What are the most sought-after stars in the universe? No doubt the so-called “population III” stars. These would be the first to be lit a few hundred million years after the big Bang . Today, they can not be found. Their crucial role in the evolution of the Universe (they have contributed to the enrichment of heavy elements) makes their discovery crucial for the understanding and improvement of cosmological models, but despite frequent research they remain almost impossible to find. Almost because several teams have potentially found the tracks they left in space. One via a gas cloud very poor in heavy elements and the other in an ultraviolet reflection on a hydrogen cloud . This time it is the oxygen that has detected an international team of astronomers: this gas would have been dropped in space at the death of these first stars, barely 250 million years after the Big Bang.
An infrared glow
It all starts when an international team of astronomers detects a very weak glow emitted by oxygen from a distant galaxy (called MACS1149-JD1) thanks to the powerful ALMA radio telescope and the four huge telescopes VLT (Very large telescope). European Southern Observatory (ESO) settled in Chile. ” We have observed the most distant galaxy known to date, “enthuses Nicolas Laporte.” This detection pushes the limits of the observable Universe “, said Takuya Hashimoto of Sangyo University of Osaka, Japan, co-author of the study published in the journal Nature . Astronomers calculate that this signal was emitted some 13.28 billion years ago, 500 million years after the Big Bang. ” This galaxy appears to us as it was when the Universe was only 500 million years old “, said Nicolas Laporte.In addition to winning the title” of the most distant oxygen detected to date by a telescope “, this little glow allows scientists to argue that stars were formed there 250 million years before the signal.
According to the commonly accepted theory, after the Big Bang 14 billion years ago, the universe was filled with a uniform gas composed of light elements like hydrogen and helium created by this gigantic explosion. But the elements a little heavier like iron, carbon or oxygen have been made in the nuclei of stars. So if astronomers were able to detect oxygen, it’s because this galaxy already housed a population of old-fashioned stars “, Said Nicolas Laporte. Their training could date back to 250 million years only after the Big Bang.
This animation traces the probable history of star formation in the galaxy MACS1149-JD1. Under the effect of gravitation, the material is structured into filaments and the density of matter at filamentary intersections increases. Some 200 million years after the Big Bang, intense star formation occurs in areas of high density, giving rise to the formation of galaxies. Credit: ALMA (ESO / NAOJ / NRAO).
The first stars are imagined very different from the stars that can currently be observed in our sky. Composed of light elements from the Big Bang, they would have been gigantic, hundreds of times more massive than the Sun, and would have lived only a few million years. According to the latest theories they would have ended their lives in hypernovas, gigantic explosions ten times more energy than the classic supernovas. These hypernovas would have seeded the Universe and provided enough gas and metals to form the next generation of stars, which then, in turn, enriched their surrounding space.