The first stars in the Universe are forever invisible to human eyes
“After the Big Bang, the Universe was hot, dense and uniform, but also expanding and cooling. By time the Universe is around 380,000 years old, it’s cooled enough to form neutral atoms for the first time. But there are two barriers to seeing anything:
1. There’s nothing to see until we start creating something that emits light. 2. Even once you do that, the Universe needs to become transparent.
Although these two problems — the formation of the first stars and the Universe becoming transparent — are often conflated together as “the dark ages,” they’re two separate problems that the Universe needs to solve.”
Let there be light! You’d think that would be enough: that you form stars in the Universe, you see those stars in the Universe, and that tells you about what’s out there. If only it were that simple. In order to truly see the first stars, you need a lot more that just starlight: you need that light to be able to freely travel through space. And — as bad luck would have it — visible light, the kind of light we’ve built our telescopes to see, is opaque to neutral atoms. In other words, it’s not enough to simply have a Universe full of stars; you need a transparent Universe full of stars, otherwise they’ll be invisible to our eyes!