WoU-MMA: An Astrometric Approach to Gravitational Waves Spanning nHz to attoHz and Novel Observational Studies of a Dynamic Cosmology

Our Universe is dynamic: everything in the sky moves or appears to move. The Universe expands and accelerates, gravity pulls galaxies together, the Milky Way Galaxy moves through the Universe, the Solar System orbits the center of the Milky Way, and the Earth orbits the Sun. On top of all these motions, there are small ripples in spacetime due to Gravitational waves that arose in the early universe or were created by supermassive black holes throughout its history. In this project, scientists at the University of Colorado plan to disentangle all of these motions in order to detect and characterize the stretching and squeezing of spacetime by gravitational waves. These are new cosmological probes of our dynamic Universe. As part of this project, the team will bring novel research techniques and results into the classroom and the public domain. The team will also create and distribute visualizations that will communicate the broad ideas of gravity and cosmology to the public and to K-12 schools nationwide. Astrometry, or the measurement of the positions of celestial bodies, has entered a new era of accuracy and precision, and it is now possible to detect proper motions at the level of 1 microarcsecond per year. This project will use extragalactic proper motions to address fundamental questions about gravitational waves and our dynamic Universe. A layered approach will disentangle our motion from cosmic motions and from apparent motions caused by a rippling spacetime. This program will use current and upcoming Gaia astrometry to detect and characterize the low-frequency stochastic gravitational wave background in three dimensions spanning nHz to attoHz frequencies. The team will assess the source of the pulsar-detected stochastic background, determine whether the background is isotropic, unpolarized, transverse and traceless, and if not, will measure its anisotropy, polarization, or vector or tensor qualities. The team will also make the first measurement of the secular extragalactic parallax, the real-time growth of large-scale cosmic structures, and the secular aberration drift perturbations that may arise from the Hubble expansion and dark energy. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.