RUI: How Porous is the Warm Ionized ISM? Drilling in with Pulsars

Oberlin College, Oberlin OH

Investigators

Abstract

Our own Milky Way galaxy consists of stars but also a substantial amount of material in between the stars. Astronomers call this material the interstellar medium or ISM for short. Much of the ISM consists of neutral atoms that have the same number of protons as electrons. However, about 3% of the gas has had one or more electrons knocked free by photons from nearby stars. The investigators seek to know how porous this ionized gas is. In other words, is it like a thick, dense fog and the same density in all directions. Alternatively, their measurements may show the gas is more like group of fluffy clouds drifting overhead on a summer’s day. These questions are important for understanding the entire star-forming ecosystem of the Milky Way. This project will also support undergraduate student researchers, both during their academic year and during the summer. They will learn research, organizational, and communication skills applicable the national science and technology effort. The project leader will actively work to recruit a diverse group of students to work on this project. The investigator seeks to improve understanding of the warm ionized gas in the Milky Way. Referred to as the WIM, it is an important part of the pressure support of the Milky Way. Pulsars, which are rotating neutron stars, are excellent probes of the WIM since the radio waves they generate are delayed and scattered by passage through the WIM. When the radio pulses pass through discrete ionized structures (lens-like in character), these otherwise invisible features are revealed. The investigator and students will search for subtle, but easy-to-detect, features in the radio waves to determine the location and physical conditions of the material that scatters the radio waves. Major US radio telescopes such as the Arecibo Observatory and the Green Bank Telescope will be used for this work. One portion of the work will be pursued using a telescope in the Netherlands called LOFAR, which observes at much lower radio frequency than the two other telescopes. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.