Researchers have successfully dated some of our galaxy’s oldest stars back to a cosmic collision, using data on their oscillations and chemical composition.
The team, led by Josefina Montalbán of the University of Birmingham, UK, investigated the age of some red giant stars that were originally part of a satellite dwarf galaxy called Gaia-Enceladus, which collided with the Milky Way 11.5 billion years ago.
In their study, published in Nature Astronomy, the researchers surveyed 100 red giant stars and found that the Gaia-Enceladus stars were all similar in age or slightly younger than the other stars that began life in the Milky Way. This builds on the existing theory that the Milky Way had already started making stars before it merged with Gaia-Enceladus.
“The chemical composition, location and motion of the stars we can observe today in the Milky Way contain precious information about their origin,” says Montalbán.
“As we increase our knowledge of how and when these stars were formed, we can start to better understand how the merger of Gaia-Enceladus with the Milky Way affected the evolution of our Galaxy.”
As part of their analysis, they used a technique called asteroseismology, which measures relative frequency and amplitudes of the natural modes of oscillations of stars. This gives information about the size and internal structure of stars, which then helps estimate star age.
They combined this data with spectroscopy – a technique that measures light and radiation produced by matter – to identify the chemical composition of the stars, which also reveals information about age.
“We have shown the huge potential of asteroseismology in combination with spectroscopy to deliver precise, accurate relative ages for individual, very old, stars,” says co-author Andrea Miglio of the University of Bologna, Italy.
“Taken together, these measurements contribute to sharpen our view on the early years of our Galaxy and promise a bright future for Galactic archeoastronomy.”
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Deborah Devis is a science journalist at Cosmos. She has a Bachelor of Liberal Arts and Science (Honours) in biology and philosophy from the University of Sydney, and a PhD in plant molecular genetics from the University of Adelaide.
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