Hubble Constant

The Hubble constant H0 is given by the speed of recession v over r the distance to the receding galaxy (km s-1 Mpc-1).

The Hubble constant H0 is the proportionality factor between the distance of a galaxy and the speed it moves away from us. 

Galaxies that are further away move away increasingly faster, as expected from the expansion of space.

Without going into hair-rising algebraic details, it means that for every Megaparsec (Mpc) further away you look, galaxies appear to speed away faster by H0 kilometres per second.

H_0 = \frac{v}{r}

Now H0 can be measured in two ways using:

  • the Cosmic Microwave Background (CMB) or
  • the cosmic distance ladder.

The most recent measurement made by the Planck satellite mission was published back in July 2018, when the final results gave a value of

H0 = 67.66 ± 0.42 km s−1Mpc−1.

However, astronomers who measure the speed and distance (with the ‘standard candles’ method) of galaxies think the value is closer to

H0 = 73.52 ± 1.62 km s−1 Mpc−1.

Little 'Bytes' about Natural Phenomena, Theoretical Physics and the Latest Worldwide Scientific Findings. Edited from Glasgow, Scotland.