The Event Horizon Telescope Project announced that it has captured the first image of a black hole. The feature is located at the center of Messier 87 – a giant elliptical galaxy in the constellation Virgo. **News Bureau physical sciences editor Lois Yoksoulian** spoke with University of Illinois physics and astronomy professor Charles Gammie, who heads up the theory working group for the large, multi-institutional collaboration.

# Astrophysics, Gravitation, and Cosmology

## What is Astrophysics?

Astrophysics is the study of celestial objects such as galaxies, stars, black holes, planets, exoplanets, the Big Bang, dark matter, and dark energy. The study of cosmology is theoretical 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, theorize how long our sun will last before it exhausts its nuclear fuel (dies), discover what the universe looked like billions of years ago, temperatures of planets, shapes of galaxies 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 astrophysics. The development and application of numerical relativity to tackle problems by computational means are major activities. The merger of binary compact objects (including binary black holes) and the generation of gravitational waves are areas of great interest.

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 U. of I. 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.