sign in sign up
<<
Home , Bok globule

Group 3 Week 7 Notes: Monday:

Thermal or Blackbody radiation: a spectrum of continuous radiation -a blackbody is an idealized substance that doesn't exist in nature. It's a perfect absorber and a perfect emitter of radiation -These blackbodies can be charted with the formula: wavelength = .0029/T

-Apparent brightness vs. "appears to be" "really is"

-1 watt = 1 joule / 1 -Apparent brightness drops off at 1/d^2 -"The Flux": Joules/(second*meter^2) -The flux is what is coming off a square meter of a sphere (luminosity would be the whole sphere)

or you can also write this equation as: L=4*pi*r^2*f

-The Stefan–Boltzmann law, also known as Stefan's law, states that the total energy radiated per unit surface area of a black body per unit time, j*, is directly proportional to the fourth power of the black body's thermodynamic temperature T (also called absolute temperature):

Heat in = heat out

(l/4pid^2)(surface area of a )(1-a) a is the albedo: the ratio of reflected radiation from the surface to incident radiation upon it. all of this equals

This formula isn't exactly perfect. -The in our don't follow it exactly -Especially the inner planets

------Molecular clouds turn into which turn into planetary systems Wednesday:

Star Formation:

In spiral , 80-90% of is found in stars -The other 10-20% is found in dust and gas

-The gas in a between the stars () is about 1/4 and 3/4 -The gas is created through a process known as nucleosynthesis -Nucleosynthesis is a type of fusion that goes on in very high temperatures. -This produces elements -The universe is mostly hydrogen, helium, and lithium because of this process happening in the Big Bang

-Conservation of Angular Momentum: -L = mvr -Imagine a record player spinning around on a turn table -The linear velocity changes because you are farther away from the center depending on what point of the disk you choose -The angular velocity doesn't change because no matter where you are on the disk, you are spinning at the same rate as any other point on the disk -The relationship between the two is L=wm(r^2) -The L before must equal the L after -In this formation process, the spinning of the clump (dense core, on the diagram above) causes the 'stuff' within it to break apart. -This makes it seem like stars shouldn't be able to form -However, the star begins spinning differently than the record player or the ice skater examples that we looked at

Friday:

4.6-4.7 billion years ago: the age of our solar system (based on radioactive dating) 13.7 billion years old: the age of our universe (general relativity calculations)

The became a inside of a . -the protostar formed inside of the disk -hot protoplanetary star -'solar ' -inside, there was 99% hydrogen and helium, but the 1% of the 'other stuff' is incredibly important to our solar system

Star formation occurs between a thick layer of dust, making it hard to see - allowed us to look 'through' the dust in order to witness star formation

The thick dustlooks like this and is known as a bok globule

This is a protoplanetary disk: The dust near the center is so concentrated that it blots out the light, and the dust dissipates as you get farther out.

Moving from this to an actual solar system: -As the cold clump of gas compresses thanks to , it actually heats up -In the protostar, there is a conversion of gravitational potential energy into kinetic energy (energy of motion) and this is then turned into thermal energy -As you move away from a gravitational field, gravitational potential energy increases -The gas is gaining kinetic energy, which means they are heating up -When this happens, it's known as the Kelvin-Helmholtz contraction. -This is why the cold clumps becomes a hot protostar -When the center of the protostar gets hot enough, thermonuclear fusion occurs. -This gives the star an energy source -The energy source at the center fights off the collapse form the gravity, thus making it a stable object known as a star

-The disk isn't all that different. -The gravitational force is strongest near the midplane, and the durst gets hottest along this plane -The gets so hot that it vaporizes the dust that surrounds it.

-Once it is stabilized, it starts cooling -It cools so that it is coldest farther away from the stable center energy source. -As the disk cools down, particles that were in gaseous form begin to condense out -e.g. iron bis all over the disk begin to start solidifying again - particles with a high melting point and is known as a refractory material -Depending on where the particles are located, it may or may not be in solid form. -This depends on the object's melting point and also how far away (and therefore how cool) it is from the center -These particles with low melting points are known as volatile -Helium and Hydrogen never condense because their melting point it too low

-These particles, as they condense, begin to form dust again. -However, this dust is arranged into 'zones'

-The dust starts gathering closer and closer. It goes from dust-sized to 'dust bunnies' through electrostatic processes and collisions (1m-10m) -It gets harder to get from this size to something 1km in size. Up until this point, gravity isn't really important because the two things aren't big enough to be attracted to one another -However at this size, the gravity actually pulls fragments together. -Known as planetesimals - The closer to the center, the more metallic -The farther away, the more icy (frozen anything) -this ice can attach itself to the planetesmials and make them bigger and bigger. -As they grow in size, they attract the gas that surrounds them, getting bigger -This is the difference between the terrestrial and gas planets.