Cosmology and the Hubble Constant: On the Megamaser Cosmology Project (MCP)

摘要

The Hubble constant H _0 describes not only the expansion of local space at redshift z ~ 0, but is also a fundamental parameter determining the evolution of the universe. Recent measurements of H _0 anchored on Cepheid observations have reached a precision of several percent. However, this problem is so important that confirmation from several methods is needed to better constrain H _0 and, with it, dark energy and the curvature of space. A particularly direct method involves the determination of distances to local galaxies far enough to be part of the Hubble flow through water vapor (H_2O) masers orbiting nuclear supermassive black holes. The goal of this article is to describe the relevance of H 0 with respect to fundamental cosmological questions and to summarize recent progress of the Megamaser Cosmology Project (MCP) related to the Hubble constant.