Cosmic microwave background
The cosmic microwave background (CMB) is black-body radiation that is often referred to as leftover radiation from the big bang, though it was scattered or emitted several hundred thousand years after the big bang. The spectrum is consistent with that of a 2.7 kelvin black body, with a peak in the microwave region of the electromagnetic spectrum.
The CMB was first detected by Arno Penzias and Robert Wilson in 1965. For their discovery, Penzias and Wilson were awarded a share of the 1978 Nobel Prize in physics.