Describe the future of the sun

Describe the future of the sun. Roughly how long will it takefor the Sun to leave th main sequence? What will happen when itleaves the main sequence? Will the Sun go supernova?


The lifespan of sun began roughly 4.6 billion years ago, andwill continue for about another 4.5 – 5.5 billion years, when itwill deplete its supply of hydrogen, helium, and collapse into awhite dwarf.

The Sun, like most stars in the Universe, is on the mainsequence stage of its life, during which nuclear fusion reactionsin its core fuse hydrogen into helium. Every second, 600 milliontons of matter are converted into neutrinos, solar radiation, androughly 4 x 1027 Watts of energy. For the Sun, this process began4.57 billion years ago, and it has been generating energy this wayevery since.

However, this process cannot last forever since there is afinite amount of hydrogen in the core of the Sun. So far, the Sunhas converted an estimated 100 times the mass of the Earth intohelium and solar energy. As more hydrogen is converted into helium,the core continues to shrink, allowing the outer layers of the Sunto move closer to the center and experience a strongergravitational force.

This places more pressure on the core, which is resisted by aresulting increase in the rate at which fusion occurs. Basically,this means that as the Sun continues to expend hydrogen in itscore, the fusion process speeds up and the output of the Sunincreases. At present, this is leading to a 1% increase inluminosity every 100 million years, and a 30% increase over thecourse of the last 4.5 billion years.

In 1.1 billion years from now, the Sun will be 10% brighter thanit is today, and this increase in luminosity will also mean anincrease in heat energy, which Earth’s atmosphere will absorb. Thiswill trigger a moist greenhouse effect here on Earth that issimilar to the runaway warming that turned Venus into the hellishenvironment we see there today.

In 3.5 billion years from now, the Sun will be 40% brighter thanit is right now. This increase will cause the oceans to boil, theice caps to permanently melt, and all water vapor in the atmosphereto be lost to space. Under these conditions, life as we know itwill be unable to survive anywhere on the surface. In short, planetEarth will come to be another hot, dry day in the distantfuture, the Sun will run out of hydrogen fuel and slowly slouchtowards death. This will begin in approximate 5.4 billion years, atwhich point the Sun will exit the main sequence of itslifespan.With its hydrogen exhausted in the core, the inert heliumash that has built up there will become unstable and collapse underits own weight. This will cause the core to heat up and get denser,causing the Sun to grow in size and enter the Red Giant phase ofits evolution. It is calculated that the expanding Sun will growlarge enough to encompass the orbit’s of Mercury, Venus, and maybeeven Earth. Even if the Earth survives, the intense heat from thered sun will scorch our planet and make it completely impossiblefor life to survive.

Once it reaches the Red-Giant-Branch (RGB) phase, the Sun willhaves approximately 120 million years of active life left. But muchwill happen in this amount of time. First, the core (full ofdegenerate helium), will ignite violently in a helium flash – whereapproximately 6% of the core and 40% of the Sun’s mass will beconverted into carbon within a matter of minutes.

The Sun will then shrink to around 10 times its current size and50 times its luminosity, with a temperature a little lower thantoday. For the next 100 million years, it will continue to burnhelium in its core until it is exhausted. By this point, it will bein its Asymptotic-Giant-Branch (AGB) phase, where it will expandagain (much faster this time) and become more luminous.

Over the course of the next 20 million years, the Sun will thenbecome unstable and begin losing mass through a series of thermalpulses. These will occur every 100,000 years or so, becoming largereach time and increasing the Sun’s luminosity to 5,000 times itscurrent brightness and its radius to over 1 AU.

t this point, the Sun’s expansion will either encompass theEarth, or leave it entirely inhospitable to life. Planets in theOuter Solar System are likely to change dramatically, as moreenergy is absorbed from the Sun, causing their water ices tosublimate – perhaps forming dense atmosphere and surface oceans.After 500,000 years or so, only half of the Sun’s current mass willremain and its outer envelope will begin to form a planetarynebula.

The post-AGB evolution will be even faster, as the ejected massbecomes ionized to form a planetary nebula and the exposed corereaches 30,000 K. The final, naked core temperature will be over100,000 K, after which the remnant will cool towards a white dwarf.The planetary nebula will disperse in about 10,000 years, but thewhite dwarf will survive for trillions of years before fading toblack.

When people think of stars dying, what typically comes to mindare massive supernovas and the creation of black holes. However,this will not be the case with our Sun, due to the simple fact thatit is not nearly massive enough. While it might seem huge to us,but the Sun is a relatively low mass star compared to some of theenormous high mass stars out there in the Universe.

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