Astronomers have found what could be one of the universe’s oldest stars, which almost entirely made of materials spewed from the Big Bang.
It’s called 2MASS J18082002–5104378 B.It opens up the possibility of observing even older stars.The discovery of this approximately 13.5 billion-year-old tiny star means more stars with very low mass and very low metal content are likely out there—perhaps even some of the universe’s very first stars.
Unlike other stars this star has very low metal content, it is part of the Milky Way’s “thin disk”—the part of the galaxy in which our own sun resides.
Researchers say it’s possible that our galactic neighborhood is at least 3 billion years older than previously thought. The findings are published in The Astrophysical Journal.
“This star is maybe one in 10 million,” said lead author Kevin Schlaufman, a Johns Hopkins University assistant professor of physics and astronomy. “It tells us something very important about the first generations of stars.”
The universe’s first stars after the Big Bang would have consisted entirely of elements like hydrogen, helium, and small amounts of lithium. Those stars then produced elements heavier than helium in their cores and seeded the universe with them when they exploded as supernovae.
The next generation of stars formed from clouds of material laced with those metals, incorporating them into their makeup. The metal content, or metallicity, of stars in the universe increased as the cycle of star birth and death continued.
The newly discovered star’s extremely low metallicity indicates that, in a cosmic family tree, it could be as little as one generation removed from the Big Bang. Indeed, it is the new record holder for the star with the smallest complement of heavy elements—it has about the same heavy element content as the planet Mercury. In contrast, our sun is thousands of generations down that line and has a heavy element content equal to 14 Jupiters.
Astronomers have found around 30 ancient “ultra metal-poor” stars with the approximate mass of the sun. The star Schlaufman and his team found, however, is only 14 percent the mass of the sun.
The star is part of a two-star system orbiting around a common point. The team found the tiny, almost invisibly faint “secondary” star after another group of astronomers discovered the much brighter “primary” star. That team measured the primary’s composition by studying a high-resolution optical spectrum of its light. The presence or absence of dark lines in a star’s spectrum can identify the elements it contains, such as carbon, oxygen, hydrogen, iron, and more. In this case, the star had extremely low metallicity. Those astronomers also identified unusual behavior in the star system that implied the presence of a neutron star or black hole. Schlaufman and his team found that to be incorrect, but in doing so, they discovered the visible star’s much smaller companion.