Question

the big bang produced an imprint of leftover heat called

Answer 1

That's called the "Cosmic Microwave Background".  (CMB)
It was discovered in 1965, and its discoverers were awarded
the Nobel Prize in Physics in 1978.

Answer 2

Answer:

Cosmic Microwave Background

Explanation:

The cosmic background radiation gives us a glimpse into the formative years of our universe. The cosmic background radiation contains radiation from the epoch of recombination of the Big Bang. The radiation is most visible in the microwave region of the electromagnetic spectrum. The radiation poses a strong case that the universe originated from the big bang.