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The three oldest stars in the universe were found in the galactic halo

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Credit: Serge Brunier; NASA

Astronomers have discovered three stars that, at 12-13 billion years old, are the oldest stars in the universe. They are also (relatively) close to us, in the Milky Way’s rim, a spherical veil that surrounds a flat disk with a spiral arm. The MIT team that made the discovery speaks “Small Accreted Stellar System stars” or from SASS. They mean that the stars originally belonged to another, smaller galaxy that later merged with the Milky Way galaxy.

Magellan telescopes at the Las Campanas Observatory in Chile, credit: Anna Frebel

The three stars are remnants of those original primordial galaxies. There must still be such dwarf galaxies (in addition to the already known dwarf galaxies around the Milky Way), but they are difficult to see due to their ultralight dimness. Anna Frebel and her team discovered the three stars by analyzing data collected by the 6.5-meter Magellan-Clay Telescope at the Las Campanas Observatory in Chile. In the spectra of observed stars, they looked for spectra with a few heavy elements called metals. Twelve or thirteen billion years ago, there were few heavy elements, most stars consisted only of the elements hydrogen and helium, which were created during the Big Bang (which happened 13.8 billion years ago).

They found, among others, the oldest stars: Ananda Santos, Casey Fienberg and Anna Frebel. Authors: Photo: Courtesy of the researchers

My own sun was taken as a reference and the astronomers (Frebel’s students) looked in particular at the amount of strontium, barium and iron in the spectrum. One of the oldest stars they found had less than 1/10,000 of the Sun’s iron-to-helium ratio. Three stars emerged from the study, which turned out to be very old. They are located about 30,000 light years from Earth. Data from the European Gaia satellite show that they have “retrograde” motions, that is, they have opposite motions compared to the “normal” stars orbiting the galactic center. This retrograde motion is a sign that they must have an external origin located outside the Milky Way.

For more on the study of the oldest stars, see the professional article by Hillary Diane Andales, Ananda Santos Figueiredo, Casey Gordon Fienberg, Mohammad K Mardin, and Anna Frebel. The oldest stars with few neutron-capturing elements, originating from ancient dwarf galaxies. Monthly Bulletins of the Royal Astronomical Society, 2024; 530(4):4712.

Bron: WITH.

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