Unknown things about dark matter

Although thought to be ubiquitous in the universe, dark matter has yet to be precisely defined. To date, many aspects of dark matter remain unanswered questions.

Dark matter is thought to be six times more abundant than normal matter. What is dark matter? First and perhaps most confusingly, researchers are still unsure what exactly dark matter is. Initially, some scientists surmised, the missing mass in the universe was made up of faint small stars and black holes. However, detailed observations have not shown enough evidence to explain the effects of dark matter. The current leading hypothesis is a hypothetical particle known as the weakly interacting mass particle, or WIMP. This particle would behave like a neutron and be 10-100 times heavier than a proton. However, this conjecture has opened a series of other unanswered questions. Is it possible to detect dark matter? In the 1930s, Swiss astronomer Fritz Zwicky discovered that galaxies in a distant cluster were orbiting each other much faster than they should have been visible. At the time, he suggested, an invisible substance, dark matter, could be pulling gravity on these galaxies. Since then, researchers have confirmed, this mysterious matter can be found throughout the universe. They are six times more abundant than ordinary matter. If dark matter were produced from WIMPs, they would be all around us, invisible and virtually undetectable. While they won’t interact much with normal matter, there’s always some small chance that a dark matter particle could bump into an ordinary particle like a proton or electron as it travels through space. So the researchers carried out a series of experiments to study the huge numbers of ordinary particles deep underground, where they are shielded from interfering radiation. These particles can behave like a collision between dark matter particles. After decades of searching, none of these detectors have made a reliable discovery. Earlier this year, China’s PandaX experiment reported failing to detect WIMP. According to physicist Hai-Bo Yu at the University of California, Riverside, it seems that dark matter particles are much smaller than WIMP, or lack properties that make them easy to study. Does it include more than one particle? Ordinary matter is made up of particles like protons and electrons, as well as more exotic particles like neutrinos, muons, and pions. So some researchers have wondered, could dark matter, which makes up 85 percent of the matter in the universe, be just as complex? “There is no good reason to assume that all dark matter in the universe is made up of one type of particle,” said Harvard physicist Andrey Katz. According to Katz, dark protons can combine with dark electrons to form dark matter. From there, create configurations as varied and interesting as those found in the physical world. However, this problem has not been elucidated so far by scientists. Does the dark force exist? Some researchers have been looking for “dark photons,” analogous to photons exchanged between ordinary particles that generate the electromagnetic force. However, dark photons will only be sensed by dark matter particles. Physicists in Italy are preparing to break a beam of electrons and their antiparticles, called positrons, into a diamond. If dark photons exist, electron-positron pairs could annihilate and create one of the strange force carriers. From there, it is possible to open up a whole new realm of the universe. Is it made up of axions? As physicists pay more and more attention to understanding WIMPs, other dark matter particles are starting to gain favor. One of the top substitutes is the axion. This hypothetical particle is very light, smaller than a proton. Axion is currently being searched for in a few trials. Recent computer simulations have raised the possibility that these axions can form star-like objects. At the same time, they can produce radiation that is easily detected, similar to the mysterious phenomenon known as fast radio bursts. What are the properties of dark matter? Astronomers have discovered dark matter through its gravitational interaction with ordinary matter. This is also an indication that it is the main way that the presence of dark matter is known in the universe. According to some theories, dark matter particles must be their own antiparticles. This means that the two dark matter particles will annihilate each other when they meet. The Alpha Magnetic Spectrometer (AMS) experiment aboard the International Space Station has been looking for amazing signs of this destruction since 2011. As a result, AMS detected hundreds of thousands of events. Scientists are still unsure if these come from dark matter, and have yet to determine exactly what dark matter is. Does it exist in every galaxy? Because of its greater mass than normal matter, dark matter is often thought to be the driving force that organizes large structures such as galaxies and galaxy clusters. So it was strange that earlier this year, astronomers announced that they had found a galaxy called NGC 1052-DF2. Surprisingly, this galaxy barely contains any dark matter. At the time, Pieter van Dokkum of Yale University said: “Dark matter does not seem to be a necessary element to form a galaxy.” However, another team of researchers analyzed and showed that van Dokkum and colleagues miscalculated the distance to the galaxy. This means that visible matter is much fainter and lighter than first detected.