Year: 2026
Type: preprint
Abstract: We forecast the sensitivity of a dedicated, fast-spinning astrometric survey to a stochastic gravitational-wave background (SGWB) in the microhertz gap between pulsar timing arrays (PTAs) and LISA. Spinning the satellite faster samples each star more often, raising the Nyquist frequency and opening higher frequencies at no cost in noise: the shorter, noisier exposures are exactly compensated by their number, so the white-noise floor of each position stream is independent of cadence. High frequencies are where astrometry is most competitive, because the deflection measures the strain directly: its strain noise is white, whereas the equivalent noise of pulsar timing grows as $f^2$. With a cross-correlation estimator over $N$ reference stars and the astrometric overlap computed in the distant-source limit, we find that a Gaia-like satellite scanning the ecliptic poles, with $N\sim10^4$ bright stars over $10$~yr, falls short of the background measured by PTAs by a factor $\sim\!60$. A larger, $8$-m-class aperture, or a constellation of satellites covering the whole sky, reaches it, while extending the reach continuously across the $μ$Hz band.
Source: arXiv (Cornell University)
Authors: Mentasti, Giorgio, Contaldi, Carlo
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funder: Agence Nationale de la Recherche
OpenAlex ID: W7223129338