Earth," Aguiar said.As noted by the…