Artist's impression of a hypernova explosion involving a red giant star. (Image credit: Shutterstock)
Astronomers believe that a star discovered by them is a stellar remnant or fossil of one of the first stars in the universe.
AS0039 is located around 290,000.000 light-years away from the solar system in the Sculptor dwarf galaxies. The stellar remnant is the star with the lowest concentration of metal (especially iron) outside of the Milky Way. Researchers believe that this finding is evidence that the star's remnant is a direct descendant of one of the earliest stars in the universe, which had very little metal.
The team discovered that AS0039's primordial parent star would have had around 20 solar masses. It also likely died in a Hypernova, a stellar explosion 10 to 100x more powerful than a regular Supernova.
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This discovery could reveal new information about the first stars in the universe, which were not directly or indirectly observed before. Live Science spoke out about the unusual chemical composition of AS0039, which allows us to study the nature of first stars, and in particular their stellar mass, said Mike Irwin (an astronomer at University of Cambridge in England).
The very first stars
All stars are made up of plasma (hot gas) that is fusioned from elements in the core. However, their properties make them extremely versatile and can vary in size and color. Based on their chemical composition or metallicity, all stars can be divided into three groups: Population I, Population II, and Population III.
Like the sun, Population I stars are high in metals, particularly iron, and rich in heavy elements like calcium and magnesium. These stars are rarer than the Population II stars like AS0039. They contain very little heavy elements. The Population III stars, which are rarer than ever, have almost no heavy elements and are completely metal-free.
Although Population III stars were never detected, astronomers know that Population III stars were the first stars to be born in the universe, according to Irwin.
Artist's impression of Population III stars from the early universe. Image credit: Nasa/Wmap Science Team
The process of nuclear fusion is when hydrogen atoms fuse together to form helium. This creates a tremendous amount of energy. Stars are the most abundant.
Up to 1.4 solar masses gradually use up hydrogen fuel, swelling up to red giants, and finally collapsing into white dwarfs.
Larger stars, however, quickly exhaust their hydrogen and start to fuse helium and carbon, and eventually carbon into iron. This is the most heavy element that a star can make. These stars eventually become too dense and collapsing in on themselves. The supernova explodes, dispersing the star's elements into space and releasing enough energy to make heavier elements than iron.
The remnants of previous stars often form new stars. They take some metal and heavy elements from those exploding stars to help them grow. Because they are made from leftovers of stars before them, all stars we see today are Population I and II stars.
Irwin stated that the first stars of the universe, Population III, were formed from pure hydrogen. This element was created immediately after the Big Bang. "Population III stars have been defined as the first generation stars to form in the universe. They are therefore made from zero metallicity.
Because no supernovas have created them, these primary stars were also devoid of heavy elements.
Researchers were shocked at the metal-poorness of AS0039 when they discovered it, even in comparison to other Population II stars.
AS0039 has the lowest star concentrations of metals and the lowest star carbon ever observed in the universe. Additionally, it has very low levels of heavy elements such as magnesium and calcium. These results suggest that AS0039 could be a second-generation star formed from the remnants of a Population III star.
A photograph of the Sculptor dwarf galaxies. (Image credit: Eso/Digitized Sky Survey 2)
Computer simulations indicated that the Population III star which gave rise to AS0039 died in a powerful supernova explosion. Irwin stated that Population III stars are generally larger than the stars we see today. Therefore, it is not surprising that a Population III star would end up as a supernova.
Researchers hope that the discovery of AS0039 can help astronomers locate additional second-generation metal-poor Population II star, which in turn will shed light on the size, distribution, and role of the Population III star in the transformation of the early hydrogen-filled universe to the one we see today.
Irwin stated that AS0039 proves it's possible to find out about the properties and signposts the path to more examples. This is crucial in understanding how the universe evolved into what we see today.
The study was published online in The Astrophysical Journal Letters on July 13.
Original publication on Live Science