The Life and Death of Stars

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Based on an article by Melany Mclean
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The life and death of stars form the chemical elements that make up Earth, making stars critical to life as we know it.

Look up at the stars. They may seem like permanent fixtures in the night sky, but did you know that stars eventually die? The life and death of stars form the ingredients that make up Earth, making stars critical to life as we know it.

The early universe contained nothing but the chemical elements hydrogen, helium, and tiny amounts of lithium and beryllium. During their life cycles, stars create elements with low atomic masses. These are the first 26 elements in the periodic table up to and including iron. When most stars die, these light elements spread across the universe, including to planets like Earth.

How are stars born? 

Early in the history of the universe, before stars and planets existed, giant clouds of hydrogen and helium began to form. Slowly, these clouds collected enough mass for their own gravity to form. This created extremely dense balls of gas. In other words, they formed stars.  

When a new star is formed, its core is exposed to very strong gravitational forces. This force is so great that the star is in danger of collapsing in on itself. Luckily, nuclear fusion provides the energy the star needs to push back against the collapsing core. Nuclear fusion is a process where the nuclei of two or more elements combine to produce nuclei of heavier elements. Nuclear fusion also releases energy.

In the core of a newly formed star, hydrogen nuclei begin to fuse into helium. The inward pull of gravity and the outward push of nuclear fusion eventually balance out. For a time, hydrogen fusion prevents the collapse of the star.

Nuclear fusion showing the fusing of protons and neutrons to form helium
Nuclear fusion showing the fusing of protons and neutrons to form helium (Source: © 2019 Let’s Talk Science based on an image by Borb [CC BY-SA 3.0] via Wikimedia Commons).

Did you know? 

The closest star to Earth, the Sun, is fusing hydrogen atoms into helium as you read this! 

When the young star runs out of hydrogen, its core will once again begin to collapse. The extreme forces on the core causes it to heat up. Soon, the core is hot enough that it can begin to fuse helium into carbon and oxygen. Once again, nuclear fusion pushes back against gravity to prevent the star from collapsing. One by one, the star fuses each new element. This successively produces elements with low atomic masses like carbon, oxygen, and neon. Not only does nuclear fusion keep stars from collapsing, it enabled the first stars in the universe to create new elements that had never existed before! Depending on their size, stars can create elements through fusion, up to iron, which has an atomic number of 26.

But there are 118 elements in the periodic table. So, where do all the elements with an atomic number higher than iron come from? From the death of stars.

birth, lives and deaths of different sizes of stars
The birth, lives and deaths of different sizes of stars (Source: Infographic by JPLPublic posted to NASA/JPL-Caltech).

How do stars die?

Even though stars are not living things, they have “life cycles” and at some point they are said to “die.” How a star lives and dies depends on how large it is. 

The smallest stars, brown dwarf stars, are too large to be considered planets, but too small to be considered stars. They are unable to sustain the fusion of hydrogen because of their low mass, and are often called "failed stars." The small, slow-burning red dwarf stars have very long lives. Their lives last between one and ten trillion years! Scientists believe that when red dwarf stars eventually collapse, they will become white dwarf stars. These are very dense stars that no longer burn fuel. Scientists also believe that eventually, the white dwarf stars in the universe will cool off and become black dwarf stars

Did you know? 

The color of a star is defined by its temperature. The coolest stars appear red, while the hottest stars appear blue.

When mid-sized stars, like the Sun, run out of hydrogen, their cores will contract and heat up. The outer layers of gas will expand and the stars will become red giant stars. Eventually when the core of a red giant star cools, the remaining gas will float into space, forming a planetary nebula. Each planetary nebula has a white dwarf star at its core. 

Did you know? 

When the Sun becomes a red giant, it will grow so huge that it will swallow Mercury, Venus and possibly Earth before becoming a planetary nebula.

The Hubble Planetary Nebula
The Hubble Planetary Nebula (Source: NASA via Wikimedia Commons ).

 The very largest stars first become blue supergiant stars before dying in a dramatic fashion. In fact, they create the biggest explosions in the universe when they collapse. We call these explosions supernovas.

Did you know? 

A supernova is so bright that it can outshine an entire galaxy of a hundred billion stars!

The initial explosion of a supernova has so much energy that it can split atoms apart at the core, sending protons and neutrons flying into the universe. In the moments following the explosion, these particles crash into each other with enough energy to fuse back together. Light elements continue colliding with protons and neutrons in this way, constantly growing larger and larger. This process, which is similar to nuclear fusion, is called nucleosynthesis. The nucleosynthesis that occurs during the explosion of a supernova produces elements with a higher atomic number than iron, which cannot be created by nuclear fusion. When the first stars died out this way, brand new elements, including gold, were formed. Eventually, those elements ended up here on Earth.

After a supernova explodes, the core that remains becomes a neutron star. This is an extremely small and dense type of star. For the largest stars of all, the remaining core is so massive and has such a strong gravitational pull that not even light can escape. This is called a stellar black hole.
 

A simulated Black Hole with the Milky Way in the background
A simulated Black Hole with the Milky Way in the background (Source: Ute Kraus, Physics education group Kraus, Universität Hildesheim; background image of the milky way: Axel Mellinger [CC BY-SA 2.0 de] via Wikimedia Commons ).
This zoom video starts with a view of the ALMA telescope array in Chile and zooms in on the heart of M87. It shows increasingly detailed observations until, finally, it shows the first direct visual evidence of a supermassive black hole’s silhouette (0:54 min.).

No matter how a star dies, its life cycle can transform the universe. Without stars, the universe would contain nothing but clouds of hydrogen and helium. It is the life and death of stars that are responsible for the elements that make up everything you see on Earth!

Did you know? 

Models of supernova explosions predict the creation of elements that aren’t even found on Earth! Scientists call them exotic nuclei

Starting Points

Connecting and Relating

  • How is the life cycle of a star similar to the life cycle of a living thing? How is it different?
  • Have you ever heard the saying, “We are made of star-stuff. There are pieces of stars within us all,” by the famous astrophysicist and science communicator Carl Sagan? Before reading this article, what did you think this quote meant? Did your understanding of this quote alter after you read the article? If so, how?

Connecting and Relating

  • How is the life cycle of a star similar to the life cycle of a living thing? How is it different?
  • Have you ever heard the saying, “We are made of star-stuff. There are pieces of stars within us all,” by the famous astrophysicist and science communicator Carl Sagan? Before reading this article, what did you think this quote meant? Did your understanding of this quote alter after you read the article? If so, how?

Relating Science and Technology to Society and the Environment

  • The life cycle of a star takes place over billions of years. How have astrophysicists been able to understand how stars change over such huge expanses of time?

Relating Science and Technology to Society and the Environment

  • The life cycle of a star takes place over billions of years. How have astrophysicists been able to understand how stars change over such huge expanses of time?

Exploring Concepts

  • Under what conditions do stars produce different chemical elements?
  • How is nuclear fusion different from nucleosynthesis? 
  • What is a supernova? How does a supernova result in the formation of elements?
  • How does the size of star impact on its lifecycle?

Exploring Concepts

  • Under what conditions do stars produce different chemical elements?
  • How is nuclear fusion different from nucleosynthesis? 
  • What is a supernova? How does a supernova result in the formation of elements?
  • How does the size of star impact on its lifecycle?

Nature of Science/Nature of Technology

  • Why is it important to understand chemistry and physics when learning about the life cycle of stars? 
  • What is astrophysics? What is the difference between astrophysics and astronomy?

Nature of Science/Nature of Technology

  • Why is it important to understand chemistry and physics when learning about the life cycle of stars? 
  • What is astrophysics? What is the difference between astrophysics and astronomy?

Media Literacy

  • Do you know any songs or musical compositions about stars? Why do you think the stars have been inspiration for music?

Media Literacy

  • Do you know any songs or musical compositions about stars? Why do you think the stars have been inspiration for music?

Teaching Suggestions

  • This article supports teaching and learning in chemistry and the topic of space. The concepts of nuclear fusion and nucleosynthesis are introduced in the context of the life cycle of stars and the formation of the elements.
  • Before reading the article, teachers could ask students questions from the Connecting & Relating section to get them thinking about life cycles in general and to access their prior knowledge about stars. 
  • Prior to reading the article, teachers may also wish to provide students with a Vocabulary Preview to introduce the new terms that will be encountered in the reading. Download Vocabulary Preview learning strategy reproducibles in [Google doc] and [PDF] formats. 
  • To consolidate learning, Students could create their own infographic depicting the life cycle of a certain type of star.

Teaching Suggestions

  • This article supports teaching and learning in chemistry and the topic of space. The concepts of nuclear fusion and nucleosynthesis are introduced in the context of the life cycle of stars and the formation of the elements.
  • Before reading the article, teachers could ask students questions from the Connecting & Relating section to get them thinking about life cycles in general and to access their prior knowledge about stars. 
  • Prior to reading the article, teachers may also wish to provide students with a Vocabulary Preview to introduce the new terms that will be encountered in the reading. Download Vocabulary Preview learning strategy reproducibles in [Google doc] and [PDF] formats. 
  • To consolidate learning, Students could create their own infographic depicting the life cycle of a certain type of star.

Learn more

The last light before eternal darkness: Black dwarfs & white dwarfs (2017)

This video (6:28 min.) from Kurzegagst contains useful information on black dwarfs, white dwarfs and other types of stars.

Making new elements (2013)

An article explaining how scientists make superheavy elements.

Life Cycle of A Star

Article from the National Schools Observatory explains the processes in simple terms with hyperlinks to all the related keywords.

The life cycle of stars (2012)

A video from the Institute of Physics that explains how we believe stars are born, live, and die.
 

References

Cain, F. (2015, April 9). How quickly does a supernova happen? Universe Today.

Freudenrich, C. (2016, November 17). How stars work. HowStuffWorks.

ITER Organization. (2016, November 24). Fusion.

Redd, N. T. (2018, February 24). Neutron stars: Definition & facts. Space.com.

Science Learning Hub. (2009, October 22). How elements are formed.

Smith, H. R. (2018, August 21). What Is a black hole? NASA.