Chapter 19: Stars Flashcards
planets
Object that:
- orbits the sun
- sufficient mass for self-gravity
- cleared the neighbourhood around its orbit
dwarf planet
planet that has not cleared the neighbourhood around its orbit
planetary satellites
bodies that orbit a planet
asteroid
too small and uneven to be planets
near circular orbit around the Sun
comet
small, irregular sized balls of rocks, dust and ice.
orbit sun in eccentric elliptical orbit
solar system
A planetary system consisting of a star and at least one planet in orbit around it
galaxies
a collection of stars, dust and gas
nebulae
gigantic clouds of dust and gas, birthplace of stars
How are protostars formed?
Gravity draws matter towards dense regions in nebulae
GPE converted into thermal, resulting in a hot, dense sphere of dust and gas
How are main sequence stars formed?
Hydrogen nuclei overcome electrostatic repulsion and fuse to form helium
During fusion, outward pressure and inward gravity are in equilibrium
Describe how a low-mass main sequence star becomes a red giant
Small, cooler core, so MS for longer
Once H low, gravity causes core to collapse and outer layer expands and cools.
Core becomes hotter as GPE converts to thermal, and helium fuses into heavier elements
H fuses in layers around core
Describe the evolution of a red giant to a white dwarf?
When star runs out of fuel, expels outer layers, creating planetary nebula
Core remaining contracts further, now dense white dwarf. White dwarf of around 3000K, and no fusion occurs.
Photons produced earlier leak out, dissipating heat
As core collapse, electron degeneracy pressure prevents collapse, now stable due to Chandrasekhar limit
Describe the evolution of a high-mass main sequence star into a red supergiant
As H depletes, core contracts.
GPE turns to thermal and core much hotter due to higher mass, allowing He fuse to C
Outer layer expand and cool, form red supergiant
Describe the process of the death of a high mass star
When red supergiant fuel used up, fusion stops
Gravity greater than outward pressure and core collapses, becomes rigid
Outer layer falls in and rebound off rigid core, launching shockwave
Remaining core of supernova is neutron star or black hole, depending on mass
Describe the evolution of a red supergiant to a neutron star
if core greater than 1.44Mo, gravity forces protons and electrons together to form neutrons, producing small, dense neutron star
Describe the evolution of a red supergiant to a black hole
If core greater than 3Mo, gravitational force is so strong that escape velocity is higher than the speed of light.
Describe the process of electrons exciting in discrete energy levels
Electrons can only exist in discrete energy levels, they cannot have an energy level between two levels.
Each element has its own set of energy levels
Electrons move from a lower energy state to a higher energy state, obtained by the input of external energy
True or False: All energy level values are negative
True.
Ground state is most negative and completely free is 0.
Negative shows energy required to remove electron from atom
What are emission line spectra?
A series of coloured lines on a black background
How are emission line spectra formed?
Light passes through the outer layer of the star, and the electrons absorb the photons and become excited
When they de-excite, they release photons of specific wavelengths
What are continuous line spectra?
All visible of light are present. They are produced by atoms of solid heated metals
What are absorption line spectra?
Dark lines against continuous background, each line corresponding to a wavelength of light absorbed by atoms in outer layer
What happens when an electron de-excites?
It releases energy as a photon with a specific wavelength, difference between energy levels
What are diffraction gratings?
Components with regularly spaced slits that can diffract light. Different colours of light have different wavelengths, so will diffract at different angles
Wien’s Displacement Law
The wavelength of emitted radiation at peak intensity is inversely proportional to the temperature of the black body
Stefan’s Law
The power output of a star is directly proportional to its surface area and absolute temperature^4
Between what masses can a star form red giants?
0.5Mo and 10Mo
Electron Degeneracy Pressure
electrons are squeezed together to protect core from collapsing further
Chandrasekhar Limit
Electron degeneracy pressure only sufficient to prevent the collapse of cores of a mass less than 1.44Mo
