The Conversation contributed the article to Space.com's expert voices.
Ben is based in Perth and is a scientist. He is employed at the University of Western Australia.
One of the greatest mysteries of the universe is the nature of invisibledark matter.
The ORGAN experiment, Australia's first major dark matter detector, recently completed a search for a hypothetical particle called an axion.
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New limits on the possible characteristics of axions have been put in place by ORGAN. We need to be careful before we get ahead of ourselves.
The fundamental particles of matter were compressed into a hot region about 14 billion years ago.
Everything flew apart after the big bang. All kinds of exotic matter were created when the particles combined into atoms.
Earth crawled with humans after a few billion years. It's a cool story. It's not the entire story, it's just half.
All of us are made of "regular matter." Regular matter makes up just one sixth of the universe.
Dark matter is what the rest is made of. It's name tells you a lot about it. It doesn't emit light and it has mass.
We can't explain our observations if we only look at what we see.
There are many examples, including spinning galaxies. The pull from visible matter alone is not enough to explain the speeds of most galaxies.
There must be dark matter in these galaxies that gives them extra gravity and allows them to spin faster. We believe dark matter holds the universe together.
Dark matter pulls on everything we can see in the universe. It's moving through you like a phantom. It's hard to feel it.
Scientists think dark matter could be composed of axions. The "strong CP problem" is a major problem in particle physics, and a solution to it was proposed.
The particle can make up dark matter under certain conditions. Axions are expected to have weak interactions with regular matter but still have some mass.
How do you find axions.
Since dark matter is believed to be all around us, we can build detectors here on Earth. The theory that predicts axions predicts that axions can convert into particles of light.
We're great at detecting particles. This is what the organization does. It looks for weak photon signals that are caused by dark matter passing through the detector.
The idea of an axion haloscope was first proposed in the 1980's. There are a few in the world that are very different.
In the presence of a strong magnetic field, an axion is thought to convert into a photon. A haloscope uses a big electromagnet to generate a magnetic field.
We place hollow chambers of metal inside the magnetic field in order to trap the photons and make them harder to detect.
There is a problem. Thermal cameras work because everything that has a temperature emits small flashes of light. It's hard to detect faint dark matter signals because of the random emissions.
We put our resonator in a refrigerator to work around this. The experiment is cooled to a temperature of 273C, which reduces the noise.
The colder the experiment is, the better we can hear the faint sound of a light source.
A photon of a certain color is created by converting axion of a mass into a photon. Since the mass of axions is unknown, experiments have to look for it in different parts of the world.
The experiment is not sensitive enough to hear the signal above the noise if there is no dark matter in the axion mass region.
The "exclusion limit" is a way of saying "we didn't find any dark matter in this mass range to this level of sensitivity." The rest of the dark matter research community is told to go somewhere else.
The most sensitive experiment is Organ. There were no dark matter signals detected recently. The possible characteristics of axions have been excluded by this result.
There is a multi-year plan to find axions. The next experiment will be more sensitive and will target a new mass range.
We know from the past that investing in fundamental physics leads to the development of important technologies. Modern computing depends on our understanding of quantum mechanics
If we didn't pursue things that appeared to be strange, we wouldn't have discovered electricity or radio waves. It is the same substance.
Imagine what would happen if we unlocked the rest of the universe.
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