What term is used to describe the clouds made of gas and dust that are the building blocks of stars?

Nebulae are vast clouds of gas and dust in space, primarily composed of hydrogen, helium, and other ionized gases. They play a crucial role in the formation of stars and planetary systems. As these clouds collapse under their own gravity, they can create dense regions where nuclear fusion begins, leading to star formation.

The other terms do not describe the building blocks of stars accurately. Galaxies are massive systems that contain billions of stars, gas, dust, and dark matter, thus being much larger structures than nebulae. Comets are small icy bodies that develop tails when they approach the Sun; they do not contribute directly to star formation. Black holes are regions of spacetime where gravity is so strong that nothing, not even light, can escape. While they are fascinating cosmic objects, they are not related to the initial stages of star creation. Hence, nebulae are rightly identified as the fundamental components from which stars are born.