What was it like when the first stars began to shine?

For perhaps as long as the first 100 million years after the start of the hot Big Bang, the Universe was devoid of stars. The matter in the Universe required just half-a-million years to finish forming neutral atoms, but stars would take much longer to form for a variety of reasons. For one, gravitation on cosmic scales is a slow process, made even more difficult by the high energies of the radiation the Universe was born with. For another, the initial gravitational imperfections were small: just 1-part-in-30,000, on average. And for yet another, gravity only propagates at the speed of light, meaning that when the Universe is very young, there’s only a very small distance range over which other masses can “feel” the gravitational force from any particular initial mass. <a href="https://medium.com/starts-with-a-bang/what-was-it-like-when-the-first-stars-began-to-shine-a715e9c1688f">Read More</a>