Tiny old star has huge impact

A tiny star found in our galactic neighborhood is presenting astronomers with a compelling glimpse into the history of our galaxy and the early universe. The star has some very interesting characteristics: it's small, it's old, and most significantly it's made of material very similar to that spewed by the Big Bang. To host a star like this suggests that the disk of our galaxy could be up to three billion years older than previously thought.

"Our Sun likely descended from thousands of generations of short-lived massive stars that have lived and died since the Big Bang," said Kevin Schlaufman of Johns Hopkins University, leader of this study to be published in the November 5th issue of The Astrophysical Journal. "However, what's most interesting about this star is that it had perhaps only one ancestor separating it and the beginnings of everything," Schlaufman adds.

The Big Bang theory dates our universe at about 13.7 billion years and suggests that the first stars were made almost exclusively of hydrogen and helium. As stars die and gradually recycle their materials into new stars, heavier elements formed. Astronomers refer to stars which lack heavier elements as low metallicity stars. "But this one has such low metallicity," said Schlaufman, "it's known as an ultra metal poor star - this star may be one in ten million."

The star also challenges the assumption that the first stars in the universe were large, exclusively high-mass and short-lived stars. In addition, its location within the usually active and crowded disk of our galaxy is unexpected.

The star is a part of a binary star system. It is the smaller companion to a larger low-metallicity star observed in 2014 and 2015 by the European Southern Observatory's Very Large Telescope UT2. Before the discovery of the tiny star, astronomers mistakenly believed that this binary system might contain a black hole or neutron star.

From April 2016 to July 2017, Schlaufman and his team used both the Gemini Multi-Object Spectrograph (GMOS) on the Gemini South telescope in Chile and the Magellan Clay Telescope at Las Campanas Observatory to dissect the star system's light and measure the object's relative motions, thus discovering the tiny star by detecting its gravitational tug on its partner.

"Gemini was critical to this discovery, as its flexible observing modes enabled weekly check-ins on the system over six months," Schlaufman confirms.

"Estimating the age of the Milky Way is fundamental to our understanding of the broader history of the universe, and it's thrilling to know that Gemini is contributing to this important research," said Chris Davis of the U.S. National Science Foundation (NSF). NSF funds the Gemini Observatory on behalf of the U.S. community, in collaboration with international partners in Canada, Brazil, Argentina, Korea and Chile.

The star, which goes by the designation 2MASS J18082002-5104378 B, has only about 14% the mass of our Sun making it a red dwarf star. While average-sized stars like our Sun live for approximately 10 billion years before extinguishing their nuclear fuel, low-mass stars can burn for trillions of years.

"Diminutive stars like these tend to shine for a very long time," said Schlaufman. "This star has aged well. It looks exactly the same today as it did when it formed 13.5 billion years ago."

The discovery of 2MASS J18082002-5104378 B gives astronomers hope for finding more of these old stars which provide a glimpse at the very early universe. Only about 30 ultra metal poor stars have been identified. "Observations such as these are paving the way to perhaps one day finding that ever elusive first generation star," concludes Schlaufman.

Related Links
Gemini Observatory
Stellar Chemistry, The Universe And All Within It

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