Dark Matter May Exist in Two States, Explaining Missing Signals in Dwarf Galaxies

What if not finding something was actually a clue? In the search for dark matter, missing signals in some galaxies can help explain what is detected in others.

At the center of the Milky Way, telescopes have captured an unusual glow of gamma rays, the most energetic form of light. One possible explanation is that dark matter particles collide and destroy each other, releasing bursts of energy. Yet the same signal did not appear elsewhere where it should have.

This mismatch has become one of the main sticking points in signal interpretation. If dark matter is responsible, why doesn’t it appear everywhere?

A new model described in the J.journal of cosmology and astroparticle physics offers a different way of thinking about this question. Instead of assuming that dark matter behaves the same way throughout the universe, the work suggests that its signals could depend on local conditions, appearing in some galaxies while remaining undetectable in others.

“What we are trying to point out in this article is that there could be another type of environmental dependence,” explained Gordan Krnjaic in a press release. “Dark matter could simply be made of two different particles, and the two different particles have to be together to annihilate each other.”

Why dark matter signals are missing in dwarf galaxies

Dwarf galaxies, which orbit the Milky Way, are full of dark matter and have relatively little background radiation. This makes them ideal places to look for clear signals. If interactions with dark matter produce gamma rays in a galaxy, similar signals would also be expected in these smaller systems. But these signals did not appear.

This gap has led some researchers to look for alternative explanations for the Milky Way’s glow, such as large populations of faint pulsars clustered near the galaxy’s center. Others see it as a sign that the simplest models of dark matter may be incomplete.

Learn more: Antarctica’s mysterious radio pulses remain unexplained – but better particle experiments could change that

How dark matter behaves differently in different galaxies

This model takes a different approach to what dark matter might be. Instead of a single particle, it describes two closely related states: a lighter version and a slightly heavier version. For a signal to appear, particles in the lighter state need enough energy to move to the heavier state before they can interact and produce gamma rays.

In large galaxies like the Milky Way, dark matter particles move faster, giving them enough kinetic energy to make this transition. Once this is done, the interactions between the two states can generate the gamma ray signal detected by the telescopes.

In dwarf galaxies, particles move much more slowly. Without enough energy to reach the heaviest state, these interactions become extremely rare, cutting off the signal. The same particles are present in both environments, but the conditions are not.

Rethinking what a missing signal means

Missing signals in dwarf galaxies no longer contradict the idea that dark matter could be the source of the Milky Way’s gamma-ray glow. They fit into this framework.

The usual expectation that similar galaxies should produce similar signals does not hold true if these interactions are energy dependent. Some systems would turn on, while others would remain silent.

As more observations come in, especially those from dwarf galaxies, it should become clearer whether the weak signals are just below current limits or whether they are absent altogether.

Either result helps refine what dark matter can and cannot be. For now, the situation is less uniform than it once seemed, with the lack of a signal becoming part of the explanation rather than the problem.

Learn more: Is dark matter real? Most experts say yes, but it’s still hotly debated

Article sources

Our Discovermagazine.com editors use peer-reviewed research and high-quality sources for our articles, and our editors review the articles for scientific accuracy and editorial standards. See the sources used below for this article:

• This article refers to information from a study published in the Journal of Cosmology and Astroparticle Physics: dSph-obic dark matter