A new map of the Milky Way has revealed a surprising fact about the stars living in our galaxy — nearly a third have moved far from their stellar birthplace.

This discovery was made by astronomers using the Sloan Digital Sky Survey-III (SDSS), which spectroscopically linked chemical elements in stars with the locations within our galaxy known to be abundant in those specific elements. And it turns out that 30 percent of the stars surveyed have migrated far from home.

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“We were able to measure the properties of nearly 70,000 stars in our galaxy for this particular study using the innovative SDSS infrared spectrograph,” Donald Schneider, of Penn State University, Pa., and study coauthor, said in a press release. “This exercise can be described as galactic archaeology. These data reveal the locations, motions, and compositions of the stars, which provide insights into their formation and their history.”

As each population of stars are born and eventually die, heavier elements are can be found in the atmospheres of each progressive stellar population. The spectroscopic signature of any given star acts almost as rings can be used to age a tree, but for stars, the chemical fingerprint in their atmospheres can also reveal where and when they formed in our galaxy.

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“Stellar spectra show us that the chemical makeup of our galaxy is constantly changing,” added astronomer Jon Holtzman, of New Mexico State University (NMSU). “Stars create heavier elements in their cores, and when the stars die, those heavier elements go back into the gas from which the next stars form.”

“In our modern world, many people move far away from their birthplaces, sometimes halfway around the world,” said Michael Hayden also from NMSU and lead author of the study published in the Astrophysical Journal. “Now we’re finding the same is true of stars in our galaxy. About 30 percent of the stars in our galaxy have traveled a long way from where they were born.”

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The researchers leveraged data from the SDSS Apache Point Observatory Galactic Evolution Explorer (APOGEE) to map the quantities of 15 different elements (including carbon, silicon and iron) found in the sample of stars located throughout the galaxy. They found that 30 percent of the sample contained quantities of these elements that wasn’t typical for the location of the galaxy they were found in, meaning they had moved a long way from where they were born.

“While on average the stars in the outer disk of the Milky Way have less heavy-element enrichment, there is a small fraction of stars in the outer disk that have heavier element abundances that are more typical of stars in the inner disk,” said Jo Bovy of the Institute for Advanced Study and the University of Toronto.

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It seems that these motions throughout the Milky Way’s history can be explained a migratory model of our galaxy. Irregularities in the distribution of mass in the galactic disk, such as the Milky Way’s spiral arms, drive this inward and outward stellar migration. Although evidence for stellar migration in the solar system’s neighborhood has been revealed in the past, this is the first time evidence for galaxy-wide migration has been uncovered.

“These latest results take advantage of only a small fraction of the available APOGEE data,” said Steven Majewski, the Principal Investigator of APOGEE. “Once we unlock the full information content of APOGEE, we will understand the chemistry and shape of our galaxy much more clearly.”