5.5 - Astrophysics and cosmology

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Cards (82)

Doppler shift
A change in frequency (or wavelength) observed due to the relative motion of the source and observer
Other than matter, state what else may be present in the universe that may affect its density
Dark matter
Black holes
An astronomer has claimed to find a white dwarf with a mass twice of the sun. Suggest why this claim is incorrect.
A white dwarf has a mass less than or equal to 1.4x solar masses
State hubble's law
Recessional speed is proportional to its distance from us
Homogeneous
Uniform distribution of matter
State how an emission line is produced
Electrons make a transition to a lower energy level and emit photons
Suggest why hydrogen spectral lines play an important role in determining the redshift of galaxies
Hydrogen commonly found in stars
State and explain how stellar parallax is used to measure distance in space
Apparent motion or displacement of a star relative to the position of more distant stars Caused by the Earth's orbit around the Sun.
An angle of parallax of 1 arcsecond when displacement of earth is 1 AU Corresponds to distance 1 parsec
Describe and explain the next stages of evolution of our sun (exam question 4 marks)
reduction in energy released by fusion gravitational force is greater than that from radiation and gas pressure core collapses fusion no longer takes place in the core fusion continues in the shell around the core outer layers of star expand and cool outer layers are released reference to planetary nebula reference to white dwarf (left as remnant hot core)
State characteristics of black holes
Escape velocity is more than speed of light
Infinitely dense
Emits hawking radiation
Describe the evolution of the universe up to the formation of the first nuclei
At the big bang the universe is very dense High energy photons but no matter Quarks and leptons form Quarks combine to form neutrons Nucleons combine to make nuclei
Define luminosity of a star
Total radiant power of a star
Explain how a specific absorption line is produced in this type of spectrum in terms of photons and electron
Continous spectrum
Electrons excited and jump up to higher energy levels
Photons absorbed by electrons
Photons remitted in different directions
A comet
A dusty, ice object in a highly elliptical orbit around a star (which lies at one focii)
A galaxy
A collection of stars orbiting a Central mass
A galaxy
A collection of stars orbiting a Central mass
A nebula
Clouds of gas and dust from previous exploded stars
A neutron star
A very dense star formed by a collapsed supernova, where all protons have been decayed into neutrons
A solar system
A series of planets orbiting a star; formed from the accretion disc of the protostar
Anti matter
Particles that have the opposite properties of matter
Black hole
An extremely dense neutron star that has collapsed under gravity to a point singularity
1 Astronomical unit AU
Mean distance of earth's orbit radius
Dark matter
Mass that can only be observed by the effect of its gravitational fields. Majority of the universe
Electron degeneracy pressure
A limiting factor as an atom collapses, when all lower levels are filled, so the electrons prevent further condensing to occur
Energy levels
A quantised amount of energy that orbiting electrons of an atom have
Line spectra
Discrete frequencies of light emitted/absorbed by a gas, corresponding to energy level differences
Line spectra
Discrete frequencies of light emitted/absorbed by a gas, corresponding to energy level differences
Planet
A natural satellite of a star (with enough mass to be spherical and clear its orbit of debris)
Planetary satellite
A natural or man-made object orbiting a planet
The big bang theory
Is our best theory of the start of the universe due to rapid expansion fork a high energy explosion (as evident by CMBR + redshift)
The chandrasekhar limit
The upper limit of a stars mass for it to form a white dwarf (rather than go supernova)
The cosmological principle
That matter is evenly distributed across the universe and looks the same in all directions
The cosmological principle
That matter is evenly distributed across the universe and looks the same in all directions
Formation of stars
Stars are formed from nebula - areas of dust and gas - over time the gravitational force brings them together
As the mass increases gravitational collapse is accelerated. Gravitational energy is converted to thermal. The temperature is increased until it glows which forms a protostar. The pressure and temperature continue to rise until nuclear fusion occurs and produces helium. The star has now entered main sequence
State some of the properties of the microwave background radiation observed from the Earth. Discuss how the background microwave radiation is linked to the big bang model (3 marks)  
The intensity of the microwaves is the same in all directions. These microwaves correspond to a temperature of 2.7 K or The temperature of the universe is 2.7 K. The expansion of the universe following the big bang led to cooling and hence we observe microwaves rather than short wavelength e.m. waves / gamma waves.
White dwarf
A star left behind after a red giant
Suggest how microwave background radiation may evolve in the future
Further expansion leads to cooling. Temperature below 3 kelvin
Wavelength of Electromagnetic radiation gets longer so microwaves become radiowaves
Explain what is meant by fusion and explain the conditions necessary for fusion to occur in the core of a star (4 marks)
Fusion is the joining together of nuclei
Mass decreases in the reaction and this is transformed into energy
High temperature needed for fusion
High pressure and density required in the core
Describe and explain the evolution of a star much more massive than our Sun.
When hydrogen and helium run out the outer layers will expand.
A super red giant is formed
Core of star collapses. Forms a supernova
Depending on mass of star a black hole or neutron star is formed
Explain why the galaxies do not collapse on each other.
Galaxies are moving away from each other due to big bang
Acceleration is too small to collapse