New dark matter theory explains two puzzles in astrophysics

Thought to make up 85% of matter within the universe, dark matter is nonluminous and its nature isn’t properly understood. Whereas regular matter absorbs, displays, and emits mild, dark matter can’t be seen immediately, making it more durable to detect. A principle referred to as “self-interacting dark matter,” or SIDM, proposes that dark matter particles self-interact via a darkish drive, strongly colliding with each other near the middle of a galaxy.

In work published in The Astrophysical Journal Letters, a analysis crew led by Hai-Bo Yu, a professor of physics and astronomy on the College of California, Riverside, stories that SIDM concurrently can clarify two astrophysics puzzles in reverse extremes.

“The primary is a high-density dark matter halo in a large elliptical galaxy,” Yu mentioned. “The halo was detected via observations of sturdy gravitational lensing, and its density is so excessive that this can be very unlikely within the prevailing chilly dark matter principle. The second is that dark matter halos of ultra-diffuse galaxies have extraordinarily low densities and they’re troublesome to clarify by the chilly dark matter principle.”

A dark matter halo is the halo of invisible matter that permeates and surrounds a galaxy or a cluster of galaxies. Gravitational lensing takes place when mild touring throughout the universe from distant galaxies will get bent round large objects. The chilly dark matter, or CDM, paradigm/principle assumes dark matter particles are collisionless. As their identify suggests, ultra-diffuse galaxies have extraordinarily low luminosity and the distribution of their stars and fuel is unfold out.

Yu was joined within the research by Ethan Nadler, a joint postdoctoral fellow on the Carnegie Observatories and College of Southern California, and Daneng Yang, a postdoctoral scholar at UCR.

To point out SIDM can clarify the 2 astrophysics puzzles, the crew carried out the primary high-resolution simulations of cosmic construction formation with sturdy dark matter self-interactions on related mass scales for the sturdy lensing halo and ultra-diffuse galaxies.

“These self-interactions result in warmth switch within the halo, which diversifies the halo density within the central areas of galaxies,” Nadler mentioned. “In different phrases, some halos have larger central densities, and others have decrease central densities, in comparison with their CDM counterparts, with particulars relying on the cosmic evolution historical past and atmosphere of particular person halos.”

In accordance with the crew, the 2 puzzles pose a formidable problem to the usual CDM paradigm.

“CDM is challenged to clarify these puzzles,” Yang mentioned. “SIDM is arguably the compelling candidate to reconcile the 2 reverse extremes. No different explanations can be found within the literature. Now there may be an intriguing risk that dark matter could also be extra advanced and vibrant than we anticipated.”

The analysis additionally demonstrates the facility of probing dark matter via astrophysical observations, with the software of laptop simulations of cosmic construction formation.

“We hope our work encourages extra research on this promising analysis space,” Yu mentioned. “It will likely be a very well timed improvement given the anticipated inflow of information within the close to future from astronomical observatories, together with the James Webb Area Telescope and upcoming Rubin Observatory.”

Since round 2009, work by Yu and collaborators has helped popularize SIDM within the particle physics and astrophysics communities.