Evidence Detected of Ancient Impacts That Shaped the Milky Way



A team of astronomers has observed evidence of ancient impacts that are thought to have shaped and structured our Milky Way galaxy. Their research presents observational evidence of asymmetric ripples in the stellar disk of our galaxy, which had long been thought to be smooth. Using observations from the Sloan Digital Sky Survey (SDSS) telescope in New Mexico, the University of Kentucky team analyzed the spatial distribution of 3.6 million stars and found ripples interpreted as evidence of the Milky Way’s ancient impacts, which could include an impact with the massive Sagittarius dwarf galaxy some 0.85 billion years ago.

“These impacts are thought to have been the ‘architects’ of the Milky Way’s central bar and spiral arms,” said co-author Susan Gardner, a University of Kentucky professor of physics and astronomy . “Just as the ripples on the surface of a smooth lake suggest the passing of a distant speed boat, we search for departures from the symmetries we would expect in the distributions of the stars to find evidence of ancient impacts. We have found extensive evidence for the breaking of all these symmetries and thus build the case for the role of ancient impacts in forming the structure of our Milky Way.”

This new paper continues Gardner’s earlier studies of the breaking of north/south symmetry in the stellar disk of the Milky Way. Their earlier work revealed an asymmetry that appears as a vertical “ripple” in the number counts of the stars as one samples in vertical distance away from the center of the galactic disk. In the new paper, the team analyzed the largest sample yet, and confirmed their earlier interpretation of the north/south asymmetry and found evidence for symmetry breaking in the plane of the galactic disk as well.




“Having access to millions of stars from the SDSS allowed us to study galactic structure in an entirely new way by breaking the sky up into smaller regions without loss of statistics,” said Deborah Ferguson, who first reproduced the vertical asymmetry results Gardner and Yanny found in their earlier analysis. “It has been incredible watching this project evolve and the results emerge as we plotted the stellar densities and saw intriguing patterns across the footprint. As more studies are being done in this field, I am excited to see what we can learn about the structure of our galaxy and the forces that helped to shape it.”

Ferguson is the lead author on a paper that published this week in the Astrophysical Journal (ApJ). Ferguson conducted the research as an undergraduate student with co-authors Susan Gardner, a professor of physics and astronomy in the UK College of Arts and Sciences, and Brian Yanny, a staff scientist and astrophysicist in the Fermilab Center for Particle Astrophysics.

The Daily Galaxy via University of Kentucky

Image credit: ESO


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