How fast is the Universe expanding? (Intermediate)

Can you give me the exact velocity of the Universe to date please?

The parameter that is used to describe how fast the Universe is expanding is the Hubble constant (which tells us how fast the objects appear to be moving away from us as a function of distance). Historically there has been much debate over the exact value of the Hubble constant, but as experimental techniques have improved a consensus on the value of 70 km/s per Megaparsec (3.26 million light-years) has formed, with essentially all modern experiments agreeing on this value.

The techniques used to estimate the Hubble constant involve looking at astronomical objects we understand the behaviour of, and comparing the observations at various distances from us. Some of the objects used are Cepheid variables (young and massive stars whose luminosity change periodically), supernovae (explosion of a star at the end of its life) and globular clusters (dense groups of old stars found in the centre of galaxies). We use these objects because we get to have an estimate of their distances, which is generally very hard to do in astronomy. Knowing the distance and the redshift of these galaxies (i.e. how fast they are moving away), which is relatively easy to get, astronomers can then get a measurement of Hubble's constant.

About the Author

Amelie Saintonge

Amelie is working on ways to detect the signals of galaxies from radio maps.

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