Predicting the electromagnetic signatures of astrophysical processes occurring near black holes remains a significant challenge. Using various numerical and mathematical techniques, students will explore how to create fast and accurate approximation schemes to predict how black holes bend the light produced during mergers and other relativistic phenomena and how this will affect the signals seen by observational astronomers.
The last five years have seen ~3,500 new planets discovered outside of our solar system. Coupled with the fact that at least ~50% of stars orbit in binary systems with either main-sequence companions or compact objects, it's very likely that all stars have at least one orbiting companion with 40% harboring two or more companions. The physics of these multi-body systems is largely unexplored yet rich with dynamical and evolutionary processes. With the recent development of the IAS15 integrator, orbital calculations that conserve energy to machine precision over one billion orbits are now possible. The REU students and mentor will integrate full stellar evolution models into the IAS15 code infrastructure. The primary science goal is to quantify which initial orbital configurations for multi-body compact object systems result in the formation of short-period binaries over the full lifetime of the star.
One of the fundamental drivers of galaxy evolution and thus the buildup of stellar and black hole mass over time is mergers between galaxies. Simulations have made a range of predictions for how the galaxy merger rate should evolve over time, and how this evolution depends on fundamental galaxy properties, such as stellar and/or halo mass. However, the galaxy merger rate has yet to be robustly constrained beyond z~1. This project will make use of publicly available data from a number of deep galaxy surveys (e.g., COSMOS, CANDELS, UltraVISTA) in order to measure the evolution of the galaxy merger rate and its stellar mass dependence. Eventually, the merger of two galaxies is expected to lead to the merger of their supermassive black holes. Robust merger rate measurements will enable predictions for the expected rate of supermassive black hole mergers across a range of black hole masses.
LIGO (along with the Virgo detector in Italy) will soon identify hundreds of coalescing binaries a year, providing a first census of coalescing compact binaries throughout the universe. If compact binaries form from isolated stars, then many complementary ongoing and near-future observations of related objects (supernovae, X-ray binaries, pulsars, and GRBs) will help GW measurements constrain the highly uncertain astrophysical processes that allow them to form. This project will make use of public data from LIGO and other sources to constrain the formation mechanisms for compact binaries. REU students will operate parameterized synthetic binary star evolution codes, using machine learning, classification, and Bayesian methods to accelerate these codes by targeting computational effort on the most informative formation channels; to constrain parameters of formation models
Long-lived, nearly periodic gravitational waves from rapidly rotating neutron stars are a potential source of future detections by LIGO and Virgo. Unlike the transient ``chirps'' already detected in LIGO's first observing run, these continuous waves will be present throughout the observation, allowing detection through the accumulation of a signal over a long period of time. Here, Whelan and student researchers will develop an enhancement to current cross-correlation methods that enables extraction of unknown extrinsic parameters such as the inclination of the neutron star spin to the the line of sight, helps to quantify the potential impact of additional electromagnetic observations in constraining computing cost and achievable sensitivity, and works to identify the parameter space to search for other low-mass X-ray binaries.
Numerical relativity simulations have shown that supermassive black holes (SMBH) can be significantly displaced from the centers of their host galaxies by gravitational recoil kicks generated during the coalescence of an SMBH binary, which itself formed in the aftermath of a galaxy merger. In this project, the student will work in close collaboration with a PhD student to search for SMBH displacements in large elliptical galaxies, by analyzing archival Hubble Space Telescope images to directly measure the magnitude and direction of the displacement between the active galactic nucleus (locating the SMBH) and the centroid of the stellar light distribution (locating the dynamical center of the galaxy).
The first observation of gravitational events was a scientific marvel, and communicating the impact of these results to the broadest possible audience, many of whom are now hearing about gravitational waves for the first time, is one of the primary challenges faced by those working with the LIGO Scientific Collaboration (LSC) on outreach efforts. Using actual LIGO data, students will both visualize and “sonify” observations of gravitational wave signals. The latter technique, which makes use of the fact that the frequencies at which LIGO is most sensitive correspond conveniently to those in the human hearing range, allows us to combine these two sensory channels together to create a more comprehensive experience.
Stars rarely travel alone; most are found in binary or hierarchical binary systems. Theory predicts that, in many cases, these (gravitational) relationships can become rather unhealthy for binary system members or their planetary offspring. The ejection of a star from a hierarchical binary system, the ejection or destruction of a planet that is unlucky enough to have formed in a binary system, or the close approach or merger of two stars at late stages of evolution are all thought to be commonplace events. But how do we identify such catastrophic short-lived events, place constraints on their frequency, and understand their near- and long-term observable impacts on stellar and planetary system environments? The student will confront one or more of these fundamental questions by reducing and analyzing observations of binary or suspected binary star systems obtained with some of the most advanced contemporary observing facilities, such as NASA's Chandra X-ray Observatory, ESA's Gaia space astrometry mission, and the Atacama Large Millimeter Array.
A comprehensive understanding of the physics that led to the formation of first stars, galaxies, and black holes is a fundamental goal of extragalactic astrophysics. Though a great deal has been learned in the past two decades, many key questions remain. First, how and when did the first UV-bright stars that reionized the universe form from pristine primordial gas? Second, what is the history of stellar, dust and metal build-up during reionization? Third, what is the contributionof quasars and other compact objects to the reionization history of the universe, and what might be the gravitational radiation signature we can expect from such objects? In this REU project, we hope to develop new methods and detectors to determine the initial mass function of stars in the first galaxies, whether there was an appreciable contribution to the reionizing budget from active galactic nuclei, and the formation paths of SMBH and nascent quasars.
Radio emission traveling through the interstellar medium undergoes many propagation effects that cause distortions in the clock-like ticks used to measure low-frequency gravitational waves from a pulsar timing array. Much work has gone into understanding these deterministic and stochastic effects, and while significant progress has been made to measure the distortions from the data, unmodeled pulse shape changes and arrival-time delays will cause biases in nanohertz gravitational wave detection and characterization. Students will perform analyses on pulse arrival times along with dispersion, scintillation, and refraction time series, to understand the impact on gravitational-wave parameter estimates.
Pulsar timing can reach very high accuracy and recycled millisecond pulsars show a remarkable stability when comparing the observed times of arrivals of their pulses to predictions. This makes them excellent probes to analyze their physical environment. Our main goal is to detect a “stochastic background” of low-frequency gravitational waves, originating from an ensemble of unresolved supermassive black hole binaries (SMBHBs). We are currently monitoring PSR J04374715 at 1400 MHz for several hours per day, and hope to use these measurements to help make the first gravitational wave observations of SMBHBs across the cosmos as part of the NANOGrav consortium.
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