Gravitational waves - minute ripples in spacetime first predicted by Einstein - have so far been observed only at high and ultra-low frequencies. Ground-based interferometers such as LIGO and Virgo detect high-frequency waves, while pulsar timing arrays sense waves at extremely low frequencies. Between these extremes lies the unexplored "mid-band" region.
A collaborative team from the Universities of Birmingham and Sussex has now introduced a detector concept that targets this mid-band, spanning from 10?5 to 1 Hz. The design leverages advances in optical cavity and atomic clock technology to measure phase shifts in laser light caused by passing gravitational waves. Compact and highly stable, these tabletop instruments are less affected by seismic and Newtonian noise than traditional interferometers.
"By using technology matured in the context of optical atomic clocks, we can extend the reach of gravitational wave detection into a completely new frequency range with instruments that fit on a laboratory table," said Dr Vera Guarrera from the University of Birmingham. "This opens the exciting possibility of building a global network of such detectors and searching for signals that would otherwise remain hidden for at least another decade."
The milli-Hertz range is predicted to host gravitational signals from white dwarf binaries, merging black holes, and relic waves from the early universe. While space missions like LISA will eventually probe this band, their launches are years away. The proposed optical resonator detectors could begin observing these phenomena much sooner.
"This detector allows us to test astrophysical models of binary systems in our galaxy, explore the mergers of massive black holes, and even search for stochastic backgrounds from the early universe," said Professor Xavier Calmet of the University of Sussex. "With this method, we have the tools to start probing these signals from the ground, opening the path for future space missions."
Each unit contains two orthogonal ultrastable optical cavities and an atomic frequency reference, providing multi-channel detection and enabling the identification of wave polarisation and source direction. Researchers also propose linking these detectors to existing clock networks to further enhance sensitivity and extend gravitational wave detection to even lower frequencies.
Research Report:Detecting milli-Hz gravitational waves with optical resonators
Related Links
University of Birmingham
The Physics of Time and Space
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