Microarcsecond Astrometry: Science Highlights from Gaia

Abstract

Access to microarcsecond astrometry is now routine in the radio, infrared (IR), and optical domains. In particular, the publication of the second data release ( Gaia DR2) from the Gaia mission made it possible for every astronomer to work with easily accessible, high-precision astrometry for 1.7 billion sources to twenty-first magnitude over the full sky. ▪ Gaia provides splendid astrometry, but at the limits of the data small systematic errors are present. A good understanding of the Hipparcos– Gaia astrometry concept, and of the data collection and processing, provides insights into the origins of the systematic errors and how to mitigate their effects. ▪ A selected set of results from Gaia highlight the breadth of exciting science and unexpected results, from the Solar System to the distant Universe, to creative uses of the data. ▪ Gaia data release 2 provides, for the first time, a dense sampling of Galactic phase space with high-precision astrometry, photometry, and radial velocities, allowing researchers to uncover subtle features in phase space and the observational Hertzsprung–Russell diagram. ▪ In the coming decade, we can look forward to more accurate and richer Gaia data releases, and new photometric and spectroscopic surveys coming online that will provide essential complementary data. ▪ The longer term promises exciting new opportunities for microarcsecond astrometry and beyond, including the plans for an IR version of Gaia that would offer the dense sampling of phase space deep into the Milky Way's nuclear regions.