Helvi Witek specializes in black holes, gravity, and gravitational waves and how we can use them to understand open questions about the universe.
Astrophysics, Gravitation, and Cosmology
What are Astrophysics, Gravitation, and Cosmology?
The cosmos plays host to physical phenomena across scales of distance, time, and energy far beyond those accessible in terrestrial laboratories. Astrophysical phenomena span scales from the size of nuclei to the edge of the observable universe, from the unimaginable temperatures of our universe’s first moments to its evolution over the succeeding eons. Gravitation undergirds all of this, and directs the dramatic phenomena near black hole event horizons. Cosmology explores the universe’s history, composition, and largest-scale structures. Astrophysics, gravitation and cosmology research has made critical contributions to our understanding of physical principles, and continues to reveal new insights into fundamental physics and our place in the universe.
What are we doing in Astrophysics, Gravitation and Cosmology research at Illinois?
Our research efforts span theory, computation, instrumentation, and data analysis. Our work is intrinsically cross-disciplinary, and our faculty collaborate closely with many other research units on campus, including the high-energy physics group, the nuclear physics group, the astronomy department, the National Center for Supercomputing Applications (NCSA), the Illinois Center for Advanced Studies of the Universe (iCASU), and the Center for Astrophysical Surveys (CAPS). Key research themes include the following:
Astrophysical Fluid Dynamics
Research in astrophysical fluid dynamics is dedicated to the study of gas flow problems in astrophysics requiring large-scale numerical modeling. Relevant physical phenomena include collisional and collision-less gas dynamics, magnetic fields, gravitation, radiation transport, and chemical/nuclear reactions. Applications include the origin of the moon, interacting binary stars, galaxy and galaxy cluster evolution, and black hole accretion flows from stellar to galaxy cluster scales. Recent work includes theoretical modeling within the groundbreaking Event Horizon Telescope collaboration.
The implosions of massive stars and collisions of stars with stellar remnants produce spectacular explosions--supernovae, gamma-ray bursts, and more--that can now be observed using all four fundamental forces. Illinois theorists and observers embrace this multimessenger view of the cosmos to unveil physics under extreme conditions. Theoretical work includes study of stellar evolution leading to mergers (common envelope); study of neutron star mergers; supernovae as neutrino sources, element factories, particle accelerators, Galactic energy sources, and near-Earth threats. Observationally we will be a world hub for discovery of explosions of all kinds with LSST, we work closely with the LIGO Scientific Collaboration and the LISA Consortium, and we follow up the most interesting events with telescopes around the world and in space.
The Cosmology Group explores the universe's content and evolution from a variety of perspectives. Theoretical work includes models of inflation and the early universe, as well as elucidating new observational signatures of fundamental physics, including the natures of dark matter and dark energy. Observations of the cosmic microwave background (CMB) are a major focus of instrumentation and analysis efforts, including searches for primordial gravitational waves, measurements of gravitational lensing, and the identification of our universe’s first galaxies. Gravitational lensing is a powerful tool in cosmology and astrophysics. As nature’s magnifying glass, it provides existing telescopes with higher resolution and greater sensitivity to probe the physics and chemistry of the distant universe. It is also a useful method to "see" dark matter and its influence on the large scale distribution of matter in the Universe. Our group is developing a variety of new instruments for observations at GHz and THz frequencies from ground, balloon, and space. These include CMB experiments such as BICEP, SPT, SPIDER, and CMB-S4, as well as astrophysical experiments such as the Terahertz Intensity Mapper (TIM) and the Origins Space Telescope. Illinois contributes to a number of current (SDSS, DES, SPT) and future (LSST, CMB-S4, WFIRST) large-scale astrophysical surveys.
The Illinois Relativity Group focuses on the application of general relativity to forefront problems in relativistic gravitation. One major activity includes the development and application of analytical and numerical relativity techniques to understand the coalescence of compact objects and the emission of gravitational waves. We then use these models to characterize the gravitational waves detected by ground-based instruments, like advanced LIGO and Virgo, and future space-based instruments, like LISA. Another major activity is the creation and implementation of new ways to test Einstein’s theory of general relativity in new regimes of extreme gravity, using gravitational waves, binary pulsar and neutron star observations. A final major activity is the study of the structure of black holes and neutron stars, and its connections to particle physics and nuclear physics. We employ black holes as novel probes to search for new particles that may constitute dark matter in a range that is complementary to traditional collider or direct detection experiments. We use neutron stars as a laboratory to learn about nuclear physics above nuclear saturation densities.
The Physics of Galaxy Evolution
Our group at Illinois is actively trying to discover the first galaxies in the Universe and understand the history of cosmic star formation. These distant galaxies are enshrouded in cosmic dust, rendering them invisible at optical wavelengths. Cosmic dust is a crucial constituent in the formation and evolution of everything from planets to massive black holes in the centers of galaxies. Half of the energy produced since the Big Bang has been absorbed and re-emitted by dust, indicating its cosmic importance. Highlights from our group's observational program include the discovery of the most distant dusty, star forming galaxy discovered at z = 6.9, less than a billion years after the Big Bang, when the Universe was a mere 5% of its current age. Our group regularly observes with the most advanced telescopes on Earth, including ALMA, Hubble, and Chandra, and is among the first groups that will observe the James Webb Space Telescope (JWST).