What do astronomers call a cloud of gas and dust in space where new stars form?

Astronomers refer to a cloud of gas and dust in space where new stars form as a stellar nebula. This is a critical concept in understanding the lifecycle of stars. Stellar nebulae serve as the primary birthplace for stars due to their composition, which consists of hydrogen, helium, and other ionized gases.

In these nebulae, regions of higher density can collapse under their own gravity, leading to star formation processes. The heat and pressure from the collapsing material can trigger nuclear fusion, marking the birth of a new star.

Other options refer to different astronomical objects: a galaxy is a massive system that can contain billions of stars, while a planetary nebula is an earlier stage of evolution for some types of stars that have exhausted their nuclear fuel. A red giant is a late-stage phase of stellar evolution when a star has expanded and cooled after exhausting its hydrogen fuel. Each of these terms describes distinct phases and types of astronomical phenomena, whereas a stellar nebula specifically denotes the region where new stars originate.