September 21: Jeff Andrews (University of Florida)
Title: It Takes Two to Tango: Modeling Binary Stellar Populations in the Gravitational Wave Era
Between the discovery of gravitational waves from dozens of merging compact objects and the advent of micro-arcsecond astrometry realized by the Gaia space telescope, the study of the complexities binary stellar evolution - including mass transfer, tides, and r-process nucleosynthesis - has taken on a new urgency. In this talk, I will describe the current status of modeling binary star populations as well as several critical shortcomings that my collaborators and I are working to systematically address. In particular, I will focus on how we are using modern statistical and machine learning methods using dedicated supercomputers to improve our physical models of binary star populations.
September 28: Felipe Guzman (Texas A&M University)
POSTPONED DUE TO HURRICANE IAN
Title: Laser-interferometric and optomechanical technologies for astrophysics and Earth science
Coherent light enables length measurements of exquisite sensitivity that lie at the core of fascinating technological advances and engineering applications, as well as observations in fundamental physics, astrophysics, geodesy, and measurement science in general. Novel technologies and measurement principles find application in areas that are paradigm-changing; not only in fundamental science, but that directly impact the global economic and political stage. Detections from ground- based gravitational-wave observatories, like LIGO and VIRGO together with measurements of their electromagnetic counterparts, have opened a new window to observe the universe’s gravitational spectrum and have reshaped astronomy and astrophysics through Gravitational Wave and Multi-Messenger observations. Plans for future observatories in space, such as LISA, have already started through the extremely successful LISA Pathfinder mission. Moreover, GRACE follow-on continues GRACE’s legacy of providing information regarding climate change and our planet’s geo-dynamics through valuable observations of the Earth’s gravitational field. Compact and integrated optics and photonics combined with low-loss devices and optomechanically coupled coherent light fields enable us to reach unprecedented measurement accuracies near the quantum sensing limit, which may be relevant for novel approaches to observe gravitational waves and detect dark matter. At the core of these exciting scientific endeavors lie innovative optomechanical technologies and precision laser interferometers that make this all possible. In my presentation, I will comment on these applications and discuss the research work conducted in my research group at Texas A&M University on the advances and implementation of novel optomechanical technologies in areas of precision measurements, inertial sensing, and scientific space missions.
October 19: Tiziana Di Matteo (Carnegie Mellon University)
Title: Seed and ultramassive BHs in cosmological simulations
Understanding the origins of massive black holes in galaxies goes hand in hand with understanding the origins of other structures in the cosmic web. Hydrodynamic cosmological simulations self-consistently combine the process of structure formation at cosmological scales with the physics of smaller, galaxy scales. MBHs are not born ”massive” but grow by several orders of magnitude from ”seed" black holes. Gas accretion and black hole mergers are the drivers of their growth inside galaxies. I will discuss recent simulation predictions for the origin of rare ultramassive BHs and their assembly in massive galaxy mergers and triple quasar systems. I will also explore using simulations to investigate seed intermediate black holes and their relation to a 'wandering' black hole population. GW signals from coalescing massive black holes on all scales include mergers with wandering, remnant seed IMBHs.
October 26: Tarun Souradeep (Raman Research Institute)
Title: Structured Test of the Cosmological Principle
The Cosmological Principle, a fundamental tenet of the 'standard model of cosmology', predicates a statistically isotropic distribution of fluctuations in the measured Cosmic Microwave Background (CMB) temperature and polarisation sky maps. Enigmatic anomalies claimed in the WMAP and Planck CMB sky maps could challenge the standard model. However, these claims need to be cast in an objective mathematical framework and established with statistical rigour. Bayesian inference of the underlying covariance structure of random fields on the sphere in the Bipolar Spherical Harmonic (BipoSH) representation developed in our research program provides such a framework. We review the recent inferences drawn from Planck data and dwell on the future prospects with proposed CMB observations.
November 2: Lee McCuller (Caltech)
Title: Wielding Quantum Optics for Gravitational Physics
Optical interferometer observatories such as LIGO have begun a new era of astrophysics by measuring the length of their vast arms to such precision that gravitational waves from distant collisions of black holes and neutron stars are now regularly observed. This past run, the global gravitational wave network itself entered a new era, whereby every detector has enhanced sensitivity using quantum squeezed states of light, limited by mechanical back-action and optical loss. LIGO is now commissioning the "Frequency-dependent squeezing" upgrade for its next observing run. This technique suppresses back-action in the form of quantum radiation pressure, seemingly bypassing trade-offs from Heisenberg uncertainty. This talk will: overview squeezing for enhancing astrophysics; introduce Cosmic Explorer, next-generation gravitational wave observatories with deep cosmological reach; and detail a tabletop experiment at Caltech that hopes to realize a different type of quantum enhancements to shed light on experimental techniques where quantum measurement and astronomical signal analysis can collide.
November 9: Amy Reines (Montana State University)
Title: Dwarf Galaxies and the Smallest Supermassive Black Holes
Despite traditional thinking, an appreciable population of (relatively small) supermassive black holes may be lurking in dwarf galaxies. Before the last decade, nearly all known supermassive black holes were in the nuclei of giant galaxies and the existence of such black holes in dwarf galaxies was highly controversial. The field has now been transformed, with a growing community of researchers working on a variety of observational studies and theoretical models of dwarf galaxies hosting supermassive black holes. Work in this area not only is important for a holistic understanding of dwarf galaxy evolution and feedback, but may also just tell us how the first ‘seeds’ of supermassive black holes formed in the early Universe. In this talk, I will highlight some of my group's work in this field that has taken us from a few rare examples to large systematically assembled samples of dwarf galaxies hosting the smallest known supermassive black holes.
November 30: Clifford Will (University of Florida)
Title: Hierarchical Triple Systems in Newtonian and post-Newtonian gravity - or - Adventures of a general relativist in a 3-body world
The gravitational three-body problem has a history that goes back to Newton himself, has been studied by some of the world's greatest physicists and mathematicians, and continues to be relevant in modern astrophysics, from exoplanet research to understanding the origins of binary black holes. Following a brief history of the problem, we focus on hierarchical triple systems, in which an inner binary is perturbed by a distant body. This problem is amenable to a perturbative expansion in powers of the ratio of the two semimajor axes. We will review some of the remarkable phenomena that occur at various orders in the expansion, such as the famous Kozai-Lidov oscillations at quadrupole order and orbital flips at octupole order, and will discuss our own work to push the expansion to and beyond hexadecapole order. At dotriocontopole order, a new class of effects arises from the second-order interaction of quadrupole terms, affecting systems where the third body is much more massive than the inner binary. When GR corrections are introduced, additional effects occur, including suppression of Kozai-Lidov oscillations, and new contributions to Mercury’s perihelion advance, potentially detectable by the current Bepi-Colombo mission.
December 7: TBD
Spring 2022 Schedule
January 12: Special Colloquium: Craig Group (University of Virginia)
Title: Expanding the search for dark matter with new accelerator-based experiments
The evidence for dark matter is strong. However, the constituents of dark matter are still unknown, and the viable possibilities span a very large mass range. Specific scenarios for the origin of dark matter sharpen the focus on a narrower range of masses: the natural scenario where dark matter originates from thermal contact with familiar matter in the early Universe requires the DM mass to lie within about an MeV to 100 TeV. Considerable experimental attention has been given to exploring Weakly Interacting Massive Particles in the upper end of this range (few GeV - ~TeV), while the region ~MeV to ~GeV is largely unexplored. Most of the stable constituents of known matter have masses in this lower range, tantalizing hints for physics beyond the Standard Model have been found here, and a thermal origin for dark matter works in a simple and predictive manner in this mass range as well. It is therefore a priority to explore. If there is an interaction between light DM and ordinary matter, as there must be in the case of a thermal origin, then there necessarily is a production mechanism in accelerator-based experiments. The most sensitive way, (if the interaction is not electron-phobic) to search for this production is to use a primary electron beam to produce DM in fixed-target collisions. The Light Dark Matter eXperiment (LDMX) is a planned electron-beam fixed-target missing-momentum experiment that has unique sensitivity to light DM in the sub-GeV range. I will give an overview of the theoretical motivation, the main experimental challenges and how they are addressed, as well as projected sensitivities in comparison to other experiments.
February 2: Alexx Perloff (Univ. of Colorado)
Title: Searching for a Strongly Coupled Dark Sector with the CMS Detector
Searches for long-lived particles (LLPs), especially those associated with a dark matter (DM) candidate, have become a major focus of the Compact Muon Solenoid (CMS) physics program. During Run 2 of the Large Hadron Collider (LHC) at CERN, CMS became the first experiment to publish a search for a strongly coupled dark sector which contains a composite dark matter particle. This model contains a striking phenomenological signature consisting of emerging jets, whose tracks seem to appear not from the proton-proton collision vertex, but from multiple vertices within the CMS tracking detector. I will discuss this search as well the updated and ongoing version of the search. I will also discuss ongoing work to upgrade the CMS level-1 hardware trigger in order to prepare this system for the High Luminosity LHC (HL-LHC) with its unprecedented numbers of simultaneous proton-proton collisions. I will focus on the parts of the system which reconstruct the trajectories of charged particles, how these tracks are used by the downstream trigger systems, and how these upgrades will enable future dark sector searches at CMS.
February 9: Dylan Rankin (MIT)
Title: Novel Methods for Enabling Discovery at the LHC and Beyond
The discovery of the Higgs boson in 2012 was a momentous achievement for the LHC experiments and high energy physics in general. However, the LHC has not yet produced a discovery of physics beyond the Standard Model, and therefore both measurement and searches must begin to adapt and explore regions of phase space that have been left uncovered up until now. Doing so most effectively will require novel methods of data acquisition and analysis. In this talk I will present work from the ongoing development of the Compact Muon Solenoid (CMS) Level-1 trigger system upgrade for the High-Luminosity Large Hadron Collider. I will also discuss a new search at CMS for a light resonance decaying to two leptons which makes use of novel machine learning training methods and architectures.
February 16: Tamara Vazquez Schroeder (CERN)
Title: F(ℓ)avoured searches: leptoquarks - present status and future prospects
Recent anomalies observed in the B-meson sector may be one of our first promising hints of new physics beyond the Standard Model (BSM), suggesting that BSM may indeed have a different flavour structure than the SM. Leptoquarks, already hypothesised in the 1970s and predicted by many grand unified theories, are one of the preferred explanations of these tensions. It is also possible that they could be in reach at the collision energies at the Large Hadron Collider (LHC) at CERN. These hypothetical particles can mediate flavour-changing-neutral-currents and enable violation of lepton flavour universality. In the spirit of leaving no stones unturned, the ATLAS and CMS experiments at the LHC have developed a broad and diverse leptoquark search programme, paving the way to a potential discovery that could address many of the unanswered questions in Particle Physics.
February 23 (*special time: 3pm*): Bernard Kelly (NASA GSFC)
Title: Finding a Dance Partner for LISA: EM Emission from Black Hole Mergers in Plasma
Binary black hole (BBH) mergers provide a prime source for current and future interferometric GW observatories, especially by the Laser Interferometer Space Antenna (LISA), expected to launch in the mid-2030s. Massive BBH mergers may often take place in plasma-rich environments, leading to the possibility of a concurrent EM signal observable by traditional astronomical facilities. However, many questions about the generation of such counterparts remain unanswered, with details dependent on the precise form of the surrounding matter and magnetic field. I will discuss our current state of knowledge of these signals, and a set of investigations in numerical relativity with ideal general relativistic magnetohydrodynamics (GRMHD) to extract robust predictions that can inform multimessenger planning for the coming decades.
March 2: Michael Himes (UCF)
Title: Accelerating Computational Modeling via Neural Networks: Application to Exoplanet Atmospheric Retrieval
In physics and astronomy, computationally expensive forward models are often an integral part of preparing experiments/observations, analyzing data, and/or planning future instrumentation/telescopes. In many of these cases, machine learning (ML) models, such as neural networks (NNs), can offer a significant reduction in compute time with minimal loss in accuracy. We demonstrate this approach on the problem of exoplanet atmospheric retrieval, which involves on the order of 10^5 -- 10^6 radiative transfer (RT) model evaluations. We find that the ML RT approach yields the same scientific conclusions as the traditional method, while requiring ~1000x less compute cost. We present our open-source software packages that implement this technique, and we discuss broader applications of this NN surrogate modeling approach.
April 6: Kate Dooley (Cardiff University)
Title: Searching for signatures of quantized space-time and other physics mysteries with precision laser interferometry
The detection of gravitational waves required the design and construction of large laser interferometers that push the limits of precision measurement techniques. The extreme sensitivity of these instruments begs the question whether they -- or similar ones -- can be used to shed light on other questions in fundamental physics. One of the first experiments to probe this alternate use of gravitational wave detector technology was the Fermilab "holometer", a set of co-located 40m-long laser interferometers designed to search for the potential quantization of space-time.
I will present a bit of this history and then introduce our experiment at Cardiff: table-top co-located interferometers that will be more displacement-sensitive than the original holometer thanks to an increase in laser power and the application of squeezed vacuum states of light. Recently widened theoretical interest has renewed the motivation for the search for signatures of quantized spacetime and new predictions are currently being consolidated. The Cardiff interferometers will also be able to set new upper limits on scalar field dark matter, and they will be the most sensitive high-frequency and broadband (10 MHz to 100 MHz) gravitational-wave detectors to date.
September 22: Angelo Ricarte (Center for Astrophysics/Harvard)
Title: Supermassive Black Holes from Microparsecs to Megaparsecs
We believe that a supermassive black hole lurks at the center of every massive galaxy, where they can shine as an active galactic nucleus (AGN) when supplied with gas to accrete. These black holes are believed to be important for regulating gas cooling in massive galaxies and clusters via "AGN feedback," whose details are poorly understood. The problems of supermassive black hole growth and feedback span roughly 10 orders of magnitude in spatial and temporal scale, an intractable problem for a single simulation. In this seminar, I will discuss my theoretical work spanning this range in spatial scales: from modeling AGN central engines for the Event Horizon Telescope, to studies of the black hole-galaxy co-evolution with the Romulus cosmological simulations and semi-analytic models. These studies help stitch together properties of AGN central engines and how they are connected to their host galaxies.
Link to recording
October 6: Astrid Lamberts (Observatoire de la Côte d'Azur)
Title: Neutron stars and black holes, what do we know of the astrophysical populations observed with GW?
The last 5 years have brought the first detections of binary black hole mergers, binary neutron star mergers, and the merger of mixed neutron star-black hole pairs was announced very recently by the LIGO/Virgo/KAGRA collaboration. To date, more than fifty detections have been made public, allowing for the first statistical studies of the underlying populations. After a brief introduction to GW detections, I will present general trends that can be inferred from the observed population, focussing mostly on the binary black holes. Then I will highlight a few recent « exceptional » detections, including the neutron star black hole merger events. I will explain how these discoveries are connected to massive stellar evolution, high energy astrophysics and global star formation accros cosmic time.
November 3: Benny Trakhtenbrot (Tel Aviv University)
Title: New Types of Transient Phenomena from Accreting Supermassive Black Holes
Our understanding of the evolving population of supermassive black holes (SMBHs) beyond the local universe is fundamentally limited to actively growing SMBHs, where relatively stable accretion of gas persists over several hundreds of millions of years. A growing number of transient phenomena in galaxy nuclei have recently begun to shed new light on SMBH demographics and the physics of gas accretion onto these objects, tracing events where this accretion has drastically intensified, diminished, and/or otherwise disturbed. These include “changing look AGN”, and other, yet poorly understood UV-bright flares from accreting SMBHs. I will review some of these new classes of transients, focusing on new results obtained with responsive, multi-wavelength follow-up observations. While these events observationally differ from the (stellar) tidal disruption events known to date, the physics behind them may be interlinked. Together, these phenomena can greatly advance our understanding of SMBH accretion, teach us how and why SMBHs turn their accretion “on” and “off”, and reveal the sought-after signs of super-Eddington accretion. I will finally mention how new surveys, such as the SDSS-V, are going to discover & survey many more SMBH-related transients.
November 17: Orion Sauter (Univ. of Florida)
Title: Simulating LISA for Mission Planning
The Laser Interferometer Space Antenna (LISA) is set to launch in the 2030s, and measure gravitational waves in the mHz band. The detector consists of three spacecraft orbiting the Sun in an equilateral triangle, each carrying two free-falling test masses. This system must be kept in stable orbit, and avoid disturbance of the test masses for the duration of the mission. To test different drag-free and attitude control systems (DFACS) prior to launch, the LISA Consortium has developed a number of simulations of the detector. We will discuss the methods behind these simulators, as well as their strengths and limitations.
December 1: Christopher Berry (University of Glasgow)
Title: New coalescing binary observations with LIGO and Virgo
Gravitational waves provide an unparalleled means of observing merging black hole and neutron star binaries. Following completion of the most recent LIGO and Virgo observing run (O3b), the LIGO and Virgo catalog of gravitational waves contains 90 candidates with a probability of astrophysical origin greater than 50%. Using these observations, it is possible to start to unravel the mysteries of how black holes and neutron stars form, and merging binaries evolve. We will discuss the results of O3b, reviewing how gravitational-wave data is analysed to understand the source population, and highlighting some of the most interesting discoveries to come from O3b.
December 8: Evan Hall (MIT)
Title: The future of ground-based gravitational-wave astronomy
Ground-based gravitational-wave astronomy is poised to enter a new era in the next decade. A global network of new observatories will detect collisions of black holes and neutron stars across the entire stellar history of the universe, and will probe dense matter, extreme gravity and fundamental physics with greatly improved sensitivity compared to today’s observatories. In the United States, planning is underway for Cosmic Explorer, a 40 km observatory that will leverage advancements in a number of technologies — nonclassical states of light, high-quality materials, inertial isolation, geophysical engineering, among others — to open a new window onto the gravitational-wave universe.
Students may receive credit for attending the Astrophysics Seminar by registering for PHY 6391.