solar system and star formation. solar system and star formation both happen at the same time, but...
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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
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
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