Solar System-scale interferometry on fast radio bursts could measure cosmic distances with sub-percent precision

TL;DR

A proposed Solar System-scale interferometry method using fast radio bursts can measure cosmic distances with sub-percent accuracy, enabling precise cosmological parameters and additional astrophysical insights.

Contribution

This paper introduces a novel interferometry setup with detectors beyond 10 AU to measure cosmic distances and parameters with unprecedented precision.

Findings

Distance measurement precision improves quadratically with baseline length.

A four-detector constellation can achieve sub-percent accuracy in cosmological parameters.

The setup can also resolve pulsar emission regions and detect low-frequency gravitational waves.

Abstract

The light from a source at a distance d will arrive at detectors separated by 100 AU at times that differ by as much as 120 (d/100 Mpc)^{-1} nanoseconds because of the curvature of the wavefront. At gigahertz frequencies, the arrival time difference can be determined to better than a nanosecond with interferometry. If the space-time positions of the detectors are known to a few centimeters, comparable to the accuracy to which very long baseline interferometry baselines and global navigation satellite systems (GNSS) geolocations are constrained, nanosecond timing would allow competitive cosmological constraints. We show that a four-detector constellation at Solar radii of >10 AU could measure distances to individual sources with sub-percent precision and, hence, cosmological parameters such as the Hubble constant to this precision. The precision increases quadratically with baseline length. FRBs are the only known bright extragalactic radio source that are sufficiently point-like. Galactic scattering limits the timing precision at <3 GHz, whereas at higher frequencies the precision is set by removing dispersion. Furthermore, for baselines greater than 100 AU, Shapiro time delays limit the precision, but their effect can be cleaned with two additional detectors. Accelerations that result in ~1 cm uncertainty in detector positions (from variations in the Sun's irradiance, dust collisions and gaseous drag) could be corrected for with weekly GNSS-like trilaterations. Gravitational accelerations from asteroids occur over longer timescales, and so a setup with a precise accelerometer and calibrating the detector positions off of distant FRBs may also be sufficient. The proposed interferometer would also resolve the radio emission region of Galactic pulsars, constrain the mass distribution in the outer Solar System, and reach interesting sensitivities to ~0.01-100 micro-Hz gravitational waves.