Earliest Generation of Stars Discovered in Universe

Using the European Southern Observatory's (ESO) Very Large Telescope (VLT), astronomers have found the best evidence yet of a long-sought type of star - the earliest stars.

It has long been believed that the first generation of stars - known as Population III stars - exists. In theory, they were born out of the primordial material from the Big Bang that created the early Universe. However, they have never been directly observed.

Population I stars (like the Sun), on the other hand, are quite abundant. They are full of heavy chemical elements - such as oxygen, nitrogen, carbon and iron, which are essential to life. Meanwhile, Population II stars, which are older stars, contain less heavy elements, and have also been observed.

But there must have been a first generation of stars that kicked off the process of creating these elements for future galaxies and planets. These stars would have been enormous - several hundred or even a thousand times more massive than the Sun - and hot, exploding as supernovae after only about two million years. And until now, proof of their existence has been inconclusive.

Researchers have peered into the distant past, observing a far-away galaxy from approximately 800 million years after the Big Bang - a period known as reionization.

The galaxy, CR7, is by far the brightest galaxy ever observed at this stage in the Universe - three times as bright, to be exact. The X-shooter and SINFONI instruments on the VLT found signs of strong ionized helium emission in CR7, but no signs of the heavier elements. This meant the team had discovered the first good evidence for clusters of Population III stars that had ionized gas within a galaxy in the early Universe.

"The discovery challenged our expectations from the start," study author David Sobral of the Institute of Astrophysics and Space Sciences said in a statement, "as we didn't expect to find such a bright galaxy. Then, by unveiling the nature of CR7 piece by piece, we understood that not only had we found by far the most luminous distant galaxy, but also started to realize that it had every single characteristic expected of Population III stars. Those stars were the ones that formed the first heavy atoms that ultimately allowed us to be here. It doesn't really get any more exciting than this."

If they're right about the presence of Population III stars in CR7, researchers say, it could mean that the rare stars are actually easier to spot than we thought. The team plans to conduct further observations with the VLT, ALMA, and the NASA/ESA Hubble Space Telescope to confirm their existence beyond a doubt.

The findings were published in The Astrophysical Journal.

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