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NASA illustration of a “dark matter star.” | Image source: NASA/JPL-Caltech
Have you ever looked up at the night sky and wondered what you were up to? no vision? The sky may be full of invisible “boson stars,” which are made up of a strange form of matter that doesn’t shine.
We strongly doubt that the universe is full Dark matterWhich constitutes about 25% of the total mass and energy in the universe. But while circumstantial evidence abounds and we believe that dark matter is some type of undiscovered particle, we have no direct evidence that such a particle exists.
For decades, we thought we were on the right track with a new type of particle known as weakly interacting massive particles (WIMP). Predicted by several theories of supersymmetry, the WIMP would have a mass somewhere in the range of the heaviest known particles, such as the upper Quark. But otherwise, it would be largely invisible, interacting with natural matter only occasionally.
but Searches for WIMPs failed to find anything. This is good; Nature is never bound to agree with our first guess. Fortunately, we have another candidate particle waiting for us: the Accion.
Axion was introduced to solve a nasty problem involving… Strong nuclear power. According to all observations, the strong force obeys two important symmetries in nature: charge and valence. This means that if you did a strong force interaction, flipped the charges of all the molecules to their opposite values, and looked at the reaction in the mirror, you would get the same result.
But there is nothing in the theory itself that says it must obey these symmetries. Physicists tried to fix this by adding a new parameter to the equations and setting this parameter to zero, but that seemed a bit forced. Then came an innovative solution: perhaps this new parameter represents a new quantum field, and interactions with this field naturally produce symmetry.
This was Axion, named after a brand of dishwashing detergent because it cleaned up the mess caused by the asymmetry problem.
If axions existed, they would make excellent dark matter, because they would be abundant and would only rarely interact with ordinary matter. They were also doing some wild things.
Axions are incredibly light, trillions and trillions of times lighter even than axions Neutrinothe lightest known particle. With such slight masses, their quantum wave nature would appear on microscopic scales. While every particle also has a wave associated with it, we typically do not notice or care about those waves unless we are dealing with subatomic quantum systems. But not so for the axion, which likely spreads its wavelength across an entire galaxy.
The second great thing about axions is that they are Bosons. Bosons are a type of particle that can all share the same quantum state, which means you can cram as many of them into a compact volume as you want. This is similar to photons (you can put as much light as you want in the box) and different from particles e.g Electrons (You can only cram so many before the box is full.)
These two properties of axons mean that they are exceptionally good at collapsing into incredibly high densities, being held together by their own (slight) densities. attractiveness. Basically, they can form a kind of star. It is completely invisible, does not emit light and does not interact with anything, but it is a star nonetheless.
these The stars — which have various names, including axion stars, boson stars, and dark stars — can be small, roughly the same mass as regular stars. They can also be massive, extending into the entire core of the galaxy.
The possible existence of boson stars is a double-edged sword. On the one hand, it can make direct detection very difficult. Unless there is a boson star wandering through our solar system and passing through Earth, we are unlikely to see axons in our detectors.
Related stories:
—“Axion stars” that bloomed after the Big Bang could shed light on dark matter
—An exotic star system may hold the first evidence of an extremely rare ‘dark matter star’
—Do mythical “dark stars” really exist? The James Webb Space Telescope detects 3 candidates
Boson stars, on the other hand, can do all sorts of things that could make them detectable, like messing with nuclear fusion in stellar cores or exploding on their own in an event known as a bosonova.
We don’t know if axions exist, or if they do exist, if they are responsible for dark matter. But it’s still fun to imagine a universe filled with silent, invisible, harmless dark stars.
