By measuring the ages of 70,000 stars throughout the Milky Way and using that data to create the largest-ever map of its kind, astronomers from the Max Planck Institute for Astronomy and their colleagues have confirmed that the galaxy formed in the middle and grew outward.
Lead investigator Melissa Ness from the Heidelberg, Germany-based space research center, and her colleagues calculated the age of each individual star using data from both the Apogee Project and NASA’s Kepler space telescope, according to BBC News and the Daily Telegraph.
The instruments allowed them to first establish each star’s chemical composition, then establish their respective masses, which could then be used to determine how old they were, Ness told the BBC. That information was then used to construct a map showing the stars’ age and mass based on their place in the color spectrum, with the youngest appearing blue and the oldest red.
Their findings, which were presented during the 227th meeting of the American Astronomical Society in Florida last week, confirm the long-held belief that the oldest stars in the Milky Way formed near the center of the disc—meaning that the galaxy originally formed in the center.
Innovative new method uses spectra to determine stellar age
Ness called the research “somewhat revolutionary” due to the fact that “ages have previously been considered very hard to get, particularly from stellar spectra. They’re important, but they’re difficult.”
“This is really the first time that we’ve been able to infer ages for such a large number of stars, rather than relying on this small subset of stars with special observations,” she continued. “Our galaxy started out as a small disc, and it’s grown from the inside out. That’s something we very much suspected, but now we have the details that confirm all of this.”
They did so by first sampling stars in batches of 300 in a variety of different wavelengths using data from the Apogee project, which is part of the ground-based Sloan Digital Sky Survey, BBC News explained. This spectra enabled them to work out the chemical composition of these stars, which was combined with the Kepler data to establish their masses, and thus their ages.
The map takes this information and relates the age and mass to the color spectrum of the stars, as previously determined through the Apogee data. The end result was an innovative new model that could be used to calculate the ages for the rest of the galaxy’s stars by using only their place in the color spectrum.
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Feature Image: G. Stinson (MPIA)
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