Astrophysics & Cosmology
The research of the CMU Astrophysics and Cosmology group covers a wide range of problems in theoretical, computational, and observational cosmology. These problems include the study of the earliest energy emission in the universe -the Cosmic Background Radiation- to the evolution of galaxies and the formation of large-scale structure. We are part of the worldwide scientific effort to put constraints on the basic cosmological parameters that describe the evolution of the universe. Many of these parameters are expected to be tied down over the next decade using data from the current and planned ground-based and space-based observatories. The analysis of these new data sets is very challenging and will require both the development of highly sophisticated numerical simulations and the application of the latest tools in data-mining, statistics, and computer science, which is a major goal for our researchers at the McWilliams Center for Cosmology.
Our group has full institutional membership in the ongoing Sloan Digital Sky Survey IV, including the extended baryon oscillation spectroscopic survey (eBOSS) and the mapping nearby galaxies at APO experiments (MaNGA) and in the Large Synoptic Survey Telescope (LSST) collaboration, focusing primarily on involvement in the scientific activities and leadership of the Dark Energy Science Collaboration (DESC). Together these surveys will provide data for premier cosmological analyses until 2030. Some members of our group also have access to other ongoing or future surveys. In terms of computing infrastructure, the McWilliams Center has a ≈1500 core computer cluster available for use by researchers in cosmology.
Rupert Croft's research interests are in computational cosmology, involving both simulations and the analysis of data from large surveys. This includes the physics of the intergalactic medium and its use as a probe of cosmology and of galaxy and quasar formation. He is participating in the SDSS surveys of galaxies and quasar absorption lines which are constraining dark energy, and is making the first "intensity mapping" measurements of structure using optical emission lines. Croft also works on the re-ionization of the Universe, and high redshift galaxies, as well as new cosmological probes of modified gravity, such as gravitational redshifts and other relativistic effects which are just starting to be measured from galaxies and large-scale structure. He makes use of the McWilliams Center's high performance computing facilities, including the Warp and Coma clusters to analyze SDSS data and perform cosmological hydrodynamic and radiative transfer simulations.
Tiziana Di Matteo is a theorist with expertise in both high energy astrophysics and cosmology. Her interests focus on state-of-the-art cosmological simulations of galaxy formation with special emphasis on modeling the impact of black holes on structure formation in the Universe. Her research makes extensive use of high-performance computing. Recently she has led an effort to run simulations of uniquely large volume and high resolution to study to the formation of the first large galaxies and quasars at the cosmic dawn of the Universe. This first population of galaxies and black holes will be investigated with the next generation telescopes (Euclid, JWST and WFIRST). Large hydrodynamical cosmological simulations provide the direct link between the baryonic component and dark matter and are becoming useful in all stages of major observational projects in cosmology. Di Matteo is a member of the LSST Dark Energy Science Collaboration.
Scott Dodelson is interested in learning about fundamental physics by analyzing data from cosmic surveys. Astrophysicists have pieced together a remarkably successful cosmological model, but it requires three new pieces of physics: dark matter, dark energy, and inflation. His perception of the goal of cosmology over the coming decade is to extract as much information as possible from increasingly sensitive surveys to either learn about this new physics: What is the dark matter? Is the dark energy vacuum energy? If so, why does it have such a peculiar value? Did inflation really happen? If so, is there any way to relate the fields that drove inflation to those we know about today?
Fred Gilman's research is in theoretical particle physics, particularly in understanding the nature of CP violation, which is a required ingredient in explaining the dominance of matter over antimatter in the universe. Together with dark matter, dark energy, the field(s) responsible for inflation, and neutrino masses, these fundamental questions about the nature of the universe all point to physics beyond the Standard Model. Gilman is a member of LSST Dark Energy Science Collaboration from the time of its creation. He is the Chair of the AURA Management Council for the LSST (AMCL), the committee that oversees the construction and commissioning of the LSST Project, and is a member of the Board of Directors of the Association of Universities for Research in Astronomy (AURA).
Shirley Ho is a cosmologist whose interest ranges from theory to observations, and whose research involves both simulations and analyses of large scale structure via novel techniques developed in Machine Learning and Statistics. Utilizing large scale structure and the cosmic microwave background, she seeks to understand the beginning of the Universe and its evolution, its dark components (dark energy and dark matter), and the light, elusive neutrinos. Her recent research focuses on the use of a standard ruler called Baryon Acoustic Oscillations via various large scale structure tracers such as the 3D clustering. In this way, she plays leading roles in large scale structure analyses in the SDSS-III, SDSS-IV, and Large Synoptic Sky Telescope collaborations (in particular, within the LSST Dark Energy Science Collaboration). In addition, she is a member of the future Dark Energy Spectroscopic Instrument (DESI) and Euclid surveys.
Tina Kahniashvili's research areas include investigation of physical processes in the Universe at very early epochs, as well as late times. In particular, she studies (i) fundamental symmetries tests at very high energies (early epochs of the universe expansion) using currently available data of astrophysical, cosmological, and particle physics experiments; (ii) gravitational waves signal from very early universe (inflation, phase transitions); (iii) CMB fluctuations in beyond standard cosmological models. She is interested in alternative scenarios to explain the accelerated expansion of the universe, such as modifications of general relativity (especially massive gravity models). She also works on cosmological magnetic fields and the origins, evolution, and observable signatures of primordial turbulence.
Rachel Mandelbaum's research interests are predominantly in the areas of observational cosmology and galaxy studies. This work includes the use of weak gravitational lensing and other analysis techniques, with projects that range from development of improved data analysis methods, to actual application of such methods to existing data. Currently, she is focusing on data from the SDSS (including SDSS-III and the ongoing SDSS-IV) and Hyper-SuprimeCam (HSC), and is working on upcoming surveys including LSST, Euclid, and WFIRST.
Jeffrey Peterson's group carries out cosmological observations using the 21 cm emission line of neutral hydrogen. The group pioneered the field of 21-cm Intensity Mapping using existing telescopes to make the first detection ofcosmic structure at redshifts near one. The team now contributes to the design of custom-built 21-cm telescopes in Canada, Mexico and China. Currently, Peterson leads the RF design program for the HIRAX telescope in South Africa, an array of 1024 six-meter dishes slated for the South African Radio Astronomy Reserve. This telescope will map cosmic structure from redshift 0.8 to 2.5 allowing a sharp test of models of Dark Energy. These telescopes can also be used to study the mysterious, rare Fast Radio Bursts. The team recently reported the detection of the first convincingly extra-galactic radio burst.
Carl Rodriguez is a theoretical and computational astrophysicist studying the dynamics of stars, black holes, and the gravitational waves they create. Using a wide array of techniques from perturbation theory to supercomputer simulations, he studies the formation and evolution of multi-star systems such as binary stars, triple stars, globular clusters, and nuclear star clusters. These systems are uniquely efficient at producing binary black holes and other merging compact objects, and may have produced many, if not the majority, of the black hole collisions detected by the LIGO/Virgo gravitational-wave detectors. Rodriguez is broadly interested in general relativity, black holes, and gravitational-wave astrophysics, and how these new discoveries can inform our understanding of stellar physics and cosmology. He is also interested in the formation, evolution, and destruction of star clusters in galaxies, and how we can better understand them through theory and observations.
Hy Trac is a theoretical and computational cosmologist whose scientific interests include cosmic evolution and structure formation. His work includes the development and application of numerical simulations to model and interpret the observable Universe. He is currently developing a novel mesh-free hydrodynamic code. In cosmology, he is especially interested in complex problems involving the gas, stars, galaxies, quasars, and clusters of galaxies that provide information about the underlying dark matter and dark energy. In astrophysics, he would particularly like to work on star and planet formation and the development of planetary atmospheres. He also collaborates with machine learning experts and statisticians to apply modern approaches to improve multi wavelength data analysis and numerical simulations. He is a member of the Atacama Cosmology Telescope (ACT) and Simons Observatory (SO) Collaborations.
Matthew Walker studies the astrophysical properties of dark matter, thus far via optical imaging, spectroscopy and dynamical modelling of the dwarf galaxies that surround the Milky Way and neighboring Andromeda. The dwarf galaxies include the oldest, smallest and 'darkest' (i.e., composed almost entirely of dark matter) galaxies known, and currently represent the smallest physical scales (sizes of ≈100 light years, speeds of a few kilometers per second, masses of ≈100,000 Suns) that are associated empirically with dark matter. If dark matter is made from some kind of new fundamental particle, then the manner in which dark matter clumps at such small scales can help to decide among various ideas about the properties of that particle. By measuring the spatial distribution of dark matter in dwarf galaxies, Walker aims to help figure out what the dark matter actually is. His research is at the intersection of dynamics, cosmology and particle physics. He uses some of the world's largest optical telescopes, including the 6.5-meter Magellan telescopes at Las Campanas Observatory in Chile, the 6.5-meter MMT at Mt. Hopkins, Arizona, and the 8.2-meter Very Large Telescope at Cerro Paranal in Chile. He is also a member of the SDSS IV collaboration.