[ad_1]
2MASS J18082002-5104378 B, an ultra-poor metal star located about 1,950 light-years from Earth, about 13.53 billion years old, making it one of the oldest stars of our Milky Way .
This image shows the binary star system 2MASS J18082002-5104378. Image credit: Strasbourg Astronomy Data Center / SIMBAD / DSS2.
The first stars of the Universe after the Big Bang would have been entirely composed of elements such as hydrogen, helium and small amounts of lithium.
These stars then produced heavier elements than helium in their nuclei and seeded the Universe when they exploded as supernovae.
The next generation of stars formed from clouds of materials related to these metals, incorporating them into their composition.
The metal content, or metallicity, of the stars of the universe has increased parallel to the cycle of birth and death of the stars.
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 Milky Way's "thin disc" – the part of the galaxy in which our own Sun resides.
"This star is perhaps one in 10 million. This tells us something very important about the first generation of stars, "said lead author Kevin Schlaufman, a researcher at Johns Hopkins University.
The extremely weak metallicity of 2MASS J18082002-5104378 B indicates that, in a cosmic family tree, it could only occur a generation away from the Big Bang.
Indeed, it is the new star record holder with the smallest addition of heavy elements – it has about the same content in heavy elements as the Mercury planet. On the other hand, our Sun is in this lineage and has a heavy element content equal to 14 Jupiters.
Astronomers have discovered about thirty stars very poor in metals, an approximate mbad of our Sun. 2MASS J18082002-5104378 B, however, represents only 14% of the mbad of the Sun.
The star is a tiny, almost invisible secondary element in the 2MASS J18082002-5104378 binary system.
Dr. Schlaufma and her colleagues found it after another group of astronomers discovered the much brighter "primary" star.
This team, led by Dr. Jorge Meléndez of the Universidade de São Paulo, measured the composition of the primary by studying a high-resolution optical spectrum of its light.
The presence or absence of black lines in the spectrum of a star makes it possible to identify the elements it contains, such as carbon, oxygen, hydrogen, iron, etc. In this case, the star had a very weak metallicity.
Dr. Meléndez and his co-authors also identified unusual behavior in the stellar system involving the presence of a neutron star or a black hole.
Dr. Schlaufman's team felt that was incorrect, but in doing so, she discovered the much smaller companion of the visible star.
The existence of the smallest companion star turned out to be the great discovery.
Dr. Schlaufman and his colleagues were able to deduce from his mbad by studying the slight "wobbling" of the main star at the moment when the gravity of the little star was pulling him.
As recently as the 1990s, astronomers thought that only mbadive stars could form in the earliest stages of the Universe. But as astronomical simulations became more sophisticated, they began to suggest that, in some situations, a star of that time with a particularly small mbad could still exist, even more than 13 billion years since the Big Bang.
Unlike big stars, the smaller mbades can live very long. Red dwarfs, for example, with a fraction of the mbad of the sun, would live up to billions of years.
The discovery of 2MASS J18082002-5104378 B opens the possibility of observing even older stars.
"If our inference is correct, the low mbad stars that have a composition exclusively from the Big Bang may exist. Even though we have not yet found an object of this type in our galaxy, it may exist, "said Dr. Schlaufman.
A report on the discovery is published in the Astrophysical Journal (pre-print arXiv.org).
_____
Kevin C. Schlaufman et al. 2018. An ultra-poor metal star close to the limit of combustion of hydrogen. ApJ 867, 98; doi: 10.3847 / 1538-4357 / aadd97
Source link
