Gravitational wave detection with photometric surveys

Abstract

Gravitational wave (GW) detections have considerably enriched our understanding of the universe. To date, all the known events were observed via direct detection. In this paper, we study a GW detection technique based on astrometric observation and demonstrate that it offers a highly flexible frequency range that can uniquely complement existing detection methods. Using repeated point-source astrometric measurements, periodic GW-induced deflections can be extracted and wave parameters inferred. We illustrate how high-cadence observations of the galactic bulge, such as offered by the Roman Space Telescope's Exoplanet MicroLensing (EML) survey, have the potential to be a potent GW probe with complementary frequency range to Gaia, pulsar timing arrays (PTAs), and the Laser Interferometer Space Antenna (LISA). We calculate that the Roman EML survey is sensitive to GWs with frequencies ranging from 7.7 × 10 −8 Hz to 5.6 × 10 −4 Hz, which opens up a unique GW observing window for supermassive black hole binaries and their waveform evolution. While the detection threshold assuming the currently expected performance proves too high for detecting individual GWs in light of the expected supermassive black hole binary population distribution, we show that binaries with chirp mass Mc > 10 7.6 M out to 10 Mpc can be detected if the telescope is able to achieve an astrometric accuracy of 0.11 mas. To confidently detect binaries with Mc > 10 7 M out to 50 Mpc, a factor of 100 sensitivity improvement is required. We propose several improvement strategies, including recovering the mean astrometric deflection and increasing astrometric accuracy, number of observed stars, field-of-view size, and observational cadence. We also discuss how other existing and planned photometric surveys could contribute to detecting GWs via astrometry.

Asteroids for $μ$Hz gravitational-wave detection

“…VI), existing EPTA limits [12] (dark green; converted to hc per the discussion in Sec. VI), the LISA L3 design sensitivity (solid black) [20], the µAres strawman mission concept projected sensitivity (darker, short-dashed purple, plotted above ∼ 2 µHz; see text) [6], and projected future astrometric GW detection reach using Gaia or Roman Space Telescope survey data [55] (gold and orange, respectively; converted to hc per the discussion in Sec. VI).…”

“…Additionally, in the µHz band, we present projected sensitivities of stellar astrometric GW detection making use of future Gaia and/or Roman Space Telescope largescale survey data taken from Ref. [55]. The projections of Ref.…”

“…The projections of Ref. [55] are however again presented as 'the detectable instantaneous (time-domain) strain, h, of monochromatic GWs, assuming end-of-survey performance' [55]. As such, they must also be converted to 44 h c = h √ f gw T obs .…”

“…Proposals utilizing astrometric techniques on large-scale survey data (e.g., Gaia [47] and Roman Space Telescope [48] surveys) are also able to access this band (see, e.g., Refs. [49][50][51][52][53][54][55]), but existing projections indicate that the levels of strain sensitivity attainable are somewhat modest [55]; such approaches are however able to overcome some important noise sources [56] that limit all local-TM-based techniques operating in the inner Solar System below ∼ µHz frequencies. Recent work has also studied how orbital perturbations (of, e.g., binary millisecond pulsars, or the Moon) that arise specifically from a broadband stochastic GW background could access this band [57,58].…”

All-sky analysis of astrochronometric signals induced by gravitational waves

“…This suggests that a survey of some 10 9 stars, over several years at angular precision of a few µas, would achieve upper bounds on the cosmological background of GWs comparable to limits currently imposed by LIGO-VIRGO observations [20] at higher frequencies. Today, the GAIA [21] satellite survey is already operating with a few orders of magnitude of this baseline, and similar missions in the future may go well beyond this [22]. Different approaches have been adopted in defining the formalism through which the signal of isotropic GWs is imprinted in both timing residual and astrometric observations, including their induced anisotropies.…”