Detecting Dark Matter

Image Credit: NASA, ESA, M. J. Jee and H. Ford et al. (Johns Hopkins Univ.)

Ruby O’Connor delves into the mysterious subject of dark matter and dark energy, and comprehensively examines the most recent scientific work on detecting dark matter.

In the 1990’s, scientists believed that the expansion of the universe was slowing down due to the forces of gravity. However, in 1998, observations through the Hubble Space telescope showed that the expansion of the universe was instead accelerating. The presence of a substance that scientists call dark energy was theorized as an answer to why the expansion of the universe is accelerating.

Scientists believe that the Universe consists of 68% dark energy, 27% dark matter, and 5% normal matter. Normal matter makes up all visible phenomena made up of atoms, such as the Earth and our Solar System.

There are many theories which attempt to explain what dark energy actually is. However, none to present day have been one hundred percent confirmed.

Albert Einstein theorized the idea of a cosmological constant, essentially a force which counteracts gravity. Now, as National Geographic explains, we could very well understand dark energy as Einstein’s idea of a cosmological constant, explaining the acceleration of the expansion. Einstein’s theory also included the idea that a property of space is the possession of its own energy, meaning that as space expands, so does energy; this could explain the acceleration of the expansion as well. Quintessence is another theory which attempts to explain what dark matter is. Quintessence is a name given to a different form of energy which has an impact on the universe contrasting that of normal matter and energy.

What is dark matter then? The most common theory is that dark matter is made up of particles called Weakly Interacting Massive Particles, known as WIMPS.

However, more recent theories propose an alternative, that dark matter is composed of a “dark electromagnetism” which would include “dark photons” and other particles.

If we can’t observe it, how do scientists know that it is really there? What evidence is given for the existence of dark matter? The gravitational effects of dark matter can be seen with reference to stars. National Geographic explains that stars on the outside of a spiral galaxy should travel slower than stars in the centre according to physics. However, according to our observations, stars travel at approximately the same speed regardless of their position in the galaxy. Scientists have therefore concluded that a gravitational force (which is dark matter) must exist to explain this phenomenon.

Another piece of evidence is the appearance of rings and arcs of light in pictures of the galaxy. This light is potentially a distortion created by the presence of a mass, which could be dark matter. This phenomenon is known as “gravitational-lensing”. An additional possibility is that Einstein’s general theory of relativity is incorrect, and that scientists need to find another theory which can explain the acceleration. As one can see, there is much that is unknown in the field of study of the Universe.

Up to this point, the basics of what is known of dark energy and dark matter have been explained. But what current research is being carried out in relation to dark matter and dark energy? In January 2019, a study investigating data from NASA’s Chandra X-ray Observatory found evidence that that the amount of dark energy is growing with time. The DAMA experiment in Italy claims to have detected dark matter as of March 2019.

Two studies, ANAIS’ and COSINE-100 then attempted to verify the results found by DAMA’s study. ANAIS’ is a dark matter detector at the University of Zaragoza in Spain, and COSINE-100 is a collaboration between the Korea Invisible Mass Search and Yale University at Yangyang Underground Laboratory in South Korea. The results? Highly inconclusive. However, as Juan Collar of the University of Chicago says to Nature magazine, “There is really no conclusion to be drawn at this point, other than mounting suspense.”

In June 2019, further new ideas emerged. Researchers John Terning and Christopher Verhaaren expand on the theory of dark matter being composed of “dark electromagnetism” and propose a new option, the existence of a dark magnetic “monopole” that would interact with the dark photon. A monopole is a particle acting like one end of a magnet. They propose a new way to detect dark matter, based on their theory of its composition. They argue that the dark “monopole” could be detected because of the way it shifts the phase of electrons as they pass by it. Their research was supported by a grant from the U.S. Department of Energy.

Another study investigating the amount of dark matter in a galaxy called Markarian 1216 found that it has more dark matter in its core than scientists expected. The method they used to determine the amount of dark matter is X-Ray analysis, acquired from data from NASA’s Chandra X-ray Observatory. They studied the X-Ray brightness and temperature to determine how much dark matter was at the centre of the galaxy.

A different study proposed using “high-purity lab-grown diamond crystal” to detect dark matter. The diamond crystal would theoretically be designed with sensors to detect soundwaves at the collision of a dark matter particle with an atomic nucleus or an electron in the diamond. The researchers explain the benefits of using a diamond crystal as opposed to germanium and silicon, which has been used in the past. They say that a diamond will allow them to detect dark matter particles of a lower mass, as well as ease the measuring of vibrations set off by the collision of the dark matter particle, due to the (mostly) single carbon isotope composition of the diamond.

With regards to the detection of dark matter particles, it seems many new experiments are being designed and tested. But only time will tell if they operate as theorized by researchers.