July 31st, 2015 by James Ayre
Stellar orbits within the Milky Way can change considerably over time, according to new research published in The Astrophysical Journal.
The new work shows — via the use of map created via the Sloan Digital Sky Survey (SDSS) — that roughly a third of the stars in the Milky Way have dramatically changed their orbits.
“In our modern world, many people move far away from their birthplaces, sometimes halfway around the world,” stated Michael Hayden, NMSU astronomy graduate student and lead author of the new study. “Now we’re finding the same is true of stars in our galaxy — about 30% of the stars in our galaxy have traveled a long way from where they were born.”
The new map that resulted in the new findings was the result of researchers utilizing the SDSS Apache Point Observatory Galactic Evolution Explorer (APOGEE) spectrograph to observe 100,000 stars over a 4-year period of time.
Essentially, the researchers analyzed the elements in the atmospheres of the stars surveyed to learn more. “From the chemical composition of a star, we can learn its ancestry and life history,” noted Hayden.
“Stellar spectra show us that the chemical makeup of our galaxy is constantly changing,” stated Jon Holtzman, NMSU astronomy professor who was involved in the study. “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.”
A recent press release provides more:
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 compounds. Astronomers can tell what a star is made of by reading these spectral lines.
Hayden and his colleagues used APOGEE data to map the relative amounts of 15 separate elements, including carbon, silicon, and iron for stars all over the galaxy. What they found surprised them — up to 30% of stars had compositions indicating that they were formed in parts of the galaxy far from their current positions.
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 radially, moving closer or farther from the galactic center 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 throughout the galaxy.
“These latest results take advantage of only a small fraction of the available APOGEE data,” stated 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.”
With the SDSS work set to continue for several more years, the new findings will likely be fleshed out some in the near future.
Image Credit: Dana Berry/SkyWorks Digital, Inc; SDSS collaboration
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