The 2MASS J18082002-5104378 B, a star with a metallic star that is about 1,950 light years away from the Earth, is about 13.53 billion years old, making it one of the most ancient stars in our Milky Way.
The first stars of the universe after the Big Bang would be wholly elements like hydrogen, the sun and the few lithium.
These stars then produced elements heavier than the sun in their nuclei and sow the universe with them when they exploded as a supernova.
The next generation of stars was formed from clouds of materials with these metals, incorporating them into their makeup.
The metal content, or the metallicity, of the stars in the Universe grew as the circle of stargate and death continued.
The 2MASS J18082002-5104378 B, also known as Gaia DR2 6702907209758894848 B, is unusual because, unlike other stars with very low metal content, it is part of the Milky Way's "thin disk" – the part of the galaxy in which the galaxy lives our Sun.
"This star is perhaps one in 10 million. It tells us something very important for the first generation of stars," said lead author Kevin Schlaufman, a researcher at Johns Hopkins University.
The extremely low metallicity of 2MASS J18082002-5104378 B shows that in a secular family tree, it could be as small as a generation to remove from the Big Bang.
Indeed, he is the new record holder for the star with the smallest number of heavy elements – he has roughly the same heavy content content as Mercury. Instead, our sun is generations below this line and has a heavy content content equal to 14 Jupiters.
Astronomers have found some 30 ancient "extremely metal poor" stars with the approximate mass of our Sun. 2MASS J18082002-5104378 B, however, is only 14% the mass of the Sun.
The star is a tiny, almost invisible, secondary member in the binary 2MASS system J18082002-5104378.
Dr. Schlaufma and his colleagues found that after another group of astronomers he discovered the much brighter "primary" star.
This team, led by Dr. Jorge Meléndez of the University of Sao Paulo, measured the composition of the primary one, studying a high-resolution optical spectrum of its light.
The presence or absence of dark lines in the spectrum of a star can identify the elements it contains, such as carbon, oxygen, hydrogen, iron and much more. In this case, the star had extremely low metallicity.
Dr. Meléndez and the co-authors also recognized unusual behavior in the star system that implied the presence of a neutron star or black hole.
Dr Schlaufman's team found that it was wrong, but in doing so they discovered the very youngest companion of the visible star.
The existence of the youngest companion star turned out to be the great discovery.
Dr. Schlaufman and his colleagues were able to conclude their mass by studying the light "shake" of the primary star as the gravity of the little star took it.
Since the 1990s, astronomers have believed that only the huge stars could have formed in the early stages of the Universe. But as astronomical simulations became more sophisticated, they began to imply that in some cases, a star of this time with very low mass could still exist, even more than 13 billion years from the Big Bang.
Unlike huge stars, low masses can live for too long. Red dwarfs, for example, with a fraction of the Sun's mass, are believed to live in trillions of years.
The discovery of 2MASS J18082002-5104378 B opens the possibility of observing even bigger stars.
"If our conclusion is correct, then there may be low-mass stars that have a composition exclusively the result of the Big Bang." Although we have not yet found such an object in our Milky Way, there may be, "said Dr. Schlaufman.
A report about the discovery is published in Astrophysical Journal (preprint of arXiv.org).
Kevin C. Schlaufman et al. 2018. A star with much metallic light near the hydrogen burning limit. ApJ 867, 98; doi: 10.3847 / 1538-4357 / aadd97