New code helps scientists map dark matter halos

Dark matter and its impact on cosmology have puzzled physicists for nearly a century. Now, a new paper from Perimeter Institute researchers reveals a new code to study the evolution of one dark matter candidate, self-interacting dark matter halos, cosmological structures that the Milky Way and other galaxies live in.

The paper, published in Physical Review Letters, provides a new way to research a broader range of dark matter particle interactions and understand how they impact the evolution of such cosmological structures.

Self-interacting dark matter gets its name because its particles can collide and bounce off one another, but they don’t interact with ‘ordinary’ baryonic matter, like protons, neutrons, and electrons. This has implications for dark matter halos – cosmological structures that theorists think play a key role in star formation and galaxy evolution.

"Dark matter forms relatively diffuse clumps which are still much denser than the average density of the universe,” says James Gurian, a postdoctoral fellow at Perimeter Institute. “The Milky Way and other galaxies live in these dark matter halos.”

Self-interacting dark matter halos are driven by a process called gravothermal collapse – a consequence of the unlikely fact that gravitationally-bound systems get hotter, not cooler, when energy is removed. Since self-interacting dark matter transports energy, it moves outward in halos; the inner core gets hot and dense as energy moves outwards.

To map the structures formed by self-interacting dark matter, scientists typically use one approach for when dark matter is less dense with infrequent collisions, and a different approach for dark matter that is denser with more frequent collisions – but they lacked a mapping approach for in-between characterizations. Gurian and his co-author Simon May, a former Perimeter postdoctoral fellow, developed a code, KISS-SIDM, that is faster and more accurate than previous codes that came before it and is publicly available for researchers to use.

Understanding the core collapse process also intrigues physicists because it could have observable implications for black hole formation. But the details of how the process ends is an open question in physics, and this code is a step towards answering it.

“The fundamental question is, what’s the final endpoint of this collapse? That’s what we’d really like to do -- study the phase after you form a black hole,” says Gurian.

Read more from Perimeter Institute.