The death of a star occurs when its _____ stops.

--nuclear fusion
--nebular clouds
--stellar gravity
--rotation

Nuclear fusion

It is the nuclear fusion that creates the heat which radiates energy from the star.

The death of a star occurs when its nuclear fusion stops.

To understand why, we need to know a little bit about the life cycle of a star. Most stars, including our Sun, generate energy through a process called nuclear fusion. In the core of a star, hydrogen atoms are constantly being converted into helium through the release of a tremendous amount of energy. This process, which involves the fusion of atomic nuclei, powers the star and allows it to shine.

However, stars have a finite fuel supply. Eventually, the hydrogen in the core begins to run out, and the star enters the later stages of its life cycle. Depending on the mass of the star, different processes occur during its death.

For stars like our Sun, the core runs out of hydrogen, causing it to shrink and heat up. This increased heat and pressure triggers the fusion of helium atoms, forming heavier elements like carbon and oxygen. This phase is known as the red giant phase. Eventually, the fusion reactions in the core come to a halt, and the outer layers of the star are expelled into space, forming a glowing shell called a planetary nebula. The core that remains behind is known as a white dwarf.

In more massive stars, the process is slightly different. These stars undergo multiple stages of fusion, producing more massive elements, such as iron. When there is an insufficient supply of fuel (less stable elements than iron), the core can no longer sustain fusion reactions. Without the energy generated by nuclear fusion, the core collapses under its own gravity. This event is called a supernova. The outer layers of the star are violently expelled into space, and what remains is either a dense, rapidly rotating object called a neutron star or a black hole.

So, the death of a star happens when its nuclear fusion reactions cease because it has exhausted its nuclear fuel supply, leading to the collapse and subsequent expulsion of its outer layers.

According to the condensation theory, the most important factor for the formation of our planets was _____.

the gravitational pull of the Sun
the interstellar dust attracting heat away from the protosun
the process of nuclear fusion
the nebular cloud condensing