Dark MatterDark matter is a mysterious substance that makes up about 27% of the universe. It does not emit, absorb, or reflect light, which is why it is invisible and extremely difficult to detect. Despite its elusiveness, scientists have strong evidence for the existence of dark matter based on its gravitational effects on galaxies and the large-scale structure of the universe.Properties of Dark Matter: 1. **Invisibility:** Dark matter does not interact with electromagnetic forces, so it cannot be seen with telescopes or detected using any form of electromagnetic radiation. 2. **Gravitational effects:** Dark matter interacts with normal matter and other dark matter particles through gravity, which is how its presence is inferred. 3. **Distribution:** Dark matter is thought to be distributed in a "halo" around galaxies, providing the gravitational scaffolding that holds galaxies together.Evidence for Dark Matter: 1. **Galactic rotation curves:** Observations of the rotational speeds of stars and gas in galaxies show that they do not behave as expected based on the visible mass alone. Dark matter is thought to provide the extra gravitational force that keeps the galaxies from flying apart. 2. **Gravitational lensing:** Dark matter can bend and distort light from distant objects through gravitational lensing, providing another indirect way to detect its presence. 3. **Cosmic microwave background:** Measurements of the cosmic microwave background radiation, the afterglow of the Big Bang, also support the existence of dark matter.Study Guide: - What is dark matter? - What are the properties of dark matter? - What evidence do scientists have for the existence of dark matter? - How does dark matter interact with normal matter? - What role does dark matter play in the structure of the universe?Use this study guide to learn more about dark matter and its role in shaping the universe!.