- Astrometric Gravitational-Wave Detection via Stellar Interferometry Michael A. Fedderke, Peter W. Graham, Bruce Macintosh, Surjeet Rajendran

We evaluate the potential for gravitational-wave (GW) detection in the frequency band from 10 nHz to 1 μHz using extremely high-precision astrometry of a small number of stars. In particular, we argue that non-magnetic, photometrically stable hot white dwarfs (WD) located at ∼ kpc distances may be optimal targets for this approach. Previous studies of astrometric GW detection have focused on the potential for less precise surveys of large numbers of stars; our work provides an alternative optimization approach to this problem. Interesting GW sources in this band are expected at characteristic strains around hc∼10−17×(μHz/fGW). The astrometric angular precision required to see these sources is Δθ∼hc after integrating for a time T∼1/fGW. We show that jitter in the photometric center of WD of this type due to starspots is bounded to be small enough to permit this high-precision, small-N approach. We discuss possible noise arising from stellar reflex motion induced by orbiting objects and show how it can be mitigated. The only plausible technology able to achieve the requisite astrometric precision is a space-based stellar interferometer. Such a future mission with few-meter-scale collecting dishes and baselines of (100 km) is sufficient to achieve the target precision. This collector size is broadly in line with the collectors proposed for some formation-flown, space-based astrometer or optical synthetic-aperture imaging-array concepts proposed for other science reasons. The proposed baseline is however somewhat larger than the km-scale baselines discussed for those concepts, but we see no fundamental technical obstacle to utilizing such baselines. A mission of this type thus also holds the promise of being one of the few ways to access interesting GW sources in this band.

https://arxiv.org/abs/2303.12676

Cosmological studies with VLBI; C. Spingola

Current cosmological controversies can be solved if a sufficient level of precision is achieved by observations. Future surveys with the next generation of telescopes will offer significantly improved depth and angular resolution with respect to existing observations, opening the so-called "era of precision cosmology". But, that era can be considered already started at the radio wavelengths with Very Long Baseline Interferometry (VLBI). In this paper, we give an overview on how VLBI is contributing to some open questions in contemporary cosmology by reaching simultaneously the largest distances and the smallest scales.

https://arxiv.org/abs/2204.07677

Astrometric Gravitational-Wave Detection via Stellar Interferometry; Michael A. Fedderke, Peter W. Graham, Bruce Macintosh, Surjeet Rajendran

We evaluate the potential for gravitational-wave (GW) detection in the frequency band from 10 nHz to 1 μHz using extremely high-precision astrometry of a small number of stars. In particular, we argue that non-magnetic, photometrically stable hot white dwarfs (WD) located at ∼kpc distances may be optimal targets for this approach. Previous studies of astrometric GW detection have focused on the potential for less precise surveys of large numbers of stars; our work provides an alternative optimization approach to this problem. Interesting GW sources in this band are expected at characteristic strains around hc∼10−17×(μHz/fGW). The astrometric angular precision required to see these sources is Δθ∼hc after integrating for a time T∼1/fGW. We show that jitter in the photometric center of WD of this type due to starspots is bounded to be small enough to permit this high-precision, small-N approach. We discuss possible noise arising from stellar reflex motion induced by orbiting objects and show how it can be mitigated. The only plausible technology able to achieve the requisite astrometric precision is a space-based stellar interferometer. Such a future mission with few-meter-scale collecting dishes and baselines of (100 km) is sufficient to achieve the target precision. This collector size is broadly in line with the collectors proposed for some formation-flown, space-based astrometer or optical synthetic-aperture imaging-array concepts proposed for other science reasons. The proposed baseline is however somewhat larger than the km-scale baselines discussed for those concepts, but we see no fundamental technical obstacle to utilizing such baselines. A mission of this type thus also holds the promise of being one of the few ways to access interesting GW sources in this band.

- https://arxiv.org/pdf/2207.12540.pdf Theia : science cases and mission profiles for high precision astrometry in the future
- https://arxiv.org/abs/2205.06517. Simulations of astrometric planet detection in alpha Centauri by intensity interferometry
- Interferometry helps weigh a galactic microlens, Physics Today
- The Milky Way, Coming into Focus: Precision Astrometry Probes its Evolution, and its Dark Matter, Susan Gardner, Samuel D. McDermott, Brian Yanny. https://arxiv.org/abs/2106.13284
- Constraining ?0 Via Extragalactic Parallax, Nicolas C. Ferree, Emory F. Bunn https://arxiv.org/pdf/2109.07529.pdf
- Inferring dark matter substructure with astrometric lensing beyond the power spectrum https://arxiv.org/pdf/2110.01620.pdf
- Asteroid g-2 experiments: new fifth force and ultralight dark sector tests, Yu-Dai Tsai, Youjia Wu,Sunny Vagnozzi and Luca Visinelli - how improved tracking of asteroids helps to study fundamental forces.