The Life Cycle of a Star

1. The Life Cycle of a Star A Really “Hot” Topic By Samantha Edgington

2. Objectives • Describe how stars are formed. • Explain the concept of equilibrium. • Define the “death” of a star. • Identify the different types of stars. • Describe how the process of nuclear fusion works within a star.

3. What is a Nebula? • A nebula can be defined as a thinly spread cloud of interstellar gas and dust. • Some nebulae are the remains of a supernova explosion. • the death and collapse of a massive star can cause this explosion, this means nebulae can be the remains of old, dead stars. • Most nebulae are gravity-induced condensations of gases where protostars are born.

4. How is a Protostar Formed? • Inside a nebula, there are areas where gravity causes dust and gas to “clump” together. • As these “clumps” gather more and more mass their gravitational pull increases, forcing more atoms together. • This process is known as accretion, and the result is a protostar.

5. How does a Protostar Become a Star? • In order to comprehend this process, the concept of equilibrium must be understood. • Equilibrium is in essence a balance. • In the case of star formation this balance exists between gravity and gas pressure.

6. Achieving Equilibrium • First gravity pulls gas and dust inward towards the core of the prospective star. • Inside the core, density and temperature increases as atomic collisions increase, causing a rise in gas pressure. • Finally when gas pressure is equal to gravity, the protostar has reached equilibrium and is therefore reached a reasonably stable size.

7. The Birth • Once the protostar has achieved equilibrium one of two things occur: • If there is not a sufficient mass, it becomes a brown dwarf which is a “star” that doesn’t radiate much heat and light. • In the event it does contain an appropriate amount of matter, nuclear fusion begins and light is emitted.

8. The Main Sequence • A star is basically a huge ball of gas undergoing nuclear fusion. • The main sequence phase is where stars spend the majority of their “life” by fusing hydrogen into helium. • There are two types of main sequence stars: • a red giant which is alarge bright star with a cool surface. • a red dwarf which are very cool, faint and small stars

9. The Ending of Main Sequence • The star slowly shrinks over billions of years as the hydrogen is used by fusion. • The star’s temperature, density, and pressure at the core continues to increase. • Once the hydrogen is depleted, the helium is fused into carbon, when this occurs the star has reached “old age”.

10. The Death • There are one of two ways a star can die depending on its size. • If the star is of low mass, it expands its outer layers, creating nebulae and a white dwarf forms from the core. • If it is of high mass, death occurs in a massive explosion known as a supernova, the remaining core then transforms into a neutron star or a black hole.

11. What is a White Dwarf? • They form from the core of a dead red giants that were too small to fuse carbon. • Since they do not undergo fusion, they have no energy source and gradually fade. • When they radiate away all of their energy they will theoretically become a black dwarf. • Since white dwarfs cannot be older than the universe (13.7 billion years) no black dwarfs are currently in existence.

12. What is a Supernova? • They can form when the gravitational potential energy—created by a sudden gravitational collapse of a large red giant—heats and expels the star's outer layers, resulting in an explosion. • Also, they can form when a white dwarf ignites carbon fusion, which results in a runaway nuclear fusion reaction and causes a supernova. • Supernovae can be so immense that the energy produced can equal the energy the Sun creates over a time period of 10 billion years!

13. What is a Neutron Star? • A neutron star is formed as a result of a massive star being compressed. • The core material, known as neutron degenerate matter, mostly consists of neutrons with a few protons and electrons. • The gravity is so intense that if an object were to reach the surface it would disperse all of its subatomic particles and merge with the star! • The matter is so dense that a teaspoon would weigh billions of tonnes! • Some people view neutron stars as giant atoms.

14. What is a Stellar Black Hole? • If a collapsing star exceeds the maximum mass a neutron star can be it will develop into a stellar black hole. • Black holes are extremely dense areas with a gravitational pull so powerful not even light can escape! • What could be a reason why black holes are black?

15. Chart of the Stars

16. The Sun’s Life • Now that a basic overview of a star’s life cycle has been covered, the details of the most important star’s life can be revealed. • Can you guess what type of star the Sun is?

17. The Sun in Main Sequence • The Sun was born like any other star, out of a nebulae and into a protostar. • It is now in its main sequence and can be classified as a yellow dwarf. • The Star is about 4.57 billion years old, about halfway through its complete lifecycle.

18. The Sun’s Death • Since the Sun is considerably smaller it will not explode in a supernova. • Instead it is predicted that it will become a red giant in about ~6 billion years. • When this occurs, all the water on earth will be vaporized and life will cease to exist. • In the final phase the Sun will form a white dwarf and slowly fade out of existence.

19. Works Cited • www.dictionary.com • aspire.cosmicray.org/labs/star_life/starlife_proto.html • www.astro.keele.ac.uk/workx/starlife/StarpageS_26M.html • http://www.telescope.org/pparc/res8.html • www.antonine-education.co.uk • www.darkstar1.co.uk • www.pbs.org • outreach.jach.hawaii.edu • www.spaceflightnow.com • wikipedia.org • www.cosmographica.com