Could someone explain exactly *why* the sun is going to swell to the size of a red giant in 5 billion years?

Question

I'm not doubting that it is, I'm just curious to what the process behind it is. Thanks in advance everyone!

Answer 1

I learnt about this last term so yeah, good timing lol.

Average stars like our sun are from collapsing clouds of gas, that get smaller due to gravity. As they compress, they get hotter and eventually start to burn. They will continue to burn as yellow stars for about 10 billion  years. After this time, they will have used up most of their fuel and begin to cool down. At this point, they begin to expand and become red giants. They last like this for a few million years but then they loose their outer layer of gas and begin to shrink down to white dwarfs. They gradually fade, leaving behind a dull cloud of gas, sometimes called a brown dwarf.

Answer 2

It think it's cause it runs out of hydroge fuel.

Answer 3

When a star has nearly completed fusing all of its hydrogen into helium it has  slowly exhausted almost all of the hydrogen.  When this has concluded, the core "stops" making nuclear reactions, and the core contracts...  but the outer shell, where hydrogen still remains,  still can be fused into hydrogen, creating a teperature increse at the shell of the core.  These  higher temperatures produce higher reaction rates and luminosity, and the outer layer of the star begins to expand.

As far as the "5 billion year" mark, it varies based upon the initial mass of the main sequece star, but I honestly haven't been explained WHY that makes such a significant difference.

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In response to PortPowerrBabee's answer, I believe most of it is fairly correct, but I always thought a brown dwarf was a "failed star" in the sense that it's formation was massive enough to create minimal fusion, but not great enough to become a main sequence star.  Perhaps I am mistaken, though???

Answer 4

that's part of God's plan

Answer 5

The Sun has about 5 billion years worth of hydrogen with which it can produce energy.

When five billion years are up, fusion in the Sun's core will cease, and gravity will cause the star to collapse. The heat from collapse will exceed the heat from fusion; in fact, it will reach 150,000,000° F (about 80,000,000° C), and the Sun will expand for a few hundred million years, eventually engulfing the planet mercury. As the Sun grows, it will become a red giant. By that time, its surface will be so large that it will emit 500 times as much light as it emits now.

The core will be hot enough then to fuse helium into carbon and oxygen. This fusion will produce more heat, in fact too much for the new helium-rich core to radiate. In a few hours, the core will explode. The outer layers of the Sun will absorb the blast. The core will lose enough heat to stabilize, and it will begin to collapse. Again it will produce too much heat, and again it will explode, causing the Sun to swell drastically. This process will repeat itself, causing the Sun to grow and shrink many times.

Eventually, enough carbon will accumulate in the core to prevent the explosions. The heat from helium fusion will cause the outer layers to expand; 30 million years later, the Sun will be so large that it will have swallowed the earth. The outer layers will keep expanding until they escape the core's gravity and float away into space.

The core will shrink to what is called a white dwarf, a glowing white dot 8,000 miles (13,000 kilometers) in diameter. The white dwarf will still fuse helium, but it will eventually exhaust its reserves and glow solely from the heat caused by the collapse.

But eventually this too will be exhausted. The Sun will glow no longer. It will be an invisible entity known as a black dwarf.  

Answer 6

multiplying fussion

Answer 7

this is what I've watched at National geographic channel. Gas on the sun is actually, overtime weakens and loses it's explosive energy on its core. As it approaches on being a red giant, it loses more gas and the pressure produced by the energy of the sun  will decline and will cause the sun to expand... that's all. the much more energy a star has, the smaller it is.

Another explanation is that the core of the sun contains gaseous and explosive elements and as the sun consume the gas on the core, it will eventually lose some pull of it gravity and will scientifically cause a planet to expand