The chemical information comes from spectra, which are detailed measurements of how much light the star gives off at different wavelengths. Spectra show prominent lines that correspond to elements and molecules present. Reading the spectral lines of a star can tell astronomers what the star is made of.
This brief animation shows how stars can change orbits. The animation shows two pairs of stars (marked as red and blue). Within each pair of stars, both start in the same orbit. At random times, one star of the pair changes orbit, moving in our out in our Galaxy. Lines trace the path of each star. Because of the higher density of the inner Galaxy, more stars move in than out. Credit: Dana Berry / SkyWorks Digital, Inc.; SDSS collaboration. 300 DPI JPG 1080p Quicktime Movie (.mov, 118 MB)
"While on average the stars in the outer disk of the Milky Way have less heavy element enrichment, there is a fraction of stars in the outer disk that have heavier element abundances that are more typical of stars in the inner disk," says Jo Bovy of the Institute for Advanced Study and the University of Toronto, another key member of the research team.
When the team looked at the pattern of element abundances in detail, they found that much of the data could be explained by a model in which stars migrate into new orbits around the Galactic Center, moving nearer or farther with time. These random in-and-out motions are referred to as "migration," and are likely caused by irregularities in the Galactic disk, such as the Milky Way's famous spiral arms. Evidence of stellar migration had previously been seen in stars near the Sun, but the new study is the first clear evidence that migration occurs for stars throughout the Galaxy.
Future studies by astronomers using data from SDSS promise even more new discoveries. "These latest results take advantage of only a small fraction of the available APOGEE data," says 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."
Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the U.S. Department of Energy Office of Science.
SDSS-III is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS-III Collaboration including the University of Arizona, the Brazilian Participation Group, Brookhaven National Laboratory, Carnegie Mellon University, University of Florida, the French Participation Group, the German Participation Group, Harvard University, the Instituto de Astrofisica de Canarias, the Michigan State/Notre Dame/JINA Participation Group, Johns Hopkins University, Lawrence Berkeley National Laboratory, Max Planck Institute for Astrophysics, Max Planck Institute for Extraterrestrial Physics, New Mexico State University, New York University, The Ohio State University, Pennsylvania State University, University of Portsmouth, Princeton University, the Spanish Participation Group, University of Tokyo, University of Utah, Vanderbilt University, University of Virginia, University of Washington, and Yale University.
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