Dark matter, as far as scientists can tell, is present all throughout the Milky Way galaxy. The mystery substance appears to give the galaxy more mass than astronomers can observe, meaning it is hiding just beyond our sight. Dark matter is called dark precisely because of this – it does not reflect or emit light and is undetectable and unobservable. And yet astrophysicists estimate dark matter accounts for about 85 percent of the observable universe.
Ordinary matter, the kind from which our bodies and houses are built, only adds up to about five percent of the universe’s mass.
So what exactly is dark matter and how can we ever hope to crack the mystery?
Dr Paul Sutter, an astrophysicist at Ohio State University, has proposed the dark matter enigma could be solved with the aid of axions.
Axions are a hypothetical sub-atomic particle, first theorised in 1977, which could explain the motions of galaxies abundant in dark matter.
However, one major problem with this theory is axions, just like dark matter, are purely hypothetical particles.
It can generally explain all the usual dark matter observations
Dr Paul Sutter, Ohio State University
In an article for Universe Today, Dr Sutter said: “If we let the axion be the dark matter it can generally explain all the usual dark matter observations.
“It can explain the rotation curves inside of galaxies. It can explain the motions of galaxies within galaxy clusters.
“It can be manufactured in sufficient abundance in the early Universe to fit observations of the cosmic microwave background. And so on.”
Axions, although hypothetical, are useful in maintaining a balance between matter and antimatter particles.
For all intents and purposes, antimatter particles are the flipped mirror image of matter, with reverse charge and spin.
There is a symmetry between the two – dubbed CP symmetry – which stipulates switching out particles’ charges for the opposite and running the process “in a mirror” will yield the same results.
But this is not always the case and there are instances where CP symmetry is violated unless axions are present to maintain a balance.
So how do axions fit into the dark matter equation? The key could be hidden in the breakdown of black holes.
Dr Sutter said: “We can’t observe the black holes directly. So they might not be black holes at all.
“They might be axion cores hiding in the centres of those galaxies.”
In this scenario, the physicist argued axions can clump into a “massive ball”, which at first glance would be reminiscent of a supermassive black hole.
This clump of axions would be undetectable by not interacting with light and would lurk at the heart of galaxies.
In 1974, theoretical physicist Stephen Hawking theorised could be the remnants of ancient, primordial black holes.
However, until scientists can directly detect either dark matter or axions, the theory will remain just that – theory.
Dr Sutter said: “Hopefully someday we can shed some light on the situation.”
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