Thunch is a weekly grad-student run seminar series which gives local and visiting scholars, especially students, the opportunity to present their research to a broad audience at the Princeton Department of Astrophysical Sciences. Potential visiting speakers should contact the Thunch Czars, Hanpu Liu and Eritas Yang.
When: Thursdays at 12 pm (food), 12:15 pm (talk)
Where: Peyton Hall, "grand central" (big room in the center of the building)
What: food + 45 minute talk and discussion
Rules
- Priority goes to students and to those who have not given a talk recently.
- Visiting speakers must be explicitly invited by the department.
- There is no money in Thunch to pay for travel, so visitors need another source of funding.
- Speakers must send a title and abstract to the Thunch Czars at least one week in advance of their talk.
Now you know everything you need to know about Thunch. Join us for good food and good science. Reach out to the Thunch Czars with any questions.
Spring 2025 Upcoming Speakers:
| Date | Name and Institution | Title and Abstract |
|---|---|---|
| January 30th | Gabriela Sato-Polito | Title: Where are the supermassive black holes measured by PTAs? Abstract: Pulsar timing arrays (PTAs) consist of a set of regularly monitored millisecond pulsars with extremely stable rotational periods. The arrival time of pulses can be altered by the passage of gravitational waves (GWs) between them and the Earth, thus serving as a galaxy-wide GW detector. Evidence for the first detection of low-frequency (~nHz) gravitational waves has recently been reported across multiple PTA collaborations, opening a new observational window into the Universe. Although the origin of the GW signal is yet to be determined, the dominant sources are expected to be inpiralling supermassive black holes (SMBHs). I will discuss a recent work in which we compare the GW detections by PTAs with the expected signal implied by existing electromagnetic observations in a simple but robust manner. We highlight that there is a simple upper limit to the GWB amplitude and that the currently measured GW amplitude is somewhat larger than expected. I will then show that additional information regarding the typical number of sources contributing to the background can already be inferred from current PTA data. |
| February 6th | Tatsuya Akiba (University of Colorado Boulder) | Title: On the Hunt for Recoiling Supermassive Black Holes Using Tidal Disruption Events Abstract: Following the merger of two supermassive black holes (SMBHs), a gravitational wave recoil kick is imparted on the merger remnant due to the anisotropic emission of gravitational waves. These recoil kicks can be as high as ~10^3 km/s which exceeds the escape velocity of most galaxies, and these super-kicks can lead to ejected or rogue SMBHs. While there are several candidates, recoiling SMBHs are difficult to uniquely identify since observations so far cannot rule out alternate possibilities such as dual active galactic nuclei. Here, we present a novel observational signature: off-nuclear or extragalactic tidal disruption events of stars by recoiling SMBHs. When a super-kick is imparted on a SMBH, there is a tightly bound cluster of stars recoiling with it. We show that these bound stars should be in an eccentric, apse-aligned disk where stars are strongly torqued to extremely high eccentricities. The corresponding rate of tidal disruption events in an eccentric disk is expected to be of order ~0.1 yr^-1 gal^-1, several orders of magnitude higher than in an isotropic cluster. We show that this high expected rate of tidal disruption events in an eccentric disk implies off-nuclear or extragalactic tidal disruption events as viable and likely observables of a recoiling or rogue SMBH. |
| February 13th | Jake Rule (visiting student from Oxford) | Title: Simulating the Plunging Region of Thin Black Hole Accretion Disks Abstract: A feature of General Relativity is the existence of a plunging region between the ISCO and the event horizon of a black hole. As a consequence of their simplifying ‘zero-stress’ boundary condition at the ISCO, traditional accretion disk models fail to incorporate the plunging region since all thermodynamic quantities vanish at the ISCO. However, successive global GRMHD simulations have confirmed the presence of a magnetic stress at the ISCO and non-vanishing plunging region thermodynamics. This presents a source of systematic error for some existing black hole spin measurements, which use zero-stress disk models as a basis for their emission modelling. A set of analytic solutions for the plunging region thermodynamics have been developed recently under the assumption that the fluid undergoes a gravity-dominated plunge into the black hole. We test this model against a dedicated 3D global GRMHD simulation of a thin accretion disk around a Schwarzschild black hole using the code AthenaK. Provided we account for observed non-adiabatic heating from grid-scale magnetic reconnection, we find an excellent agreement between the analytic model and the simulated quantities. |
| February 20th | Yilun Ma, David Setton, Jenny Greene | Title: All About Little Red Dots Abstract: Early results of JWST observation have revealed an unexpected abundance of red compact objects dubbed little red dots (LRDs) at z>4. These objects display a faint blue rest-frame UV continuum followed by a steep red rise in the rest-frame optical. The presence of broad emission lines with FWHM>2000km/s suggests their AGN nature, but the lack of X-ray and hot dust emission commonly associated with accreting SMBHs as well as the Balmer breaks in LRD spectra seem to defy such an explanation. The high number density of LRDs (100x more than UV-selected quasars and a few percent of galaxy population at high-z) signifies the important roles they could play at galaxy/SMBH growth and evolution, but their nature remains unclear. In this talk, we will update the department on our ongoing efforts to understand the nature of these intriguing objects. |
| February 27th | Anirudh Patel (Columbia University) | Title: Magnetar Giant Flares: A New Site for the r-Process Abstract: We present nucleosynthesis and light-curve calculations for a new site of the r-process from magnetar giant flares (GFs). Motivated by radio afterglow observations which indicate sizable baryon ejecta from GFs, Cehula et al. (2024) recently proposed a scenario whereby magnetar crustal material is ejected as a result of a shock driven into its surface layers during the GF. We confirm and characterize the r-process in these ejecta with nucleosynthesis calculations. We use the nucleosynthesis output to make light-curve predictions of kilonova-like optical/UV transients and gamma-ray transients powered by the radioactive decay of the unbound debris. We show that the predicted gamma-ray emission properties (light-curve, fluence, and spectrum) match a previously unexplained hard gamma-ray signal observed in the aftermath of the famous December 2004 giant flare from the magnetar SGR 1806-20. This MeV emission component is direct observational evidence for the synthesis of ~10^-6 Msun of r-process elements. The discovery of magnetar giant flares as confirmed r-process sites, contributing at least 1-10% of the total Galactic abundances, has implications for the Galactic chemical evolution, especially at the earliest epochs probed by low-metallicity stars. |
| March 20th | Sanghyuk Moon | Title: Prestellar Cores in Turbulent Clouds Abstract: Stars form via gravitational collapse of compact (< 0.1 pc), centrally-concentrated gaseous objects called prestellar cores. Understanding the physical processes responsible for the formation and evolution of these cores thus constitutes a necessary step toward developing a theory that can predict the star formation rate and initial mass function across widely varying physical conditions. While a detailed core-by-core analysis in numerical simulations should reveal, in principle, the exact physical mechanisms leading to collapse, progress has been hindered by the lack of a proper theoretical model for turbulent prestellar cores, compounded by technical difficulties in tracking individual cores in numerical simulations and characterizing their physical properties over time. In this talk, I will highlight some of our latest results using both theory and numerical simulations to address these challenges. I will introduce our new model for turbulent equilibrium sphere (TES) generalizing the Bonnor-Ebert sphere in the presence of turbulent velocity field obeying power-law linewidth–size relations. I will also provide an overview of our numerical simulations of turbulent, self-gravitating clouds, with a special focus given to the resolution requirements and the analysis of dynamical evolution of individual cores forming in the simulations. By utilizing the TES model, I will provide physical interpretations of our results and discuss some implications on, e.g., critical conditions for collapse, collapse dynamics, and core mass function. |
| April 3rd | Philipp Frank (KIPAC) | Title: Mapping the 3D structure and components of the Milky Way’s ISM Abstract: Understanding the three-dimensional distribution of dust and gas within the Milky Way is essential for unraveling Galactic structure, star formation, and the interstellar medium's dynamics. The advent of the Gaia mission has provided an unprecedented wealth of precise photometric and spectroscopic data, offering new opportunities and challenges in characterizing Galactic components on a large scale. In addition, mapping out the spatial-spectral information of gas emission data as well as magnetic field tracers such as the Faraday rotation measure complements the structural information provided by interstellar dust. Fully leveraging this wealth of information requires novel development and usage of probabilistic machine learning, statistical inference, and forward modeling techniques. Their successful application allows exploration and extraction of robust astrophysical insights and lays the groundwork for next-generation datasets. |
| April 10th | Lizhong Zhang (IAS) | Title: A Parameter Survey of Neutron Star Accretion Column Simulations Abstract: Accretion-powered X-ray pulsars are neutron stars that accrete matter from a companion star in a binary system. The strong magnetic field of the neutron star channels material onto the magnetic poles, which are typically misaligned with the spin axis, producing pulsating X-rays as the star rotates. At sufficiently high accretion rates, radiation pressure supports this magnetically confined flow, forming a column structure near the poles. In this study, we conduct a parameter survey using radiation relativistic MHD simulations to investigate the dynamics of the accretion column as a function of accretion rate, magnetic field strength, and accretion geometry. Our simulations incorporate a comprehensive opacity table that accounts for magnetic electron scattering, magnetic bremsstrahlung, cyclotron resonance, vacuum polarization, and electron-positron pair production. We also explore two distinct accretion geometries: solid and hollow column structures. In this talk, I will discuss the dynamical effects introduced by these factors and highlight results relevant to observations. In our future work, we plan to compute the spectrum and polarization based on our current numerical models to establish a more direct connection with observational data. |
| April 17th | Yen-Ting Lin (ASIAA) | Title: Formation and Evolution of Brightest Cluster Galaxies: nature vs nurture? Abstract: The formation and evolution of brightest cluster galaxies (BCGs), the most massive galaxies in the universe, is not a well-understood issue in astrophysics. Are BCGs special compared to other cluster member galaxies? If so, were they born special, or they were formed initially just like other galaxies, but gradually became special? To answer these questions, we first show that the merger rates of BCGs based on MaNGA integral field spectroscopic data are in reasonable agreement with the predictions from IllustrisTNG. Encouraged by the success of the model, we then employ statistical tools to examine the growth history of model BCGs in IllustrisTNG to see whether BCGs are a special population, and try to answer the "nature" vs "nurture" issue regarding BCGs. |
Fall 2024:
September 5th: Zack Andalman (Princeton University), Matt Sampson (Princeton University) Christian Kragh Jespersen (Princeton University)
September 12th: Bob Kirshner (Harvard University)
September 19th: Jacqueline Antwi-Danso (University of Toronto)
September 26th: Haowen Zhang (University of Arizona)
October 3rd: Bingjie Wang (Penn State University)
October 10th: Austen Gabrielpillai
October 17th: Jean Somalwar (Caltech)
October 24th: David Robinson (University of Michigan)
October 31st: Xiaowei Ou (MIT)
November 7th: Nicholas Rui (Caltech)
November 14th: Christina Willecke Lindberg (Johns Hopkins University)
November 21st: Claire Ye (University of Toronto)
December 5th:Viraj Pandya (Columbia University)
December 12th: Andrew Casey-Clyde (Yale University)
Spring 2024
February 8th: Benjamin Remy (Princeton University)
February 15th: Lauren Weiss (University of Notre Dame)
February 22rd: Martin Elvis (Harvard)
February 29th: Dom Rowan (Ohio State University)
March 7th: Yubo Su (Princeton University)
March 21st: Pascal Marichalar (French National Center for Scientific Research)
March 28th: Yuanhong Qu (University of Nevada, Las Vegas)
April 4th: Nick Kokron (Princeton University)
April 11th: Kovi Rose (University of Sydney)
April 18th (double talk)
Jamila Pegues (Space Telescope Science Institute)
Kris Pardo (University of Southern California)
April 25th: Jackie Faherty (American Museum of Natural History)
May 2nd: Trung Ha (University of North Texas)
May 16th: Stephane Werner (Durham University)
Fall 2023:
September 7th: Andrew Saydjari (Harvard)
September 14th: Samantha Wu (CalTech)
September 21st: Viraj Karambelkar (CalTech)
September 28th: Fan Zou (Penn State)
October 5th: Zhuhai Li (CalTech)
October 12th: Prof. Yue Shen (University of Illinois Urbana-Champaign)
October 19th: Mor Rozner (Israel Institute of Technology)
October 26th: Shangjia Zhang (University of Nevada)
November 2nd: Teodor Grosu
November 9th: Hsiang-Chih Hwang (IAS)
November 16th: Kishore Patra (Berkeley)
November 30th: Princeton Graduate Students
Spring 2023:
February 16th: Chia-Yu Hu (University of Florida)
February 23rd: Dan Foreman-Mackey (CCA)
March 2nd: Lyla Jung (ANU)
March 16th: Vicente Valenzuela-Villaseca (Princeton University)
March 30th: Roohi Dalal (Princeton)
April 6th: David Velasco (Princeton)
April 13th: Zili Shen (Yale)
April 20th: Sabrina Appel (Rutgers)
May 4th: Ewine van Dishoeck Leiden (Leiden Observatory, the Netherlands)
May 11th: Charlotte Ward (Princeton University)
Fall 2022:
September 15th: Aritra Ghosh (Graduate Student, Yale University)
September 22nd: Thales Gutcke (NASA Hubble Fellow and Lyman Spitzer, Jr. Postdoctoral Fellow, Princeton)
September 29th: Fengwu Sun (Graduate Student, University of Arizona)
October 6th: Yubo Su (Lyman Spitzer Jr. Postdoctoral Fellow, Princeton)
October 13th: Yinhao Wu (Graduate Student, Leicester University)
October 20th: Fall break
October 27th: Lizhong Zhang (Graduate Student, University of California, Santa Barbara)
November 3rd: Oliver Zier (Graduate Student, Max Planck Institute for Astrophysics, Garching, Germany)
November 10th: Chang-Goo Kim (Post-Doctoral Associate Research Scholar, Princeton)
November 17th: Tsun Hin Navin Tsung (Graduate Student, University of California, Santa Barbara)
December 1st: Ore Gottlieb (Rothschild Fellow, CIERA Postdoctoral Fellow, Northwest University)
December 8th: Sihao Cheng (Postdoc Member at the Institute for Advanced Study)
Spring 2022:
February 3rd: Benjamin Crinquand (Post-Doctoral Associate Research Scholar, Princeton)
February 10th: Matthew Coleman (Post-Doctoral Associate Research Scholar, Princeton)
February 17th: Riddhi Bandyopadhyay (Post-Doctoral Associate Research Scholar, Princeton)
February 24th: Alex Gagliano (Pre-Doctoral Fellow, CCA Flatiron)
March 10th: Igor Andreoni (Postdoctoral Fellow, Joint Space-Science Institute)
March 17th: Sihao Cheng (Postdoctoral Fellow, Johns Hopkins University)
March 24th: Keith Hawkins (Assistant Professor, University of Texas at Austin)
March 31th: Frank van den Bosch (Professor of Theoretical Astrophysics, Yale)
April 7th: Mor Rozner (Graduate Student, Technion - Israel Institute of Technology)
April 14th: Sam Yee (Graduate Student, Princeton)
Click here for the latest schedule information
