Dark matter is one of the biggest mysteries in science. It cannot be seen directly because it does not emit, absorb, or reflect light.
Yet scientists know it exists because its gravity influences galaxies and other objects in the universe. In fact, dark matter is thought to make up about 85% of all matter in the cosmos.
For many years, researchers have assumed that dark matter is relatively simple.
The standard view is that dark matter particles interact with the rest of the universe—and with each other—mainly through gravity.
But what if dark matter particles also experience another hidden force?
A new study published in the Journal of Cosmology and Astroparticle Physics explored this possibility.
Surprisingly, the researchers found that such a force might actually slow the growth of large cosmic structures instead of speeding it up.
Interest in a possible “dark force” has increased in recent years because some of the most precise observations of the universe do not perfectly agree with one another.
Scientists measure the universe in different ways. Some observations examine how the universe has expanded over time, while others look at how galaxies and cosmic structures have grown. In a few cases, the results do not fit together as neatly as expected.
These differences are small, but they are intriguing enough to make scientists wonder whether something may be missing from current theories of the universe.
One possibility is that dark matter particles interact through an additional force that acts only among themselves. Because ordinary matter cannot detect this force directly, scientists call it a dark force.
Researchers from the Perimeter Institute for Theoretical Physics investigated what would happen if such a force existed. They created theoretical models and compared them with observations of the universe.
At first glance, the answer seemed obvious. If dark matter particles pull on each other through an extra attractive force, they should gather together more efficiently. Larger clumps of dark matter would then help galaxies and other structures form more quickly.
However, the calculations revealed an unexpected twist.
Although the extra force did help dark matter particles cluster together, it also changed the way dark matter behaved as the universe expanded. In the models studied, the dark matter particles effectively became lighter over time.
This second effect turned out to be very important. The particles still clustered more efficiently, but their changing properties reduced the overall impact on the growth of large cosmic structures.
Instead of producing denser structures, the combined effect usually suppressed their growth.
The findings suggest that the universe may be more complicated than our intuition suggests. Simply adding an attractive force does not necessarily produce more structure. Different physical effects can interact in surprising ways and even cancel each other out.
The research may also help scientists evaluate other theories that attempt to explain puzzling observations from major sky surveys, including recent findings from the Dark Energy Spectroscopic Instrument (DESI).
As new telescopes and observatories gather increasingly precise data, researchers hope to learn more about the hidden nature of dark matter. Studies like this help narrow down which ideas are possible and which are not.
The work is another reminder that the universe often behaves in ways that defy simple expectations, and understanding its deepest mysteries may require scientists to think beyond intuition.
