Even after decades of uninterrupted research, the exact nature of dark matter continues to slip through physicists’ fingers. At present, we still do not know what this mysterious substance is made of, although we suspect it to represent around 25% of our universe. Recently, however, a team of researchers proposed a new approach based on black holes which could finally give us some answers.
This study, spotted and explained by astrophysicist Paul Sutter in an article in Space.com, is based on a hypothesis which suggests that dark matter could be made up ofaxions. These are hypothetical elementary particles whose existence has been proposed in order to explain certain major inconsistencies in cosmology and particle physics. Their main characteristic is their extremely low mass: it would be at least a thousand times less than that of electrons, which are nevertheless incredibly light. Other models attribute an even lower mass to it, several orders of magnitude below this already tiny figure.
It’s certainly an exciting idea, but also a bit problematic. Indeed, detecting such light objects is practically impossible with our current technology. An obstacle which risks considerably delaying the first direct observation of dark matter, assuming that this model is correct. To achieve this, we would therefore have to wait for a major technological breakthrough… or a very original idea which is based on mechanisms that are currently under-exploited. And this is precisely what the authors of the works dissected by Sutter propose.
A detectable gravitational resonance?
The approach described in this study relies on black holes. According to the authors, this could be the ideal environment to test the axion-based dark matter hypothesis because of a fascinating phenomenon: superradiance.
It is a quantum phenomenon where objects in an excited state can collectively emit extremely intense and coherent radiation. In the case of black holes, these are generally photons which find themselves trapped nearby by the gigantic gravitation which reigns there. They then begin to rotate faster and faster around this cosmic ogre while accumulating an enormous amount of energy. The majority of these photons end up crossing the event horizon, the famous point of no return beyond which nothing can escape the black hole. But some have the chance to bounce off other particles, and therefore escape from its orbit with absolutely insane energy.
At the same time, under the influence of the enormous gravitational forces originating from the black hole, dark matter would also accumulate in the vicinity of the singularity in the form of a much denser cloud than in the rest of the universe. However, this cloud would be directly exposed to these supercharged photons. The authors of the study therefore suggest that this superradiance could cause a energy transfer from the black hole to dark matter.
Beyond a certain energy threshold, the rotation of dark matter around the black hole would begin to slow down. This loss of speed would trigger a massive release of dark matter particles — and that’s where this scenario becomes very exotic and absolutely fascinating.
This ” cascade of emissions » would be completely invisible, and would not emit the slightest radiation capable of being measured with measuring instruments. On the other hand, Paul Sutter explains that this deluge of particles would directly affect space-timewho would start “ ring like a bell » around the black hole!
More precisely, the dark matter thus ejected would manifest itself in the form ofgravitational waves which, in theory, could be detected using state-of-the-art interferometers like LIGO or Virgo.
Clear limits, but real potential
This isn’t the first time researchers have proposed harnessing gravitational waves to track down elusive dark matter. Last year, another team again suggested looking at those resulting from black hole mergers.
But as always when we talk about dark matter, this was quite exploratory work – and this is also the case with this new study, which remains at the pre-publication stage for the moment. We must therefore take our conclusions with a pinch of salt.especially since it is based on completely hypothetical bases. For example, the existence of these famous axions has still not been demonstrated to date.
But it is still very interesting work. In fact, they offer a clear path to confirm or refute this hypothesis full of potential. Astrophysicists will be able to look back on previous observations of gravitational waves coming from black holes in order to look for statistical patterns likely to betray the existence of this phenomenon. If successful, the implications would be far-reaching; this would not only allow demonstrate that axions are realbut also to achieve a real giant leap in our understanding of dark matter.
Conversely, if this cosmic treasure hunt produces no results, it will not be dramatic. This will simply indicate to astrophysicists that other avenues will probably have to be favored. It will therefore be very interesting to look at the other work that this study will perhaps inspire, because in all cases, this will allow us to better understand the nature of this oh-so-mysterious substance.
The text of the study is available here.
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