# IB Physics Option E Astro

## 54 terms · Physics IB Option E

### parsec

Average distance between stars (3.26 ly)

### pulsar

A rapidly rotating neutron star emitting electromagnetic radiation in the radio region.

### when parallax method fails

if star is too far away

### Parallax method

d (in parsecs) = 1/arcseconds

### light year

distance traveled by light in one year

### Stability of a star

depends on gravitation (collapses it) and radiation pressure (expands it)

### Radiation pressure

high pressure in stars => fusion => radiation (lots of particles moving) => stabilize the star

### Luminosity

amount of E radiated by the star per sec

L= (5.67E-8) AT^4

### apparent brightness

the received energy per sec per unit area of a detector
b = L/(4pi d^2)
unit: W m^-2

### how is apparent brightness measured?

a charge-coupled device
CDD - records number of photons released by an image in space. The # of photons recorded is proportional to brightness.

### Wien displacement

(lamda) * T = 2.9E-3

lamda = peak wavelength (highest point/value on graph)

### Why do stars show different absorption spectra

different temperatures

(Hydrogen in hot star is ionized ---> no electrons ---> can't absorb light)

### Makeup of stars

Hydrogen (70%) and helium.

### red giant

high luminosity, low temperature star

### white dwarfs

low luminosity, high temperature star

### cepheids

a periodic variable star due to periodic interaction of radiation with matter in atmosphere

relationship between the period of the light curve and peak luminosity

longer period = larger Luminosity

### apparent magnitude

how bright a star appears to earth

= -(5/2) log(b/b_0)

### absolute magnitude

how bright a star would look if placed 10 pc from you.

m-M = 5log (d/10)

### How to use thr spectroscopic parallax

start out with known wavelength and apparent brightness

wavelength ---> use Wien's law ----> to find temperature ----> use HR diagram ----> to find luminosity ----> use d = sqrt(L/4pi b) = distance!

### homogeneity principle

on a large scale, the universe looks uniform

### isotropy principle

no one direction of the universe is special in comparison with another

### cosmological principle

universe has no edge and no center

### Olber's paradox

Olbers' paradox is the argument that the darkness of the night sky conflicts with the assumption of an infinite and eternal static universe. It is one of the pieces of evidence for a non-static universe such as the current Big Bang model.

### why a finite universe?

1. Finite star #
2. Finite universe age
3. redshift

### isotropy of radiation

2.7K ----> cosmic background radiation -----> remnant of the hot explosion @ beginning of time. As universe kept expanding, T fell to current 2.7 K

### Evidence for Big Bang

1. expansion of Universe
2. cosmic background radiation
3. Helium abundance

### closed Universe

radius of Universe increases and decreases back to zero

p is actual density of universe
p_c is critical density
p > p_c

### open Universe

increases w/o limit

p is actual density of universe
p_c is critical density
p < p_c

### flat Universe

increases, but increases slower after time

p is actual density of universe
p_c is critical density
p = p_c

### what is dark matter

Too cold to see matter.

### Types of dark matter

1. WIMPS i.e. neutrinos
2. MACHOS i.e. black and brown dwarfs

### dark energy

1.A repulsive force that counteracts gravity on a large scale.
2. Stronger than gravity.
3. causes universe to accelerate expansion.

### How are stars formed

1. cool gas collapse under own gravitation
2. heats up
3. visible light ----> protostar
4. pressure increases
5. core is formed
6. Temp is high; nuclear fusion starts

L ~ M^4

T ~ M^-3

### Formation of red giant

1. H in core exhausted
2. no nuclear reactions to counteract pressure
3. contracts under own weight
4. Gravitational PE released
5. Heats up core and surrounding envelope of H
6. H fuses, releases Energy
7. Outer layers of star expands
8. Because of expansion, outer layers cool

### <0.25 Solar Masses

white dwarf with He core

### 0.25 - 4 Solar Masses

White dwarf w/ oxygen core

### 4-8 Solar Masses

White dwarf w/ O/Ne/Mg core

Neutron star

Black hole

### How are white dwarfs still stable

pressure created by electrons restricts further contraction.

### Chandrasekhar limit

1.4 Solar Masses (of just the core)
If core is heavier -----> Neutron star or Black hole

### Neutron star formation

1. >8 Solar Masses
2. Nuclear fusion produces LOTS of photons
3. Very energetic photons
4. Photons rip nuclei apart
5.. Only protons and neurons left
6. High density makes protons into neutrons
7. Are now stable because of pressure of neutrons (similar to how pressure of electrons in white dwarfs keep them stable)

### Evidence of black holes

gravitation influences surrounding stars

### Hubble's Law

More distant objects move faster away.

v=Hd

### Evolution of Universe: 10^-43 s

1. All forces were unified turning all existing particles into the same thing
2. Temp ~ 10^32 K

### Evolution of Universe: 10^-35 s

1. Strong nuclear force separates
2. T falls to 10^27 K
3. rapid expansion

### Evolution of Universe: 10^-12 s

1. All four known Forces separate
2. T~ 10^ 16 K

### Evolution of Universe: 10^-2 s

1. protons and neutrons form

1. Nuclei form

### Evolution of Universe: 3E5 years

1.atoms form
2. matter dominates existance

### Evolution of Universe: 0.5E6 years

Stars and galaxies form

### matter vs. antimatter

1. antimatter forms into matter
2. matter forms into antimatter
3.Universe cools, and matter can't form into antimatter anymore
4. Now more matter