The Milky Way is often described as an average galaxy but this cosmic modesty might be misplaced. Analysis from a new survey suggests that our home in the cosmos might not be as typical as previously thought.
The study, which is published in the Astrophysical Journal, is based on the Satellites Around Galactic Analogs (SAGA) Survey, which looks at what goes on around galaxies similar to the Milky Way. Big galaxies like ours tend to be surrounded by smaller satellite galaxies and SAGA discovered that almost all of these satellites are very active, forming new stars. Meanwhile, only a small fraction of the Milky Way’s ones are doing the same thing. We appear to be a peculiarly quiet system.
"We use the Milky Way and its surroundings to study absolutely everything,” Dr Marla Geha, from Yale University, said in a statement. “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 has so far studied eight galaxies analogous to our own, discovering and gaining information on 14 new satellites (another 11 require more data). Combined with the 13 previously known satellites of these galaxies, there’s a total of 27 objects, 26 of which are star forming. In comparison, only 40 percent of the Milky Way satellites are actually star forming.
“Our work puts the Milky Way into a broader context,” said 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.”
The survey hopes to reach 25 Milky Way siblings over the next two years and to have 100 when the survey is finished. All these galaxies are within 130 million light-years. “I really want to know the answer to whether the Milky Way is unique, or totally normal,” Geha said. “By studying our siblings, we learn more about ourselves.”
Once the SAGA Survey is complete we will not only better understand our galaxy but we might have to revise our cosmic measuring stick if it’s no longer an adequate representation.