The first stars that ever shone in the universe, 150 million years after the Big Bang, have yet to be observed. Their life was too short for our telescopes. They were too big and bright, and so they quickly turned into spectacular supernovae

But although our instruments are still not good enough to observe them directly, astronomers from the University of Notre Dame have come up with an ingenious method to learn about their nature. They look for very old stars, formed from the ejected material of the first stars, and study their composition.

They were lucky enough to find a particularly good star for this project. In a paper, published in the Astrophysical Journal, the team details the elements found in BD+44 493, the brightest second-generation star in the sky.

The first stars were made mostly of pure hydrogen and they were very massive, with estimates suggesting up to hundreds of times the mass of the Sun. Their gargantuan size would force them to quickly and energetically burn through their nuclear fuel, creating new elements, and explode in just a few million years.

The explosions disseminated the elements, like oxygen, carbon, etc., throughout the universe. These went to enrich the interstellar medium where new stars were being formed, so the second generation of stars has a bit of the first stars in them.

By looking at the UV light emitted by BD+44 493 using the Hubble Space telescope, the team discovered that the star contains traces of phosphorus, sulfur (never seen before in this kind of star), and zinc. Comparing the abundances of these elements to theoretical prediction they were able to constrain the properties of one of these mysterious first stars.

The progenitor of BD+44 493 is likely to be a star weighing just over 20 solar masses, which is actually quite a modest mass for one of the first stars.

The next generation of UV telescopes will be able to study hundreds more of these objects, and hopefully the James Webb Space Telescope will observe the first stars directly. It might seem weird, but we know more about the Big Bang than what came after, so to discover more about the first stars will be fascinating.