MAS February Monthly Meeting

The Mysterious Radiation Field in the Milky Way (and Other Galactic Surprises)

Dr. Bob Benjamin

Our Milky Way Galaxy is an “island” of stars, interstellar gas, and dark matter in the vast expanses of intergalactic space. In this talk, I will focus on the interstellar (mostly hydrogen) gas. This gas fills the space between the stars, and some fraction of it is ionized: radiation from the stars has enough energy to remove the electron from the proton. By studying the resulting emission lines from this gas with the Wisconsin H-alpha Mapper, we have discovered that the central parts of the Milky Way are permeated by an unusual radiation field. I describe how we ended up making the discovery and why it is significant. As a bonus, I will describe the discovery of a thirty-degree arc of ionizing gas centered on the handle of the Big Dipper.

Prof. Bob Benjamin obtained his Ph.D. at the University of Texas at Austin in 1994, and joined the physics faculty of the University of Wisconsin-Whitewater in 2003. He is interested in all things Milky Way, having participated in two major Wisconsin surveys of the Milky Way galaxy: the Wisconsin H-alpha Mapper and the NASA-sponsored Spitzer Space Telescope GLIMPSE survey of the galactic plane.

The February 12th meeting will be a virtual event, hosted with Zoom. Members will receive an email with a link and instructions to join a day or two before the event. Again this month we are opening the virtual meeting up to our web followers who may want to join in. If you would like to attend the MAS virtual meeting, send an email to by noon Friday, Feb 12 to let us know of your interest. We will email you the Zoom link at 3pm that day which will get you into the meeting by 7:30 on Friday evening.