Final answer:
Dark matter is a problem in physics, referring to the existence of non-luminous matter that outweighs visible matter in the universe. Astronomers have ruled out various objects as the source of dark matter and have used the general theory of relativity to study its effects on light. The study of dark matter has implications for particle physics and cosmology, but its nature and composition are still unknown.
Step-by-step explanation:
Dark matter is a problem in physics that refers to the existence of non-luminous matter in the universe that is far more abundant than visible matter. The motion of stars in galaxies and the motion of galaxies in clusters indicate that there is about 10 times as much dark matter as there is visible matter. However, the nature and composition of dark matter are still unknown.
Astronomers have ruled out the possibility that dark matter is made up of objects such as brown dwarfs, Jupiter-like planets, or white dwarfs because these objects do not have enough mass to account for the observed dark matter. They have also used the general theory of relativity to study the effect of mass on the path of light and have found no evidence that dark matter is composed of small objects with masses between one-millionth and one-tenth the mass of the Sun.
Overall, the study of dark matter has implications for particle physics and cosmology, as it may shed light on the existence of unknown particles and the expansion of the universe. However, more research is needed to understand what dark matter is and how it contributes to the overall mass of the universe.