What Is Dark Matter? Here are the Top 5 Unanswered Questions About the Largest structure in the Universe

The visible universe includes all the planets, stars, and galaxies, which are made of protons, neutrons, and electrons bonded together as atoms. But in the 1930s, Swiss astronomer Fritz Zwicky noticed that galaxies in a distant cluster were orbiting each other at a faster pace than they should have been.

Per Britannica, he proposed that an invisible substance, which he called dark matter, must be affecting the gravitational pull of these galaxies. But proving its existence was not easy, so studying distant galaxies helped calculate dark matter. Since then, researchers have confirmed that this mysterious material is found throughout the cosmos and is six times more abundant than baryonic (normal) matter.

What Is Dark Matter?

According to CERN (the European Organization for Nuclear Research), dark matter does not interact with electromagnetic force and that means it does not absorb, reflect or emit light, making it more difficult to spot. Astronomers were able to infer the existence of dark matter from the gravitational effect on visible matter.

CERN said that dark matter accounts for roughly 27% of all the mass energy in the cosmos, outweighing visible matter which only accounts for 5%. Astronomers explain that dark matter could contain "supersymmetric particles," although experiments at the Large Hadron Collider may provide more clues about it.

Why Scientists Have Not Detected Dark Matter Yet?

Live Science reported, some astronomers claim that the dark matter's mantle is a hypothetical particle called a Weakly Interacting Massive Particle (WIMP), which behaves like a neutron but would be about 10 to 100 times heavier than a proton. But if that is the case, why do scientists have not found any yet?

Although dark matter is invisible and barely detectable, there is always some slight chance that a dark matter particle could hit a normal particle, like a proton or electron, while traveling through space. After decades of searching, scientists failed to detect dark matter and astronomers think that dark matter particles could be smaller than WIMPs.

What Is Dark Matter Made Of?

Dark matter's discovery suggests that it makes its presence known through gravitational interactions with baryonic matter. Some theories claim that dark matter particles should be their own antiparticles, which means that two dark matter will annihilate the other one if ever they meet.

Since 2011, the Alpha Magnetic Spectrometer (AMS) experiment on the International Space Station has been searching for signs of this annihilation and has detected hundreds to thousands of events. However, they are not sure if they came from dark matter.

Does Each Galaxy Have Its Own Dark Matter?

Given that it outweighs visible matter, dark matter is considered to be the controlling force that organizes large structures in galaxies and galactic clusters. But the recently-discovered galaxy NGC 1052-DF2 seemed to contain hardly any dark matter, which is strange.

Pieter van Dokkum of Yale University told Space.com that this could mean that dark matter is not a requirement in galaxy formation. But a separate team over the summer posted an analysis of the discovery, which said that van Dokkum's team mismeasured the distance to the galaxy. They found that visible matter was dimmer and that more of its mass was in dark matter than previously suggested.

Does Dark Matter Really Exist?

Proving dark matter's existence is truly difficult and that is why many would question whether it really exists. Some physicists have pushed the idea that perhaps some theories of gravity are incorrect and that the fundamental force works differently than as it was expected.

Physicist Don Lincoln wrote in an explainer for Live Science that dark matter is still an unconfirmed model. But it does not convince most scientists that it does not exist given the latest evidence, which suggests that dark matter is real.