Stellar (Nuclear) Fusion

Stellar (Nuclear) Fusion

Nuclear Fusion = Process of energy generation. (Nuclear Energy)

Nuclei of lighter elements combine under extreme temperatures to transform into heavier elements and releasing TONS of energy!

Birth of a star!

•  A star’s life begins when high temperatures and pressures within its core make the start of nuclear fusion possible.

• Gravitational forces pull the materials from a nebula inward.

• Decrease in space, causes an increase in molecular collisions (less place to roam)

• Increased molecular movement results in increased pressure and temperatures, too.

• Once protostar hits 10 million degrees, fusion of hydrogen begins!

• Fusion releases tons of energy, protostor ignites bright and A STAR TURNS ON (Birth).

Multiple Choice

What is a protostar?

• A star that has died

• A smaller than average star

• A big, blue star that is on the main sequence of the HR diagram

• A contracting mass of gas which represents an early stage in the formation of a star

Multiple Choice

What is not produced when light elements undergo nuclear fusion?

• Heavier elements
• Energy 
• Lighter elements
• Light

Multiple Choice

In nuclear fusion, smaller atoms are forced together to create larger atoms. Does this process release, absorb or maintain energy?

• Absorb energy
• Maintain energy
• Release energy

Multiple Choice

When a young, developing star becomes hot enough and dense enough, the process of _______ begins.

• H --> He fusion

• He --> C fusion

• He --> C --> O fusion

• fission

Multiple Choice

How is nuclear fusion different from nuclear fission?

• In fusion, the product is a larger atomic nucleus.
• Fission produces energy but fusion does not.
• Fusion produces energy but fission does not.
• In fission, the product is a larger atomic nucleus.

Battle of the forces!

Gravity is constantly pushing the star inward. Nuclear fusion (energy release) generates the forces that push back! The result of this balance or imbalance of forces is what dictates the changes of a star (temperature, size, brightness, etc)

Multiple Choice

Where does fusion occur naturally?

• Underwater
• All around us
• In the radioactive waste
• On the sun

Multiple Choice

The sun is considered stable on the main sequence stage. Which statement below represents the MAJORITY of atoms combining together during the sun's fusion process?

• Helium and Hydrogen atoms

• Hydrogen atoms

• Hydrogen and Lithium atoms

• Hydrogen and Carbon atoms

Multiple Choice

When stars are in the main sequence, fusing hydrogen into helium, and are neither expanding nor contracting, they are said to be...

• dying

• in hydrostatic equilibrium

• white dwarfs

• red hypergiants

Why is main sequence the longest stage?

All stars begin with hydrogen and some helium. It isn't until all of the hydrogen has fused that the nuclear fusion will slow down. This process for all hydrogen to change, takes millions of years! During this time, the gravitational and nuclear forces are said to be in a balance = hydrostatic equilibrium.

Multiple Choice

From your lab, how will this star change based on the interaction of the gravitational forces and the nuclear forces?

• It is in equilibrium and will not change

• The gravitational forces are greater therefore the star's size will get smaller

• The gravitational forces are greater therefore the star's size will get larger

• The nuclear forces are greater therefore the star's size will get smaller

• The nuclear forces are greater therefore the star's size will get larger

How will this star change?

The nuclear forces (gray arrows) are larger than the gravitational (black arrows) therefore the nuclear forces will push against the gravity and allow the size of the star to INCREASE.

Consider, with an increase in size, what will happen to the molecular pressures and temperatures of the star overtime.....