Dark matter is one of the most elusive and mysterious components of the universe. It is invisible, yet its existence is inferred from the gravitational effects it has on visible matter, such as stars and galaxies. Despite being a significant part of the cosmos, dark matter has yet to be directly detected, which makes it an intriguing subject for astrophysicists. It is believed to make up about 27% of the universe's total mass and energy, far outpacing the visible matter that forms stars, planets, and galaxies.
The name "dark matter" was coined to reflect the fact that it does not emit, absorb, or reflect any form of electromagnetic radiation, making it invisible to current instruments. This absence of interaction with light or other electromagnetic forces is why it cannot be seen directly. However, dark matter's presence is undeniable when looking at the way galaxies move. Without dark matter, galaxies would not have the gravitational pull necessary to prevent their stars from flying apart as they spin. This leads scientists to believe that dark matter provides the gravitational glue that holds galaxies, and indeed the entire universe, together.
One of the key pieces of evidence for dark matter comes from the study of galaxy clusters. When observing these massive cosmic structures, scientists noticed that the visible matter within them didn't account for the full gravitational force required to keep the clusters intact. This discrepancy suggested the presence of an unseen substance, later named dark matter, that was exerting additional gravitational pull. Another significant clue comes from the phenomenon of gravitational lensing, where light from distant objects bends around large masses. Dark matter's influence on this bending further supports the idea that it is present in quantities far larger than what we can observe.
