10-billion-year-old red giant stars help researchers understand how our galaxy evolved © NASA/JPL-Caltech/ESA/CXC/STScI

10-billion-year-old red giant stars help researchers understand how our galaxy evolved

The stars reveal information about the early Milky Way, before its collision with a satellite galaxy called Gaia-Enceladus around 10 billion years ago.

Some of the oldest stars in our galaxy have been dated with unprecedented precision, scientists say.

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Researchers surveyed roughly 100 red giant stars and determined that some of these were originally part of a satellite galaxy called Gaia-Enceladus, which collided with the Milky Way early in its history.

The study revealed that the group of stars observed all have similar ages, or are slightly younger than the majority of the stars known to have started their lives within the Milky Way.

This corroborates existing theories suggesting the Milky Way had already started forming a significant fraction of its stars when the merger with the Gaia-Enceladus (also known as the Gaia Sausage) occurred, around 10 billion years ago.

By the time of the collision, the Milky Way was already efficiently forming stars, most of which now reside within its thick disc, one of two disc-like structures that make up the galaxy.

“The chemical composition, location and motion of the stars we can observe today in the Milky Way contain precious information about their origin,” said lead author of the paper Dr Josefina 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.”

Read more about the history of our galaxy:

In making the calculations, the team used data from the Kepler satellite in combination with data from the Gaia and Apogee instruments, using a technique called asteroseismology.

This relatively new technique involves measuring the oscillations caused by sound waves trapped inside the star, which enables scientists to assemble information about the star’s size and internal structure, and allows accurate estimations of the star’s age to be made.

In the study published in Nature Astronomy, the team used information on the individual oscillation modes of each star, rather than averaged properties of their pulsations.

Researchers were able to use asteroseismology in combination with spectroscopy – which enables the chemical composition of the stars to be measured.

“We have shown the huge potential of asteroseismology in combination with spectroscopy to deliver precise, accurate relative ages for individual, very old, stars,” said co-author Professor Andrea Miglio, from the University of Bologna.

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“Taken together, these measurements contribute to sharpen our view on the early years of our galaxy and promise a bright future for galactic archeoastronomy.”