Stars and their Physical Properties

1. Stars and their Physical Properties

2. Background Information • Name: Isabel Baransky • School: Fu Foundation of Engineering and Applied Science • Major: Applied Physics • Minor: Music

3. OVERVIEW OF FORCE

4. THE BIG BANG

5. Big Bang • Occurred 13.7 billion years ago. • All matter, energy, and light were all compacted into an infinitely dense point • It spread out rapidly in an explosion, similar to a “big bang”

6. Formation of Hydrogen/Helium • Around 300,000 years after the Big Bang, the universe was abundant with floating subatomic particles (electrons, protons, etc) • The universe had cooled enough for the particles to come together to make the simplest elements: hydrogen and helium

7. WHAT IS A STAR?

8. BIRTH OF STARS

9. Gas clouds Dense clouds of gas, called nebulae or nebula, are the birthplace of stars Due to gravity, the mass in the clouds collapses in on itself, creating something called a protostar

10. Achieving equillibrium • Gravity pulls gas and dust inward toward the core. • Inside the core, temperature increases as gas atom collisions increase. • Density of the core increases as more atoms try to share the same space. • Gas pressure increases as atomic collisions and density (atoms/space) increase. • When gas pressure = gravity, the protostar has reached equilibrium

11. Two options for a protostar Option 1 Option 2 If the critical temperature to counteract gravity is reached, then the protostar begins nuclear fusion in its core This is the moment it becomes a real star! • If the critical temperature to counteract gravity is not reached, then the protostar becomes a brown dwarf

12. Brown Dwarfs Brown dwarfs are not large enough to cause fusion in their core Most brown dwarfs are 15 to 75 times the mass of Jupiter! Brown dwarfs are considered failed stars

13. MAIN SEQUENCE STARS

15. Stars in the Main Sequence • L = 4πR2σT4 • L ∝ M3.5 (proportional)

16. Hydrogen Fusion • When a star is in the main sequence, it will carry out something called hydrogen fusion • Convert hydrogen molecules in its core to helium molecules • Four hydrogen are combined to produce a helium atom • According to Einstein, because we start out with more mass then we end up with, the mass is converted to massive amounts of energy • This helps prevent the gravitational force from making the star collapse in on itself

17. Hydrostatic Equillibrium Gravity = gas pressure (equilibrium) Out of fuel Fusion stops, temperature drops Gravity reduces core Increased temperature Provides enough energy for nuclear, and the cycle begins again at step 1

18. A little more information • Because interstellar medium is 97% hydrogen and 3% helium, a star primarily burns hydrogen during its lifetime. • Our sun, a medium-size star, will live in the hydrogen phase, called the main sequence phase, for about 10 billion years • Once hydrogen fuel is gone, the star has entered “old age.”

19. WHICH STARS “LIVE” LONGER: LARGE STARS OR SMALL STARS?

20. VEERING FROM THE MAIN SEQUENCE

21. New fuel is used! The star begins fusing other elements Helium Carbon Iron The larger the star, the more gravitational energy, the more thermal energy, the heavier the fusion element Once iron is reached, fusion is halted

23. WHERE DO ALL THE ELEMENTS HEAVIER THAN IRON COME FROM?

24. Supernova! The core and outer layers of the star start to collapse at up to the speed of light! The imploding matter hits the rigid core and bounces back The energy released during this explosion is so immense that the star will out shine an entire galaxy for a few days. Supernova are responsible for all elements heavier than iron These are called supernovas

25. Stars smaller than 1.44 Solar Masses • These stars become white dwarfs! • Very dense • A teaspoon of a white dwarf would weigh 5 tons • Electron Degeneracy keeps equilibrium

26. Degeneracy Paulis’ Exclusion Principle: no two identical fermions may occupy the same quantum state simultaneously The resistance from particles to be in the same orbitals creates a pressure that can outstand gravitational force under 1.44 solar masses If over 1.44 solar masses, electron degeneracy is overwhelmed and we enter neutron degeneracy, which is overwhelmed after 3 solar masses

27. Neutron stars • 1 billion tons per teaspoon • Create pulsars • A 0.033 sec pulsar was discovered in the Crab Nebula • Neutron stars are so massive that they have overwhelmed electron degeneracy

28. LITTLE GREEN MEN Summer of 1967, approximately a radio transmission was discovered that pulsated consistantly once ever second Attributed to intelligent life and labeled “LGI1” Soon it was discovered to just be the signal given off from neutron stars

29. What are black holes? • An object so dense that even light cannot escape from it (hence the term “black”) • They are so massive that they overwhelm neutron degeneracy • Since black holes by their very definition cannot be directly observed, proving their existence is difficult

30. The Schwarzschild Radius • Also called the “event horizon” • Any mass can become a black hole if it collapses down to the Schwarzschild radius

31. How can we prove their existence? X-ray emissions Binary systems with no evidence of a secondary star

32. ANY QUESTIONS?