A decrease in the overall volume of gases like hydrogen can prevent nuclear fusion in a nebula.
Step-by-step explanation:
Nuclear fusion: The reaction of combining two or more atomic nuclei to form one or more different atomic nuclei and subatomic particles is known as nuclear fusion. A single heavy nucleus is formed from two lighter nuclei. Helium is made by fusing Hydrogen atoms together.
Nebula: A nebula is a giant cloud dust and gas in space. Nebulae are formed out of the gas and dust that are thrown out by the explosion of a dying star.
A decrease in the overall volume of gases like hydrogen can prevent nuclear fusion in a nebula.