When did the first stars form? Probably when the universe was only 100 million years old. Now, thanks to the Gemini North telescope, an international team of astronomers has discovered an unusual proportion of chemical elements in the clouds surrounding the ancient quasar. According to astronomers, they could have found the chemical traces of one of the first stars, one of the first generation stars that formed shortly after the Big Bang and that exploded in a “supersupernova”.
The first stars in the universe are known as Population III, first generation stars. However, despite the fact that they ended their lives in titanic supernova explosions that seeded the universe with chemical elements that the stars had forged during their lifetime, we had not been able to find direct evidence of one of these early Population III stars, until now.
The material from these stars, which would have been even up to 1,000 times more massive than our own Sun, was incorporated into the next generation of stars after the Big Bang and, these in turn, would become new stars, planets or even, in ourselves, which is why it is so important to understand its evolution throughout these 13.7 billion years of history of the cosmos.
They left us a very important legacy, with chemical substances that enriched our universe.
The discovery, described in a new paper published in The Astrophysical Journal, was made by the 8.1-meter Gemini North telescope in Hawaii. During the analysis of the clouds surrounding ULAS J1342+0928, one of the most distant known quasars, astronomers identified material left over from the explosion of a first-generation star. The curious thing is that this material contained more than 10 times more iron than magnesium compared to the proportion of these elements found in our star.
“There are only two ways to find evidence of them. The first is to catch a supernova with pair instability at the time it occurs, which is a highly unlikely fluke. The other way is to identify their chemical signature from the material they expel into interstellar space”, explains Yuzuru Yoshii from the University of Tokyo and leader of the work.
Scientists believe that such material was left behind by a first-generation star that exploded as a pair-instability supernova. It can only be explained by the consequences of a ‘supersupernova’ explosion.
Pair-instability supernova explosions occur when photons at the center of a star spontaneously convert into electrons and positrons , the positively charged antimatter counterpart of the electron.
Astronomers have yet to witness a pair-instability supernova, but they theorize that these dramatic explosions occur when giant stars with masses between 150 and 250 times that of the sun reach the end of their lives.
“According to Big Bang cosmology, nucleosynthesis does not produce heavy elements due to the rapid decrease in density and temperature as the universe expands. This has led to an immediate interpretation that the heavy elements observed in various objects in the universe are synthesized inside massive stars and are ejected by supernovae”, explains Yoshii.
If this is evidence for an early star and pair-instability supernova remnant, this discovery will help complete our picture of how matter in the universe evolved into what it is today.
“Now we know what to look for; we have a way,” said Timothy Beers, an astronomer at the University of Notre Dame and co-author of the research. “If this happened locally in the early universe, which it should have, then we would expect to find evidence of it.”
Referencia: Yuzuru Yoshii et al, Potential Signature of Population III Pair-instability Supernova Ejecta in the BLR Gas of the Most Distant Quasar at z = 7.54*, The Astrophysical Journal (2022). DOI: 10.3847/1538-4357/ac8163