A vast cloud of dust and gas, mainly hydrogen, in space is known as a:

A nebula (plural: nebulae) is a huge cloud of dust and gas, mostly hydrogen and helium, in interstellar space. The word comes from the Latin for "mist" or "cloud".

Role of nebulae:

Many nebulae are star nurseries. Gravity pulls parts of the cloud together; as they contract and heat up, new stars are born.

Some nebulae are formed from the material thrown out by dying stars.

Main types of nebulae:

Emission nebulae: clouds of glowing gas, heated by nearby young, hot stars. They often glow red because of hydrogen. Example: the Orion Nebula and the Lagoon Nebula.

Reflection nebulae: clouds of dust that reflect the light of nearby stars; they usually look blue. Example: the nebula around the Pleiades.

Dark nebulae: dense clouds of dust that block light from objects behind them. Example: the Horsehead Nebula.

Planetary nebulae: shells of gas thrown off by a dying Sun-like star near the end of its life. The name is misleading; they have nothing to do with planets, but looked like planets in early telescopes. Example: the Ring Nebula and the Helix Nebula.

Supernova remnants: the expanding debris of a massive star that exploded as a supernova. Example: the Crab Nebula, from a supernova recorded by Chinese astronomers in 1054 CE.

The "Pillars of Creation" in the Eagle Nebula are a famous star-forming region photographed by the Hubble and James Webb telescopes.

Nebular theory of the solar system:

The Sun and the planets are believed to have formed from the collapse of a nebula about 4.6 billion years ago. This is called the nebular hypothesis.

Why not the other options?

• ✗A quasar is an extremely bright core of a distant galaxy, powered by a supermassive black hole.
• ✗An asteroid is a small rocky body orbiting the Sun.
• ✗A constellation is a recognised pattern of stars in the sky.