Dark matter makes up about 80 percent of the universe’s mass-energy content. It’s so mysterious that scientists don’t even know what it is — but they do know where it comes from, where it goes and how much of it there is. Let’s take a look at dark matter in the universe and learn some facts about this strange material that seems to control our very reality.
What is dark matter?
In order to explain why galaxies are spinning so fast, scientists have theorized that there must be something else out there exerting a gravitational force on them. This invisible substance is called dark matter. Scientists don’t know what dark matter really is but we do know that it accounts for about 80% of all of the mass in the Universe. Dark matter has an effect on light by bending its path as it travels through space. Astronomers were able to detect this because stars behind the Milky Way’s disk appear slightly distorted when they are being observed. When you look at these stars, they seem to move faster than they should if they were only influenced by gravity. It is speculated that other forces like magnetic fields or radiation may also contribute to their movement. The search for dark matter continues today with astronomers focusing on dwarf galaxies near our own galaxy, the Milky Way. They believe that this type of galaxy might be surrounded by more dark matter than others due to their small size which will give us clues as to what kind of particles make up the mysterious material.
What do we know about dark matter?
We know that dark matter exists, but we don’t know much about it. We know that dark matter clumps together to form large structures like galaxy clusters. Dark matter can be measured by its effects on visible light, such as how fast stars are rotating around galaxies. Scientists theorize that dark matter interacts with other forms of normal matter through gravity and some other unknown force, but they have yet to find evidence of this interaction. The existence of dark matter was first proposed back in 1933 when astronomer Fritz Zwicky observed a cluster of galaxies with more mass than could be accounted for based on the number and types of observable objects. There are different theories about what type of substance makes up dark matter, but scientists think that most likely candidates include neutrinos or axions; however, all attempts to detect these particles have failed so far. A leading candidate for dark matter’s identity is weakly interacting massive particles (WIMPs), which might be created during particle collisions at the Large Hadron Collider. If WIMPs exist, they would react only very rarely with regular matter, meaning scientists would need experiments to catch them in order to prove their identity. Another possible candidate is called sterile neutrinos: subatomic particles related to regular neutrinos but which do not interact through any of the known forces other than gravity.
Why can’t we see it?
Invisible to our eyes, dark matter accounts for nearly a quarter of all the mass-energy in our Universe. It doesn’t emit or reflect light, so we can only detect its presence by observing its gravitational effects on other objects. We know it exists but still don’t fully understand what it is made of. But scientists think that dark matter could consist of as-yet undiscovered particles that are their own antiparticles – mirror images of normal particles like electrons, protons and neutrons that make up ordinary matter. These hypothetical particles could be some form of lightweight ‘dark’ particle such as WIMPs (Weakly Interacting Massive Particles) which are predicted by theories that attempt to explain the missing baryonic (ordinary) matter in the Universe. They may also be axions, extremely light particles which have never been observed directly but have been inferred from strong indirect evidence. The axion was originally proposed as a solution to an unsolved problem in quantum chromodynamics: why had no one ever seen any quarks or gluons when they were expected to interact frequently with each other?
Where did it come from?
There are many theories that have tried to answer this question, but none of them have been able to provide any conclusive evidence. One theory suggests that dark matter could be made up of particles called axions. This theory states that these particles would not interact with anything else outside of their own cloud, so they would not emit any light. Other scientists believe that dark matter might be made up of neutrinos, which are subatomic particles that do not interact with other types of atoms very easily. Scientists also theorize that there may be as much as 100 times more dark matter than visible matter in our galaxy. Scientists don’t know exactly how much of the Universe’s mass consists of dark matter, but they estimate it to be around 27%. Scientists now want to find out just what this mysterious material is. The most popular theory at the moment is that dark matter consists of a type of elementary particle called a WIMP (Weakly Interacting Massive Particle). Experiments like LUX-Zeplin hope to detect WIMPs within the next few years. However, astronomers still have yet to find any conclusive proof for dark matter’s existence on Earth or in space.
How much is there of this strange stuff in the Universe?
The amount of dark matter in the Universe is difficult to measure, but astronomers have developed a number of techniques to estimate its properties. These techniques suggest that dark matter makes up about 26% of all the mass-energy content in our Universe, with ordinary stuff (like people, planets and stars) making up about 4%. The rest – about 68% – seems to be made up of something unknown. Scientists call this unknown material dark energy, and nobody really knows what it is or where it comes from. There are many ideas for new experiments to try to find out more about dark energy, including hunting for rare particles called neutrinos at underground laboratories like Fermilab near Chicago or building huge telescopes like the proposed Square Kilometre Array radio telescope in Australia and South Africa.
