MISSING: THE FIRST STARS

They shaped the Universe, yet the first stars ever born continue to evade the searches of astronomers like Dr Emma Chapman

- DR EMMA CHAPMAN

As an astronomer, I collect stars. There are several hundred billion of them in our Galaxy, the Milky Way, so it's important to find a way to categorise them. While others might rank their stars by colour or size, I prefer to order them chronologically. That way, we can simply look through them to read the history of the Universe.

There is, however, a glaring gap in my collection: the very first generation of stars are missing. And I'm not the only one to have encountered this problem. All the world's astronomers - despite the multitude of telescopes at our disposal and centuries of diligent observation - have failed to find a single one. If we're trying to read through the history of the Universe, then our library is missing the first volume.

And this is a problem. Stars are the way the Universe grows and evolves. They're powered by fusion, where light elements, such as hydrogen, fuse together to form heavier elements. When they die, they explode in a supernova, flinging all the heavy elements they created inside their core into the surrounding neighbourhood. This instantly enriches the pristine, primordial gas with the heavy elements required for new stars, planets and even life.

You see, these first stars are different from all those that came after. Their novelty comes from their unique chemistry. Like all stars, they were born from clouds of gas that collapsed under their own gravity. As they were the first stars, they only contained the hydrogen, helium and a sprinkling of lithium that was created in the Big Bang.

This unique chemistry meant they had fewer ways to lose heat than younger stars do, and so the clouds stayed puffed up. This allowed the clouds to grow much larger before they collapsed, meaning those early stars could be several hundred times more massive than our Sun.