Tuesdays at 4:00 PM in the Marlar Lounge, Room 37-252
MIT Kavli Institute for Astrophysics and Space Research
70 Vassar Street, Cambridge, MA
(unless location otherwise noted)
Refreshments are served at 3:45 PM.
the Astrophysics Division of the MIT Department of Physics and
the MIT Kavli Institute for Astrophysics and Space Research.
Tuesday Feb 7:
Cosmology with Shadows in the Microwave Sky
Host: M. McDonald
Tuesday Feb 14:
New Probes of Old Structure: Cosmology with 21cm Intensity Mapping and the Cosmic Microwave Background
Host: J. Hewitt
Current cosmological measurements have left us with deep questions about our Universe: What caused the expansion of the Universe at the earliest times? How did structure form? What is Dark Energy and does it evolve with time? New experiments like CHIME, HIRAX, and ACTPol are poised to address these questions through 3-dimensional maps of structure and measurements of the polarized Cosmic Microwave Background. In this talk, I will describe how we will use 21cm intensity measurements from CHIME and HIRAX to place sensitive constraints on Dark Energy between redshifts 0.8 -- 2.5, a poorly probed era corresponding to when Dark Energy began to impact the expansion history of the Universe. I will also discuss how we will use data from new instruments on the ACT telescope to constrain cosmological parameters like the total neutrino mass and probe structure at late times.
Tuesday Feb 21:
Tracing the Cosmic Shutdown of Star Formation in Massive Galaxies
University of Connecticut
Host: M. Vogelsberger
Over the last few decades, astronomers have progressed from archeological studies of nearby galaxies to direct observations of the early universe. We have uncovered billions of years of cosmic growth that present new challenges to galaxy formation theories. In this talk, I will review the recent innovative techniques developed to probe the distant universe, and the key observations constraining the formation histories of galaxies over the past 11 billion years. We have discovered a population of surprisingly compact and massive “red and dead” (quiescent) galaxies that are no longer actively forming stars. The physical mechanisms responsible for shutting down star formation and the subsequent buildup of this quiescent population at such early times is one of the most outstanding questions in astrophysics today. We don’t yet understand why these enigmatic galaxies are so compact, with sizes a factor of 5 smaller than nearby galaxies of similar mass. I will present promising paths forward towards solving this puzzle that leverage the capabilities of the Hubble Space Telescope, as well as a look toward the future with exciting upcoming public facilities.
Tuesday Feb 28:
The Physics and Astrophysics of Merging Neutron-Star Binaries
Goethe University of Frankfurt
Host: S. Hughes
I will argue that if black holes represent one the most fascinating implications of Einstein's theory of gravity, neutron stars in binary system are arguably its richest laboratory, where gravity blends with astrophysics and particle physics. I will discuss the rapid recent progress made in modelling these systems and show how the inspiral and merger of a binary system of neutron stars is more than a strong source of gravitational waves. Indeed, while the gravitational signal can provide tight constraints on the equation of state for matter at nuclear densities, the formation of a black-hole--torus system can explain much of the phenomenology of short gamma-ray bursts, while the ejection of matter during the merger can shed light on the chemical enrichment of the universe.
Tuesday Mar 7:
Stellar Streams and the Milky Way's Dark Matter Halo
University of Toronto
Host: P. Schechter
Stellar tidal streams originating from disrupting globular clusters in the Milky Way's halo hold enormous promise as probes of both the large-scale structure of the Milky Way halo's density distribution and its small-scale structure. As such, the observed density, spatial, and kinematic structure of stellar streams can provide important new constraints on the interactions and small-scale structure of dark matter. I will discuss the simple gravitational dynamics of tidal-stream formation and evolution and how we can use it to build simple and fast models for tidal streams. I will show some examples of this machinery in fitting observed streams and what it tells us about the shape of the Milky Way's halo. I will further present a fast perturbation theory for computing the effects of impacts between a stream and many small dark-matter subhalos and its application to existing and future data sets.
Tuesday Mar 14:
Host: M. McDonald
Tuesday Mar 21:
Dark Matter Substructure: Cosmological Treasure Trove or a Pandora's Box?
Frank van den Bosch
Host: P. Schechter
Hierarchical structure formation in a LCDM cosmology gives rise to virialized
dark matter halos that contain a wealth of subtructure. Being able to accurately
predict the abundance and demographics of dark matter subhaloes is of paramount
importance for many fields of astrophysics: gravitational lensing, galaxy evolution,
and even constraining the nature of dark matter. Dark matter substructure is
subject to tidal stripping and tidal heating, which are highly non-linear processes
and therefore best studied using numerical N-body simulations. Unfortunately, as I
will demonstrate, state-of-the-art cosmological simulations are unable to adequately
resolve the dynamical evolution of dark matter substructure. They suffer from a
dramatic amount of artificial subhalo disruption as a consequence of both inadequate
force softening and discreteness noise amplification in the presence of a tidal field.
I discuss implications for a variety of astrophysical applications, and briefly
discuss potential ways forward.
Tuesday Mar 28:
NO COLLOQUIUM: SPRING VACATION
Tuesday Apr 4:
University of Chicago
Tuesday Apr 11:
Max Planck Institute für Astrophysik
Host: C. Canizares
Tuesday Apr 18:
NO COLLOQUIUM: PATRIOT'S DAY
Tuesday Apr 25:
University of Bern
Host: N. Weinberg
Tuesday May 2:
University of Washington
Host: S. Vitale
Tuesday May 9:
Host: D. Chakrabarty
Tuesday May 16:
Scuola Normale Superiore
Host: J. Hewitt