cosmology midterm #2

General Relativity

Einstein’s acc of gravity, gravity is built on the actual structure of space and time. Space like rubber sheet

prediction 1

light follows straight lines through curved space → matter can bend light

predict 2

if 4D, when move object creates gravitational waves

LIGO

was able to measure gravitational waves of black holes combined.

Universal Law of Gravitation

all objects w/ mass attract eachother in a very specific relationship.

universal law of gravitation equation:

Fg= G M1 M2 /d² 

Center of Mass

bc of momentum conservation, orbiting objects orbit around their center of mass

COM

½ D M1/M2

Why are galaxies and solar systems flat?

cloud collapses along dimension that is not supported by L=disk. 

Why are stars not flat?

they have nuclear fusion at their core = uniform outward pressure in all directions resisting collapse.

Pressure Balancing Gravity

what spherical shapes in cosmology are often in result of

Angular Momentum balancing gravity along one dimension 

what disk shapes are the result of

origin of galaxies/stars

primodial hydrogen cloud

Energy 

takes many forms. Ability to impart a force or cause damage. 

Kinetic Energy

movement of massive particles

KE eq

½ mv² 

Energy conservation

total energy is conserved. Not KE bc it transfers.

Thermal Energy

the collective KE of many particles, adding up all particles and energies (2 of them = twice)

Temperature

the avg KE of particular substance ( 2 of them = same)

Thermal energy eq

TE or V= 3/2 (h) KB T

Density

particles per volume

Energy eq

E = h * F

higher frequency

higher energy

Gamma rays Xrays UV Visible Light Infared Radio waves

light spectrum

Black Body Radiation

the electromagnetic radiation emitted according to the temp of the opaque object

Wien’s Law

the higher the temp the lower wavelenght of maximum emission.

Wavelength Peak Eq

lambda = b / T

Frequency

the number of complete wave cycles per second

Period

1/f amt of timer per cycle

wavelength

total distance covered to complete one wave

Amplitude

height

Potential Energy

Ability to perform/ dissapate energy

Gravitational Potential Energy

Eg =mgh

Total Orbital Energy

Gravitational + Kinetic Energy stays constant if there is no external force

Mass Energy

Mass Itsef is a form of potential energy

Mass energy eq

E = MC²

White Light

made up of many diff colors

Fizeau

first to discover speed of light (44% error)

Isac Newton in debate

believed light was particles

Robert Hook in debate

believed light was waves

Young’s Double Slit Experiment

had two slits which demonstrated diffraction and Interference of light = proof its waves

Diffraction

bending of waves around a barrier

Interference

two or more waves combining together

Speed of Light eq

C = d/t

atoms

consits of small dense nucleous containing protons and neutrons surrounded by electrons

Further outer shell 

higher the orbital potential energy

Emission

Photons are emitted from an atom when an electron moves from higher energy level to lower energy level.

Absorption

Photons are absorbed by an atom as an electron moves from a lower energy level to a higher energy level. 

Rutherford

found atomic structure through golf foil experiment

Backlight Emission

No need because its the atom that emitts the light. Emittion happens spontanious in an excited gas

Backlight Absorption

Need it because need photons from this backlight to absorb.

Refraction

prism produces a spectrum as light passes through it. 

Constructive Interference

troughts and crests align (add together 1+2=3)

Destructive Interference

aligned inversely (subtract 1-2 = 1)

Radio Astronomy Interferometer

synthesises a larger telescope- adds up small dishes to create imaginary large dish

Doppler Shift

If an object is moving at constant speed, and you are standing along direct line of motion there will be a shift in sound.

Blueshift

object approaching waves appear shorter

Redshift

Object receeding waves appear longer

Redshift eq

z = Vrad/ C = Lambda shift - lambda rest / lambda rest

Brightness (Watts/m²)

how bright/how much light appears when observed from a specific location.

Luminosity (watts)

total amout of light a star or collection of stars emits intrinsic property

brightness eq

B = L/ 4pi D²

Standard Candle method

find 1 object in universe, measure brightness of object within a specific galaxy to measure distance.

Herietta Leavit

discovered Cepheid variable stars and the period lumiosity relation

Cepheid Variable Stars

specific stars found at any spiral galax. Balance between pressure and gravity.

Leavitt Law

Cepheid period - luminosity relation. The longer the more luminous.

Edwin Hubble

finds “nebula” external galaxy outside of our own milky way by finding cepheids within this galaxy and calculating distance. 

Hubble Diagram

relates recession speed to distance, the farther the faster moving away. Uses redshift to find velocity.

Hubble’s Law

expanding faster the farther; implies space is growing

Olber’s Paradox

why is the nightsky dark? 

Steeper slope 

expanding faster universe is younger

shallow slope

expanding slover the universe is older

the observable universe

not the same as generic universe

scale factor eq

a = 1 + z

scale factor

the average seperation between galaxies. Set to 1 tdy and 0 at Big bang.

Recollapsing

gravity wins, enough matter to cause collapse → Big Crunch

Critical

asymptomatic, innitial kick = escape velocity, expansion forever

Coasting

exceeded escape velocity expansion forever

Deceleration parameter

qnot = ½ density matter

Found Supernova through

spectral observations: showed lack of hydrogen, photometric observation: measured brightness

Dark energy

what creates the universe expanding. counteracts gravity

Einstein’s cosmological constant

he assumed the universe was static so this counteracts gravity

Type 1a Supernovae

farther than cepheids, so they can tell us more, but are harder to find. always the same luminosity.

1.4 solar masses

the limit required for explosion. is achieved through binary system where a white dwarf star gets this from a companion star.