Scientists have published the first good estimate of the Hubble constant, pegging it at 73.3 km/s/Mpc. This is closer to other measurements of the local expansion, including the gold standard using Type Ia supernovae. The new estimate highlights the mismatch with estimates from the early universe.
Using a relatively new and potentially more precise technique for measuring cosmic distances, which employs the average stellar brightness within giant elliptical galaxies as a rung on the distance ladder, astronomers calculate a rate, 73.3 kilometres per second per megaparsec, give or take 2.5 km/sec/Mpc -- that lies in the middle of three other good estimates, including the gold standard estimate from Type Ia supernovae. This means that for every megaparsec, 3.3 million light-years, or 3 billion trillion kilometres, from Earth, the universe is expanding an extra 73.3 ±2.5 kilometres per second. The average from the three other techniques is 73.5 ±1.4 km/sec/Mpc.
The new value of H0 is a byproduct of two other surveys of nearby galaxies, one of which uses space and ground-based telescopes to exhaustively study the 100 most massive galaxies within about 100 Mpc of Earth. A major goal is to weigh the supermassive black holes at the centres of each one.