Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe.
Dark matter is a mysterious substance that makes up a significant portion of the total mass in the universe. It is called "dark" because it does not emit, absorb, or reflect light, making it invisible to our telescopes and other instruments that rely on detecting light.
Here are some key points to understand about dark matter:
1. Existence and Discovery:
- The existence of dark matter was first proposed in the 1930s by Swiss astronomer Fritz Zwicky. He noticed that the visible matter in galaxy clusters did not account for the gravitational forces observed.
- Since then, numerous astronomical observations and calculations have provided strong evidence for the presence of dark matter.
2. Composition and Properties:
- The exact nature of dark matter is still unknown, but scientists have several theories. One of the leading hypotheses suggests that dark matter is made up of particles that interact very weakly with normal matter.
- These particles do not emit or absorb light, hence they are not easily detectable.
- Dark matter is thought to be "cold," meaning it moves at relatively slow speeds compared to the speed of light.
3. Effects of Dark Matter:
- Dark matter's main impact is through gravity. It exerts gravitational forces on normal matter and influences the motion of galaxies and galaxy clusters.
- It helps explain why galaxies rotate faster than they should based on their visible mass alone.
- Dark matter also plays a significant role in the large-scale structure of the universe, influencing the distribution of galaxies and the formation of galaxy clusters.
4. Dark Matter vs. Dark Energy:
- It's important to distinguish dark matter from dark energy, which is a separate concept. Dark energy is believed to be responsible for the accelerated expansion of the universe.
- While dark matter acts as a gravitational "glue," holding galaxies together, dark energy is responsible for the universe's overall expansion.
In conclusion, dark matter is a mysterious form of matter that does not emit, absorb, or reflect light. Although its exact composition is unknown, its presence is inferred from its gravitational effects on visible matter in the universe. Dark matter plays a crucial role in shaping the structure of galaxies and the overall large-scale structure of the universe.