Study puts the Milky Way’s disc at 10 billion years old

Astronomers have used asteroseismology to estimate the age of our home Galaxy.

A view of the centre of the Milky Way by the Very Large Telescope. Credit ESO/Nogueras-Lara et al.
Published: January 30, 2020 at 2:58 pm
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The conundrum surrounding the age of the Milky Way’s disc might have finally been solved, as a new analysis of data from the Kepler Space Telescope has set the age of the disc at around 10 billion years old.


The Milky Way has two discs: a thin disc and a thick extended one surrounding it. The thick disc is very sparse, with only 20% of the number of stars found within the thin disc.

The stellar population of the thick disc is predicted to be much older, but exactly how much older has been
a long-running question.

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“This finding clears up a mystery,” says Sanjib Sharma from Australia’s ASTRO 3D (ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions) who led the study.

“Earlier data about the age distribution of stars in the disc didn’t agree with the models constructed to describe it, but no one knew where the error lay in the data or the models. Now we’re pretty sure we’ve found it.”

Sharma’s team measured stellar ages in the disc using asteroseismology, which looks for brightness fluctuations caused by starquakes.

“The quakes generate soundwaves inside the stars that make them ring or vibrate,” says Dennis Stello from ASTRO 3D.

“The frequencies produced tell us things about the stars’ internal properties, including their age. It’s a bit like identifying a violin as a Stradivarius by listening to the sound it makes.”

Using this technique on Kepler data, the team initially measured the ages of the stars being much younger than models predicted, leaving the astronomers wondering where their error lay.

However in 2013, Kepler was reprogrammed to observe the sky in a different way, when it went into its K2 mission.

During this time, the telescope observed patches of sky for 80 days at a time. This new deep observation allowed the ASTRO 3D team to analyse the chemical composition of the stars in a new level of detail.

These differed from previous measurements, affecting the ages predicted by their computer simulations.

When the team reran the models, the ages of the stars came out in close agreement with those obtained by asteroseismology.

Did you know that the Andromeda Galaxy is set to collide with our own Milky Way galaxy in the distant future? Find out more in our guide to the Andromeda-Milky Way collision.


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Elizabeth Pearson
Ezzy PearsonScience journalist

Ezzy Pearson is the Features Editor of BBC Sky at Night Magazine. Her first book about the history of robotic planetary landers is out now from The History Press.


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