Solar System and Star Formation

1. Solar System and Star Formation

2. Solar System and Star Formation • Both happen at the same time, but we’ll look at the two events separately

3. Solar System Formation • Ingredients: • 1 cold solar nebula (-442°F) made up of dust and gas left over from the big bang • 1 shockwave, perhaps from a nearby supernova

4. The Eagle Nebula 7,000 light years from Earth

5. Solar System Formation • Shockwave causes gas and dust to compress • Even small objects have gravity, so nebula begins to collapse inward and rotate • This forms a protoplanetary (early planet) disk . . . but why?

6. Solar System Formation • Nebula rotated slowly at first • As nebula collapsed, it rotated faster and flattened out

7. Solar System Formation • Eventually, a star forms at the center of the protoplanetary disk (more on this in just a bit) • Throughout the disk, small, solid pieces of matter come together through the process of accretion • The resulting small, irregularly shaped planetisimals have constant collisions, eventually becoming protoplanets

9. Solar System Formation • Eventually, protoplanets become large enough to exert gravity on surrounding objects • With gravity, protoplanets become rounder and continue to grow into true planets

10. Solar System Formation Evidence for ‘Disk’ Theory • Most planets rotate in the same direction • All planets revolve in the same direction • Planet’s orbits are all in the same plane (almost)

11. Star Formation • Ingredients: • 1 cold solar nebula (-442°F) made up of dust and gas left over from the big bang • 1 shockwave, perhaps from a nearby supernova • Wait a minute . . .

12. Star Formation • Shockwave compresses dust and gas • Most of the gas and dust in the nebula clumps together in the center of the protoplanetary disk • Eventually, it gets big enough to get hot through increased friction and becomes a protostar

13. Star Formation • When the temperature in the star reaches 10 million °Kelvin (~20 million °F), Hydrogen fusion begins • If the star does not have critical mass, the chain reaction does not continue • The result is a brown dwarf star with no heat or light • If star does have critical mass, it enters main sequence

14. Star Life Cycle Main Sequence • Longest portion of the solar life cycle • Hydrogen fusion occurs • Outward force of fusion equals inward pull of gravity

15. Star Life Cycle Main Sequence • Fusion continues, gradually forming larger and larger elements, which sink to the core • This happens until Iron (Fe) or Carbon (C) form and/or Hydrogen fuel runs out, then the star dies • For a star like our sun, this takes ~10 billion years

16. Star Life Cycle

17. Death of a Low Mass Star (Up to 1.5 times the size of the sun) • Hydrogen fuel begins to run out, the core cools and contracts • As the core contracts, fusion continues up through Carbon • Hydrogen fusion continues in outer layers • Outer portion of star expands into a red giant • Compared to our sun it will be bright, cool and large

19. Death of a Low Mass Star • Eventually, outer layer is blown away in a burst of gas called a nova • All that is left is a planetary nebula and a white dwarf • Small, dense, and cool

20. Death of a High Mass Star (More than 1.5 times the size of the sun) • Hydrogen fuel begins to run out, the core cools and contracts • Due to greater mass, as the core contracts, fusion continues up through Iron • Hydrogen fusion continues in outer layers • Outer portion of star expands into a red super giant • Compared to our sun it will be bright, cool and huge

21. Red Giant vs Red Supergiant

22. A Fairly Big Bang: Supernova • Fusion cannot proceed past Iron • When Iron in core reaches 1.44 times the mass of our sun (Chandrasekhar Limit) there is not enough outward energy, so gravity wins and the star implodes • The implosion continues until gravity creates enough energy for a rebound explosion: a supernova

23. Supernova 1987A

24. A Fairly Big Bang: Supernova • Supernova releases as much energy in a few weeks as our sun will release in 10 billion years • Brighter than a galaxy for a short period of time • Energy causes fusion of all natural elements above Iron • Core of star collapses to unimaginable density

25. Star Life Cycle

26. After the Fact: Neutron Stars • Stars between 1.5 and 25 times the size of our sun become neutron stars • After supernova, electrons and protons of all remaining mass compress and become neutrons • All atomic space is gone • Result is the size of a city • Can be pulsars or magnetars

28. After the Fact: Black Holes • Stars greater than 25 times the size of our sun become black holes • After supernova, all remaining mass collapses into infinitely small point called a singularity • immense mass / 0 volume = undefined (infinite) density

29. After the Fact: Black Holes

30. After the Fact: Black Holes • Gravity is so strong even light cannot escape • Surface or edge of black hole defined by event horizon • Point at which nothing can escape • Also a bad movie

31. Hertzsprung-Russell (HR) Diagram