Final answer:
A star goes through stages such as nebula, protostar, main-sequence star, red giant, white dwarf, neutron star, or black hole. The different paths stars take depend on factors like mass and composition. Nuclear fusion is a key process that powers a star.
Step-by-step explanation:
A star goes through several stages in its life cycle. It begins as a nebula, a cloud of gas and dust. Gravitational forces cause the nebula to contract, forming a protostar. As the protostar continues to contract, its core becomes hot and dense, leading to nuclear fusion, where hydrogen atoms combine to form helium and release energy. This marks the birth of a main-sequence star, where it remains stable for millions or billions of years.
Eventually, a main-sequence star depletes its hydrogen fuel, causing it to expand and become a red giant or a red supergiant. In this phase, the star fuses helium into heavier elements until it exhausts its nuclear fuel. The size and mass determine whether it becomes a white dwarf (for low-mass stars like the Sun), a neutron star (for moderately massive stars), or a black hole (for very massive stars).
The different paths stars take in their life cycle depend on factors such as their initial mass, composition, and rate of nuclear fusion. These factors determine how long a star remains in each stage and the outcome after its nuclear fuel is depleted.