Astrophysics seminars are held at 1:30 PM on Thursdays in Serin room W330, with refreshments to follow in room W332. Departmental colloquia are at 10:30 AM on Wednesdays in the Physics Lecture Hall. Special dates and/or times are noted in bold in the table below.

Date/Time Location Speaker Title Hosts
Thu Jan. 24
1:30 PM
Serin 330 TBA TBA TBA
Thu Jan. 31
1:30 PM
Serin 330 Amiel Sternberg (Tev Aviv University, Flatiron Institute, Max Planck Institute for Extraterrestrial Physics) The Atomic to Molecular (HI-to-H2) Transition in Galaxy Star-Forming Regions
The atomic to molecular hydrogen (HI-to-H2) phase transition is of fundamental importance for star-formation and the emergence of chemical complexity in the interstellar medium of galaxies. I will present an overview, and discuss recent theoretical studies, numerical and analytic, of the HI-to-H2 transition in irradiated systems, with applications to the multi-scale behavior observed in star-forming galaxy disks from low- to high-redshift.
Andrew Baker
John Wu
Thu Feb. 7
1:30 PM
Serin 330 Phil Chang (U. Wisconsin, Milwaukee) The Turbulent Origin of Stars.
Recent numerical experiments on the star formation rate on small scales find that the star formation rate is much faster than the Kennicutt-Schmidt law which well-characterizes star formation on galactic scales, and also shows that star formation accelerates with time. Motivated by these results, I will discuss a new dynamical theory of star formation in a turbulent medium that seeks to explain these observed numerical results. I will survey the various theories of star formation and their shortcomings. I will then discuss how we extend previous theories of collapse by considering turbulence as a dynamical variable and closing the fluid equations with a new form of the energy equation. The resulting theory explains these previous numerical results and makes a few predictions that have recently been numerically verified as well as some numerical surprises. I will discuss the implications of this theory on observations.
Tad Pryor
Kyle Dettman
Thu Feb. 14
1:30 PM
Serin 330 No Seminar This Week
Thu Feb. 21
1:30 PM
Serin 330 Elisabeth Mills (Brandeis) The Journey or the Destination: Isolating the Origin of the Physics Driving Gas Conditions in Galaxy Nuclei

Centers of galaxies are some of the most extreme objects in our universe: hosting starbursts and active supermassive black holes that can launch jets and winds far outside the compact galaxy nucleus. While there are relics of an active past in the center of our own Milky Way, at present it does not exhibit any of this activity. However, the central 300 parsecs of our Galaxy does contain a sizable reservoir of molecular gas that is the fuel for future star formation and black hole accretion. Constraining the physical conditions of this gas is critical for understanding how this reservoir will evolve to influence future activity in the Milky Way’s nucleus. Determining the origin of these conditions is also key to determining whether the same physics that govern gas conditions in this region can help us interpret more distant and active galaxy nuclei. I will present the results of my recent work following the changes in physical properties of this gas as it approaches the black hole; increasing in temperature, density, and turbulence, while largely resisting the onset of star formation. This work provides evidence that the extreme gas conditions in this region are driven largely by infall processes: the journey it takes to reach the central parsecs, rather than the energetic phenomena (supernovae, cosmic rays, massive star winds, UV radiation, and occasional X-ray flaring) encountered at its destination. However, as our Galactic center is relatively inactive, the next challenge is determining the extent to which the understanding gained from a detailed study of this region can be applied to more active systems. I will end by discussing work underway to double my sample size of galaxy nuclei by making parsec-scale observations of the ionized and molecular gas in the center of NGC 253, a nearby galaxy with an order of magnitude more star formation. Comparison of these two galaxy centers will isolate the gas conditions that both govern and are influenced by a nuclear starburst, and allow the definition of local templates for understanding the gas physics in these regions.

Andrew Baker
Thu Feb. 28
1:30 PM
Serin 401 Wolfgang Kerzendorf (NYU/Michigan State) Type Ia supernovae: Explosions and Progenitors
Type Ia supernovae are known as the precise distance indicators that allowed the remarkable discovery of the accelerated expansion of the universe. Despite this astounding feat, there still remain large uncertainties in many of the key issues surrounding these extremely energetic events. These uncertainties, while not being horribly detrimental to their use as distance indicators, hamper the understanding of the far-reaching consequences these cosmic factories of heavy elements have on the chemical evolution of the Universe.

Type Ia Supernovae can be divided into three distinct phases. The pre-supernova evolution, the explosion itself and the expansion phase. In this talk, I will first present our findings on the progenitor question (pre-supernova phase), then shortly touch on our understanding of the explosion itself, and finally, present our work on modeling the spectra resulting from the expansion phase. I will close by giving an outlook of the future of spectroscopic modeling and its consequences for our understanding of pre-supernova evolution and explosion physics.

Tad Pryor
Yssavo Camacho-Neves
Thu Mar. 7
1:30 PM
Serin 330 Tina Peters (Toronto) Classification to Cosmology
The Large Synoptic Survey Telescope (LSST) is the largest astronomical survey ever planned. During the ten-year survey of the southern sky, this 8-meter telescope has the ability to image the entire sky in optical light every three nights. It is expected that LSST will increase the number of known quasars and Type Ia supernovae by an order of magnitude, generating photometrically classified catalogs of ten million quasars and half a million SNe by the end of the survey.
I will demonstrate how these extragalactic variable sources can be identified in the LSST data using supervised classification, giving examples from the recent Photometric LSST Astronomical Time Series Classification Challenge (PLAsTiCC). I will conclude by describing some of the new population studies and cosmological studies that will be possible with a photometric census of this scale.
Eric Gawiser
Thu Mar. 14
1:30 PM
Serin 330 Karen Masters (Haverford) Galaxy Evolution from Large Surveys of Nearby Resolved Galaxies

The morphology of a galaxy provides information on the orbits of stars within it. As such, important clues to the formation history of galaxies is revealed by their morphologies, and this information is complimentary, but not identical to, their star formation history and chemical composition as revealed by photometry and spectra.

The Galaxy Zoo project ( has provided quantitative visual morphologies for over a million galaxies (including the entire Sloan Digital Sky Surveys, or SDSS Main Galaxy Sample), and has been part of a reinvigoration of interest in the morphologies of galaxies and what they reveal about the evolution of galaxies.
Mapping Nearby Galaxies at Apache Point Observatory (MaNGA, part of SDSS-IV), is well over halfway through its 6 year plan to obtain spatially resolved spectral maps for 10,000 nearby galaxies (all of which have Galaxy Zoo morphologies). MaNGA is now by far the largest sample of resolved spectroscopy in the world, with over 6000 galaxies observed. The most recent data release from MaNGA happened in December 2018.

In this talk I will review these projects, and show results from them which demonstrate why a resolved view of the internal morphology in large samples of galaxies is interesting and how it provides a unique constraint of our understanding of galaxy evolution.

Andrew Baker
Wed Mar. 27
10:30 AM
PLH Gabriela González (LSU/LIGO)
Robbins Lecture
TBA Matthew Buckley
Thu Mar. 28 Serin 401 NO SEMINAR THIS WEEK
Thu Apr. 4
1:30 PM
Serin 330 Senior Honors Talks TBA Chuck Keeton
Thu Apr. 11
1:30 PM
Serin 401 Vivienne Baldassare (Yale) Searching for Active Galactic Nuclei in Low-Mass Galaxies
The population of massive black holes (BHs) at the centers of nearby low-mass galaxies provides some of the best observational constraints on the masses of “black hole seeds” at high redshift. Furthermore, while BHs are ubiquitous and well-studied in Milky Way-sized and larger galaxies, relatively little is known about the population and properties of BHs in smaller galaxies. I will discuss recent observational efforts to find accreting BHs in low-mass galaxies via an array of multi-wavelength techniques, concentrating on searches using optical spectroscopy and optical photometric variability. I will also describe the multi-wavelength properties of active galactic nuclei in low-mass galaxies and discuss how they compare to more massive systems. Finally, I will discuss the properties of the active dwarf galaxy RGG 118, host to the smallest reported nuclear black hole.
Chuck Keeton
Ramon Sharma
Thu Apr. 18
1:30 PM
Serin 330 Jennifer Barnes (Columbia) Panning for gold with things that go bang in the night
Abstract: Electromagnetic follow-up observations of the gravitational wave-detected binary neutron star merger (NSM) GW1701817 suggested that material ejected from the accretion disk formed in the merger underwent a robust r-process nucleosynthesis, producing heavy elements like Au, Pt, and Eu. These observations seemed to answer a long-standing question about the origin of the heaviest elements in the Universe. However, the conditions that characterize the disks formed in NSMs are also found in other systems, raising the question of whether mergers are unique sites of r-process production. Of particular interest for this question is the collapse of rotating massive stars, called "collapsars." Like NSMs, collapsars form accretion disks around stellar mass compact objects and are associated with ultrarelativistic outflows that give rise to gamma-ray bursts. I will discuss recent work that explored whether these collapsar disks could successfully produce the r-process, and what the signs of collapsar disk r-process nucleosynthesis might be.
Alyson Brooks
Thu Apr. 25
1:30 PM
Serin 330 Evan Schneider (Princeton) The origin of multiphase galaxy outflows
Star-forming galaxies are often observed to host galactic winds - gas that is flowing out of the galaxy in phases ranging from cold molecular clouds to hot X-ray emitting plasma. While these multiphase outflows are routinely observed, theoretically constraining their origin and evolution has proven difficult. Explaining the prevalence and velocities of the cool ionized phase (T~10^4 K) in particular poses a challenge. In this talk, I will discuss a potential dual origin for this cool gas. Through a series of extremely high-resolution simulations run with the GPU-based Cholla code, I will show that in high star formation surface density systems, dense disk gas can be pushed out by the collective effect of clustered supernovae, explaining the low-velocity material. Simultaneously, shredding and mixing of these clouds increases the density of the hot phase of the wind, leading to large-scale radiative losses that produce high velocity cool gas. In addition to explaining the nature of outflows themselves, these multiphase winds could potentially be a source of the cool photo-ionized gas that is found in abundance in galaxy halos.
Alyson Brooks
Thu May 2
1:30 PM
Serin 330 Wynn Ho (Haverford) Pulsar glitches are fun(damental physics) and NICER
Pulsars are famous for having very precisely measured spin rates, and this spin evolves extremely regularly for most pulsars. However, the spin of young pulsars can occasionally undergo sudden changes, known as glitches. Glitches are thought to be due to interactions between normal and superfluid matter in the crust and core of the star. Thus observations and understanding of glitches allow us to probe fundamental nuclear physics and superfluidity. I will give an introduction to pulsar glitches and the superfluid model. I then describe a novel, non-gravitational method for measuring the mass of isolated pulsars using glitches. Finally I discuss the unique glitching pulsar PSR J0537-6910, which is being monitored by the NICER experiment on the International Space Station. NICER data is crucial for LIGO/Virgo searches of gravitational waves from this pulsar, whose spin behavior could be due in part to emission of gravitational waves.
Jack Hughes
Prasiddha Arunachalam
Past Schedules