British scientists believe that a completely new fundamental particle could explain the mystery of “dark matter,” a substance thought to account for most of the universe’s mass.
What is Dark Matter?
In astrophysics, the term dark matter refers to a hypothetical type of matter in the universe whose composition is not yet understood. Dark matter does not emit or reflect enough electromagnetic radiation to be observed with current telescopes or measuring instruments, but it can be inferred from its gravitational effects on solid matter and/or other objects, as well as on the universe as a whole. Based on current understanding of larger cosmic structures and widely accepted theories about the Big Bang, scientists believe that dark matter is a fundamental component that makes up about 70% of the universe’s total mass (dark matter + ordinary matter).
The scientific community estimates that dark matter constitutes 26.8% of the total energy-mass of the universe, while ordinary matter accounts for just 4.9%. When considering mass alone, dark matter is believed to comprise up to 84.5% of the universe.
For astronomers, dark matter reveals its presence through the way its gravitational force affects stars and galaxies, helping them connect these celestial bodies and establish the structure of the universe. Traces of dark matter can also be detected in the Cosmic Microwave Background (CMB), which is the remnant radiation from the Big Bang.
A few scientists believe that dark matter is an illusion.
However, despite numerous research efforts, no one has yet directly observed dark matter.
Who Discovered Dark Matter?
In the late 19th century, astronomers began hypothesizing about unseen matter, such as dying stars or gas and dust in the universe. Researchers even started estimating their masses, with most concluding that this mysterious substance was a small component of the total mass of the universe.
It wasn’t until 1933 that Swiss-American astronomer Fritz Zwicky noticed that distant galaxies were rotating around each other much faster than they should be, based on the visible matter observed through telescopes. He remarked, “If this is confirmed, we will have a surprising result that dark matter is much more abundant than visible matter.”
However, many researchers remained skeptical of Zwicky’s findings until the 1970s when astronomers Kent Ford and Vera Rubin conducted detailed studies of stars in the outer regions of our neighboring Andromeda Galaxy. These stars were orbiting the galaxy’s core at extreme speeds, as if some unseen matter were pulling them and pushing them along—a phenomenon that scientists later observed occurring in all galaxies throughout the universe.
Researchers did not know what this invisible mass contained. Some speculated that dark matter was composed of small black holes or other solid objects that emitted extremely little light, making them difficult to detect with telescopes. In the 1990s, observational results became even stranger when the Wilkinson Microwave Anisotropy Probe (WMAP) revealed that dark matter is up to five times heavier than ordinary visible matter.
Why is Dark Matter Still a Mystery?
Telescope surveys seem never to find enough small solid objects to explain the vast amount of dark matter. Most astronomers today believe that dark matter consists of subatomic particles with properties significantly different from the protons and neutrons we know.
Scientists are unsure about what dark matter is, and some even question whether it exists at all.
The leading candidate for dark matter is known as a Weakly Interacting Massive Particle (WIMP). These hypothetical entities are not found in the Standard Model of particle physics, which describes most particles and forces. WIMPs could be similar to ghostly neutrinos, except they are 10 to 100 times heavier than a proton. (The exact mass of neutrinos has yet to be determined, but they are much lighter than electrons.)
Like neutrinos, WIMPs only interact with two of the four fundamental forces in the universe: gravity and the weak nuclear force. These dark matter particles do not interact with electromagnetic forces, the basis of light, and therefore will always remain invisible.
Physicists have built massive detectors and placed them deep underground to protect them from cosmic rays in their quest to find WIMPs, but so far, no experiment has detected evidence of them. In recent years, this failure has led some researchers to begin questioning whether we are pursuing a type of particle that may never be found.
As a result, some scientists have shifted their focus to a newer dark matter candidate called an axion, a particle that is millions or even billions of times smaller than an electron. These hypothetical particles are particularly intriguing to researchers because they might also solve another difficult problem in physics: how they interact with neutrons to explain why they sense magnetic fields but not electric fields.
In June 2020, scientists at the Gran Sasso National Laboratory in Italy announced that they had accidentally discovered a small signal that could be explained by axions. This result shocked the scientific community, but it has yet to be confirmed by other experiments.
Is Dark Matter Real?
When asking this question, researchers find themselves still scratching their heads over what dark matter is. Some theorists wonder whether there is indeed a completely dark sector in the universe, with many types of particles and even dark forces that only act on dark matter, similar to the complexity of the subatomic world in the visible universe.
At the same time, a few scientists believe that dark matter is an illusion. They reference an idea called Modified Newtonian Dynamics (MOND), a hypothesis suggesting that on a large scale, gravity behaves differently than we think, which explains the rotation of stars and galaxies. However, most experts do not see the need to start with such a far-fetched idea compared to conventional physics, as that would require altering our understanding of much of the well-established reality.
Dark matter is not related to dark energy, another mysterious phenomenon that causes the universe to expand at an accelerating rate. The two concepts simply share the term “dark,” which scientists use to describe phenomena that they do not yet fully understand.
