Dark matter is a form of matter that does not emit, absorb, or reflect light, making it invisible and detectable only through its gravitational effects. It is thought to make up about 27% of the universe's total mass and energy content. Despite being unseen, dark matter plays a crucial role in the formation and structure of the universe.
Several lines of evidence suggest the existence of dark matter:
Observations of the rotation speeds of galaxies reveal that the outer regions rotate much faster than expected based on the visible matter alone. This discrepancy suggests the presence of an unseen mass, attributed to dark matter, providing the necessary gravitational pull.
Gravitational lensing occurs when light from a distant object is bent by the gravitational field of a massive foreground object. Observations show that the amount of bending cannot be explained by visible matter alone, indicating additional mass in the form of dark matter.
The cosmic microwave background (CMB) radiation provides a snapshot of the early universe. The observed fluctuations in the CMB match theoretical predictions that include dark matter, suggesting its presence during the universe's infancy.
The distribution and formation of galaxies and galaxy clusters in the universe align with simulations that include dark matter. Without dark matter, the observed large-scale structures would not have formed in the way they have.
Dark matter has several distinct properties:
Several hypothetical particles have been proposed as candidates for dark matter:
WIMPs are a leading candidate for dark matter. These particles would interact only through the weak nuclear force and gravity, making them difficult to detect. Various experiments are currently searching for WIMPs.
Axions are another hypothetical particle that could account for dark matter. They are predicted by certain extensions of the Standard Model of particle physics and are being actively searched for in laboratory experiments.
Sterile neutrinos are a type of neutrino that does not interact through the weak nuclear force, unlike the known types of neutrinos. They could contribute to dark matter and are being investigated as a possible candidate.
Detecting dark matter directly has proven to be challenging due to its weak interactions. Researchers are employing various methods, including direct detection experiments, indirect detection through astrophysical observations, and particle collider experiments, to uncover the nature of dark matter.
Dark matter is a mysterious and invisible form of matter that makes up a significant portion of the universe's mass. While its exact nature remains unknown, various lines of evidence point to its existence and influence on the cosmos. Ongoing research aims to detect and understand dark matter, which could unlock new insights into the fundamental nature of the universe.
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