Yes. It is as mysterious as it sounds and equally awe-striking. Dark matter, which might be one of the most shocking discoveries of the 20th century, is something that is yet to be “seen”. Our Universe consisting of the Earth, Sun, Moon, and Stars as we know it, is made of ordinary or, Baryonic matter.
Baryonic matter, in a large sense of the term, means the protons and the neutrons that constitute the matter around us. Now, it might come as a surprise but only five percent of our Universe is visible, meaning that the rest of the 95 percent of our Universe is unkown. Scientists speculate Dark Matter to constitute 25 percent of the Universe, and a gravity-repulsive force, Dark Energy, to be the rest 70 percent.
Dark Matter being an undiscovered particle, as of yet, has never been witnessed. The evidence for the presence of this matter is, however, in certain interactions that it makes with the baryonic matter. These interactions produce unexpected results therefore, giving the proof that there does exist a force that is accountable for the inaccuracies. Talking about the reasons that led experts to acknowledge its presence.
Galaxy Clusters: In 1933, Swiss astrophysicist Fritz Zwicky, while studying the Coma cluster, the nearest large galaxy cluster, found some shocking proofs that led to one of the earliest evidence available of the existence of Dark Matter. He used the virial theorem, to obtain the gravitational mass of the cluster and compared it to the mass produced by the luminous matters in the galaxy. Surprisingly, he found that not only the gravitational and the luminous masses differed from each, but also, that the luminous mass was too less to bind the clusters together. This led him to believe in the presence of dunkle Materie (Dark Matter), a term he coined, that described the matter which quietly held the clusters from flying apart.
Star Rotational Speed: Considering the Sun to be the galactic center of our Universe, it is considered that it is the gravitational pull of the Sun itself, which keeps the planets and the stars bound together. Extending the same theory, we would expect that as the stars move further from the Sun, they would travel in slower speeds. However, in the 1960s, during studying the Andromeda Galaxy, it was discovered that no matter how far they are from the galactic center, their velocities remain more-or-less the same. This led to the formulation of the theory that there must an unseen mass whose gravitational effects are felt by the stars altering their velocities. This mass is considered to fill up the halo around the luminous galaxy.
An amazing enigma yet to be discovered has kept the minds of several enthusiasts and scientists curious and longing for more about the Dark Matter.