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 is Astrophysics?

Astrophysics is a branch of science that uses physics to understand the cosmos, from the life and death of stars and galaxies, to the formation of black holes, neutron stars and white dwarves, and the evolution of the universe itself. The study of gravitational physics focuses on Einsteinâ€™s theory of General Relativity, and its applications to compact objects and gravitational wave distortions of spacetime. The study of cosmology is astrophysics at scales much larger than the size of particular gravitationally-bound objects in the universe.

Astrophysicists have contributed many important insights to our understanding of the universe we live in. They have discovered the approximate age and size of our universe, theorized how long our sun will last before it exhausts its nuclear fuel and dies, discovered what the universe looked like billions of years ago, what the temperatures of planets are, what happens when black holes collide and neutron stars merge with each other, what the shapes of galaxies are, and the way that matter is distributed across the observable universe.

## What are we doing in Astrophysics at Illinois?

The Center for Theoretical Astrophysics encompasses many different groups studying various aspects of astrophysics. The Illinois Relativity group focuses on the application of Einstein's theory 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. Another major activity is the creation and implementation of new ways to test Einsteinâ€™s theory of general relativity in new regimes of extreme gravity. 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. This last activity is being done in collaboration with the nuclear physics group and the high energy physics group.

The Cosmology group researches topics including but not limited to properties of clusters, Big Bang nucleosynthesis, extragalactic astronomy, the early universe, structure formation and the properties of dark matter and dark energy. Our work on the last three topics is being done in collaboration with the high energy physics group.

The Astrophysical Fluid Dynamics group is dedicated to the study of problems in astrophysics requiring numerical modeling where they often employ parallel computing.

Astrophysics at Illinois is also pursued in the Department of Astronomy. All of the Physics faculty in astrophysics work closely with their colleagues in the Department of Astronomy and many have joint appointments.