Did you know, that 80% of our universe is made up of material that’s not even visible to us. Scientists believe that this matter exists because otherwise the action and behavior of planets, galaxies, and stars wouldn’t add up.
This invisible matter is known as dark matter and it’s completely invisible. It’s something that is not visible to scientists as well. They are still trying to understand it and here’s what they know about it till now.
Dark Matter and Its Invisibility
As the dark matter fills the universe, and it’s completely invisible with no light or energy emission, scientists believe that its secret to invisibility and elusiveness lies within its composition. As the visible matter is composed of baryons, a combined name for subatomic particles like electrons and protons. Scientists think that whatever the dark matter is composed of, it can be making it invisible.
They can only speculate on the material it’s composed of. They think it could also be composed of baryons like everything else, but then it could also be made up of non-baryonic material. Most scientists vote on the idea of dark matter being composed of non-baryonic material, something different than electrons and protons.
The lead participants for this non-baryonic material are Weak Interacting Massive Particles (WIMPS) that have a hundred times heavier mass than protons, but their weak interaction with normal matter makes them difficult to detect.
The second candidate that scientists have shortlisted is called Sterile neutrinos. These neutrinos do not make up any regular matter. They are observed as a river of neutrinos streaming from the sun. but they never interact with any normal matter, they just pass through Earth.
There is another candidate called the antimatter which is composed of matter that’s opposite to visible matter. The composition of antimatter includes antiprotons and positrons. However, when antimatter reacts with visible matter, explosions occur because the two opposite forces cancel each other out. So, scientists have ruled this candidate out, because if that was the case, nothing would have been left standing.
Why do Scientists Believe that Dark Matter Exists and is Real?
It’s a valid question, if we can’t see and observe something, how can we believe it exists? The answer lies in another force not visible to the naked eye but is observed in the entire universe: Gravity. Gravity, the force that is exhibited by all matter and is proportional to their mass.
It has been an ongoing hypothesis since the 1920s that the universe must be composed of more matter than we can see because the gravitational forces that exist in the universe are stronger than visible matter can account for.
Some scientists that have studied the motion of stars, state that the motions of stars tell you about the matter. They don’t care about the type of matter; their movement just indicates that there’s something there.
In the 1970s, astronomers inspecting the spiral galaxies expected the center material to be moving faster than the material on the outer edges. But they were surprised to see that the stars in all locations were moving at the same velocity. This indicated that there is more mass in the galaxies than observable.
In 2018, a team of scientists led by Van Dokkum found a galaxy named Dragonfly 44, which was a galaxy composed almost entirely of dark matter. After that, in 2018, scientists have found galaxies that have no dark matter at all, giving rise to many questions and indicating that all galaxies have different amounts of dark matter.
Where Does It Come from?
Obviously, scientists don’t have the answer to that right now, but there are a few theories that have been accepted and could be the truth. One study published in December 2021 states that dark matter could be something originating from the black hole. It could be found in high concentration in these holes of nothingness.
Or, this dark matter could also be the production of the Big Bang, which also created everything else in the universe. The remnants of stars that being the neutron stars and white dwarfs are also things that could be filled with this dark matter. Similarly, they could be the work of brown dwarfs, the stars that failed to absorb much material to start nuclear fission in their core.
How Do Scientists Study Something Invisible?
Since scientists cannot observe dark matter, there are two different approaches to studying this mysterious substance. The astronomers are looking at the distribution of dark matter by observing the motion of all the objects found in the universe.
Secondly, particle physicists are looking for methods that will reveal the basic material particles that create dark matter.
In order to study the composition of dark matter, an experiment has been mounted atop the International Space Station named as the Alpha Magnetic Spectrometer (AMS) which is set up to detect antimatter in cosmic rays. Since 2011, this experiment has been hit by about 100 billion cosmic rays, which have provided many fascinating insights into the composition of all the particles traveling the universe.
Many experiments to discover this dark matter on Earth have also been set up, but they are yet to produce any positive results.
All in all, this dark matter is completely invisible; therefore, observing it is quite difficult. But scientists have discovered many pieces of evidence that solidify its existence. So, its composition is still in question and under the observation of scientists.