Larry Widrow
Queen's University

Abstract

The disk of the Milky Way comprises some 100 billion stars on nearly circular orbits about the Galactic centre. Within a few years, the Gaia Space Telescope will measure positions and velocities for over 1% of these stars. By combining equilibrium models of the Galaxy with these observations we can construct the Galactic rotation curve, which allows us to infer the large-scale structure of the dark matter halo. We can also construct a model for the mass distribution in the Solar Neighbourhood, which allows us to infer the local density of dark matter. However, even a cursory study of the Milky Way reveals structures that signal a departure from equilibrium. The most prominent of these are the Galactic bar, spiral arms, and warping of the outer disk. I will describe recent observations of some more subtle departures from equilibrium and discuss ways in which these observations can lead to refined models of the Galaxy and a more complete picture of the Galaxy's dynamics.

Seyda Ipek
Carleton University

Abstract:

One of the most famous dark matter candidates is the weakly interacting massive particles, WIMPs. Our theories for WIMPs rely on a standard cosmological history, in which WIMP particles annihilate into (massless) SM fermions. At some point these annihilations freeze out and the WIMP number density becomes a constant. However, the parameter space for this simple is under increasing scrutiny from various direct detection experiments. I will give an example of a non-standard cosmological history in which the WIMP scenario works as well without being excluded by direct detection experiments.

McDonald Institute seminars bring together experimental and theoretical astroparticle physicists and astronomers. They are held approximately fortnightly, September to November and January to March, and on an ad hoc basis outside of term. They currently take place on Thursdays at 3:30 PM in STI 501 and/or on Zoom. Contact Aaron Vincent if you would like to attend.

Samantha Lawler
University of Regina

Abstract

Several companies are planning to launch megaconstellations of thousands of communication satellites (satcons), which would increase the number of active satellites in Low Earth Orbit at least twenty-fold in the next few years. SpaceX's Starlink satcon is currently largest (almost 2,000 satellites) and is adding 60 new satellites every couple of weeks.  While these satcons do allow internet access in many underserved rural and remote locations, the costs are prohibitively high for all but the most well-off customers. These thousands of satellites each reflect sunlight, causing serious problems for research astronomy, and making anthropogenic light pollution a fully global phenomenon that cannot be escaped anywhere on Earth.  Our recent simulations show that because of geometry and the chosen satellite orbits, latitudes near 50 degrees N and S will see the worst light pollution from these satcons, with hundreds of naked-eye visible satellites all night long in the summer. These satellites also contribute to significant atmospheric pollution, both on launch and re-entry, contribute to diffuse sky emission, and drastically increase the very real threat of Kessler Syndrome. I will talk about how these satellites will affect stargazers and astronomers worldwide, and what you can do to help mitigation efforts.