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The Life Cycle of a Star. A Really “Hot” Topic. By Samantha Edgington . Objectives. Describe how stars are formed. Explain the concept of equilibrium. Define the “death” of a star. Identify the different types of stars.

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The Life Cycle of a Star

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The life cycle of a star

The Life Cycle of a Star

A Really “Hot” Topic

By Samantha Edgington



  • 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.

What is a nebula

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.

How is a protostar formed

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.

How does a protostar become a star

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.

Achieving equilibrium

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.

The birth

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.

The main sequence

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

The ending of main sequence

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”.

The death

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.

What is a white dwarf

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.

What is a supernova

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!

What is a neutron star

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.

What is a stellar black hole

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?

Chart of the stars

Chart of the Stars

The sun s life

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?

The sun in main sequence

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.

The sun s death

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.

Works cited

Works Cited












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