Astrophysical Enigmas Solved by Emerging Dark Matter Theory

Researchers have advanced the understanding of dark matter through simulations that support the self-interacting dark matter (SIDM) theory. This theory could potentially resolve the inconsistencies in dark matter densities observed in different galaxies, posing a challenge to the traditional cold dark matter (CDM) model and highlighting the dynamic nature of dark matter. Source:

Dark matter may be more energetic than previously thought, a UC Riverside study reports.

Believed to make up 85% of the matter in the universe, dark matter is not luminous and its nature is poorly understood. While normal matter absorbs, reflects, and emits light, dark matter is not directly visible, making detection difficult. A theory called “self-interacting dark matter,” or SIDM, proposes that dark matter particles themselves interact through a dark force, violently colliding with each other near the center of one. galaxy.

In work published in the Astrophysical Journal Lettersa research group led by Hai-Bo Yu, a professor of physics and astronomy at the University of California, Riverside, reports that SIDM can simultaneously explain two astrophysics puzzles at opposite extremes.

Understanding Dark Matter Halos and Gravitational Lensing

“The first is a high-density dark matter halo in a large elliptical galaxy,” Yu said. “The halo was detected by observations of strong gravitational lensing, and its density is so high that it is not possible with the existing theory of cold dark matter. The second is that the dark matter is almost in the ultra-diffuse galaxies have extremely low densities and are difficult to explain by the cold dark matter theory.

A dark matter halo is a halo of invisible matter that permeates and surrounds a galaxy or a cluster of galaxies. Gravitational lensing occurs when light traveling across the universe from distant galaxies bends around massive objects. The cold dark matter, or CDM, paradigm/theory assumes collisionless dark matter particles. As their name suggests, ultra-diffuse galaxies have extremely low luminosities and the distribution of their stars and gas is spread out.

Hai-Bo Yu

Hai-Bo Yu is a theoretical physicist at UC Riverside with expertise in the properties of dark matter particles. Credit: Samantha Tieu

Yu was joined in the study by Ethan Nadler, a postdoctoral fellow at Carnegie Observatories and the University of Southern California, and Daneng Yang, a postdoctoral scholar at UCR.

To show that SIDM can explain two astrophysics puzzles, the team performed the first high-resolution simulations of cosmic structure formation with strong dark matter self-interactions at relevant mass scales for strong lensing halo and ultra-diffuse galaxies.

“These self-interactions lead to heat transfer in the halo, which varies the density of the halo in the central regions of galaxies,” Nadler said. “In other words, some haloes have a higher central density, and others have a lower central density, compared to their CDM counterparts, with details depending on the cosmic evolutionary history and environment of the individual almost.”

Challenging the CDM Paradigm and Future Research

According to the team, both puzzles present a formidable challenge to the standard CDM paradigm.

“CDM is challenged to explain these puzzles,” Yang said. “SIDM can be a compelling candidate to reconcile the two opposite extremes. There are no other explanations available in the literature. Now there is an interesting possibility that dark matter may be more complex and energetic than we expected.

Research has also demonstrated the power of probing dark matter through astrophysical observations, using the tool of computer simulations of cosmic structure formation.

“We hope that our work encourages further studies in this promising area of ​​research,” said Yu. “This is a timely development given the expected influx of data in the near future from astronomical observatories, including the James Webb Space Telescope and the upcoming Rubin Observatory.”

Since around 2009, the work of Yu and collaborators has helped popularize SIDM in the particle physics and astrophysics communities.

Reference: “A Self-interacting Dark Matter Solution to the Extreme Diversity of Low-mass Halo Properties” by Ethan O. Nadler, Daneng Yang and Hai-Bo Yu, 30 November 2023, The Astrophysical Journal Letters.
DOI: 10.3847/2041-8213/ad0e09

The research was supported by the John Templeton Foundation and the US Department of Energy.

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