Final answer:
Dark matter in galaxies is of unknown nature and does not emit or absorb light, yet it exerts significant gravitational effects. It is a key factor in the motion of stars within galaxies and the evolution of the universe. Distinguishing it from dark energy, which is linked to the accelerating expansion of the universe, is essential for a full understanding of cosmic phenomena. Correct option is d.
Step-by-step explanation:
The dark matter that all galaxies apparently contain is d. of unknown nature. It is a mysterious substance that does not emit or absorb light, and it exerts gravitational influence on other matter and on the motion of galaxies. While some dark matter might consist of ordinary matter such as faint stars or black holes, most of it is thought to be made of some new type of particle that has not yet been detected on Earth.
The presence of dark matter is inferred from phenomena such as the motions of stars in galaxies being too fast for the visible matter alone to account for, and through the gravitational lensing of light, which is light being bent by the gravitational field of mass, including mass that we cannot see.
Understanding dark matter is one of the principal challenges in modern astronomy, and it plays a crucial role in the evolution of galaxies and the overall structure of the universe. It is important to note that dark matter is distinct from dark energy, which is another mysterious component of the universe that contributes to the acceleration of the universe's expansion.