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Concept

Hubble constant

The image depicts a swirling galaxy with the text "Hubble constant" overlaid, symbolizing the concept of the Hubble constant in astronomy.

The proportionality factor in Hubble's law: a galaxy's recession velocity equals the constant times its distance. Its value, currently around 70 kilometres per second per megaparsec, fixes the age and size of the observable universe. Measurements from the cosmic microwave background and from local distance ladders disagree by about 9% — the so-called Hubble tension — and the discrepancy is one of the sharpest open problems in cosmology.

Mentioned in 4 articles