Chemicals left by the first stars in the universe may be revealed

Astronomers may have discovered the chemical remains of the oldest stars in the universe.

Using innovative technology at the Gemini North telescope in Hawaii, researchers have found an unusual proportion of the elements, which they say can only come from debris from the explosive death of a first-generation star 300 times larger than our sun.

The universe is now estimated to be 13.7 billion years old, and contains an estimated 1 septillion (1 with 24 zeros after it, or 1 million billion billion) stars. But scientists believe that the first stars likely formed when the universe was only 100 million years old.

These first-generation stars are known as “third population” stars. Astronomers believe that it began to produce chemical elements heavier than hydrogen, which are necessary for the formation of the planet, and of course life.

Cluster III stars would have been so massive that a supernova that experienced the turbulent ends of their lives would have scattered vast swaths of space with heavy elements. But direct evidence for these primordial giant stars has eluded astronomers, until now.

Astronomers who believe they have found the remains of a first-generation star have published their results in Astrophysical Journal.

The researchers used the Gemini North’s 8.1-meter telescope to look at the clouds surrounding one of the most distant known quasars, and observed more than 10 times more iron than magnesium compared to the ratio of these elements in our sun. The quasar itself is 13.1 billion light-years away, so what scientists see through the telescope is the quasar because it was only 700 million years after the Big Bang.

Scientists believe the most likely explanation for this chemical composition is that the material was left by a first-generation star that exploded as an “unstable binary supernova”. Although never seen, these versions of a supernova have been positioned as indicating the death of giant stars between 150 and 250 solar masses (one solar mass is the mass of our sun)

By spectroscopy of different wavelengths of infrared radiation coming from the quasar, the team was able to infer what elements are inside the cloud. But since the brightness of the lines on the spectrometer that correspond to different elements depends on several factors, determining the amount of each element is a bit tricky.

The researchers addressed this problem by analyzing the intensity of wavelengths in the spectrum to estimate the abundance of elements in the cloud around the quasar.

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“It was clear to me that the supernova candidate for this would be a pairwise instability supernova for the Population III star, in which the entire star explodes without leaving any remnants behind,” says first author Yozuru Yoshi of the University of Tokyo. “I was somewhat pleased and surprised to discover 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.”

An earlier preliminary identification of a first-generation star was published in 2014 by research analyzing the corona around our Milky Way. But Yoshi believes that the new result showing a very low abundance of magnesium to iron is the clearest indication of an unstable binary supernova.

If they are correct and have found the remains of one of the universe’s first stars, the team’s findings help advance our understanding of how matter in the universe evolved into what it is today.

The chemical fingerprints of these first stars can be found near home.

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

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