What Will Happen When Sun Dies?

One of the most profound rules in all the Universe is that nothing lasts forever. Even the stars. Stars are born, they live and they die. The Sun is no different and when it goes, the Earth goes with it. The sun gives energy to life on Earth and without Sun, we would not be here. But like most things in space, even stars have limited lifetime and someday our Sun will die.

An example of a planetary nebula, Abell 39. Five billion years from now, our own sun will look like this, when it goes through the planetary nebula stage of star death. (Credit: WIYN/NOAO/NSF/University of Manchester).

In around 5 billion years, the sun will run out of fuel and it will stop the internal thermonuclear reactions that enable stars to shine. It will expands into a red giant, whose outer layers will consume Mercury, Venus and Earth. It will vaporize the Earth and life on it will end.

So what will happen when the Sun is near to death? To know this answer we have to know how the Sun shines. Stars begin their lives as big assemblage of gas, mostly hydrogen and little amount of helium. Our star is powered by nuclear fusion and it turns hydrogen into helium in a process that converts mass into energy. The hydrogen atoms, each containing a single proton, fuse with other hydrogen atoms to become helium, which has two protons and two neutrons. The fusion releases energy in the form of light and heat. But when all the hydrogen fused into helium. At that time, the Sun won't be able to generate as much energy and collapse under it's own weight. Now this weight won't be able to generate as much pressure to fuse helium with hydrogen. But what helium is left on the core, will start to collapse on it's own and releases energy, but not through fusion. This released energy results in more light and heat, making the Sun more brighter. This energy causes the Sun to grow dramatically. It's outer layers will expand until they consume much of the solar system, as it becomes what astronomers call a 'Red Giant'. Red giants are red because their surface temperatures are lower than stars like the sun.

And what will happen to the planets once the sun enters the red giant phase? A study by astronomers Klaus-Peter Schröder and Robert Connon Smith suggested that the sun will get so large that its outermost surface layers will reach about 108 million miles (about 170 million kilometers) out, engulfing the planets Mercury, Venus and Earth. The whole process of turning into a red giant will take about 5 million years.

The life cycle of the sun takes it from the life-giving star we know today into a swelling red giant and, eventually, a planetary nebula surrounding a tiny white dwarf. (Credit: S. Steinhöfel/ESO)

What happens next? To predict the life cycle of stars, an international team of astronomers used a new stellar data model. Their research is published in the journal Nature Astronomy. The study suggests that the sun is almost exactly the lowest mass star at the end of its life – produces a visible, though faint, planetary nebula. Planetary Nebula describes a massive sphere of luminous gas and dust, material sloughed off an aging star. 

Astronomers already knew that most of all stars end their lives as planetary nebula. They were sure that our sun at the end of its life, though forming a planetary nebula, will remain faint.

Albert Zijlstra of the University of Manchester in England is a co-author of the study. He said in a statement:

When a star dies it ejects a mass of gas and dust – known as its envelope – into space. The envelope can be as much as half the star’s mass. This reveals the star’s core, which by this point in the star’s life is running out of fuel, eventually turning off and before finally dying.

It is only then the hot core makes the ejected envelope shine brightly for around 10,000 years – a brief period in astronomy. This is what makes the planetary nebula visible. Some are so bright that they can be seen from extremely large distances measuring tens of millions of light-years, where the star itself would have been much too faint to see.

What next? The planetary nebula will dissipate and fade. When all the thermonuclear fuel gone, the sun will no longer be able to shine. The high pressures and temperatures in its interior will slacken. The sun will shrink down to become a dying star, known as a white dwarf, only a little larger than Earth.

The slow death of the Sun will kill off the life on Earth. But it may also create habitable worlds, maybe which are the coldest reaches of the solar system.  

Any humans which left around might find shelter on Pluto and other distant dwarf planets out in the Kuiper Belt, a region past Neptune packed with icy space rocks. As the sun expands, these worlds will find necessary conditions for the evolution of life.

These are the “delayed gratification habitable worlds,” says planetary scientist Alan Stern of the Southwest Research Institute.

“Late in the life of the sun — in the red giant phase — the Kuiper Belt will be a metaphorical Miami Beach,” Stern says.

The End Notes

That's all in this article. Will that be the fate of our sun? Humanity may be long gone by then, or perhaps we'll have already colonized another planet. We don't know anything yet. I hope you liked it. Please share your views below.

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  1. The sun will first become a “White-Dwarf star”, a degenerate remnant that is cool but incredibly dense.

    Keep up!


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