Astrophysics - ignore Flashcards
(37 cards)
1
Q
Nebula (2)
A
- Giant cloud of H gas and interstellar dust
- Gravitational collapse (denser & denser clumps)
2
Q
Protostar (5)
A
- Grav collapse –> work done –> Ek & temp increase
- Large core of material
- Grav field attracts matter until pressure & temp high enough for fusion
- 4 protons –> 1 helium-4 nuclei, 2 positrons, 2 neutrinos, 2 gamma photons
- momentum of photons –> radiation pressure
3
Q
Main Sequence (2)
A
- stable: radiation + gas pressure = grav pressure
- H –> He fusion in core
4
Q
Red Giant (< 10M) (4)
A
- fusion stops as H in core runs out
- radiation pressure decreases –> core collapse
- temp increases: shell H burning, core He burning
- outer layers expand and cool
5
Q
Planetary Nebula (3)
A
- He in core runs out –> collapse –> He shell burning –> increase temp
- C-O core nor hot enough to fuse heavier elements –> unstable –> collapse
- outer layers ejected
6
Q
White Dwarf (4)
A
- solid core left behind
- collapses until no further
- very hot, dense remnant of a low mass star
- grav force = Electron Degeneracy Pressure, so no further collapse
7
Q
Black Dwarf (4)
A
- fusion stops, only heavy elements remain
- radiates energy as photons leak away
- cools down
- when surface temp = few kelvin
8
Q
Red Super Giant (3)
A
- brighter than red giant
- same process
- burning forms heavier elements
9
Q
Supernova (6)
A
- iron core forms –> fusion stops –> unstable –> collapse
- immense grav pot energy force Fe protons + electrons –> neutrons
- releases huge energy
- triggers explosive blowing out of outer shell
- outer layers rebound off core –> shockwaves –> supernova
- temp high enough to fuse elements beyond iron
10
Q
Neutron Star (3)
A
- core mass > Chandrasekhar (1.4)
- core intact after explosion
- very small, extremely dense core
11
Q
Black Hole (4)
A
- core mass > 3-4
- pressure so great
- core collapses into singularity
- escape velocity > speed of light
12
Q
Singularity
A
Theoretical point at which matter is compressed to an infinitely small and dense point and the laws of physics as we understand them break down
13
Q
Electron Degeneracy Pressure (3)
A
- the pressure that stops the grav collapse of a low mass star
- core contracts, compression forces electrons into higher energy levels
- rush of electrons creates EDP
14
Q
The larger the energy level transition
A
the longer the wavelength of the photon emitted
15
Q
Value of energy level =
A
energy required to remove atom from that level
16
Q
Continuous Spectrum (3)
A
- contains all wavelengths
- hot dense sources
- fusion in stars produce this
17
Q
Absorption Spectrum (3)
A
- dark lines on continuous spectrum
- caused by light passing through an absorbing medium
- Sun’s atmosphere
18
Q
Emission Spectrum
A
- frequencies of em radiation emitted due to electron energy level transitions in that element
- unique for each element
- hot low pressure gases
19
Q
As surface temp increases
A
Peak of intensity occurs at lower wavelength
20
Q
Ideal Black Body
A
absorbs and emits all wavelengths
21
Q
Hotter/Cooler objects colours
A
Hotter: white/blue
Cooler: red/yellow
22
Q
Astronomical Unit
A
mean distance from centre of Earth to centre of Sun
1.5x10^11m
23
Q
Stellar Parallax
A
The apparent shifting in position of a star viewed against a background of distant stars when viewed from different positions of the Earth
24
Q
The Doppler Effect (2)
A
- the apparent shift in wavelength/frequency caused by the relative motion between a wave source and an observer
- moving towards observer = longer wavelength
25
Hubble's Law (4)
- showed universe expanding by observing red shift of absorption line spectra from light of distant galaxies
- distant galaxies moving away from Earth
- red shift more pronounced for further galaxies
- recessional velocity proportional to distance from Earth
26
Ober's Paradox (2)
- darkness of night sky conflicts with assumption of an infinite and eternal static universe
- if true every line of sight = star, night sky as bright as Sun
27
Cosmological Principle
On a large scale universe is uniform:
- isotropic (same in all directions)
- homogeneous (uniform density)
- subject everywhere to same physical laws and models
28
Cosmic Microwave Background Radiation (4)
- originate from early Universe
- microwave radiation received from all directions
- max wavelength corresponds to 2.7K
- Big Bang theory: hot and dense = thermal radiation
29
The Big Bang Theory
Universe created from an infinitely hot, small, dense singularity where all the universe's current mass was situated
30
Evidence for Big Bang Theory
- Hubble's Law: if expanding, point where started expanding
- No BB = No MBR
31
General Relativity
Space and time connected together as space-time
Property that connects 3 Ds of space and 4th of time
32
Evolution of The Universe
- 0s: singularity --> Big Bang
- <1s: 4 forces originated
- 100s: fundamental particles (quarks, leptons, photons + anti) formed
- matter & antimatter annihilate (gamma)
- protons cool --> fusion --> helium nuclei
- 300,000,000 years: atoms
33
The Future of the Universe: Density too High (4)
Closed
- grav forces prevent galaxies going out forever
- slow and stop
- collapse in --> Big Crunch
34
The Future of the Universe: Density too Low (4)
Open
- galaxies reach terminal velocity when far apart so negligible grav forces
- separate forever
- cool as they do
35
The Future of the Universe: Density = Critical
Flat
- universe decrease in velocity as it expands
- reached final finite size after infinite time
- galaxies slow but never stop
36
Dark Matter (5)
- matter which cannot be seen & doesn't emit/absorb em radiation
- expect velocity to decrease as move away due to weak g
- not case for galaxies
- mass spread out & not concentrated
- mass is concentrated at centre --> another type of mass
37
Dark Energy
Type of energy that permeates the whole universe & opposes the attractive force of gravitation between galaxies via exertion of a negative pressure
