A cosmic chemical fingerprint of the first stars that lit up the universe may have been found in our galaxy, according to astronomers. We could be looking at some of the first sources of cosmic light, formed some 700 million years after the Big Bang.
The Gemini North telescope in Hawai’i detected the ancient chemical remains of the first stars to light up the universe. The telescope, operated by NSF’s NOIRLab, started scanning the skies from Hawai’’s Mauna Keai in 1999. Sitting on top of a dormant volcano allows the 8.1-meter telescope to look undeterred in dry and cloudless skies.
When astronomers found an unusual ratio of elements, they theorized that the material was coming from an ancient star. Population III stars formed in ancient conditions in the universe that was much warmer and dense than our galactic neighborhood today. Some of these stars may have started forming when the universe was only 100-200 million years old. These first-born stars were much bigger than the stars in our local, stellar neighborhood — think 100 to 250 times the mass of our Sun.
These massive stars only lived for a few million years, then blasted their heavy elements through the old universe in a great, supernovae explosion. The trace remnants that astronomers found with the Gemini North telescope are theorized to come from the explosion of a 300-solar-mass first-generation star.
When astronomers believe that some first-generation stars have been destroyed by supernovae explosions so massive, these stars had their elements spread through the universe (think blowing a dandelion’s seed pods.)
Astronomers have been searching for the first generation of stars — these Population III stars — without a trace of direct evidence. And now, we finally have the evidence we need. This discovery is an important step toward understanding how the universe evolved into its present state, including us.
Quasars are supermassive black holes at the core of galaxies that emit huge amounts of light. Astronomers used a new, innovative method to extrapolate the chemical elements contained in the clouds surrounding an ancient quasar.
These Population III stars aren’t just speculation anymore — their violent and explosive deaths are what we’re seeing today. These stars were so massive that their supernovae had a special name: pair-instability supernovae. This happens when the star is so big, that it partially collapses under its own gravity. Runaway thermonuclear reaction is what creates “the grand finale,” an explosion so powerful that no stellar elements remain. No black holes or neutron stars form. Just emptiness.
Thus the conundrum astronomers had when it came to finding proof of these Population III stars.
“I was delighted and somewhat surprised to find that a pair-instability supernova of a star with a mass about 300 times that of the Sun provides a ratio of magnesium to iron that agrees with the low value we derived for the quasar,” said Yuzuru Yoshii, Laureate Professor, Department of Astronomy at The University of Arizona.
The Gemini North telescope is one of the few that were equipped to search for signs of remnants. The discovery of a low magnesium-to-iron ratio in the quasar they studied is the first clear evidence that these stars existed (in the leftover blown remnants of their supernovae.)
It’s time to start looking closer to home with this new way of seeking out ancient chemical fingerprints in the sky.
“We now know what to look for; we have a pathway,” says 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.”
