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EXPLORE: Life Cycle of the Sun

This book will describe the stages our sun will pass through in its life cycle.

Site: Mountain Heights Academy OpenCourseWare
Course: Earth Systems Q1 v2012
Book: EXPLORE: Life Cycle of the Sun
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Date: Tuesday, 17 October 2017, 10:39 AM

1 Life as a Protostar


sun protostar
Herzig-Haro 34; a protostar. Photo courtesy of

Now that you know the life cycle of stars in general, we will now compare it to our sun. Before describing the stages of our sun, you should be familiar with a few astronomy terms:

GigaYear (Gyr): 1 billion years
MegaYear (Myr): 1 million years
Astronomical Unit (AU): Distance from Earth to the sun, or about 150 million kilometers.

Before nuclear fusion, when the sun was still being created in the interstellar nebula, it was just a protostar. A protostar forms when gravity and pressure begin to condense matter in the center of the nebula, but no nuclear fusion is yet taking place. When nuclear fusion begins, a star is "born". Our sun started burning hydrogen at 4.5 billion years ago. When the sun started it was a little smaller, less bright and cooler than it is today. The sun has enough hydrogen to burn steadily for 11 billion.

This chart shows the life cycle of our sun:


life cycle sun
Chart courtesy of Tabilzer/Wikimedia.

Sources:
The text has been adapted for a 9th grade level. This was originally the hypertext version of a public lecture given on 1997 June 12 at the Perkins Observatory in Delaware, Ohio, as part of the 1997 New Vistas inAstronomy lecture series. It has been updated a number of times since then.The Once and Future Sun by Richard W. Pogge is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License. Based on a work at The Ohio State University Department of Astronomy (www.astronomy.ohio-state.edu)

2 Main Sequence

sun
The sun today. Photo courtesy of Wikimedia.


The sun is in the middle of its lifespan, and is currently in the main sequence phase. At this stage in its life the sun is fusing hydrogen into helium.

Age: 4.55 billion years
Mass: 1.99x10^33g
Radius: 700,000 km
Luminosity: 3.83x10^26 Watts
Temperature: 5779 K
Fuel Supply: ~50% of the core hydrogen has been consumed.


Sources
The text has been adapted for a 9th grade level. This was originally the hypertext version of a public lecture given on 1997 June 12 at the Perkins Observatory in Delaware, Ohio, as part of the 1997 New Vistas inAstronomy lecture series. It has been updated a number of times since then.The Once and Future Sun by Richard W. Pogge is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License. Based on a work at The Ohio State University Department of Astronomy (www.astronomy.ohio-state.edu)

3 Sun in the Next Few Billion Years


sunspot
High resolution of a sunspot. Picture courtesy of


As the Sun becomes older, it grows slightly larger, brighter and hotter. At about 1.1 billion years from now the Sun will be 10% bigger than it is now. As a result, the extra solar energy will dry up Earth's atmosphere and many kinds of life. In about 3.5 billion years, the sun will be 40% bigger and will probably mean that all life on Earth will cease to exist. The next stage will be for the sun to become a Red Giant.

4 Red Giant

sun red giant
Artist rendition of what Earth will look like when the sun enters its Red Giant phase. Courtesy of Wikimedia.


When the sun is 12.2 billion years old it will enter the Red Giant phase. At this point, the outer layers of the sun will expand, but its core will contract. The sun will become big enough to completely consume the planet Mercury. As a red giant, the sun will be cooler in temperature, but brighter. When the Sun reaches its maximum size as a red giant, helium fusion will occur in the core, and the star will begin to release more energy. As a result, the sun will shrink in size, but become hotter. The carbon within the sun begins to collapse inward, as helium begins to fuse into carbon. Elements heavier than carbon typically do not fuse inside small-mass stars. In order for nuclear fusion of heavier elements to take place, the sun would have to be about four times bigger than it is. Once the Sun is 12.3 billion years old, it will run out of helium. Since the sun doesn't have any more fuel to burn, this stage marks the beginning of the end.



Sources
The text has been adapted for a 9th grade level. This was originally the hypertext version of a public lecture given on 1997 June 12 at the Perkins Observatory in Delaware, Ohio, as part of the 1997 New Vistas inAstronomy lecture series. It has been updated a number of times since then.The Once and Future Sun by Richard W. Pogge is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License. Based on a work at The Ohio State University Department of Astronomy (www.astronomy.ohio-state.edu))

5 Planetary Nebula


planetary nebula
Planetary nebula. Photo courtesy of
Wikimedia.


As the sun nears the end of its Red Giant phase, most of its outer layers (which contain the lightest elements) will be vented off into space. This forms a planetary nebula. The lighter elements from the sun are forcefully vented into space, but this should not be confused with a supernova that happens to more massive stars. This is the shortest phase of the sun's life cycle. The result is that the sun loses mass at a high rate and becomes cooler in temperature, but very bright. Eventually, all that will be left of our star is its dense core.


6 White/Black Dwarf

white dwarf
The white dwarf in the AE Aquarii system. Photo courtesy of Wikimedia.

By the end of its planetary nebula phase, the sun will have lost most of its mass, and only its dense core will remain. At this point, the sun will become a white dwarf. A white dwarf is very dense because it contains only the heaviest elements fused over its lifetime, but no more nuclear fusion will be taking place. Because there is no more nuclear fusion occurring in its core, the sun will become much cooler in temperature and only give off a fraction of the light it once did. Over time the Sun will stop generating any heat or light. When no more nuclear fusion is taking place, the Sun will end its life as a black dwarf. Scientists aren't sure what this will look like because the process can take trillions of years, and our universe is only 13.7 billion years old.


Sources
The text has been adapted for a 9th grade level. This was originally the hypertext version of a public lecture given on 1997 June 12 at the Perkins Observatory in Delaware, Ohio, as part of the 1997 New Vistas inAstronomy lecture series. It has been updated a number of times since then.The Once and Future Sun by Richard W. Pogge is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License. Based on a work at The Ohio State University Department of Astronomy (www.astronomy.ohio-state.edu)