Theoretical physicists have proposed a candidate for dark matter that may explain its difficulty to detect. It could consist of particles that interact with normal matter only through the weak nuclear force and gravity.On June 6, researchers presented their work at the Planck 2019 conference in Granada, Spain.
What is dark matter?
Dark matter remains one of science’s greatest puzzles. It accounts for approximately 85 percent of all mass in the universe, yet its existence has yet to be observed experimentally.
Unseen by telescopes, this mysterious substance shapes galaxies and other objects by exerting its gravitational pull on them. It determines their size, motion and orientation.
Researchers are still exploring how dark matter generates those mysterious gravitational waves we hear from space. Additionally, scientists are searching for ways to detect and study it.
Theories as to what dark matter is composed of vary, but one popular hypothesis suggests it’s a particle known as a “WIMP,” or weakly interacting massive particle. Unfortunately, despite years of research into this matter, no WIMPs have been discovered so far.
Physics recently proposed another way to search for dark matter: by looking for something called an “axion.” This particle boasts several desirable qualities, such as being extremely light and lacking charge.
Harvard Physics Professor Leonid Loeb and colleagues have proposed an axion-based approach that may enable new experiments that can identify specific types of dark matter. Furthermore, it could enable astronomers to better understand how dark matter interacts with other particles such as stars and planets.
Theoretical physicists have long speculated what would happen if dark matter particles could interact with ordinary matter. This would enable them to create effects we cannot currently observe, such as dark photons and a dark magnetic monopole.
Loeb and colleagues used data from several electron microscopes to measure the effect of a dark monopole on an electron beam, which can shift its phase as it passes by. They then compared these results with measurements made of phase shifts caused by other types of dark matter.
Why do we think there’s dark matter out there?
Astronomers have long puzzled over whether there is a missing mass keeping our universe together. This mystery began in the 1930s when physicist Fritz Zwicky proposed that stars and galaxies in our universe are composed of dark matter.
Since then, several studies have discovered evidence for dark matter, including the rotation curves of galaxies and halo effects surrounding them. Now scientists believe that dark matter accounts for most of the universe’s mass.
Dark matter can be difficult to detect, which makes it so intriguing for some physicists. Some researchers are searching for a new way of detecting dark matter that would make it more like the Higgs boson particle discovered in 2012.
The WIMP is the most prominent candidate for dark matter. These particles interact with ordinary matter only through gravity, yet have yet to be detected in experiments designed to detect them.
A novel approach to searching for dark matter involves detecting magnetic monopoles in space. According to Terning and Verhaaren, these monopoles could shift electron phase as they pass near them due to the Aharonov-Bohm effect, which predicts that electrons passing by a magnetic monopole will slightly shift their orientation.
To test their hypothesis, the researchers scanned the surrounding regions of two nearby neutron stars with radio frequencies in the 1 GHz range. Their results demonstrated that they could not detect any signals from axion dark matter particles with mass less than a few micro electron volts – which has been previously identified as being the strongest limit on axon masses.
Terning and Verhaaren note that their search is far from over. They plan to explore further into the electromagnetic spectrum in search of signs of axions’ existence.
They’ve also joined forces with physicists at the Kavli Institute for the Physics and Mathematics of the Universe in Berlin to conduct an experiment similar to theirs using radio telescopes. The team will survey the surrounding regions of half a billion neutron stars.
How do we know there’s dark matter?
Physics researchers are constantly endeavoring to explain dark matter’s workings, yet until recently they weren’t sure if it existed or not. That’s because we can’t detect the particles that make up dark matter directly; therefore, finding them will be necessary – something which won’t be an easy feat.
One potential candidate for dark matter is an axion, which orbits in space but has very little interaction with regular matter. Physics researchers are testing this theory by using microwave cavities to convert axions into resonant electromagnetic waves and measuring their frequencies produced. If successful, this research could mark an important breakthrough in our understanding of the universe.