SOLAR SYSTEM AND STAR FORMATION

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

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

The Eagle Nebula 7,000 light years from Earth

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?

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

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

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

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)

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...

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

 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 Star Formation

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

 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 Death of a Low Mass Star (Up to 1.5 times the size of the sun)

 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 Death of a Low Mass Star

 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 Death of a High Mass Star (More than 1.5 times the size of the sun)

Red Giant vs Red Supergiant

 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 A Fairly Big Bang: Supernova

Supernova 1987A

 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 A Fairly Big Bang: Supernova

Star Life Cycle

 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 After the Fact: Neutron Stars

 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 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 After the Fact: Black Holes

Hertzsprung-Russell (HR) Diagram