Everything Stars Flashcards
What are safe methods to observe the Sun?
Pinhole Projection:
Sunlight passes through a pinhole lense into the opposite wall.
Telescopic Projection:
A telescope with a sun shade is pointed at the sun, the light through the telescope is then projected by it onto paper. (sun shade, shades the paper allowing for the sun to be shown)
What is a H-Alpha Filter?
A filter used in solar observation.
It only allows a wavelength of 656nm through (n=3 to n=2)
Why is a H-Alpha Filter useful?
It produces contrast on the Sun’s Surface.
Allowing for better viewing for features, such as Solar Falres, Sunspots,Chromosphere and prominences.
What is a Sunspot?
Cooler (∴ darker) regions on the Photosphere, where the convection currents are inhibited by strong localised magnetic fields.
what is the coolest part of the Sun?
Sunspots
What Temperature are Sunspots?
Umbra (darker central): 3500K
Penumbra (surrounds umbra): 4500K
Why are Sunspots in Pairs?
North and South polarity
How big are Sunspots?
1000km - 12000km
What is the Sun’s Rotaional period?
Equator: 25 days
Poles: 36 days
How can the Sun’s Rotational Period be measured?
The distance a Sunspot will move across the sun in a certain period of time is used
Why does the Sun’s Rotaional Period differ across Latitudes?
Because the Sun acts as a fluid
How long is a Solar Cycle?
11 years
What is a Solar Cycle?
The time taken for Sunspot sto travel form the poles to the equator
What is a Butterfly Diagram and what is it used for?
It shows the positioning of Sunspots and can be used to determine the length of the Solar Cycle
Where are Sunspot located?
On the Photophere.
Few Sunspots above 40°N/S
Sunspots increase as latitude decreases
Few Sunspots below 10°N/S
What happens to Sunspots over the Solar Cycle?
They move closer to the equator
What is the Diameter of the Sun?
1.4 million km
How far is Earth form the Sun?
150 million km
1 AU
What is the composition of the Sun?
71% H
27% He
2% Other
(asthe sun is 99% mass of solar system this is also the composition of the solar system)
What are the layers of the Sun?
Core: 15 million K Radiation Zone: 7-2 million K Convection Zone: 2 million - 5800 K Photosphere: 5800 K Chromosphere: 4500 K Corona: 2 million K
Why is the Corona so hot?
Temperature is average kinetic energy of particle, as there are few particle they are able to move very fast
Where on the Sun are X rays emited?
Corona and Magnetic loops.
As they require very high energies.
What is the Proton-Proton Chain?
A nuclear fusion chain reaction, which occurs in the core of the Sun
4 protons → Helium-4 nucleus
What is the Solar Wind?
A steady stream of charged particles (p, e-, α and ions), flowing outwards in all directions from the Sun’s corona
What are the energy range and speed of the Solar Wind?
0.5 - 10 keV
400 km/s (4 x 10^5)
What is Heliopause?
The point at which the solar wind is no longer strong enough to push away form the Sun.
Often considered the edge of the solar system.
What is the Van Allen Belts?
They are regions within the Earth’s magnetic field where where charged particles can become trapped
Where are the Van Allen Belts?
Magnetosphere
Inner belt: 1.5 Earth radii
Outer belt: 5 Earth radii
What are the effects of the Solar Wind?
Aurorae
Geomagnetic Field
Cometary Tails
Ionising space mission
What causes the Aurorae?
Overflow of the Van Allen Belts.
High energy electrons can enter the atmsophere at high latitudes causing excitation and de-excitation of upper atmosphere (100km up)
When are Aurorae at their greatest?
Solar Maxima
How do Geomagnetic storms effect Earth?
Can effect radio comunication
effect the transmission of power through power lines
What causes Geomagnetic Storms?
Coronal Mass Ejections
What causes a Comets Tail?
The Solar wind ionises and creates a ion/gas tail pointing away form the sun
What is the Bayer System?
The system used for denotaing the brightness of stars within a constellation.
eg. Alpha Orionis is Betelgeuse and Beta Orionis is Rigel
What is the Intensity of Light Proportional to?
1/r²
What is Apparent Magnitude?
The logarithmic scale for the brightness of astronomical objects, as they appear from earth.
Where the lower the number the brighter it is.
What are range of Apparent Magnitude?
Quasar: +26 Limit of bino/telescope: +10 Limit of naked eye: +5 Bright stars: 0 Bright Planet: -2 Moon: -11 Sun: -26
What is the base of the Apparent Magnitude scale?
100^0.2 ≈ 2.51
What are the differences in Magnitude?
Δ1 = x 2.51 = 100^(1/5) Δ2 = x 6.31 = 100^(2/5) Δ3 = x 15.85 = 100^(3/5) Δ4 = x 39.81 = 100^(4/5) Δ5 = 100 = 100^5/5)
What are examples for the brightness of stars?
- 0 = α Lyra (Vega)
- 1 = β Gemini (Pollux)
- 0 = α Ursa Minor (Polaris)
- 0 = γ Ursa Minor (Pherkad)
What is Absolute Magnitude?
The apparent magnitude a star would have if located at a distance of 10 parsecs
What is the equation for Absolute Magnitude?
M = m+5-5log(d) M = Absolute Magnitife m = Apparent Magnitude d = Distance to object (in Parsecs)
What is the range of Absolute Magnitude?
-10 to +15
Lower the number the brighter the object
What is the Sun’s Absolute Magnitude?
+5
What is a Black Body?
An object that can absorb and emit radiation of all wavelengths
What happens if the Temperature of a Black Body is increased?
The range of emited wavelengths increases (greater range of photon energy).
The Peak Wavelength decreases (Wien’s Law)
The Power output increases (Stefan’s Law)
What is the Peak Wavelength?
λmax
The Wavelength at which the intesity of light is a maximum
What is an example of a Black Body?
Stars
As they emit and absorb all wavelengths
What is a Planck Curve?
It’s the graph that shows the Wavelength and intensity of radiation from a star
What happens to a Planck curve if the temperature increases or decreases?
Increase: Peak (λmax) shifts left as higher frequency means lower wavelength. And Peak increases in height.
Decrease: Peak Shifts right and down
What is Wien’s Law?
λmax ∝ 1/T
λmax x T = Constant
Wien’s Constant = 0.00290
What is Stefan’s Law?
P = σAT^4 P = Power σ = Stefans constant = 5.67 x 10^8 A = Surface area of black body T = Temperature
What is Stellar Spectroscopy?
A system where light form a star is passed through a diffractio grating to detect absorption lines.
Why is Stellar Spectroscopy used?
It shows what elements or molecules are in a star.
It finds the radial velocity of the star.
It finds the Surface temperature of the star
It finds the Magnetic field strength of the star
What order are Star classified in?
O: 50-25 x10^3 K Blue, He is prominent
B: 25-11 x10^3 K Blue/White, H is prominent
A: 11-7.5 x10^3 K White, H is prominent
F: 7.5-6 x10^3 K White/Green, Metals are prominent
G: 6-5 x10^3 K Yellow, Metals are prominent
K 5-3.5 x10^3 K Orange, Metals are prominent
M: <3.5 x10^3 K Red, Molecules (eg TiO) is prominent
What is the Sub categories of Star classification?
0-9 0 is hottest 9 is coldest eg. F9 is hotter than G0 but F9 is colder than F8
What calssification is the Sun?
G2
Why has Star classification uneven ranges?
To offer greater resolution as most stars are between A and K
What is the Hertzsprung-Russel Diagram?
A graph showing the tempertaure and absolute magnitude of stars?
What shape is a Hertzsprung-Russel Diagram?
Go Look for one
What can be calculated from a Hertzsprung-Russel Diagram?
The distance to a star. Using its temperature/classification and its apparent magnitude.
As Absolute Magnitude can be estimated from the graph. then put in to M = m+5-5log(d).
What is Intensity proportional to?
I ∝ 1/r²
Intensity ∝ 1/distance²
What is a Lightyear?
The distance which light travels in 1 year
9.46 x 10^15 m
What is a Parsec?
The distance at which a star will give a parallax angle of 1 arc second.
How is Parallax measured?
The angle which a star appears to move compared to distant background stars.
Measure from either side of the Earths orbit around the Sun.
Paralax is measure using a right angle triangle with the sun
What equation links Parallax and Discance?
Distance (pc) = 1/ Parallax (“)
What is a Cepheid Variable?
A type of star with variable apparent magnitude.
They are used as Standard candles
Named after the first discovered Delta Cepheus
What is a Standard Candle?
An object with a known absolute magnitude.
eg:
Type 1a Supernovae, absolute magnitude of -19.5.
Why do Celpheid Varibles change in apparent magnitude?
Because they pulsate about an equilibrium.
1) Grav pulls in, increaseing temp ∴ more fusion ∴ more radiation pressure.
2) Star expands, pressure decreases ∴ temp decreases ∴ fusion slows.
3) Grav pulls in
How do you measure the distance to a Cephied Variable?
Measure its period, which allows for the calculation of absolute magnitude.
Calculate distance from average apparent magnitude and absloute magnitude.
What is the equation for the Absolute Magnitude of Cephied Variables?
M = -2.81 log(T) -1.43 M = Absolute Magnitude T = Period of star in days (sometimes π rather than T)
What are Binary Stars?
Two stars that are Gravitiationaly Bound to each other and orbiting a common centre.
What is an Opitcal double?
Stars that look close to gether due to the perspective.
One is far beyond the other.
What is the shape of the graph for the Intensity of an Eclipsing Binary?
The intensity has dips when the stars are behind each other.
What do Large and small dips mean in an Intensity-Time graph?
Large dip: Faint in front of bright
Small dip: Bright in front of faint
What does it mean for Eclipsing Binary stars if the dips are all equal size?
The stars are the same intensity
What parts of the EM Spectrum reach the Earth’s surface?
Visable
Radio
Microwaves
Small sections of the InfraRed
What is the best location for Telescopes?
Gamma: Space X-ray: Space UV: Space Visable: Ground and Space IR: Ground (at high altitudes) and Space Microwave: Ground Radio: Ground
What absorbs the EM in the Atmosphere?
Gamma: O2, N2 and Excited Nuclei X-ray: O2, N2, Atoms and Molecules UV: O3 Visable: H2O (Clouds) IR: H2O (Clouds) Microwave: H2O and O2 for short λ Radio: e- for long λ
What does a shorter Wavelength require from a Telescope?
A more accurate/smoother Surface.
What is the Rayleigh Criterion?
Two Stars cannot be resolved if θ > λ/D
θ = Angular Seperation / Radians
λ = Wavelength / m
D = Diameter of the objective(mirror) / m
What does the Rayleigh Criterion mean?
A Larger wavelength requires a larger mirror to be able to resolve well.
What is a Radio Interferometer?
AKA: Aperture Synthesis Arrays
The use of multiple telescopes operating together to increase resolution.
What is the Effective Resolution of a Radio Interferometer?
The Base Line of the Array
the distance between the telescope
What was discovered using Radio Telescopes?
Quasars: Identified in the visable using the occulation of the moon, as it showed where it was based on where the radio stopped.
Jets from Black Holes: Above and Below the plane at which matter enters the hole.
Structure of the Milky Way: 21cm wavelength can penetrate stellar gas and dust.
Neutrons Stars: Beams are Radio waves.
What are the Advantages of a Space Telescope?
It’s above the atmosphere: no refraction or scattering.
All wavelengths can be observed: no atmosphere to absorb wavelengths.
Can see the entire celestial sphere: due to the orbit shape and period.
What are Disadvantages to Space Telescope?
Expensive to develop, construct and launch.
Hard/impossible to upgrade or fix the hardware. (software is sometimes upgradable).
What is the Power of a Telescope proportional to?
Power ∝ Diameter²
as area is roughly diameter²
What is the Structure of Telescopes?
Gamma and X-ray: Series of mirrors slightly reflect the light closer and closer to focus
UV, IR and Visable: Mirrors reflect the light
Radio: Large reflecting dish
What are discoveries of IR Telescopes?
Planetary discs
Nebula / Star formation
What are the 4 types of Nebulae?
Absorption Nebulae
Emission Nebulae
Planetary Nebulae
SuperNovae Remnants
What is an Absorption Nebula?
A Nebula which contains no stars, and is just a cloud of gas and dust.
They are creation nebulae as there dust and gas can form new stars.
They are observed as a silhouette.
What is an Emission Nebula?
A creation nebula which contains newly formed stars.
They emit light as H and O atoms within the gas and dust are excited.
What is a Planetary Nebula?
It is the end state of a low mass star.
The radiation pressure within the star is stronger than gravity, causing the layers to be blown into space.
They are symetrical and form shapes such as rings and hourglasses.
They have a white dwarf at the centre.
What is a Supernova Remnant?
The end state of a high mass star.
They look like an explosion.
Containing a Black hole or Neutron star
What is an Open Cluster?
An irregular shaped clump of 100’s of stars.
The stars within are young, hot and recently formed.
They are within the Milky Way.
What is a Globular Cluster?
Regular spherical shaped clump of 10000’s of stars.
The stars are often about 10 billion years old.
There are 150 with the Milky Way.
They form a “Halo” around the Galaxy
What is the Evolutionary proccess for a Low Mass Star?
Absorption and Emmision Nebula
Main Sequence (or brown dwarf if < 0.1 solar masses)
Red Giant
White Dwarf
What does a Stars Evolutionary path depend on?
Its Mass
What happens in the Nebula Phase of Star Evolution?
Gravitaional and Ekectrostatic forces make H clouds collapse in to hot dense pockets.
These can then begin fusion.
What is a Brown Dwarf?
A Stellar body which wasn’t big enough to begin fusion.
look like jupiter
What happens in the Main Sequence?
Hydrostatic Equilibrium between the gravitaional forces and raditaion pressure, keep the amount of fusion stable.
What happens if Gravity is stronger than the Radiation Pressure?
The star will collapse, raising the core tempertaure increasing the rate of fusion. Thus increasing the radiation pressure.
What is Radiation Pressure?
It is the outwards pressure applied by the photons being emited by the fusion in a stars core.
It counter acts the inwards force of gravity and maintains the stars size.
Do High or Low mass stars have a faster rate of fusion.
High mass stars have a higher rate of fusion, due to the higher temperature caused by a higher pressure createde by gravity.
What is considered a high or low mass star?
Low Mass is less than 8 solar masses
High mass is greater than 8 solar masses
What is the Triple Alpha Process?
The fusion process from three α particles to a Carbon nuclei.
What causes a star to become a Red Giant?
When a reduction of nuclear fusion (producing H) in the core occurs. There is a reduction in Radiation Pressure, causing Gravitaional Collapse. This increases pressure and temperature causing fusion of heavier nuclei.
What happens if the Radiation Pressure from fusion of heavier elements is greater than gravity?
The layers of the star will be ripped away fomring a planetary nebula
What is the Chandrasekhar Limit.
The theoretical mass limit of a stars core as to whether it will become a supernova or planetary nebula.
≈ 1.4 solar masses
What is a White Dwarf?
Stars balenced due to gravitational collapse and electron degeneracy pressure.
What balances a Main Sequence Star?
Gravitational Collapse and Radiation Pressure
What balences a White Dwarf?
Gravitational Collapse and Electron Degeneracy Pressure.
What is Electron Degeneracy Pressure?
The Due to the Pauli Exclusion Principle, whereby no two electrons can exist in the same state (thus they cannot exist in the same energy level at the same time.
What is the Evolutionary Process of a High mass star?
Absorption and Emission Nebula Main Sequence Red Supergiant Supernova Neutron Star (lower mass) or Black Hole (higher mass)
What is a Red Supergiant?
A very large star formed by the depletion of H in the core and subsequent fusing of heavier nuclei.
What causes a Main Sequence star to become a Red Supergiant?
The depletion of H in the core, causing less fusion, causing less radiation pressure, causing a gravitaional collapse. The collapse causes a increase in pressure and temp causing a layer in the core to form of the fusing of heavier elements, this happens repeatedly up to Fe 56.
Why can stars not fuse heavier elements than Iron 56?
Iron 56 is the most stable nuclei. Therefore less energy is released than put into the fusion of a heavier nuclei.
What is the Power output of an A1 Supernova?
M = -19.5
≈10^10 Suns (the same brightness as a galaxy)
≈ 10^44 J (total energy output of the sun over its entire life)
How can the distance to an A1 Supernova be measured?
As they are standard candles their Absolute Magnitude is always -19.5, when its Apparent Magnitude is measured they can be put into the equation.
M = m + 5 - 5log(d)
What is a Neutron Star?
A Star composed entirely of Neutrons
What causes a Neutron star?
The gravitaional collapse of a Red Supergiant (if below a certain size) will collapse with such pressure it will force the electrons in the atoms into the nuclei causing Electron Capture.
What balences a Neutron Star?
Gravity and Neutron Degeneracy Pressure.
What Properties does a Neutron star have?
≈ 10km diameter (the red supergiant could reach past neptune).
Made of Neutrons
Very High density (≈240 million tonnes per cm^3)
Very High g field near the surface
Rotates very fast (100-1000Hz)
Very strong magnetic field
Emits an narrow beam of Radiowaves
Roughly how big is a Red Supergiant?
It could reach neptune if at the centre of the solar system.
What is the Observational evidence for Neutron Stars?
Radio Telescopes observe the pusling due to the rotaion and emission of lots of radiowaves.
What are Neutron stars sometimes known as?
Pulsars
What Properties does a Black Hole poccess?
Very Very large g field near to surface.
Very Very large Density (infinite?)
Very small radius (Zero? as cannot see past Swarzchild)
Most are several solar masses.
What are the requirement for the formation of a Neutron star?
The neutron star must be at least 3 solar masses
What is a Swarzchild Radius?
The Event Horizon.
The distance from the centre of the hole at which the escape velocity is the speed of light
`What evidence is there for a Swarzchild Radius?
The frequency emitted by the accretion disc increases to X-rays. As it gets hotter due to the increased velocity
How do Low mass stars move on the H-R Diagram?
Main sequence → Red giant → White dwarf
How do High mass stars move on the H-R Diagram?
Main sequence → Red supergiant
Why are Neutron stars and Black Holes not on the H-R Diagram?
Because they do not emit visable wavelengths.
What is Observational Evidence for Black Holes?
The emission of X-rays due to the accretion disc and it behaving as an eclipsing Binary around its partener star.
What is the Distance between Earth and the centre of the Milky Way?
≈ 10000pc
What is the Diameter of the Milky Way?
≈30000pc
What is the Milky Way?
A band of light across the sky whcih binoculars can resolve into thousands of stars.
This is the plane of our Galaxy
What shape is the Milky Way?
From the side it appears as a flat disc with a bulge above and below the middle.
From above it appears as a Barred Sprial galaxy
How thick is the Central Bulge of the Milky Way?
≈6000pc
What is the 21cm Line?
It is the wavelength of Atomic Hydrogen.
It is a frequency which can penetrate intersellar dust and the earths atmosphere. Allowing for the galaxy to be obseved despite many wavelengths being blocked.
What was discovered using the 21cm Line?
The rotaional velocity of the Milky Way/
What is the Local Group?
≈ 30 of the closest galaxies of which the Milky Way is part of.
What are examples of objects in the Local Group?
Large Magellanic Cloud
Small Magellanic Cloud
Andromeda (M31)
Triangulum (M33)
What is the Virgo Cluster?
It is the Cluster which the Local Group is part of.
It consists of about 3000 galaxies and is roughly centred on the elliptical galaxy Virgo (M87). It is about 33Mpc across
What is the Hydra-Centaurus Supercluster?
It is the Supercluster to which the Vigro cluster belongs.
What are the five types of Galaxy?
S Spiral SB Barred Spiral E Elliptical I Irregular S0 Lenticular
What is a Spiral Galaxy?
It has a flattened Disc conatining Star formation and a central bulge.
What is a Barred Spiral Galaxy?
It has a Central bar through the nucleus from which the arms emerge perpendicular to.
What are the sub-categories of S and SB Galaxies?
a: has the most prominent nucleus and has tight arms.
b: It is inbetween a and c
c: has a small nucleus and open spiral arms.
What is a Elliptical Galaxy?
Symetrical dense clouds of stars and gas which increase with brightness at the centre.
E0: Spherical
E7: Highly Elliptical
What is an Irregular Galaxy?
A Galaxy with no shape or structure.
They are generally quite small.
What is a Lenticular Galaxy?
A class between Elliptical and Spiral
What type of Galaxy is the Milky Way?
SBb
What is Hubble’s Tuning Fork Diagram?
A model for Galactic evolution by Edwin Hubble. It has all galaxies starting as Elliptical then splitting to either Spiral or Barred Spiral. With "a" sub class being befor "c"
What is an Active Galactic Nucleus?
A galaxy which emits X-rays and Radio waves from its nucleus.
What is a Radio Galaxy?
A primarily elliptical galaxy which emits 10^6 more energy than a normal galaxy.
The radio emissions produce two large lobes either side of the galaxy.
What is a Seyfert Galaxy?
A very bright, compact sprial galaxy which emits strong and variable IR and X-rays.
What is a Quasar?
A very optically faint galaxy which emits a huge amount of X-rays. which have been massivly red shifted.
They are very far away and thus very old.
What is a Blazer?
A quasar like object that is much closer, thus less red shifted.
Emit strongly in whole EM spectrum.
They have varying bightness generally with T ≈ 1 or 2 days.
What is Cosmology?
The Study of the large scale structure of the Universe.
Its past, present and future.
What is the Doppler Effect?
The apparent change in Wavelength(∴ frequency) of a source due to its relative radial motion with respect to the observer.
What is the equation for Doppler Shift?
Δλ/λ = v/c = Z Δλ = Differnce between actual and observed wavelength. λ = Actual Wavelength v = Radial velocity of source c = Speed of light Z = Doppler shift
What does a Blue Shift mean?
The frequency is increasing (∴ wavelength decrease).
It means the emitter is moving towards the observer.
What does a Red Shift mean?
The frequency is decreasing(∴ wavelength increasing).
It means the emitter is moving away from the observer.
What are uses of the Doppler Effect?
To calculate the relative radial motion of an object.
To identify unresolvable spectroscopic binary systems.
What is Hubble’s Law?
Except for a few nearby galaxies, the speed at which a galaxy is receding from us is proportional to its distance from us.
What is assumed by Hubble’s Law?
We are NOT the centre of the universe. All objects are moving away from each other.
The universe is not expanding quicker at the edge.
The universe has no edge.
The universe is expanding uniformly.
What is the equation for Hubble’s Law?
v =H(0) x d
v = Recession Velocity / km s^-1
H(0) = Hubble Constant (68 km s^-1 Mpc^-1)
d = Distance to galaxy / Mpc
What can be used to identify the distance to a galaxy for Hubble’s Law?
1a Supernovae
Hubble originally used the anglular width if the galaxy using the priciple that small galaxies are far away
What are the Cosmological Models created by Hubble’s Law?
The Big Bang
The Steady State Theory
The Cyclic Universe
What is evidence for The Big Bang?
Cosmic Microwave Background Radiation
Quasars
Relative Abundence of Elements
How can the age of the Universe be calculated?
Age = 1 / Hubble Constant
Assuming the universe has been expanding at a constant rate.
Why is CMB Radiation evidence against Steady State?
After the big bang and before recombination the universe was plasma and EM can’t pass through it. During the recombination epoch atoms formed and space became “transparent”. CMB is Gamma photons that were from this tiem and have been red shifted since.
What is the CMB Radiation?
A constant uniform signal from all directions at all times.
With a wavelength of 1.07mm.
What is the Temperature of Space using CMB?
Wien’s Law using CMB wavelength of 1.07mm
λ(max) x Temp = 0.00290
T = 0.00290 / λ(max) = 0.00290 / 0.00107
T = 2.71 K
How are Quasars evidence against the Steady State Theory?
They are massively Red shifted (second to only CMB).
Therefore they are far away, thus long ago.
Showing the universe has changed.
Is there evidence for The Big Bang?
Not really.
Only evidence against other theories (eg steady state)
What is Dark Matter?
Matter which constitutes about 25% of the universe, and 80-90 % of the Galaxy. Theories include Neutrinos and WIMPs (weakly interacting massive particles).
Where in the Galaxy is Dark Matter located?
Around the edge of the Spiral Arms.
What evidence is there for Dark Matter?
Spiral arms of galaxies.
They spin with a constant angular velocity, which is only possible if the majority of mass is outside the arms.
With out this the arms would have different angular velocity along them (due to circular motion) and would be pulled apart.
How does Dark Matter and Dark Energy relate?
They don’t.
They are both dark because it can’t be seen, understood or identified.
What evidence is there for Dark Energy?
The rate of expansion of the universe is increasing.
Creating the complication that there is a repulsive force opposing gravity. Which was thought to be slowing expansion.
What is the Composition of the Universe?
5% Baryonic Matter
25% Dark Matter
70% Dark Energy
What is the Big Crunch?
The theoretical end of the universe from the slowing of expansion. and collapse due to gravity.
What is Big Freeze or Heat Death?
The continued expansion would cause temperature to asymptotically approach 0k.
Matter and energy would be so spread out that no stars could form.
What is the Big Rip?
The density of Dark energy increases with time causing greater acceleration of universe expansion. Hubble constant increases.
All forms of matter disintergrate into unbound elementary particles and EM.
