ASP: Biography of a Star: Our Sun's Birth, Life, and Death Biography of a Star: Our Sun's Birth, Life, and Death Just Right Depending on the size of the original lump of gas and dust, the process of stellar birth can give rise to different sorts of stars. A small lump never develops high enough pressures and temperatures to start nuclear fusion. It is doomed to remain a dark, dismal stellar wanna-be -- a so-called brown dwarf. A larger lump becomes a large star, so hot and bright that it burns itself out in a few tens of millions of years. A lump in the middle, not too small and not too large, becomes a middling star such as the Sun. Which is good: If the Sun had been much smaller, Earth would have been a dark, dead world; much larger, and Earth would have been broiled. The middle-aged suburbanite. The Sun is a two-car-garage kind of star. Its stability and temperance make it an ideal provider for tender planets. Photo courtesy of Mount Wilson Observatory. In its early years, the Sun went through a tempestuous youth, whipping up strong winds that cleared the solar system of whatever gas had not been incorporated into a planet.

But then the Sun settled down. From studying rocks, fossils, and Antarctic ice, scientists think the Sun has been brightening over time, but only slightly. And how much longer will it continue to shine? For an idea of the Sun's life expectancy, astronomers look to clusters of stars, such as one named Messier 67, which is about the same age as our Sun. By simulating the life cycles of these stars on a computer, astronomers have ascertained how long stars live. They predict that the Sun will be able to fuse hydrogen into helium in its core at about the same rate for another 5 billion years. (What a relief!) If the Sun were a car, the gas tank would now be half full. What will happen when the Sun does run out of gas? (Hydrogen gas, that is.) Fortunately, the Sun will still have reserves of hydrogen in the layers that surround the core. The core will heat up this shell of hydrogen. When the shell gets hot enough to fuse hydrogen to helium, the release of energy will carry on there. It is as if the driver of the car poured an extra few gallons into the fuel tank. But this trick has a price.

The source of energy will no longer be the dense, massive core, but rather a shell closer to the surface -- and that will make a big (so to speak) difference in the structure of the Sun. The Sun will puff up until its radius is 30 times greater. It will become a red giant, similar to the star Arcturus, though much smaller than a supergiant such as Betelgeuse (see photo on p. 3). A red giant is red because its exterior cooled from 9,000 to 3,000 degrees Fahrenheit as it expanded; for a star, red means cool. This red-giant stage will last for about 2 billion years. That Time Bomb in the Middle The last fling. Its normal life over, Betelgeuse is now a red supergiant — red, because its surface is a comparatively cool red-hot, and supergiant, because it is hundreds of times larger than the Sun and ten times more massive. Its waistline, however, is not a sign of might, but of impending death. Photo courtesy of Andrea Dupree, Ronald Gilliland, NASA, and the European Space Agency.

The striking but now-outdated video Universe, produced by NASA in the 1970s, shows the red-giant Sun engulfing the Earth. Though certainly dramatic, this is now thought to be incorrect. Astronomers have had to scale down their estimates of the size of red giants based on data from the satellite Hipparcos and from the new optical and infrared interferometers -- networks of telescopes which can take images of large, nearby stars. Now we think the Sun will not engulf us when it becomes a red giant. But that is small comfort. In its retirement from normal core fusion, our previously nurturing star will care little for its planetary children. It will be pumping out a thousand times more energy, making Earth a good approximation to hell. To add insult to injury, the solar wind -- a stream of particles which now gives us fun things such as the aurora borealis -- will become a cyclone that will make radio communication impossible and perhaps evaporate the atmosphere altogether. Looking on the bright side, the red-giant Sun may be warm enough to melt the water-rich but now-frozen moons of Jupiter and Saturn. Humanity, if it is still around, might relocate there.

Meanwhile, what happens to all that helium being produced in the shell? It gently rains onto the dead, but still toasty, core of the Sun, making the core more massive and more compressed. This raises the temperature of the core until suddenly -- and I really do mean suddenly, as in seconds -- the helium in the core fires up and begins to fuse itself into carbon. Using the fuel-tank analogy, this is as if the exhaust itself starts to burn. The end is drawing near. Now the Sun has to rearrange its internal structure all over again, as its source of energy is once again the central core. The Sun will contract back to a bit larger than its original radius and will give off 10 times as much energy as what we are used to now. This phase only lasts another 500 million years, as there are a lot fewer helium nuclei (it took four hydrogen nuclei to make one helium nucleus, and three heliums to make one carbon) and the energy production is much less efficient. As the Sun exhausts the helium in the core, it desperately staves off the inevitable by resorting again to those reserves in its outer layers. Again the Sun expands.

This time, it grows so large that its outer edge is only weakly gravitationally bound to the core. The Sun barely holds itself together anymore. This eleventh-hour attempt at life-support is pitifully ineffective; the final red-giant stage can be maintained for only 100 million years. At this point, things will really start falling apart. The Sun's outer layers, freed from the gravitational clutches of the core, will waft away. Over the course of about 10,000 years, these layers will spread out into space as an enormous sphere of gas lit up by the now-naked hot core. These layers constitute a "planetary nebula," so called because in a small telescope the gas cloud looks a bit like the disc of a planet (see photo on p. 3). The hot core is now a "white dwarf," a stellar cinder. As a white dwarf, the ex-Sun will glow white-hot for a near-eternity. The cremation. After stars like the Sun fuse their last atom, they scatter their ashes into space as a so-called planetary nebula, such as Abell 39.

At the center of the nebula is what’s left of the star: a slowly decaying “white dwarf.” Photo courtesy of George Jacoby of the National Optical Astronomy Observatories. Alas, there will be no dramatic explosions to entertain our distant descendants: The Sun would have had to start with at least eight times more mass to die the spectacular death of a supernova. The Sun, modest in life, is subdued in death. After the planetary nebula fades, there is no nuclear fusion at all (no extra fuel, no fuel tank, not even the trunk is left), just a lump of hot carbon and some happy memories. The Sun will be well and truly dead. The sphere of gas drifts off and eventually is gathered up in a new cloud, and become part of the next generation of star formation. Perhaps one day, the ashes of the Sun will throw their lot in with another star to be born, live, die, and, perhaps, give sustenance to other warm little planets. BETH HUFNAGEL is a postdoctoral researcher at Michigan State University in East Lansing. As an auditor, she used to ferret out the secrets of corporate finance -- talents now applied to the evolution of Sun-like stars.

Her email address is hufnagel@stsci.edu . George Musser contributed to this article. What is the Life Cycle Of The Sun? - Universe Today Universe Today What is the Life Cycle Of The Sun? Article Updated: 24 Sep , 2016 by Matt Williams The Sun has always been the center of our cosmological systems. But with the advent of modern astronomy, humans have become aware of the fact that the Sun is merely one of countless stars in our Universe. In essence, it is a perfectly normal example of a G-type main-sequence star (G2V, aka. “yellow dwarf”). And like all stars, it has a lifespan, characterized by a formation, main sequence, and eventual death. This lifespan began roughly 4.6 billion years ago, and will continue for about another 4.5 – 5.5 billion years, when it will deplete its supply of hydrogen, helium, and collapse into a white dwarf. But this is just the abridged version of the Sun’s lifespan. As always, God (or the Devil, depending on who you ask) is in the details! To break it down, the Sun is about half way through the most stable part of its life.

Over the course of the past four billion years, during which time planet Earth and the entire Solar System was born, it has remained relatively unchanged. This will stay the case for another four billion years, at which point, it will have exhausted its supply of hydrogen fuel. When that happens, some pretty drastic things will take place! The Birth of the Sun: According to Nebular Theory , the Sun and all the planets of our Solar System began as a giant cloud of molecular gas and dust. Then, about 4.57 billion years ago, something happened that caused the cloud to collapse. This could have been the result of a passing star, or shock waves from a supernova, but the end result was a gravitational collapse at the center of the cloud. Artist’s concept of a star surrounded by a molecular cloud to form a swirling disk called a “protoplanetary disk.” Credit: NASA/JPL-Caltech From this collapse, pockets of dust and gas began to collect into denser regions. As the denser regions pulled in more and more matter, conservation of momentum caused it to begin rotating, while increasing pressure caused it to heat up.

Most of the material ended up in a ball at the center while the rest of the matter flattened out into disk that circled around it. The ball at the center would eventually form the Sun, while the disk of material would form the planets. The Sun spent about 100,000 years as a collapsing protostar before temperature and pressures in the interior ignited fusion at its core. The Sun started as a T Tauri star – a wildly active star that blasted out an intense solar wind. And just a few million years later, it settled down into its current form. The life cycle of the Sun had begun. The Main Sequence: The Sun, like most stars in the Universe, is on the main sequence stage of its life, during which nuclear fusion reactions in its core fuse hydrogen into helium. Every second, 600 million tons of matter are converted into neutrinos, solar radiation, and roughly 4 x 1027 Watts of energy. For the Sun, this process began 4.57 billion years ago, and it has been generating energy this way every since. However, this process cannot last forever since there is a finite amount of hydrogen in the core of the Sun.

So far, the Sun has converted an estimated 100 times the mass of the Earth into helium and solar energy. As more hydrogen is converted into helium, the core continues to shrink, allowing the outer layers of the Sun to move closer to the center and experience a stronger gravitational force. The Sun captured by NASA’s Solar Dynamics Observatory Spacecraft. This places more pressure on the core, which is resisted by a resulting increase in the rate at which fusion occurs. Basically, this means that as the Sun continues to expend hydrogen in its core, the fusion process speeds up and the output of the Sun increases. At present, this is leading to a 1% increase in luminosity every 100 million years, and a 30% increase over the course of the last 4.5 billion years. In 1.1 billion years from now, the Sun will be 10% brighter than it is today, and this increase in luminosity will also mean an increase in heat energy, which Earth’s atmosphere will absorb. This will trigger a moist greenhouse effect here on Earth that is similar to the runaway warming that turned Venus into the hellish environment we see there today.

In 3.5 billion years from now, the Sun will be 40% brighter than it is right now. This increase will cause the oceans to boil, the ice caps to permanently melt, and all water vapor in the atmosphere to be lost to space. Under these conditions, life as we know it will be unable to survive anywhere on the surface. In short, planet Earth will come to be another hot, dry Venus. Core Hydrogen Exhaustion: All things must end. That is true for us, that is true for the Earth, and that is true for the Sun. It’s not going to happen anytime soon, but one day in the distant future, the Sun will run out of hydrogen fuel and slowly slouch towards death. This will begin in approximate 5.4 billion years, at which point the Sun will exit the main sequence of its lifespan. With its hydrogen exhausted in the core, the inert helium ash that has built up there will become unstable and collapse under its 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 of its evolution.

It is calculated that the expanding Sun will grow large enough to encompass the orbit’s of Mercury , Venus , and maybe even Earth . Even if the Earth survives, the intense heat from the red sun will scorch our planet and make it completely impossible for life to survive. Final Phase and Death: Once it reaches the Red-Giant-Branch (RGB) phase, the Sun will haves approximately 120 million years of active life left. But much will happen in this amount of time. First, the core (full of degenerate helium), will ignite violently in a helium flash – where approximately 6% of the core and 40% of the Sun’s mass will be converted into carbon within a matter of minutes. The Sun will then shrink to around 10 times its current size and 50 times its luminosity, with a temperature a little lower than today. For the next 100 million years, it will continue to burn helium in its core until it is exhausted. By this point, it will be in its Asymptotic-Giant-Branch (AGB) phase, where it will expand again (much faster this time) and become more luminous.

Over the course of the next 20 million years, the Sun will then become unstable and begin losing mass through a series of thermal pulses. These will occur every 100,000 years or so, becoming larger each time and increasing the Sun’s luminosity to 5,000 times its current brightness and its radius to over 1 AU. At this point, the Sun’s expansion will either encompass the Earth, or leave it entirely inhospitable to life. Planets in the Outer Solar System are likely to change dramatically, as more energy is absorbed from the Sun, causing their water ices to sublimate – perhaps forming dense atmosphere and surface oceans. After 500,000 years or so, only half of the Sun’s current mass will remain and its outer envelope will begin to form a planetary nebula. The post-AGB evolution will be even faster, as the ejected mass becomes ionized to form a planetary nebula and the exposed core reaches 30,000 K. The final, naked core temperature will be over 100,000 K, after which the remnant will cool towards a white dwarf .

The planetary nebula will disperse in about 10,000 years, but the white dwarf will survive for trillions of years before fading to black. Ultimate Fate of our Sun: When people think of stars dying, what typically comes to mind are massive supernovas and the creation of black holes. However, this will not be the case with our Sun, due to the simple fact that it 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 the enormous high mass stars out there in the Universe. As such, when our Sun runs out of hydrogen fuel, it will expand to become a red giant, puff off its outer layers, and then settle down as a compact white dwarf star, then slowly cooling down for trillions of years. If, however, the Sun had about 10 times its current mass, the final phase of its lifespan would be significantly more (ahem) explosive. When this super-massive Sun ran out of hydrogen fuel in its core, it would switch over to converting atoms of helium, and then atoms of carbon (just like our own).

This process would continue, with the Sun consuming heavier and heavier fuel in concentric layers. Each layer would take less time than the last, all the way up to nickel – which could take just a day to burn through. Then, iron would starts to build up in the core of the star. Since iron doesn’t give off any energy when it undergoes nuclear fusion, the star would have no more outward pressure in its core to prevent it from collapsing inward. When about 1.38 times the mass of the Sun is iron collected at the core, it would catastrophically implode, releasing an enormous amount of energy. Within eight minutes, the amount of time it takes for light to travel from the Sun to Earth , an incomprehensible amount of energy would sweep past the Earth and destroy everything in the Solar System. The energy released from this might be enough to briefly outshine the galaxy, and a new nebula (like the Crab Nebula ) would be visible from nearby star systems, expanding outward for thousands of years. All that would remain of the Sun would be a rapidly spinning neutron star, or maybe even a stellar black hole. But of course, this is not to be our Sun’s fate.

Given its mass, it will eventually collapse into a white star until it burns itself out. And of course, this won’t be happening for another 6 billion years or so. By that point, humanity will either be long dead or have moved on. In the meantime, we have plenty of days of sunshine to look forward to! WMAP- Life and Death of Stars The Life and Death of Stars Where are Stars Born? Astronomers believe that molecular clouds, dense clouds of gas located primarily in the spiral arms of galaxies are the birthplace of stars. Dense regions in the clouds collapse and form "protostars". Initially, the gravitational energy of the collapsing star is the source of its energy. Once the star contracts enough that its central core can burn hydrogen to helium, it becomes a "main sequence" star. Image of "Star Birth" Clouds in M16: PRC95-44b Hubble Wide Field Image Text link to the HST press release describing this image Main Sequence Stars Main sequence stars are stars, like our Sun, that fuse hydrogen atoms together to make helium atoms in their cores.

For a given chemical composition and stellar age, a stars' luminosity, the total energy radiated by the star per unit time, depends only on its mass. Stars that are ten times more massive than the Sun are over a thousand times more luminous than the Sun. However, we should not be too embarrassed by the Sun's low luminosity: it is ten times brighter than a star half its mass. The more massive a main sequence star, the brighter and bluer it is. For example, Sirius, the dog star, located to the lower left of the constellation Orion, is more massive than the Sun, and is noticeably bluer. On the other hand, Proxima Centauri, our nearest neighbor, is less massive than the Sun, and is thus redder and less luminous. Since stars have a limited supply of hydrogen in their cores, they have a limited lifetime as main sequence stars. This lifetime is proportional to f M / L, where f is the fraction of the total mass of the star, M, available for nuclear burning in the core and L is the average luminosity of the star during its main sequence lifetime. Because of the strong dependence of luminosity on mass, stellar lifetimes depend sensitively on mass.

Thus, it is fortunate that our Sun is not more massive than it is since high mass stars rapidly exhaust their core hydrogen supply. Once a star exhausts its core hydrogen supply, the star becomes redder, larger, and more luminous: it becomes a red giant star. This relationship between mass and lifetime enables astronomers to put a lower limit on the age of the universe . Death of an "Ordinary" Star After a low mass star like the Sun exhausts the supply of hydrogen in its core, there is no longer any source of heat to support the core against gravity. Hydrogen burning continues in a shell around the core and the star evolves into a red giant. When the Sun becomes a red giant, its atmosphere will envelope the Earth and our planet will be consumed in a fiery death. Meanwhile, the core of the star collapses under gravity's pull until it reaches a high enough density to start burning helium to carbon. The helium burning phase will last about 100 million years, until the helium is exhausted in the core and the star becomes a red supergiant. At this stage, the Sun will have an outer envelope extending out towards Jupiter.

During this brief phase of its existence, which lasts only a few tens of thousands of years, the Sun will lose mass in a powerful wind. Eventually, the Sun will lose all of the mass in its envelope and leave behind a hot core of carbon embedded in a nebula of expelled gas. Radiation from this hot core will ionize the nebula, producing a striking "planetary nebula", much like the nebulae seen around the remnants of other stars. The carbon core will eventually cool and become a white dwarf, the dense dim remnant of a once bright star. Image of a Planetary Nebula: NGC 6543 Hubble Wide Field Image Text Link to the HST press release describing this image Death of a Massive Star Massive stars burn brighter and perish more dramatically than most. When a star ten times more massive than Sun exhaust the helium in the core, the nuclear burning cycle continues. The carbon core contracts further and reaches high enough temperature to burn carbon to oxygen, neon, silicon, sulfur and finally to iron. Iron is the most stable form of nuclear matter and there is no energy to be gained by burning it to any heavier element.

Without any source of heat to balance the gravity, the iron core collapses until it reaches nuclear densities. This high density core resists further collapse causing the infalling matter to "bounce" off the core. This sudden core bounce (which includes the release of energetic neutrinos from the core) produces a supernova explosion. For one brilliant month, a single star burns brighter than a whole galaxy of a billion stars. Supernova explosions inject carbon, oxygen, silicon and other heavy elements up to iron into interstellar space. They are also the site where most of the elements heavier than iron are produced. This heavy element enriched gas will be incorporated into future generations of stars and planets. Without supernova, the fiery death of massive stars, there would be no carbon, oxygen or other elements that make life possible. Image of a Supernova Remnant: Supernova 1987A Hubble Wide Field Image Text Link to the HST press release describing this image The fate of the hot neutron core depends upon the mass of the progenitor star. If the progenitor mass is around ten times the mass of the Sun, the neutron star core will cool to form a neutron star.

Neutron stars are potentially detectable as "pulsars", powerful beacons of radio emission. If the progenitor mass is larger, then the resultant core is so heavy that not even nuclear forces can resist the pull of gravity and the core collapses to form a black hole. Learn more about the late stages of stellar evolution from the Chandra mission's web pages : The Life of a Star The Life of a Star This page (as the title says) is all about the life of a star. It will show all the stages that a small star, and a massive star have to go through during their lifetime. We have all sorts of pics and links for you to look at and explore when you are just about ready to recieve that vast information that we have kindly put together. But we have one FAQ! What is a Star? Stars are hot bodies of glowing gas that start their life in Nebulae. They vary in size, mass and temperature, diameters ranging from 450x smaller to over 1000x larger than that of the Sun.

Masses range from a twentieth to over 50 solar masses and surface temperature can range from 3,000 degrees Celcius to over 50,000 degrees Celcius. The colour of a star is determined by its temperature, the hottest stars are blue and the coolest stars are red. The Sun has a surface temperature of 5,500 degrees Celcius, its colour appears yellow. The energy produced by the star is by nuclear fusion in the stars core. The brightness is measured in magnitude, the brighter the star the lower the magnitude goes down. There are two ways to measuring the brightness of a star, apparent magnitude is the brghtness seen from Earth, and absolute magnitude which is the brightness of a star seen from a standard distance of 10 parsecs (32.6 light years). Stars can be plotted on a graph using the Hertzsprung Russell Diagram (see picture below). Hertzsrung Russell Diagram It shows that the temerature coincides with the luminosity, the hotter the star the higher the luminosity the star has. You can also tell the size of each star from the graph as the higher the radius the higher the temperature and luminosity.

Small Stars- The Life of a Star of about one Solar Mass. Small stars have a mass upto one and a half times that of the Sun. Stage 1- Stars are born in a region of high density Nebula, and condenses into a huge globule of gas and dust and contracts under its own gravity. This image shows the Orion Nebula or M42 . Stage 2 - A region of condensing matter will begin to heat up and start to glow forming Protostars. If a protostar contains enough matter the central temperature reaches 15 million degrees centigrade. This image is the outflow (coloured red)and protostar. Stage 3 - At this temperature, nuclear reactions in which hydrogen fuses to form helium can start. Stage 4 - The star begins to release energy, stopping it from contracting even more and causes it to shine. It is now a Main Sequence Star. The nearest main sequence star to Earth, the Sun Stage 5 - A star of one solar mass remains in main sequence for about 10 billion years, until all of the hydrogen has fused to form helium.

Stage 6 - The helium core now starts to contract further and reactions begin to occur in a shell around the core. Stage 7 - The core is hot enough for the helium to fuse to form carbon. The outer layers begin to expand, cool and shine less brightly. The expanding star is now called a Red Giant. The star expands to a Red Giant, below Stage 8 - The helium core runs out, and the outer layers drift of away from the core as a gaseous shell, this gas that surrounds the core is called a Planetary Nebula. A Planetary Nebula (Below, NGC 6543 ). Stage 9 - The remaining core (thats 80% of the original star) is now in its final stages. The core becomes a White Dwarf the star eventually cools and dims. When it stops shining, the now dead star is called a Black Dwarf. Massive Stars - The Life of a Star of about 10 Solar Masses Massive stars have a mass 3x times that of the Sun.

Some are 50x that of the Sun Stage 1 - Massive stars evolve in a simlar way to a small stars until it reaces its main sequence stage (see small stars, stages 1-4). The stars shine steadily until the hydrogen has fused to form helium ( it takes billions of years in a small star, but only millions in a massive star). Stage 2 - The massive star then becomes a Red Supergiant and starts of with a helium core surrounded by a shell of cooling, expanding gas. The massive star is much bigger in its expanding stage. (A Red Supergiant,below). Stage 3 - In the next million years a series of nuclear reactions occur forming different elements in shells around the iron core. Stage 4 - The core collapses in less than a second, causing an explosion called a Supernova, in which a shock wave blows of the outer layers of the star. (The actual supernova shines brighter than the entire galaxy for a short time). The set of images below shows the star going into a stage called Supernova and contracting to become a neutron star The images above were from the HEASARC Homepage Stage 5 - Sometimes the core survives the explosion.

If the surviving core is between 1.5 - 3 solar masses it contracts to become a a tiny, very dense Neutron Star. If the core is much greater than 3 solar masses, the core contracts to become a Black Hole. Stages of the Sun's Life Cycle - Video & Lesson Transcript | Study.com Stages of the Sun's Life Cycle Watch short & fun videos Start Your Free Trial Today An error occurred trying to load this video. Try refreshing the page, or contact customer support. You must create an account to continue watching Register for a free trial Are you a student or a teacher? I am a student Start Your Free Trial To Continue Watching As a member, you'll also get unlimited access to over lessons in math, English, science, history, and more. Plus, get practice tests, quizzes, and personalized coaching to help you succeed. Coming up next: Supernova and Supergiant Star Life Cycle You're on a roll. Keep up the good work!

Your next lesson will play in 10 seconds 0:05 Birth of the Sun 1:49 Main-Sequence Star 3:23 Death of the Sun 3:52 Lesson Summary Add to Add to Add to Want to watch this again later? Log in or sign up to add this lesson to a Custom Course. Custom Courses are courses that you create from Study.com lessons. Use them just like other courses to track progress, access quizzes and exams, and share content. Teachers Organize and share selected lessons with your class. Make planning easier by creating your own custom course. Students Create a new course from any lesson page or your dashboard. From any lesson page: Click "Add to" located below the video player and follow the prompts to name your course and save your lesson. From your dashboard: Click on the "Custom Courses" tab, then click "Create course". Next, go to any lesson page and begin adding lessons. Edit your Custom Course directly from your dashboard. Personalize: Name your Custom Course and add an optional description or learning objective. Organize: Create chapters to group lesson within your course. Remove and reorder chapters and lessons at any time. Share your Custom Course or assign lessons and chapters.

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The Sun is so important to life on Earth that it has been worshipped and studied for centuries. In ancient times, people believed the Sun was a burning ball of fire created by the gods. Later, people thought it was a solid object or a liquid ball. Now we believe it is a huge ball of hydrogen undergoing nuclear fusion. Look at our universe. The Sun is huge! Over one million Earths could fit inside the Sun. Have you ever worried that our Sun will die? Did you ever wonder how it was born? Our Sun is the closest star to Earth. To understand how the Sun was born, you need to know how a star is born. A star's life cycle is much like our human life cycle. A star is born, lives for a while, and dies. Our Sun's life began about 4.6 billion years ago like any other star in the universe, in a nebula, a giant interstellar cloud of dust and gas so far away we would need 100,000 years to reach it. This cloud was perfectly content and quiet. Then something happened that caused the cloud to collapse and start spinning until it formed a flat disc.

Most of the material that was originally in the cloud ended up in one ball in the center of the disc. For 100,000 years the ball was squeezed tighter, and the temperature increased until it was hot enough to perform nuclear fusion in its core. Voila, a star is born. The rest of the material that didn't settle in to the center of the disc formed the planets, moons, asteroids and other parts of the solar system. Stellar Evolution — University of Leicester The evolution of a Sun-like star When a Sun-like star settles on the main sequence, it is turning hydrogen into helium; about three quarters of its material is hydrogen, the remainder being helium and very small quantities of other, heavier elements. The star will remain in this phase for around 10 billion years (our own Sun is roughly half way through this period). As more and more of the heavier helium is produced in the core of the star, the central regions begin to contract, and the temperature in the centre of the star increases. The effect of this is to cause the star to increase in brightness or luminosity.

Eventually the centre of the star is made entirely of helium, and the nuclear reactions which give the star energy by converting four atoms of hydrogen into one of helium occur in a shell surrounding the helium core. As more helium is made, the central helium region gets larger and the shell moves closer and closer to the surface of the star. The energy given off by this shell pushes the very outer layers of the star outward, and these layers cool. The star expands and becomes a Red Giant. At this stage the star can be hundreds of times larger than it was when it first entered the main sequence. During this process, the helium core has beome more and more dense as material is added to it, and so the temperature has increased. Eventually the temperature becomes so great that the star can begin new reactions, turning helium into carbon. The shell of hydrogen which pushed the outer atmosphere of the star away gradually becomes weaker and the star shrinks slightly - it is no longer a red giant. The star continues to obtain its energy by turning helium into carbon, and in the same way that hydrogen burning produced a helium core and a hydrogen-burning shell, this helium burning produces a carbon core and a helium burning shell; once again the star becomes a red giant.

However, this time the situation is different, because the temperature in the very dense central carbon region never becomes great enough to begin a new phase of nuclear reactions. Around one million years after the star becomes a red giant for the second time, nuclear reactions finally end in the core. Only the shells of hydrogen and helium burning closer to the surface now produce energy for the star. Over a period of thousands of years, the star's central region shrinks and heats up, blowing the outer regions off. Astronomers can see the effects of this process; many objects are seen which are made up of a very small, dense central star surrounded by a shell of gas which appears to be expanding. These objects are called planetary nebulae, because the round shape of the gas cloud can look like a planet as seen through a telescope. The image shown here (courtesy of the Mount Palomar Observatory) shows the "Ring Nebula" found in the constellation of Lyra. The central star responsible for the surrounding ring of gas is clearly visible. This is one of the most spectacular planetary nebulae to be seen in the night sky.

When the outer layers of the star's atmosphere are blown away to form the nebula, the object seen at the centre of the gas cloud is the core of the original star. It is still very hot - perhaps as high as 100,000K. But the material gradually cools and contracts, to become a tiny dim object called a white dwarf, which will, over a period of billions of years, cool to become a black dwarf. This, then, is the fate of our Sun and the stars like it - ending its life as a dense body not much larger than the Earth. But before the sun reaches this stage, the Earth and all the inner planets will have been consumed in the fiercely hot atmosphere of the red giant which our star will first become. The evolution of stars with several times the Sun's mass In general, the more massive the star, the more rapid its sequence of evolutionary stages become. However, that is not the only difference between "light" and "heavy" stars; more massive stars go through stages which their less weighty counterparts do not.

The more massive star will enter the main sequence with a higher temperature (typically over 10,000K for a star of over 4 times the mass of our Sun) and greater luminosity than the Sun like star. The central core regions of these stars are also far hotter than in the previous class, and this causes the star to "age" more rapidly since, although the larger star has more fuel, it uses this fuel much quicker. For example, a star with five times as much mass as the Sun will evolve into a red giant one hundred times quicker ! The star completes its hydrogen and helium burning stages in the same way as the Sun-sized star described above. However, because the star is hotter, it can burn carbon when the helium supply becomes scarce. At this point, helium is burned around a carbon core, sending the star into a red giant stage. Carbon is then burned, then neon, and each successive element is burned to exhaustion. At each stage when the star switches from burning one element to another, it again goes through the red giant phase, before returning to the main sequence for another period.

However, when the star gets so far into this process that it develops a core of iron, no further reactions are possible because iron cannot be converted into the next element without huge amounts of energy being consumed. The death of stars more massive than the sun So far we have looked at the entire evolutionary path of stars like the Sun, and we've looked at the way stars with several times the Sun's mass expend their nuclear fuel. What next? In fact, the last section applies not only to stars a few times more massive than the Sun, but to the most massive stars in the galaxy. The next major difference in behaviour comes when we consider how stars more massive than the Sun end their lives. The mass of a star at the end of its nuclear burning phase determines what happens to it next. As we've already seen, stars like the Sun will end their days as a white dwarf. In fact, stars which are slightly more massive than the sun also reach this point; the only difference is that since these stars managed to produce elements other than helium and carbon, the resulting white dwarf will be made of a different mixture of materials - but a white dwarf it is, nonetheless.

If, on the other hand, a star is so massive that even at the end of its main sequence lifetime, it still has more than 1.4 times our Sun's current mass, then the situation changes dramatically. In such cases, the star suffers a supernova explosion. The cores of these stars contain iron, which cannot be used to produce more energy. As more and more material is added to the core, the density gets higher, until it equals that found in white dwarfs. Eventually the supply of nuclear fuel runs out, and in a few seconds the star's atmosphere falls rapidly towards the centre under the influence of the powerful gravitational field. The central region is compressed to form an incredibly dense object called a neutron star, and the infalling atmosphere "bounces" off this object, and the star explodes; for a brief moment in time, the star can outshine all the other stars in the galaxy put together. The result of such a supernova explosion is the creation of the neutron star, and a rapidly expanding cloud of gas - once the stars atmosphere - called a supernova remnant.

This image (taken with the Anglo Australian Telescope) shows the supernova which appeared in the Large Magellanic cloud (visible from the southern hemisphere) in 1987. Comparison of the left hand image with the one on the right showing the same star before the explosion, illustrates just how powerful a supernova event is. This image shows an artist's impression of the death of a star in a supernova explosion, seen from within the star's planetary system. The planets in the foreground will be destroyed by the immense amount of energy from the event - but there can be no life on the planets to witness the event, since the surfaces of these worlds were baked as the star passed through its red giant phase. (Courtesy of SEDS) Share this page: The Life Cycle Of A Star PREVIOUS PAGE THE LIFE CYCLE OF A STAR Outlined below are the many steps involved in a stars evolution, from its formation in a nebula, to its death as a white dwarf or neutron star. NEBULA A nebula is a cloud of gas (hydrogen) and dust in space. Nebulae are the birthplaces of stars . There are different types of nebula. An Emission Nebula e.g.

such as Orion nebula, glows brightly because the gas in it is energised by the stars that have already formed within it. In a Reflection Nebula, starlight reflects on the grains of dust in a nebula. The nebula surrounding the Pleiades Cluster is typical of a reflection nebula. Dark Nebula also exist. These are dense clouds of molecular hydrogen which partially or completely absorb the light from stars behind them e.g. the Horsehead Nebula in Orion. Planetary Nebula are the outer layers of a star that are lost when the star changes from a red giant to a white dwarf. STAR A star is a luminous globe of gas producing its own heat and light by nuclear reactions (nuclear fusion). They are born from nebulae and consist mostly of hydrogen and helium gas. Surface temperatures range from 2000ï¿½C to above 30,000ï¿½C, and the corresponding colours from red to blue-white. The brightest stars have masses 100 times that of the Sun and emit as much light as millions of Suns. They live for less than a million years before exploding as supernovae.

The faintest stars are the red dwarfs, less than one-thousandth the brightness of the Sun. The smallest mass possible for a star is about 8% that of the Sun (80 times the mass of the planet Jupiter), otherwise nuclear reactions do not take place. Objects with less than critical mass shine only dimly and are termed brown dwarfs or a large planet. Towards the end of its life, a star like the Sun swells up into a red giant, before losing its outer layers as a Planetary Nebula and finally shrinking to become a white dwarf. RED GIANT This is a large bright star with a cool surface. It is formed during the later stages of the evolution of a star like the Sun, as it runs out of hydrogen fuel at its centre. Red giants have diameter's between 10 and 100 times that of the Sun. They are very bright because they are so large, although their surface temperature is lower than that of the Sun, about 2000-3000ï¿½C. Very large stars (red giants) are often called Super Giants.

These stars have diameters up to 1000 times that of the Sun and have luminosities often 1,000,000 times greater than the Sun. RED DWARF These are very cool, faint and small stars, approximately one tenth the mass and diameter of the Sun. They burn very slowly and have estimated lifetimes of 100 billion years. Proxima Centauri and Barnard's Star are red dwarfs. WHITE DWARF This is very small, hot star, the last stage in the life cycle of a star like the Sun. White dwarfs have a mass similar to that of the Sun, but only 1% of the Sun's diameter; approximately the diameter of the Earth. The surface temperature of a white dwarf is 8000ï¿½C or more, but being smaller than the Sun their overall luminosity's are 1% of the Sun or less. White dwarfs are the shrunken remains of normal stars, whose nuclear energy supplies have been used up. White dwarf consist of degenerate matter with a very high density due to gravitational effects, i.e. one spoonful has a mass of several tonnes.

White dwarfs cool and fade over several billion years. SUPERNOVA This is the explosive death of a star, and often results in the star obtaining the brightness of 100 million suns for a short time. There are two general types of Supernova:- Type I These occur in binary star systems in which gas from one star falls on to a white dwarf, causing it to explode. Type II These occur in stars ten times or more as massive as the Sun, which suffer runaway internal nuclear reactions at the ends of their lives, leading to an explosion. They leave behind neutron stars and black holes. Supernovae are thought to be main source of elements heavier than hydrogen and helium. NEUTRON STARS These stars are composed mainly of neutrons and are produced when a supernova explodes, forcing the protons and electrons to combine to produce a neutron star. Neutron stars are very dense. Typical stars having a mass of three times the Sun but a diameter of only 20 km. If its mass is any greater, its gravity will be so strong that it will shrink further to become a black hole. Pulsars are believed to be neutron stars that are spinning very rapidly.

BLACK HOLES Black holes are believed to form from massive stars at the end of their life times. The gravitational pull in a black hole is so great that nothing can escape from it, not even light. The density of matter in a black hole cannot be measured. Black holes distort the space around them, and can often suck neighbouring matter into them including stars. Can Life on Earth Escape the Swelling Sun? Can Life on Earth Escape the Swelling Sun? By Jeremy Hsu, Astrobiology Magazine | August 3, 2009 09:14am ET MORE Artist's conception of the view of a hypothetical planet around a distant red giant star. Our sun is expected to swell in a few billion years to first fry Earth then engulf it. Credit: James Gitlin (STScI) Editor's Note: This feature article is part of SPACE.com's weekly Mystery Monday series. Welcome to the last day on Earth. Humanity's descendants have long since died or fled, oceans have long since vaporized, and the life-giving sun has ballooned into a swollen giant filling the sky.

Scientists have debated for years what will happen to our planet when the sun's fusion furnace begins to run out of fuel and swell into a red giant a few billion years from now. The most recent simulations suggest that Earth will end up being swallowed by the dying sun. The impending doom is more dire than any fictional villain could ever wish upon a world. Yet the planet need not perish if future civilizations can somehow move Earth out beyond the danger zone. Barring that, a clever escape plan might prove useful. Red dawn The fate of life on our planet has always depended upon the sun's destiny. Astrophysicists can trace both the sun's past and future based on their understanding of stellar evolution, which comes from observing stars of many types and at different stages of life. Larger stars typically meet their end in spectacular supernova explosions , and leave behind either neutron stars or black holes. But mid-size stars like the sun experience a more gradual transformation, after they consume the last of their hydrogen fuel and start burning helium. Helium burning leads to higher core temperatures that would cause the sun to start swelling into a red giant, around 5 billion years from now. Simulations show the sun eventually expanding to around 250 times its current size.

Previous studies showed that expanding sun would engulf Mercury and Venus, while Mars would remain safely out of reach. But Earth remained in a zone of uncertainty because of its location between those planets. A faint chance existed that the sun would lose too much mass before getting too big, and would allow the Earth to escape into a wider orbit as the sun loses its gravitational grip. Final sunset Now any hope for Earth's final salvation may have finally died. British astronomers ran a simulation in early 2008 which included the sun's weakened gravitational pull, and the Earth moving outward in response. "If that were the only effect, the Earth would indeed escape final destruction," said Robert Smith, emeritus reader at the U.K.'s University of Sussex. "However, the tenuous outer atmosphere of the sun extends a long way beyond its visible surface, and it turns out the Earth would actually be orbiting within these very low density outer layers." That low-density gas would cause enough drag for the Earth to drift inwards, even as tidal forces caused by the Earth's gravity force the nearest side of the sun to bulge outwards. The Earth eventually drifts into the bulge and ends up vaporized , around 7.6 billion years from now.

However, life has even less time than the planet. Most scientists agree that every living thing faces certain extinction 1 billion years from now, when the sun's growing brightness transforms Earth into a global desert. Dropping carbon dioxide levels would starve plants of the ability to conduct photosynthesis, and that would lead to the inevitable death of all living things. Life after Earth A long shot exists for life to survive Earth's fate, but it would involve some novel solutions or a serious space colonization effort. One team at Santa Cruz University in California has proposed capturing a passing asteroid and using its gravitational effects to "nudge" Earth's orbit outward. A continuous asteroid passage every 6,000 years or so could keep Earth at a comfortable distance and give life another 5 billion years on the planet. People leery of miscalculations with the asteroid solution could also turn to good old fashioned engineering. Humans may find new homes among the asteroid belt, the outer planets, in artificial colonies, or perhaps beyond this star system. "Space is disease and danger wrapped in darkness and silence," complains Dr. Leonard "Bones" McCoy of "Star Trek," but even life aboard a starship would beat species extinction.

"A safer solution may be to build a fleet of interplanetary 'life rafts' that could maneuver themselves always out of reach of the sun, but close enough to use its energy," Smith suggested. The sun will eventually lose most of its mass as it becomes a white dwarf, and could come to resemble other burnt-out star systems spotted by NASA's Spitzer Space Telescope in a 2009 study. About 1-3 percent of white dwarf stars seem to contain dust and rocky debris, which may represent remnants of rocky planets such as Earth. By that time, humanity should have either found its new foothold in the universe or long since ceased to exist. Video: Death of the Sun Death of the Sun: How It Will Destroy Earth (Infographic) Full Story: Watery Asteroid Found Around Dying Star, Potential Habitable Planet Ingredient Stars begin their life cycle as a nebula. For 50 million years, gas and dust collapses under its own gravity and heats up from friction. Once the temperature and pressure is right for nuclear fusion, the star ignites. Hydrogen is fused into helium. For about 10 billion years, the star shines.

Eventually, all the hydrogen is fused into helium, so heavier elements begin to fuse. Pressure builds, and the star expands. Star Quiz: Test Your Stellar Smarts Ultimately, the star swells to a huge size, its radius twice the distance between the Earth to the sun . This stage is called the red giant phase. As it dies, the star blows most of its matter out into space, forming an expanding shell of gas. What remains of the star is a white dwarf. In its death throes, the sunlike star destroys its planets. In 2013, the shattered remains of a water-rich minor planet was found orbiting the white dwarf star GD 61, about 170 light-years from Earth. Video: How the Sun Will Die (and What Happens to Earth) The corpse of a sunlike star has half of the mass of the sun packed into a body the size of the Earth. White dwarf matter is composed of carbon atoms that have been crushed by gravity. White dwarfs of more than 1.4 times the sun's mass become even more compressed, to the point where all subatomic particles are crushed into neutrons. Still larger stars become black holes .

The Evolution of the Sun The Evolution of the Sun A cloud of gas and dust begins to contract under the force of gravity. In regions of star birth , we find gaseous nebulae and molecular clouds. These sites of pre-birth are dark patches called globules. The protosun collapsed. As it did, its temperature rose to about 150,000 degrees and the sun appeared very red. Its radius was about 50 present solar radii. When the central temperature reaches 10 million degrees, nuclear burning of hydrogen into helium commences. The star settles into a stable existence on the Main Sequence, generating energy via hydrogen burning . This is the longest single stage in the evolutionary history of a star, typically lasting 90% of its lifetime. Thermonuclear fusion within the Sun is a stable process, controlled by its internal structure. The hydrogen in the core is completed burned into helium nuclei. Initially, the temperature in the core is not hot enough to ignite helium burning. With no additional fuel in the core, fusion dies out. The core cannot support itself and contracts; as it shrinks, it heats up.

The rising temperature in the core heats up a thin shell around the core until the temperature reaches the point where hydrogen burning ignites in this shell around the core. With the additional energy generation in the H-burning shell, the outer layers of the star expand but their temperature decreases as they get further away from the center of energy generation. This large but cool star is now a red giant, with a surface temperature of 3500 degrees and a radius of about 100 solar radii. The helium core contracts until its temperature reaches about 100 million degrees. At this point, helium burning ignites, as helium is converted into carbon (C) and oxygen (O). However, the core cannot expand as much as required to compensate for the increased energy generation caused by the helium burning. Because the expanion does not compensate, the temperature stays very high, and the helium burning proceeds furiously. With no safety valve, the helium fusion is uncontrolled and a large amount of energy is suddenly produced. This helium flash occurs within a few hours after helium fusion begins. The core explodes, the core temperature falls and the core contracts again, thereby heating up.

When the helium burns now, however, the reactions are more controlled because the explosion has lowered the density enough. Helium nuclei fuse to form carbon, oxygen, etc.. The star wanders around the red giant region, developing its distinct layers, eventually forming a carbon-oxygen core. When the helium in the core is entirely converted into C, O, etc., the core again contracts, and thus heats up again. In a star like the Sun, its temperature never reaches the 600 million degrees required for carbon burning. Instead, the outer layers of the star eventually become so cool that nuclei capture electrons to form neutral atoms (rather than nuclei and free electrons). When atoms are forming by capturing photons in this way, they cause photons to be emitted; these photons then are readily available for absorption by neighboring atoms and eventually this causes the outer layers of the star to heat up. When they heat up, the outer layers expand further and cool, forming more atoms, and releasing more photons, leading to more expansion. In other words, this process feeds itself. The outer envelope of the star blows off into space, exposing the hot, compressed remnant core. This is a planetary nebula .

The core contacts but carbon burning never ignites in a one solar mass star. Contraction is halted when the electrons become degenerate, that is when they can no longer be compressed further. The core remnant as a surface temperature of a hot 10,000 degrees and is now a white dwarf . With neither nuclear fusion nor further gravitational collapse possible, energy generation ceases. The star steadily radiates is energy, cools and eventually fades from view, becoming a black dwarf. With this understanding of how the Sun will evolve, we can follow its evolution on the HR diagram . Suggested readings: "Giants in the Sky: The Fate of the Sun", Kaler, James, B., 1993, Mercury, Mar-Apr, pp. 34-41.

Question: What will our Sun become in the first stage of its death?
Answer: Red Giant