The Open Source Universe of Numerical Relativity

Gravitational waves were first detected by LIGO in 2015 and this has since become commonplace. The Event Horizon Telescope produced the first images of a supermassive black hole in 2019. This year numerous pulsar timing arrays simultaneously announced evidence of a stochastic gravitational wave background. All of these discoveries shed light on the most extreme gravitational physics in the universe. However, our opportunity to learn from this data is only as good as our ability to make theoretical predictions to test against it.

The research community has spent years developing a plethora of software tools, frameworks, and infrastructure to make these tests possible. Numerical relativity—the practice of solving equations from Einstein's theory of general relativity with advanced numerical algorithms—is built entirely on open-source software, much of it totally unique to the field. This makes it a wonderful open-source software success story: a research community that expands our understanding of the universe primarily by developing and sharing open-source software.

In my talk, I will provide a comprehensive overview of the open-source software projects that drive numerical relativity research.

Specifically, I will cover:

• The unique challenges faced in general relativity research
• The software frameworks on which codes simulating black hole and neutron star collisions are built, enabling modularity and efficient scaling

• Clever tools for extracting and analyzing key observables such as gravitational waveforms and black hole images

• Current and future development trends in numerical relativity

I will conclude with some reflections on what has enabled numerical relativity to become a thriving open-source ecosystem, as well as suggestions for steps we can take to further realize our potential in open-source science.