EDWARD'S LECTURE NOTES:
More notes at http://tanguay.info/learntracker
C O U R S E 
Formation of the Universe, Solar System, Earth and Life
Henning Haack, University of Copenhagen
https://www.coursera.org/course/origins
C O U R S E   L E C T U R E 
The Origin of Solar Systems
Notes taken on May 30, 2016 by Edward Tanguay
while solar systems are based on hydrogen and helium, they also also likely to include all the elements of the period table
many generations of dying stars have injected freshly synthesized matter into interstellar space
how can this widely scattered matter be used to form dense solar systems for planets
if the matter was evenly distributed throughout the universe, this would be a hopeless task
fortunately, due to the force of gravity, matter is concentrated in galaxies such as our own Milky Way galaxy
within the galaxies, most of the matter is concentrated in molecular clouds
these are enormous clouds, even when we observe them from as far away as the Earth
yet because they are also very faint, they also remain almost invisible to the naked eye
the Orion constellation which lies close to the terrestrial equator
the three bright stars are known as Orion's belt
if we zoom in and increase the brightness, the underlying cloud becomes visible
Horsehead Nebula
Orion Nebula
this is a star-forming region
we cannot observe how our own solar system formed, but observing places like this, we can deduce how solar systems form in general
the size of molecular clouds can be measured in units of light years
molecular clouds look passive but they are highly dynamic
stellar winds push the gas around at speeds up to several hundred km/s
even at these speeds, it would take a millions years to traverse the width of these clouds
we use computer simulations to fast-forward this process
can run the simulation for two million years
newborn stars light up within the cloud as the simulation runs
but we need to compress it by many orders of magnitude to form a solar system
sometimes gas gets compressed to a point that gravity is stronger than the gas pressure
the result is a runaway collapse resulting in star formation
a famous example of star formation is seen in the Hubble image of the Eagle Nebula
intense stellar winds have created a bubble in the cloud
the stellar winds not only push the gas further and further away from the star through a process known as photoevaporation
it also compresses the gas to point where a gravitational collapse is triggered
this is exactly what we need to form a new star
once a dense core is formed, it's gravity field will start to grow as attracts more and more gas and thus further increases a gravity field, which is called accretion
each of these tentacle-like structures contains a new star at the tip
eventually the gas will clear around the new star, accretion will cease, and the star will begin its life as an independent object
as the gas collapses toward the growing star, it will rotate faster and faster, much like water running out of a bathtub
the accretion prevents all of the gas from accreting directly to the star
instead, a rotating disc of gas and dust is formed around the young star
it is from these discs that planets are formed
this explains why all of the planets in our solar system orbit in the same plane around the sun
early solar systems
matter from the cloud is falling in toward the disc
most of the mass is drifting inwards toward the star
concentrated toward the mid-plane, we find solids of different sizes
near the start, milimeter-size particles known as CAI's condense out of the gas
Calcium/Aluminum-rich inclusions
calcium and aluminum condense at very high temperatures
meteorites have CAIs, e.g. white, irregular inclusions in a rock
further away from the star we find silicate spheres known as chondrules
the disc is composed of dust and gas
near the center there are no ice crystals, further out there are ice crystals
as a result, outer planets grow faster and bigger
the gas in the disc was only present for a few million years
the outer planets beyond the frost line grew big enough to capture gas from the disc while it was still there
became gas giants
inside the frost line, smaller rocky or terrestrial planets formed, e.g. Mercury, Venus, Earth and Mars
accretion of the planets
a protoplanetary core
accretes dust, condrules and CAIs
in the last stages of accretion there were only a few large planetary formations
one of the last of these later formations which accreted to the Earth was probably Mars-sized
resulted in a collision of cataclysmic proportions
the presence of our Moon was likely a consequence of this event