Dark matter accounts for approximately 85 percent of all the mass density in the known universe. The mystery substance is dark, meaning scientists cannot see it or interact with it in any meaningful way. But gravitational effects of dark matter are very much there and cause galaxies to appear much heavier than the sum total of what we can detect. Researchers at the University of Tokyo in Japan hope to finally crack the mystery with the aid of lasers and theoretical particle dubbed axions.
Axions are a hypothetical particle that, much like dark matter, struggles to interact with other forms of matter.
Everything we can touch and see, such as our cars and bodies, are built from so-called baryonic matter.
Dark matter does not appear to interact with baryonic matter and axions appear to be equally neutral in this regard.
As a result of this connection, many physicists theorise dark matter is built from axions.
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Assistant Professor Yuta Michimura from the University of Tokyo said: “We assume the axion is very light and barely interacts with our familiar kinds of matter.
“Therefore, it is considered as a good candidate for dark matter.
“We don’t know the mass of axions, but we usually think it has a mass less than that of electrons.
“Our universe is filled with dark matter and it’s estimated there are 500 grams of dark matter within the Earth, about the mass of a squirrel.”
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To detect the presence of axions, Tokyo’s scientists have designed a laser-based instrument.
The device uses lasers passing through polarising beam splitters and photodetectors to detect the modulation of light polarisation.
The intricate device is being developed at the University of Tokyo Institute for Cosmic Ray Research.
Graduate student Koji Nagano said: “Our models suggest axion dark matter modulates light polarization, which is the orientation of the oscillation of electromagnetic waves.
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“This polarisation modulation can be enhanced if the light is reflected back and forth many times in an optical cavity composed of two parallel mirrors apart from each other.
“The best-known examples of these kinds of cavities are the long tunnel arms of gravitational-wave observatories.”
He added: “There is overwhelming astrophysical and cosmological evidence that dark matter exists, but the question ‘What is dark matter?’ is one of the biggest outstanding problems in modern physics
“If we can detect axions and say for sure they are dark matter, it would be a truly exciting event indeed. It’s what physicists like us dream for.”