After many years of research – the first possible traces of the universe’s first stars have been discovered

Huge, Population III star in the early universe

This artist’s impression shows a field of Population III stars that would have appeared only 100 million years after the Big Bang. Astronomers may have discovered the first signs of their ancient chemical residue in the clouds surrounding one of the most distant quasars ever discovered. Credit: NOIRLab/NSF/AURA/J. da Silva/Spaceengine

Evidence that a first-generation star died in a “supernova” explosion was discovered by Gemini’s observation of a distant quasar.

The ancient chemical remains of the first stars that lit up the universe may have been found by astronomers. Researchers have discovered an unusual proportion of the elements that, in their opinion, could only come from debris from the mass explosion of a first-generation star 300 solar masses using an innovative analysis of a distant quasar spotted by the 8.1-meter Gemini North Telescope in Hawaii, operated by the National Science Foundation’s NOIRLab. .

The first stars most likely formed when the universe was barely 100 million years old, or less than 1% of its current age. These early stars, known as Population 3, were so massive that when they died as supernovae, they tore themselves apart, scattering a unique mixture of heavy elements through interstellar space. However, despite careful investigation by astronomers over many years, there has been no conclusive evidence for these ancient stars yet.

Astronomers now believe they’ve discovered the remnants of a first-generation star explosion after studying one of the most remotely known quasars using the Gemini North Telescope, one of the two identical telescopes that make up the Gemini International Observatory. They discovered a very unusual composition using an innovative method for determining the chemical elements present in the clouds around the quasar – the material contains almost 10 times more iron than magnesium than the proportion of these elements we see in our Sun.

A step-by-step story to find the possible first traces of the universe's first stars

The step-by-step story of how astronomers discovered the ancient chemical remains of the first stars that illuminated the universe. Credit: NOIRLab/NSF/AURA/J. da Silva/Spaceengine

Scientists believe the most likely explanation for this striking feature is that the material was left by a first-generation star that exploded as an unstable binary supernova. These remarkably powerful versions of supernova explosions have never been seen, but are assumed to mark the end of life for giant stars with a mass between 150 and 250 times the mass of the Sun.

Unstable pairwise supernova explosions occur when photons in the center of the star spontaneously convert into electrons and positrons – the positively charged antimatter counterpart of the electron. This diversion reduces radiation pressure inside the star, allowing gravity to overcome it and lead to the collapse and subsequent explosion.

Unlike other supernovae, these dramatic events leave no stellar remnants, such as a[{” attribute=””>neutron star or a
Astronomers may have discovered the ancient chemical remains of the first stars that illuminated the universe. Using an innovative analysis of a distant quasar spotted by the 8.1-meter Gemini North Telescope in Hawaii, which is operated by the National Science Foundation’s NOIRLab, scientists have found an unusual proportion of the elements that, they say, can only come from debris created by everyone else. An exploding first-generation star with a power of 300 solar masses. Credit: Images and Videos: PROGRAM/NOIRLab/NSF/AURA, S. Brunier/Digitized Sky Survey 2, E. Slawik, J.Polard Image Processing: TA Rector (University of Alaska Anchorage/NSF’s NOIRLab), M. Zamani (NSF’s NOIRLab) and D. de Martin (NSF’s NOIRLab) Music: Stellardrone – Airglow

For their research, the astronomers studied the results of previous observations taken with the 8.1-meter Gemini North Telescope using the Gemini near-infrared spectrometer (GNIRS). It divides the spectra of light emitted by celestial bodies into its component wavelengths, which carry information about the elements the objects contain. Gemini is one of the few telescopes of its size with the appropriate equipment to perform such observations.

However, inferring the quantities of each element present is a difficult endeavor because the brightness of a line in the spectrum depends on many other factors besides the abundance of the element.

Two co-authors of the analysis, Yozuru Yoshi and Hiroaki Samshima of the University of Tokyo, addressed this problem by developing a method for using the intensity of wavelengths in the quasar spectrum to estimate the abundance of elements there. Using this method of analyzing the quasar spectrum, they and their colleagues discovered the apparently low ratio of magnesium to iron.

“It was clear to me that the supernova candidate for this would be an unstable binary supernova of the Population III star, in which the entire star explodes without leaving any remnants behind,” Yoshi said. “I was somewhat pleased and surprised to find that a pair of supernovae for a star about 300 times the mass of the Sun provides a ratio of magnesium to iron consistent with the low value we derived for the quasar.”

Searches for chemical evidence of a previous generation of high-mass Group C stars have been conducted before among the stars in the space halo.[{” attribute=””>Milky Way and at least one tentative identification was presented in 2014. Yoshii and his colleagues, however, think the new result provides the clearest signature of a pair-instability supernova based on the extremely low magnesium-to-iron abundance ratio presented in this quasar.

If this is indeed evidence of one of the first stars and of the remains of a pair-instability supernova, this discovery will help to fill in our picture of how the matter in the Universe came to evolve into what it is today, including us. To test this interpretation more thoroughly, many more observations are required to see if other objects have similar characteristics.

But we may be able to find the chemical signatures closer to home, too. Although high-mass Population III stars would all have died out long ago, the chemical fingerprints they leave behind in their ejected material can last much longer and may still linger on today. This means that astronomers might be able to find the signatures of pair-instability supernova explosions of long-gone stars still imprinted on objects in our local Universe.

“We now know what to look for; we have a pathway,” said co-author Timothy Beers, an astronomer at the University of Notre Dame. “If this happened locally in the very early Universe, which it should have done, then we would expect to find evidence for it.”

Reference: “Potential Signature of Population III Pair-instability Supernova Ejecta in the BLR Gas of the Most Distant Quasar at z = 7.54*” by Yuzuru Yoshii, Hiroaki Sameshima, Takuji Tsujimoto, Toshikazu Shigeyama, Timothy C. Beers and Bruce A. Peterson, 28 September 2022, The Astrophysical Journal.
DOI: 10.3847/1538-4357/ac8163

The study was funded by the National Science Foundation. 

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