During the late stages of a star's life, what causes the star to expand into a red giant/supergiant, then explode into a nebula or supernova?

Answer 1

The age of the star.

As the star reaches a certain point in its life cycle, it runs out of hydrogen, which is basically the star's fuel for nuclear fusion.

(Nuclear fusion is the process of combining smaller atoms into larger ones. In this case, hydrogen is fused into helium, which causes the sun to release so much energy. The heat doesn't cause the star to expand because of the pressure on the core)

As it runs out of hydrogen, the pressure on the star's core decreases, and it starts increasing in volume. As a result, the star also cools down and starts glowing less brightly, forming a red giant or supergiant.

If the star is massive enough, it collapses on it's self because the core can no longer support the outer layers and explodes into a nebula. If the star is too massive, however, the collapse causes the matter present to contract into an extremely small volume, with an extremely large mass, and an infinitely large density.

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Answer 2

What happens in the late stages of a star's life depends on the mass of the star.

A star's fate is determined by its mass; its critical mass is the difference between its mass and that of eight solar masses.

Less than eight solar masses stars have relatively cool cores. During their main sequence phase, these stars fuse hydrogen into helium; however, once the hydrogen in the core is gone, the core is primarily made of helium because the core isn't hot enough to initiate helium fusion. At this point, fusion ceases and the core begins to collapse under gravity.

The star's outer layer expands into a red giant as a result of the core collapsing and heating to a point where hydrogen fusion can begin in the layer surrounding the core.

Helium fusion can begin in the core at high enough temperatures, and it can even go through a second red giant stage. In the end, the core is mostly composed of carbon and oxygen; further fusion is impossible, and the core collapses into a white dwarf, with the outer layers expanding to form a nebula.

Larger stars easily begin fusion with carbon after their hydrogen is exhausted, producing heavier elements until their core is mostly iron. At that point, no more fusion is possible, and the core collapses.

A supernova explosion occurs when the iron core collapses into a neutron star or even a black hole, releasing a great deal of energy that blasts away the star's outer layers.

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Answer 3

A star expands into a red giant or supergiant as a result of nuclear fusion producing heavier elements in its core during late stages of its life. Eventually, the core contracts, resulting in the fusion of heavier elements, and the outer layers are expelled, forming a nebula. In massive stars, this collapse causes a supernova explosion.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

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