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Could stellar evolution reveal more about dark matter? | Photo: Nazariy Neshcherensky/Getty Images
How to look for invisible hypothetical particles? One way is to see how quickly they can destroy white dwarfs—the dense remnants of the cores of dead stars.
In recent years, astronomers have become increasingly interested in a theoretical particle known as an axion, which was invented decades ago to solve a difficult problem with strong nuclear force. After initial attempts to find it in experiments at a particle collider were unsuccessful, the idea faded into the background.
But further research has shown that the axion may be a contender to explain the mystery dark matter. Theorists have realized that axions may have ways to fill the Universe, but they have so far evaded direct detection.
The fact that this small particle will be virtually invisible does not mean that it will go completely unnoticed in the Universe. In a preliminary article published November 2025 on the open access server arXivresearchers reported a way to test axion models using old archival data from Hubble Space Telescope. Although they didn't find any evidence for the existence of axions, they beat other attempts and gave us a much clearer picture of what is allowed and what is not allowed in this universe.
The objectives of this study were white dwarfs – dense, dim cores of dead stars. One white dwarf can pack solar mass into an object smaller in size Earthwhich makes white dwarfs one of the most exotic objects in the Universe. It is important to note that white dwarfs protect themselves from collapse due to the so-called electron degeneracy pressure, in which a huge sea of ​​free-floating electrons resists collapse because, according to quantum mechanics, electrons can never be in the same state.
Some models of axion behavior suggest that these particles could be created by electrons: if the electron were moving fast enough, it would cause the formation of an axion. And since the electrons deep inside the white dwarf are moving very, very quickly – almost with speed of light – as they move within their tight confines, they can produce many axions.
The axions would then fly away, leaving the white dwarf completely behind. Such production of escaping axions would starve the white dwarf of energy. And since white dwarfs don't produce energy on their own, this will cause them to cool faster than they would otherwise.
The researchers implemented this model of axion cooling into a sophisticated software package that can simulate the evolution of axions. stars and how their temperature and brightness change as their inner world develops.
This model allowed the researchers to predict the typical temperature of a white dwarf given its age, both with and without axion cooling. With the results in hand, they turned to data from the globular cluster 47 Tucanae collected by Hubble. Global clusters are crucial because the white dwarfs in them were all born around the same time, giving astronomers a large sample to study.
In short, the researchers found no evidence of axion cooling in the white dwarf population. But their results did impose entirely new limits on the ability of electrons to produce axions: they cannot do so more efficiently than once in a trillion chances.
This result does not completely rule out axions, but it does suggest that it is unlikely that electrons and axions interact directly with each other. So if we're going to continue searching for axions, we'll have to find even smarter ways to search.
