By Jim Shelton-Yale
The most-studied galaxy in the universe—the Milky Way— might not be as typical as previously thought, according to a new study of its “siblings.”
The Milky Way, home to Earth and its solar system, is host to several dozen smaller galaxy satellites that orbit around it and could be useful in understanding the Milky Way itself, researchers say.
Early results from the Satellites Around Galactic Analogs (SAGA) Survey indicate that the Milky Way’s satellites are much more tranquil than other systems of comparable luminosity and environment. Many satellites of those “sibling” galaxies are actively pumping out new stars, but the Milky Way’s satellites are mostly inert.
This is significant, because many models for what we know about the universe rely on galaxies behaving in a fashion similar to the Milky Way.
“We use the Milky Way and its surroundings to study absolutely everything,” says Yale University astrophysicist Marla Geha, lead author of the paper in the Astrophysical Journal.
“Hundreds of studies come out every year about dark matter, cosmology, star formation, and galaxy formation, using the Milky Way as a guide. But it’s possible that the Milky Way is an outlier.”
The SAGA Survey began five years ago with a goal of studying the satellite galaxies around 100 Milky Way siblings. Thus far it has studied eight other Milky Way sibling systems, which researchers say is too small of a sample to come to any definitive conclusions.
But SAGA expects to have studied 25 Milky Way siblings in the next two years.
Even so, the survey already has people talking. At a recent conference where Geha presented some of SAGA’s initial findings, another researcher told her, “You’ve just thrown a monkey wrench into what we know about how small galaxies form.”
“Our work puts the Milky Way into a broader context,” says SAGA researcher Risa Wechsler, an astrophysicist at the Kavli Institute at Stanford University. “The SAGA Survey will provide a critical new understanding of galaxy formation and of the nature of dark matter.”
Wechsler, Geha, and their team say they will continue to improve the efficiency of finding satellites around Milky Way siblings. “I really want to know the answer to whether the Milky Way is unique, or totally normal,” Geha says. “By studying our siblings, we learn more about ourselves.”
Other coauthors are from the University of Pittsburgh, the Space Telescope Science Institute, the University of Arizona, Carnegie Institution for Science, the Max Planck Institute for Extraterrestrial Physics, the University of Chile, and SLAC National Accelerator Laboratory.
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