Chapter 19,20 - Astro and Cosmology Flashcards
Define planets
Objects with mass sufficient enough for their own gravity to force them to take a spherical shape, the object exhibits no nuclear fusion and has cleared its orbit of other objects
Define dwarf planets
planets where the orbit has not been cleared of other objects
Define planetary satellites
bodies that orbit a planet
Define asteroids
objects which are too small and uneven to be planets, with a near circular orbit around the sun
Define comets
small, irregular shaped balls of rock, dust and ice. They orbit the sun in eccentric elliptical orbits
Define solar systems
system containing stars and orbiting objects like planets
Define galaxies
a collection of stars, dust and gas. Containing around 100 billion stars
Describe the formation of a star
- Nebulae are gigantic clouds of dust and gas.
- Over millions of years the gravitational attraction between dust and gas particles pull them together
- gravitational collapse becomes greater the denser parts get
- The gravitational energy is converted to thermal energy heating up these clouds
- as heating continues the dense cloud of gas starts to glow, forming a protostar
- As gravity continues to pull together particles, the temperature inncreases until 1 million kelvin where hydrogen gas nuclei overcome electrostatic forces of repulsion and create nuclear fusion.
- hydrogen fuses into helium producing a star
Describe the stars life after formation but before evolution
- initially the star remains in stable equilibrium where gravitational forces producing fusion equal the repulsive forces of radiation from the fusion
- This is known as the main phase
- smaller stars stay in the main phase for a while
- however larger mass stars use up fusion alot faster due to their heat, and so run out of available hydrogen nuclei quickly.
factors affecting life cycle of a star
mass of the stars core
Evolution of a low mass star like our sun
- low mass star is about from 0.5 solar masses to 10 solar masses
- this star has a smaller, cooler core and remains in the main sequence for longer
- Once hydrogen supplies are low, the gravitational forces inwards overcome forces due to fusion outwards
- so the star collapses inwards.
- It evolves into a red giant
- the core is too cool to fuse helium but the pressure in the outer core is great enough for fusion to occur there.
- as helium runs low the red giant evolves into a white dwarf and the outer layers drift off into space to form a planetary nebulae
- core remains a very dense white dwarf of around 3000K
- no fusion occurs in a white dwarf
- the white dwarf will be stable if below 1.44 solar masses, the Chandrasekhar limit
Evolution of a massive star to a supernova
- a star with a mass of larger than 10 solar masses
- hydrogen supplies deplete
- as mass is larger, temperature is high enough in the core for helium fusion into heavier elements
- forming a red supergiant
- The red supergiant has layers of increasingly heavy elements produced by fusion, with an inert iron core
- As the core cant fuse anymore the star becomes unstable and collapses rapidly inwards
- this collapse bounces off the dense core in an explosion out to space forming a supernova
possible evolution beyond the supernova
if the remaining core has a mass of 1.44 solar masses, ie the Chandrasekhar limit, then the protons and electrons combine to form neutrons
- this produces a neutron star
- very small but high density
if the core has a mass of over 3 solar masses, a black hole is forms
- this is where the gravitational pull causes escape velocity to be greater than the speed of light
- huge mass
- negligible volume
- infinite density
- not even photons can escape
why do electrons absent from atoms have zero energy
energy is said to be the work done required to remove an electron from its atom
describe an emission line spectra
each element produces a unique emission line spectra due to their unique set of energy levels associated with its electrons. It appears as a series of colourful lines on a black background
describe a continuous line spectra
all visible wavelengths are present. They are produced by atoms of solid heated metals e.g. lamp filament
describe an absorption line spectra
a series of dark spectral lines against the background of the continuous spectrum. The dark lines have exactly the same wavelength as the bright emission line spectrum lines of the same gas atoms
describe what energy levels are
- an electron cannot have energy of between two levels
- energy levels are negative because external energy is required
- an electron with 0 energy is free from the atom
- the energy level with the most energy is the ground level or state
What does an electron being excited mean
it moves up energy levels
what happens when an electron is de excited
- energy is conserved so the electron emits a photon of specific wavelength. The energy of the emitted photon is given by E=hc/λ. E is the difference in energy of the two levels.
What are diffraction gratings
components with regularly spaced slits that can diffract light
equation for determining wavelength of light by diffraction
dsinθ = nλ where d is the slit separation and n is the order maxima
