![]() When these stars run out of helium, they go through the same contraction process again, which in turn allows the star to fuse even heavier elements. ![]() For more massive stars, however, the fusion of helium causes further buildup of heavier elements such as carbon and oxygen. Over time, the outward flow of energy from the core blows of the outer layers of the star, forming what’s called a planetary nebula. Since the red giant has grown to such an immense size, the star’s gravity is no longer strong enough to hold the star together. For low to medium mass stars, such as our sun, the process of nuclear fusion will generally stop with helium. How a red giant evolves will be largely dependent upon its mass. The star has now been transformed into a red giant.Įventual Fate Lower mass red giants will eventually become planetary nebulae, such as the ring nebula. As a star swells, temperatures become distributed over a larger surface area, and so the surface of the star becomes colder and the star turns red. The star may expand hundreds of times larger than its original size, and this increase in size also causes the outer layers of the star to cool. Under these more extreme conditions, the star’s core is now able to fuse helium into heavier elements, releasing a tremendous amount of energy that counteracts the star’s gravity and causes the star to expand outwards. Thus the region of hydrogen fusion migrates away from the core, which causes the core of the star to become hotter and denser. ![]() The star may contract by as much as 98%, and the extreme compression causes hydrogen outside the core to fuse into helium. Once a star begins running out of hydrogen, the amount of nuclear energy flowing outwards begins to decrease, and the immense gravity of the star begins causing it to collapse inwards. The fusion of hydrogen within a star’s core produces helium, which builds up in the star’s core like ash in a fireplace. ![]() Despite stars containing vast amounts of hydrogen, it is only a finite amount, and eventually it runs out. Image credit: NASAĮvery star that is powered by the nuclear fusion of hydrogen in their core is known as a main sequence star. ![]()
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