Arno Penzias, co-discoverer of the Big Bang's afterglow, dies at age 90

Arno Penzias (right) and Robert Woodrow Wilson, who co-discovered the afterglow of the Big Bang. The Bell Lab employees, who won the 1978 Nobel Prize in physics for their discovery, are shown standing in front of their microwave antenna at Bell Labs in Holmdel, N.J., on Oct. 17, 1978. (AP)

Physicist Arno Penzias, who co-discovered the cosmic microwave background, helping to confirm the Big Bang theory of the universe's beginning, died on Monday at age 90.

In the 1960s, Penzias and colleague Robert Woodrow Wilson were working at Bell Labs in Holmdel, N.J., on a new type of microwave antenna shaped like a giant horn. They planned to use the ultrasensitive system to study radio emissions from the Milky Way. What they eventually found instead was a signal that originated from outside our galaxy that turned out to be the smoking gun proof for the Big Bang theory.