Astrophysics Flashcards
Properties of CMBR
- Uniform intensity in all directions
- Structure in background intensity/ small ripples
How the standard model of the universe affects these properties (of CMBR)
- Produced when matter and radiation decoupled
- Originally gamma radiation
- (gamma radiation) red-shifted to microwave / originally higher energy
Explain the significance of the properties (of CMBR) as evidence for the past evolution of the universe
- Evidence that universe began with big bang
- Temperature corresponds to 2.7 K / 3K / that predicted by big bang model
Formation of Neutron Star/Black Hole
- Hydrogen runs out in the star and stops burning
- This lead to the onset of Helium fusion and expand to a Red Supergiant
- Then there is a gravitational collapse of the core (as the radiation/gas pressure is now lesser than the gravitational pressure)
- Supernovae explosion takes place
- If Mass of the core is between the Chandrasekhar limit and 3 Solar Masses a Neutron Star is Formed if it is greater than 3 Solar Masses then a Black hole is formed
Cosmological Principle
Homogenous- mass is evenly distributed
Isotropic-looks the same in all directions
Why understanding of the earliest moments of universe are unreliable
- No Experimental/Physical Evidence
- States of Matter/laws of physics were unknown at the time
- The energies/ temperatures are unreproducible
Hubble’s law
v=Hnougt*d
What is the big bang and how does it explain the origin of CMBR?
-Creation of the universe (from which space/time evolved)
-(At the start) the universe was hot / infinitely dense
Expansion of the universe led to cooling
-The (current) temperature of the universe is 2.7 K / 3 K
-The (wavelength of the) gamma radiation stretched to microwaves (by the expansion).
-(Cosmological principle is supported because) CMBR is isotropic
Evidences for the Big Bang
-star-light shows red shift
-galaxies receding from Earth
-recessional velocity proportional to distance
-cosmological microwave background radiation (CMBR)
-uniform intensity in all directions
small ripple (1)
-(black body temperature) of 2.7 K (3K)-
-High ratio of helium to hydrogen (1) Indicates very high temperatures existed (1) ratio too high to originate from stellar fusion (1)
How Edwin Hubble provided evidence for an expanding universe
- red shift data for galaxies
- Which can be used to calculate velocity from red shift 1
- Which shows galaxies/ stars receding from Earth
- Distance data for galaxies can be used to calculate velocity using Hubble’s Law
- Hence, universe began at a single point
Formation of a Star such as sun and possible evolution
- (Interstellar dust and gas) cloud is drawn together by gravitational force / gravity in a gravitational collapse
- Loss in (gravitational) PE / KE increases / temperature increases
- Fusion (of protons / hydrogen nuclei) takes place
Protons / hydrogen nuclei combine to make helium (nuclei) - Energy is released in fusion reactions
- A stable star is formed when gravitational pressure is equal to internal / gas / radiation pressure
Charecteristics of a white dwarf
- (extremely) dense / (very) hot / low luminosity
- no fusion reactions occur
- it is a remnant of a low-mass star
- correct reference to Fermi pressure / electron degeneracy / Chandrasekhar’s limit
Why is the the star the brightest when its coolest
- This occurs in a red giant
- (It is cooler but has) large surface area (and therefore radiates large amounts of energy)
Evolution of Universe
- (At the start it was) very hot / extremely dense / singularity
- All forces were unified
- Expansion led to cooling
- Quarks / leptons (soup)
- More matter than antimatter
- Quarks combine to form hadrons / protons / neutrons
- Imbalance of neutrons and protons / (primordial) helium produced
- Atoms formed
- Idea of gravitational force responsible for formation of stars / galaxies
- Temperature becomes 2.7 K / 3 K or (the universe is saturated with cosmic) microwave background radiation
Absorption Spectrum
- Dark lines / bands
- against a background of continuous spectrum
