Astronomy for Kids

Question Period

What's the ultimate fate of our sun? How will the sun end its days?

The ultimate fate of our sun, like all of the stars in the Milky Way, is tied to its life cycle. The two main processes astronomers theorize in the life cycle of our sun as being mainly responsible for the ultimate fate of our sun being the fusion of lighter elements into heavier elements and the loss of the sun's mass in a second process that begins after the first is completed.

At present our sun is going through the first process of the two processes astronomers believe determines the ultimate fate of our sun, the fusing of lighter hydrogen nuclei into heavier helium nuclei. This process results in the release of energy into the solar system and is ultimately necessary for life to have started on Earth and to continue until the present day. During this process four hydrogen nuclei are fused into one helium nuclei, which results in the direct production of solar energy due to the fact that four hydrogen nuclei weigh less than one helium atom. The extra mass of the four hydrogen nuclei is converted to energy according to Einstein's famous equation energy= mass x (speed of light) x (speed of light), or E=m(c x c).

The first phase of this helium building process will continue for the next five billion years, or so, until about 10 percent of the mass of hydrogen at the center of our sun is converted to helium. At this time, the core of the sun will begin to contract and the process of converting hydrogen into helium will start again in another shell outside of the shrunken core of the sun, while the outer layers of the sun will respond by expanding to several times the sun's current size. The core of the sun will still be obtaining the energy released by the sun at this time by continuing to fuse four hydrogen nuclei into one helium nuclei, until about 50 percent of its mass has been converted to helium.

Once the sun has reached this phase of its life cycle the core of the sun will begin to switch from converting hydrogen into helium, to fusing helium into carbon and oxygen. After all of the available helium of the sun has been converted to oxygen and carbon, astronomers believe the core of the sun will once again begin fusing hydrogen into helium in another shell, until the second process astronomers believe ultimately determines the fate of our sun begins, the loss of the sun's mass.

Before this second phase of the sun's life cycle starts the sun will have reached several thousand times its current luminosity. During this part of this second phase of the sun's life cycle the sun will become unstable and begin to pulsate. It will begin to shrink and expand within a time period of about one year and become what astronomers refer too as a Mira variable. This shrinking and expanding of the sun produces compression waves in the sun's atmosphere and results in the eventual expulsion of a significant volume of the sun's mass into space.