Parts Of The Milky Way Are Much Older Than Thought, Study Reveals
According to a recent study based on an uncommon type of star discovered, the Milky Way’s thick disk is 2 billion years older than previously thought and likely formed around 800 million years after the Big Bang.
The thin disk, which contains the solar system and much of what we identify as the Milky Way, and the much sparser, bigger, and older thick disk may be divided into two major portions. A team of scientists from the Max-Planck Institute for Astronomy in Heidelberg, Germany, looked at a population of stars known as sub-giants in the Milky Way to recreate the history of these components.
Sub-giants are stars captured during the brief (in cosmic terms) transition between their regular stellar life and the red giant phase, when they expand well beyond their original envelope.
Although nuclear fusion in the cores of these stars has ceased, the stars have not yet flowered into red giants. Because a star’s sub-giant phase lasts only a few million years, astronomers can estimate its age by comparing its chemical composition to computer models of stellar evolution.
The scientists used data from the European Space Agency’s (ESA) Gaia mission and China’s Large Sky Area Multi-Object Fiber Spectroscopic Telescope to determine the ages of 250,000 sub-giants in the Milky Way (LAMOST).
The data revealed that the Milky Way’s star creation occurred in two separate waves throughout its existence. According to ESA, the first wave, connected with the thick disk, began barely 800 million years after the Big Bang, or 13 billion years ago, but accelerated 2 billion years later when the young Milky Way collided with another galaxy known as Gaia-Sausage-Enceladus.
This collision may have filled the thick disk as well as the stellar halo surrounding the entire galaxy with stars. It, however, took another 5 to 6 billions of years for the thin disk to emerge in the next big wave of star formation, which included the sun.
“Since the discovery of the ancient merger with Gaia-Sausage-Enceladus, in 2018, astronomers have suspected that the Milky Way was already there…but we didn’t have a clear picture of what that Milky Way looked like,” Maosheng Xiang, an astronomer at the Max Planck Institute for Astronomy and one of the paper’s authors, said in a statement published by the European Space Agency.
The study was published in the journal Nature on March 23.