10.7 Stellar processes and Stellar Evolution

1. 10.7 Stellar processes and Stellar Evolution William Scaruffi

2. E.5.1. Describe Conditions that Initiate Fusion in a Star • Deaths of Supernovas compress Hydrogen Clouds (Proto-Stars) enough for particles to come together. The more atoms that are pulled in by these clouds, the stronger gravitational force. • Gravity on atoms gives atoms KE temperature increases (High temperature an pressure) • Fusion Begins…

3. E.5.2 State the effect of a star’s mass on the end product of nuclear fusion • High Temp and Pressure give H atoms enough energy to overcome electrostatic repulsion. Fusion Begins:

4. E.5.3 Outline the changes that take place in Nucleosynthesis when a star leaves the main sequence and becomes a Red Giant. • When outward pressure reaches equilibrium with the gravitational pull, the star becomes a MAIN SEQUENCE STAR (like our sun) • When Hydrogen in the core runs out, fusion stops Outward thermal pressure drops, core compresses Compressing core heats outside Hydrogen Outside Hydrogen begins fusing and expands http://en.wikipedia.org/wiki/File:FusionintheSun.svg

5. E.5.4 Apply the Mass-Luminosity Relation Mass-luminosity relationship: Only Main Sequence Stars. massive main sequence stars are more luminous than smaller stars. So it is then possible to predict where (on the graph) the different stars become part of the main sequence line, and therefore it is possible to predict their evolution. The equation relating mass, m and luminosity, L is L ∝ m^3.5 (L=W/m^2; m=Solar Mass Unit) (e.g.)Question: Justify why the star Sirius is twice the size of our sun but it is about 10 times as bright. Answer: Luminosity of Our sun: 1^3.5 = 1 Luminosity of Sirius: 2^3.5 = 11.31

6. E.5.5 Explain the use of Chandraskhar and Oppenheimer-Volkoff limits are used to predict the fate of stars • Chandraskhar Limit White Dwarf can be no more than 1.4 Solar Mass Units So the limit states that White Dwarfs can’t result from stars that are more than 4 Solar Mass Units • Oppenheimer-VolkoffLimit If a Neutron star is less than 3 Solar Mass Units Neutron Star will remain stable More than 3 Solar Mass Units Neutron Degeneracy is overwhelmed Neutron Star will collapse into a Black Hole

7. E.5.6 Compare the fate of Red Giants and Red Supergiants • If a main sequence star is categorized as a Red Giant, it is destined to become a White Dwarf. Super Red Giants, on the other hand, can result into Neutron stars and, in some cases of extremely large size, into a black hole.

8. E.5.7 Draw Evolutionary Paths on an HR Diagram • Evolutionary Path: a star’s development (change in luminosity and temperature) Large Star Small Star

9. E.5.8 Outline Characteristics of a Pulsar • Neutron Star that rotates really fast because diameter has decreased, the same rotational speed over a smaller diameter results in a higher rotational speed. • Since it’s a collapsed star, the magnetic flux is spread over a smaller are, therefore Magnetic field is denser. • Strong Spinning Magnetic field causes EM radiation into a beam along poles. • Rotation Axis Beam’s Axis • Rays perceived to Pulse at a regular intervals from fixed perceiver.

10. Source: Both Graphs and Information: • Hamper, Chris. Physics Higher Level (plus Standard Level Options.” Pearson Publications. Print.