Astronomy Colloquium

The Mega-maser Cosmology Project (MCP) aims to determine the Hubble Constant, Ho, to ~3 percent accuracy by measuring the angular diameter distance to "mega-maser galaxies" that harbor circum-nuclear Keplerian disks exhibiting powerful water maser emission. Under the MCP, mega-maser search using the GBT and mapping using the VLBA and GBT have now identified 10 mega-maser galaxies with distances ranging from 30 Mpc to 140 Mpc, well in the Hubble flow. A 10% angular diameter distance determination to NGC6264 at 150 Mpc has been demonstrated. A by-product of the MCP is precise mass determination of the supermassive black-holes (BH) in the mega-maser galaxies. The mega-maser BH mass results appear to be inconsistent with the putative M-sigma relationship between black holes and galactic bulges. The status of the MCP will be described.