Could axions be the missing piece in the dark matter puzzle?
Utilizing the galactic glow of dwarf galaxies, researchers examine a hypothetical particle referred to as an axion as a attainable contender for darkish matter.
Because the Thirties, scientists have been conscious of an enigmatic type of matter that doesn’t replicate mild, which they named darkish matter. In line with our present understanding, this entity interacts with different particles primarily via gravity and accounts for about 85% of the mass within the Universe.
Scientists launched the idea of darkish matter into their theories as a result of they noticed that the amount of strange matter was not sufficient to elucidate some astronomical observations. These ranged from increased than anticipated velocities of stars inside galaxies to anomalies within the cosmic microwave background, and the fast formation of galaxies.
Regardless of there being extra darkish matter in area than every other type of matter, of its composition stays a thriller. Neutrinos, black holes, and weakly interacting huge particles often known as WIMPs have all been thought of as its constituents, however up to now none of those hypotheses has been confirmed.
Axions might be a solution
This uncertainty has prompted researchers to discover different candidates, with one significantly attention-grabbing candidate being the axion, a hypothetical particle that theorists consider couldn’t solely resolve the thriller of darkish matter, however might resolve an necessary subject within the principle of robust interactions.
“Axions are an particularly attention-grabbing darkish matter candidate as a result of they resolve two mysteries: the character of darkish matter and the robust charge-parity (CP) drawback,” defined Elisa Todarello of the Turin College in an e-mail. “The robust CP drawback is the unexplained lack of violation of the parity and cost conjugation symmetries within the robust interactions. Axion particles had been first proposed within the context of an answer to this puzzle. Because it seems, in addition they have all the proper traits to be darkish matter.”
However to verify axions as candidates for darkish matter particles, physicists have to know their mass and energy of interplay, one thing present theories are unable of predicting. This leaves experiment to find out these parameters.
To do that, Todarello analyzed the depth of sunshine coming from 5 close by dwarf galaxies to decide if any of the emitted photons originated from the decay of axions into pairs of those particles — a phenomenon that’s predicted to happen, based on the idea of axions, even when it does happen very not often.
A telescope sheds mild
In a current research revealed in Annalen der Physik, Todarello used knowledge collected by the Multi Unit Spectroscopic Explorer (MUSE), which is without doubt one of the Very Massive Telescope of the European Southern Observatory’s devices working within the seen vary.
“Axions are predicted to work together feebly with mild,” stated Todarello. “The energy of this interplay is represented by a amount that we name ‘g’. This interplay permits an axion to rework into two photons. If axions are the darkish matter that holds collectively galaxies, they’re current in extraordinarily giant portions, for instance within the dwarf galaxies noticed by MUSE.
“When darkish matter axions decay into photons, they trigger the galaxy to ‘glow’ at a selected frequency — half the axion mass [in certain units]. We analyze MUSE knowledge to seek for this glow. Its presence would point out the existence of axions, whereas its absence permits us to rule out axion darkish matter inside particular ranges of the axion mass and g.”
Todarello’s evaluation of the radiation from 5 dwarf galaxies didn’t reveal any peculiarities that indicated the decay of the axion. Nonetheless, this outcome remains to be essential, because it constrains the attainable parameters of the axion, thereby limiting the vary of parameters through which this particle needs to be sought sooner or later.
“By observing 5 dwarf galaxies with MUSE, we’re capable of exclude a darkish matter axion with a mass between 2.65 to five.27 electronvolts [which is approximately a hundred thousand times lighter than an electron] and a sure degree of interplay with photons, bigger than a threshold that is dependent upon MUSE’s sensitivity,” defined Todarello. “We discover constant outcomes throughout the 5 galaxies we think about. Since we don’t see the diffuse glow from axion decay into photons, we are able to conclude that there’s no darkish matter axion with such mass and such interplay energy.”
The writer believes that the strategy she used could be improved and used to seek for axions with a unique mass and a unique energy of interplay with photons, making it attainable to find out whether or not darkish matter certainly consists of those particles — or one thing else totally.
“Sooner or later, we’d discover completely different devices and telescopes to increase our bounds in frequency, for instance to the near-infrared,” concluded Todarello. “Because the coupling energy is predicted to be decrease for lighter axions, we have to discover an instrument with wonderful sensitivity and give attention to targets that may present a big flux, for instance, extra huge dwarf galaxies.”
Reference: Elisa Todarello, Up to date Bounds on Axion-Like Particle Darkish Matter with the Optical MUSE-Faint Survey, Annalen der Physik (2023), DOI: 10.1002/andp.202300042.
Characteristic picture credit score: ESA/Hubble & NASA
