For NYSS APS information, contact:
Dr. Erica Simoson 

"The Milky Way’s Galactic bar can punch holes in stellar streams"

Sarah Pearson, Columbia University

As clusters of stars orbit our own Milky Way, a gravitational tidal interaction unfolds and the clusters tear apart into distinct morphological and kinematic structures.  From our detailed understanding of gravity, the distribution and motions of these stellar structures enable us to work backwards in time and thereby study our Milky Way's past and evolution. Palomar 5 is an old cluster of stars orbiting our Galaxy, while disrupting into thin leading and trailing stellar arms. It is located ~16 kpc (~52000 light years) above the Galactic plane. In this talk, I will show that a previous encounter between the stream and the Milky Way’s Galactic bar (which is a collection of billions of stars coherently rotating in the plane of our Galaxy) has punched a hole in the stream which can explain why the leading arm of Palomar 5 appears to be a lot shorter than the trailing arm. The discovery that the bar can punch holes in stellar streams has important implications for cosmology, which predicts that our Galaxy should be filled with dark matter subhalos of various sizes. One proposed method to detect the dark matter subhalos, is to search for them through disturbances in the structure of stellar streams. My work demonstrates that the Galactic bar can create holes of very similar appearance to those created if dark matter subhalos pass through or close by stellar streams. I therefore caution that we should not necessarily interpret the holes in stellar streams as evidence of the existence of dark matter subhalos. Additionally, I will demonstrate how the Galactic bar’s interaction with the Palomar 5 stream provides an intriguing methodology for studying our own Milky Way’s Galactic bar in more detail.

For program, contact:  
Dr. Heather Watson – watsonh@union.edu
Dr. Nelia Mann – mannn@union.edu
Dr. Samuel Amanuel – amanuels@union.edu
Ms. Lynnette Stec – stecl@union.edu
Phone: 518-388-6254
Fax: 518-388-6947
Department of Physics & Astronomy, Union College, Schenectady, NY 12308