Scientists discover clouds containing remains of the first-ever stars

5 May 2023

Artist's impression of chemical elements in a distant gas cloud. Image: ESO/L. Calçada, M. Kornmesser

Many old stars are considered to be second-generation stars born from the ‘ashes’ of ancestral stars that formed 13.5bn years ago.

A team of researchers have discovered three very distant gas clouds in the early universe that they believe are the remnants of explosions of the very first stars ever formed.

Using the Very Large Telescope (VLT) in Chile, researchers have found that the three detected gas clouds have chemical compositions that match what scientists expect from the first stellar explosions.

The findings, published in the Astrophysical Journal earlier this week, could help scientists understand the nature of the first stars formed in the immediate aftermath of the Big Bang.

Stars that formed in the early universe around 13.5bn years ago are thought to have been very different in composition to the ones we see today, likely containing only hydrogen and helium – the simplest chemical elements in nature.

When these massive stars died in powerful explosions known as supernovae, they enriched the surrounding gas with heavier elements such as carbon, oxygen and magnesium for the first time.

However, early stars were not energetic enough to expel even heavier elements such as iron, which is only found in the cores of stars. This is why the team, led by Andrea Saccardi, looked for distant gas clouds poor in iron but rich in other, simpler elements such as carbon.

“For the first time ever, we were able to identify the chemical traces of the explosions of the first stars in very distant gas clouds,” said Saccardi, a PhD student at the Observatoire de Paris – PSL, who led this study during his master’s thesis at the University of Florence.

Uncovering ‘mysterious’ nature of first stars

While this unusual combination of chemicals has also been observed in many old stars in our own Milky Way galaxy, researchers consider them to be second-generation stars that formed directly from the so-called ‘ashes’ of the very first stars.

And now, these ashes have been found.

“Primordial stars can be studied indirectly by detecting the chemical elements they dispersed in their environment after their death,” said Dr Stefania Salvadori, an associate professor at the University of Florence and co-author of the study.

“Our discovery opens new avenues to indirectly study the nature of the first stars, fully complementing studies of stars in our galaxy.”

The VLT facility based in Chile’s Atacama Desert is operated by the European Southern Observatory, of which Ireland became a member five years ago.

The ESO was recently involved in observing the aftermath NASA’s Double Asteroid Redirection Test (DART), which completed its 10-month journey last September when it successfully collided with the asteroid Dimorphos in humanity’s first planetary defence test.

It is hoped that the latest study opens new windows for next generation telescopes, such as the ESO’s upcoming Extremely Large Telescope (ELT) and its high-resolution ArmazoNes high Dispersion Echelle Spectrograph (ANDES).

“With ANDES at the ELT, we will be able to study many of these rare gas clouds in greater detail and we will be able to finally uncover the mysterious nature of the first stars,” said Dr Valentina D’Odorico, a researcher at the National Institute of Astrophysics in Italy and co-author of the study.

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Vish Gain is a journalist with Silicon Republic