A team of American and Japanese astronomers claims it has found a chemical signature of one of the first stars in the universe embedded in another old star, BBC reports. According to the study published in Science, first stars were huge (up to several hundred solar masses) and lived very short lives.

The team led by astronomer Wako Aoki from the National Astronomical Observatory in Japan based its findings on the observations of an old, orange star, located approximately 1,000 light-years from the Earth.

Researchers employed a technique known as "stellar archaeology". It involves studying chemical composition of the second generation stars to determine what the first generation was like.

Little is known about the first stars since no direct evidence that they existed has been found. Dubbed the population III stars, they formed millions of years after the Big Bang that took place 13.8 billion years ago. Primordial stars were mostly composed of hydrogen and helium and lacked metals (that's how astronomers call any element much heavier than hydrogen and helium).

Scientists explain that the first stars were huge since no metals were present in their composition.

They were also hot which led to a short lifespan of a few million years. By comparison, the Sun, a young, population I star, is estimated to have formed around 4.5 billion years ago and has enough hydrogen fuel to last another 5 billion years.

According to astronomers, some primordial stars ended their lives in massive explosions, known as pair-instability supernova. "It's a huge thermonuclear explosion; All the fuel is burnt at once and the star rips itself apart," Dr Volker Bromm from the University of Texas, Austin, who was not part of the study, told the BBC.

As a result, elements that formed through nuclear fusion in their core - carbon, oxygen, magnesium and iron among others - were spread throughout space. Along with hydrogen and helium, they served as building blocks for the second generation of stars.

The population II stars were less massive and had enough fuel to last billions of years. Some of them can still be observed today. Aoki's team focused its research on one of such stars called SDSS J0018-0939.

That star is composed mainly of hydrogen and helium, which is a sign that it formed in the early universe. "The low abundance of heavy elements suggests that this star is quite old - as old as 13 billion years," Aoki said, as quoted by the International Business Times.

Nevertheless, SDSS J0018-0939 is rich in iron, which is not typical for population II stars. "This is quite a unique star, with a very peculiar chemical pattern that has never been found previously," Aoki told the BBC. According to the astronomer, the unique composition could only be a result of the SDSS J0018-0939 forming from a giant primordial star.

Anna Frebel, an astronomer from MIT who studies population II stars, remains unconvinced. "I'm still a little bit on the fence about whether I believe these [primordial giant stars] existed," Frebel said, as quoted by the National Geographic. "But I would be absolutely thrilled if it turns out to be correct," she added.

Scientists hope that next generation of telescopes will be able to catch the light of the first giant stars if they ever existed. That would help us understand what the early cosmos looked like and how it developed.