🧩 Three astrophysical puzzles could share a common origin

Dark matter, ubiquitous but undetectable directly, shapes galaxies and their movements. A new study proposes a more dynamic version of this substance, which could thus be capable of interacting with itself.

In an article published in Physical Review Letters, physicist Hai-Bo Yu, from the University of California at Riverside, explores an alternative hypothesis to the dominant model. This model describes so-called cold and collisionless dark matter. However, certain structures observed in the Universe seem too dense to be explained by this classical framework.


The studied approach relies on self-interacting dark matter: its particles collide and exchange energy. This behavior profoundly alters the internal structure of dark matter halos, those vast envelopes surrounding galaxies.

These interactions can trigger a phenomenon called gravothermal collapse. This process concentrates dark matter into extremely compact cores. Each cluster thus formed would reach a mass equivalent to a million Suns, while remaining completely invisible.

A first clue appears in a gravitational lensing system named JVAS B1938+666. An anomaly in the image of a distant galaxy indicates the presence of a dense object not detected directly. This type of distortion remains difficult to reconcile with non-interacting dark matter.

A second case concerns the stellar stream GD-1, in the Milky Way. This fine structure of stars presents a notch accompanied by a spur. According to the researchers, a compact invisible object would have traversed this stream, leaving a clear gravitational signature.

A third case, the Fornax satellite galaxy (also called the Fornax Dwarf Galaxy) harbors an unusual star cluster, named Fornax 6. Its compactness intrigues astronomers. A dense dark matter core could act as a gravitational trap, capturing passing stars and forming a tight grouping.

The interest of this hypothesis lies in its unity. The three phenomena, yet observed at very different scales, would be explained by the same physical mechanism. The measured densities correspond naturally to the predictions of self-interacting dark matter.

This trail does not yet overturn the dominant model, but it opens a coherent path for interpreting observations that were previously isolated. Future data will allow for more precise testing of this idea and for clarifying the true nature of dark matter.