The American astrophysicist and Nobel laureate Arno Penzias, who has died aged 90, was responsible for one of the biggest cosmological revelations of the 20th century – the discovery of cosmic microwave background, the leftover radiation from the big bang.
He first demonstrated its existence in 1965 with his collaborator Robert Wilson, and then, five years later – with Wilson and another astrophysicist, Keith Jefferts – went on to detect the presence of interstellar carbon monoxide, launching the field of molecular line astronomy.
