Dark matter is a mysterious form of matter that does not interact with light or the electromagnetic field. Its existence is inferred from gravitational effects that cannot be explained by general relativity unless more matter is present than what we can observe. Here are some key points about dark matter:

1. Gravitational Clues: Dark matter reveals itself through its gravitational pull on other objects. It affects the motion of galaxies, galaxy clusters, and the overall structure of the universe.
2. Composition: In the standard cosmological model (lambda-CDM), the universe’s mass-energy content consists of:
   • Ordinary Matter: This includes the familiar atoms and particles we can see (like stars, planets, and gas). It constitutes only 5% of the total mass.
   • Dark Matter: Comprising 26.8%, dark matter does not interact with ordinary matter or radiation except through gravity.
   • Dark Energy: Making up 68.2%, dark energy is responsible for the universe’s accelerated expansion.
3. Detection Challenges: Dark matter is elusive because it doesn’t emit, absorb, or reflect light. Detecting it in laboratories is difficult. Scientists primarily study its gravitational effects.
4. Possible Candidates:
   • Subatomic Particles: The prevailing hypothesis is that dark matter consists of yet-undiscovered subatomic particles. Examples include weakly interacting massive particles (WIMPs) or axions.
   • Primordial Black Holes: Another possibility is that dark matter is composed of primordial black holes.
5. Cold, Warm, or Hot: Dark matter is classified based on its velocity. The favored scenario is cold dark matter, where structures form gradually from particle accumulation.

Remember, dark matter remains one of the most intriguing mysteries in astrophysics, and ongoing research aims to unravel its secrets ¹²³.

References:

• en.wikipedia.org
• britannica.com
• spaceplace.nasa.gov