New Dark Matter Theory May Resolve Hubble Tension and Cosmic Anomalies

The Case for Self-Interacting Dark Matter

For decades, scientists have relied on the “cold dark matter” model, which assumes dark matter is “collisionless”—particles pass through one another without interacting. However, a study led by UC Riverside professor Hai-Bo Yu, published in *Physical Review Letters*, proposes a new framework known as Self-Interacting Dark Matter (SIDM). In this model, dark matter particles collide and exchange energy. According to Yu, who is also deputy director of the Center for Experimental Cosmology and Instrumentation (CECI), this interaction leads to “gravothermal collapse.” In this process, particles form extremely dense, compact cores. Yu compares the difference to a crowd of people: whereas the standard model imagines a crowd where individuals ignore each other, the SIDM model describes a crowd where everyone is constantly bumping into one another. This mechanism can simultaneously explain three distinct astrophysical phenomena:

• Gravitational Lenses: The ultra-dense object in the JVAS B1938+666 lens system.
• Stellar Streams: The gaps and “spur” features found in the GD-1 stellar stream, which suggest disturbances by dense clumps of dark matter.
• Satellite Galaxies: The unusually high number of dense, metal-rich globular clusters in the Fornax dwarf galaxy.

Mass Segregation and Multiple Components

Separate research from the Purple Mountain Observatory of the Chinese Academy of Sciences (CAS), published in Science Bulletin, offers a complementary perspective. Researchers Daneng Yang, Yi-Zhong Fan, Siyuan Hou, and Yue-Lin Sming Tsai propose that dark matter may not consist of a single type of particle, but rather at least two kinds: one heavier and one lighter. This “two-component self-interacting dark matter” model suggests that these particles undergo “mass segregation.” Similar to how massive stars in a cluster migrate inward, heavier dark matter particles drift toward the centers of galaxies, while lighter particles spread outward. Simulations indicate that this process creates low-density dark matter cores in dwarf galaxies, while simultaneously producing dense structures in larger environments that enhance gravitational lensing.

Challenges to the Standard Model

These new theories emerge as the standard model faces pressure from observations of galaxies that appear to lack dark matter entirely. A research team led by Yale University astrophysicist Michael Keim recently identified NGC 1052-DF9, the third galaxy in a unique chain—alongside DF2 and DF4—that exhibits motions explainable without dark matter.

Cosmological Implications and Future Testing

The search for answers extends to the expansion of the universe itself. The “Hubble tension”—the discrepancy in measurements of the universe’s expansion rate—is also being re-examined. Researchers including Kevin Croker of Arizona State University and Duncan Farrah of the University of Hawaii have proposed the “cosmologically coupled black hole” (CCBH) hypothesis. This theory suggests that black holes act as “bubbles” of dark energy, converting dead stellar matter into dark energy as they form. This could explain why the expansion rate of the universe, or the Hubble constant, appears to change over time, potentially addressing data from the Dark Energy Spectroscopic Instrument (DESI) which indicates that the strength of dark energy may not be constant. As precision in sky surveys and gravitational lensing observations continues to improve, scientists aim to test whether dark matter’s internal complexity or the unique lifecycle of black holes can provide a more accurate picture of the invisible universe. As DESI researcher Steve Ahlen noted, the field is currently prioritizing new ideas to address the persistent mysteries that the standard model cannot reconcile.

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