ISLAMABAD: Scientists analyzing tiny galaxies have identified potential constraints on dark matter properties that could help resolve longstanding puzzles about the universe's most mysterious substance.

According to a study published in Astronomy & Astrophysics on Wednesday, researchers examined ultra-faint dwarf galaxies—systems with stellar masses well below 1 million solar masses. They found evidence suggesting dark matter particles may collide with each other far more frequently than previously thought.

The study focused on stellar cores observed in six ultra-faint dwarfs. These cores appear to reflect underlying dark matter cores that cannot be formed through conventional stellar processes acting on standard cold dark matter halos.

"Ultra-faint dwarf galaxies provide a clean anchor point for constraining the velocity-dependent cross section at low velocities," said Jorge Sánchez Almeida, lead author and researcher at the Instituto de Astrofísica de Canarias.

The research examined self-interacting dark matter models, where dark matter particles undergo collisions beyond standard gravitational interactions. The analysis determined that cross sections ranging from approximately 0.3 to 200 square centimeters per gram could reproduce observed core sizes.

These values align with estimates from more massive galaxies derived through gravitational lensing, galaxy cluster collisions and rotation curves.

The findings carry significance because stellar feedback — energy from star formation — becomes negligible below roughly 1 million solar masses. Ultra-faint dwarfs fall well below this threshold, meaning their cores cannot result from conventional baryonic processes.

"Since stellar feedback is insufficient to form cores in these galaxies, ultra-faint dwarfs unbiasedly anchor the cross section at low velocities," the study states.

The research constructed a model relating stellar mass to core radius. This model reproduced stellar core sizes in ultra-faint dwarfs and predicted increasing core radius with stellar mass, matching observations of more massive dwarf galaxies.

Two scenarios could explain the observations. Dark matter halos might be forming cores with low cross sections, or approaching core collapse with high cross sections around 200 square centimeters per gram.

If the core-collapse scenario holds, ultra-faint dwarf halos would be thermalized on kiloparsec scales — approximately two orders of magnitude larger than the stellar cores themselves.

"These large thermalization scales could potentially influence substructure formation in more massive systems," according to the paper.
The study represents continued investigation into tensions between cold dark matter predictions and observational data in the faintest galaxies.

dark matter

Ultra-faint galaxies may be hiding unexpected clues to dark matter