When a massive star reaches the end of its life, it may collapse into a black hole, an object so dense that not even light can escape its gravitational pull. Despite decades of research, astronomers have never observed the actual formation of a black hole due to their elusive nature. To address this challenge, scientists turn to simulations and computational astrophysics.
A recent paper published in Astrophysical Journal Letters introduces what is described as the first three-dimensional simulation of a black hole forming from a collapsing massive star using general relativity. The research was led by Goni Halevi, Assistant Teaching Professor of Physics at Illinois Institute of Technology.
“People think about science as things you can do in a lab, but astronomy works differently. In astronomy, we can’t make a black hole in a lab,” says Halevi. “Using computers is our way of doing numerical experiments and seeing what happens when a star dies. Astronomers are either observers looking at the universe and trying to interpret it, or we’re computational astronomers doing these numerical experiments.”
The process by which massive stars end their lives can result in different outcomes. Some become neutron stars, while others collapse into black holes that are difficult to detect with telescopes. Simulations help researchers understand these events by filling gaps between observations and theoretical predictions.
Until now, no simulation had managed to model black hole formation in three dimensions while incorporating both general relativity and neutrinos. According to Halevi, “Black holes can only exist because of general relativity, and most of these (previous) simulations don’t include general relativity. They can’t actually form the black hole on the computer without including the way that space-time is curved due to mass. People have done similar things, but [it was] always with more approximations that we’re making here.”
The new simulation stands out for including detailed physics at very small scales—such as neutrinos and nuclear particles—while also modeling the intense gravitational forces involved when a star roughly 50 times the mass of the Sun collapses.
“There are these turbulent, complicated fluid motions that can affect whether a black hole forms and how long it takes,” says Halevi. “You’re solving a very complex system of equations that are all coupled to one another, and every new ingredient of physics that you add makes it slower and more expensive to do that calculation.”
To accomplish this work, the team used GRaM-X—a graphics processing unit-accelerated code capable of tracking core collapse through shock propagation up to black hole formation in full 3D. Halevi credited her co-author Swapnil Shankar for developing and adapting this code for use on GPUs.
Although this simulation marks an advance in modeling black hole formation, it currently ends immediately after the black hole forms. The next phase will involve extending its duration to observe how newly formed black holes evolve over time. Further studies will also examine how varying initial conditions affect collapse outcomes and properties of resulting black holes.
“We call it a parameter study, to explore those initial conditions and see what the results are,” says Halevi. “Now that we’ve been able to show this proof of concept, we want to get more of a population-level statistical understanding of what happens to stars once they die.”