The so-called Cosmic Microwave Background Radiation (or CMB) has been known about since 1965. It is assumed to be an echo of the Big Bang, and is offered in High School textbooks as a proof of the Big Bang. Yet, it is actually problematic for Big Bang cosmologists.

Ref: Faulkner, D. (2016), Created Cosmos, (Green Forest, AR: Master Books), p53-54. Image: The binary star system Rho Ophiuchi, by Rogelio Bernal Andreo; released to Public Domain.