Chapter 19 Stars Flashcards
How is a nebulae formed?
Tiny gravitational particles attract each other and form clouds of gas and dust. This is a nebulae
How is a protostar formed?
Gravity pulls the nebulae together and so it starts to become denser and hotter because gravitational energy is transferred into thermal energy.
Part of the cloud becomes very dense due to there not being uniformity throughout the cloud and this is a protostar which is the intermediary for the formation of a star.
How is a star formed from a protostar?
Nuclear fusion needs to start at the core. Very few protostars reach this stage.
Fusion starts because of the high pressure and temperatures overcome the electrostatic repulsion of hydrogen nuclei so helium nuclei are formed.
What are the 3 forces within a star and how do they act?
Gravity - Holds the star together and compresses it
Radiation pressure - From the photons emitted pushes outwards
Gas pressure - From the nuclei at the core pushes outwards
What does main sequence say about the forces in a star?
The forces are balanced
What is the difference between a planet and a dwarf planet?
A planet has cleared their orbit of any objects but a dwarf planet has not
What is the difference between an asteroid and a comet?
A comet it made from ice and rock.
What is a planetary satellite?
Is a body that is in orbit around a planet
What happens to stars with lower mass?
They are cooler than more massive stars and so stay in their main sequence for longer.
What is a red giant?
They have a mass between 0.5M and 10M
Fusion starts in the core but as the amount of energy released reduces the core collapses and fusion starts to happen in a shell around the core
What type of core does a red giant star have? and why?
Their cores are inert because fusion no longer happens
What happens to the layers around the red giant star?
They start to move away from the core causing it to expand and as the layers cool off, it emits the red colour
How is a white dwarf formed?
The layers around a red giant drift off into space as a planetary nebula and leave behind the hot core which is the white dwarf
What is electron degeneracy pressure?
When the core of a star begins to collapse the electrons are squeezed together and this puts an outward force/pressure. This is the electron degeneracy pressure.
What is the chandrasekhar limit?
This is the limit at which the electron degeneracy pressure is equal to the gravitational force. The limit is 1.44M. If the star is larger then it collapses further.
What happens if a star is larger than 10M?
The star expands to form a red super giant and becomes much hotter allowing for more nuclei to fuse and form heavier elements
Talk about the layers of a red super giant?
The star starts with hydrogen fusion at the core and then the helium starts to fuse to form carbon etc. The layers of the red supergiant have an iron core and then lighter nuclei from the inside out
What is a supernova?
This is when there is a huge implosion of the star and the layers bounce off the iron core and are thrown into space
What are the two things that could happen to the core of a red giant after a super nova?
It could become a neutron star if the mass of the core is larger than the chandrasekhar limit. It forms a ball of neutrons only about 10km in diameter and have a mass of 2M
A black hole could be formed if the core has a mass greater than 3M. Gravity collapses the core and the pull is so strong that an object would have to move faster than the speed of light to escape it
What is created in a supernova?
Larger and heavier elements.
What is a hertzsprung russell diagram?
It is a graph of surface temperature on the x axis and the luminocity on the y axis of stars
What is a hertzsprung russell diagram used for?
It is used to identify the type of star. Their position on the diagram indicates their stage and type.
Stars often move around the diagram throughout their life
Name 4 facts about energy levels
- An electron cannot have a quantity of energy between two energy levels
- Energy levels are negative because external energy is required to remove an electron from the atom.
- An electron with zero energy is free from the atom
- The energy level with the most negative value is the ground state
What is it called when an electron moves from a more negative energy level to a less negative energy level?
It is said to be excited
How can an electron move energy levels?
A photon is absorbed which excites and electron and raises it. After it is raised, it falls to a lower ground state and a photon is released
What is the equation for energy related to frequency?
E = hf
How was helium discovered?
It was discovered looking at the emission and absorption spectrum from light from the sun.
What is an emission line spectra?
Each element produces a unique emission line spectrum because of its unique set of energy levels. This is a measure of what frequencies of light have been emitted.
What is a continuous line spectra?
All visible frequencies are present. This is often produced by atoms of heated solid metals
What is absorption line spectra?
This type of spectrum has a series of dark spectral lines the background of a continuous spectrum. This is a measure of what frequencies of light have been absorbed.
How are elements within stars detected?
When light from stars is analysed it can be seen as an absorption spectrum. Where the lines fall is specific to certain elements
What is the defintion for a defraction grating?
It is an optical component with regularly spaced slits of lines that diffract and split light into beams of different colour travelling in different directions
How is the zero order maxima produced?
It is produced when the angle of light passing through a diffraction grating is 0
What is the equation used for diffraction gratings?
dSinθ = nλ d = diffraction grating θ = angle of maxima n = maxima number λ = wavelength
How does temperature affect the light given off?
The frequency of light given off is affected by temperature
What is a black body?
It is an object that absorbs all the em radiation that shines onto it and when in thermal equilibrium emits wavelengths at a specific temperature
What is weins displacement law?
It is a simple law that relates the absolute temperature of a black body and the wavelength (λmax) of an object
What is the equation for weins displacement law? and what is weins constant?
λmax = k x 1/t k = 2.9x10-3
What is stefans law?
This is the law that states: The total power radiated per unit surface area of a black body is directly proportional to the 4th power of the absolute temperature of the black body
What is the equation for stefans law?
L = 4πr^2σT^4
How can weins law and stefans law be used?
It can be used to estimate the radian of a distant star and once this is known, it can be used to estimate the mass and density.
