Stars Flashcards
Interstellar medium
Vast areas of dust and gas between stars and galaxies. 99%gas. It is from this material that new stars are formed. Density and temperature vary
Nebulae
Giant clouds of dust and gas (mainly hydrogen) which are the birthplace of stars
Protostar
A very hot and dense sphere of condensing dust and gas that is on its way to becoming a star
Fusion
A process in which two smaller nuclei join to form a larger nucleus
Radiation pressure
Pressure from photons emitted during fusion
Gas pressure
Pressure from the nuclei in the core
What do radiation and gas pressure do
Maintain the star in equilibrium and balance the force from gravitational attraction. They stop the star from being compressed
Main sequence
The stable phase of a stars life
Blue giant star
A large powerful, bright star in main sequence
Red dwarf star
Small, old, relatively cool star
Brown dwarf
Failed star. Fusion in a protostar does not occur and a brown dwarf is created
Satellite
A body orbiting around a planet
Planets
An object in orbit around a star with a mass large enough for its own gravity to give it a round shape, that undergoes no fusion and has cleared its orbit of most other objects
Dwarf planets
A planet that has not cleared its orbit of other objects
Asteroids
Objects too small and uneven to be planets. Usually in near - circular orbits around the sun
Comets
Small irregular bodies of ice, dust and rock. Highly elliptical orbits
Planetary satellites
A body in orbit around a planet like a moon or man made satellites
Solar systems
Contain a sun and all the objects that orbit it
Galaxies
A collections of stars and interstellar dust and gas. On average contains 100 billion stars
Red giants star
An expanding star at the end of is life, with an inert core in which fusion no longer takes place, but in which fusion of lighter elements continues in the shell around the core
Red supergiant
A huge star in the last stages of its life before it ‘explodes’ in a supernova
White dwarf star
A very sense star formed from the core of a red giant in which no fusion occurs
Planetary nebula
The outer layers of a red giant that have drifted into space leaving the hot core behind at the centre as a white dwarf
Electron degeneracy pressure
A quantum-mechanical pressure created by the electrons in the core of a collapsing star due to the Pauli exclusion principle
Chandrasekhar limit
The mass of a stars core beneath which electron degeneracy pressure is sufficient to prevent gravitational collapse
Supernova
The implosion of a red supergiant at the end of its life, which leads to subsequent ejection of stellar matter into space, leaving an inert remnant core
Neutron star
The remnant core of a massive star after the star has gone supernova (and if the mass of the core is greater than the Chandrasekhar limit) the core has collapsed under gravity to an extremely high density as it is almost entirely made up of neutrons
Neutron degeneracy pressure
The pressure that balances the gravitational force inwards in a neutron star
Singularity
In the centre of a black hole there is a gravitational singularity where a huge mass in an infinitely small space is contained and laws of physics do not operate
Black hole
The remnant core of a massive star after it has gone supernova and the core has collapsed so far that in order to escape it an object would need an escape velocity greater than the speed of light and therefore nothing, not even photons, can escape it
What star mass causes evolution into red giants?
0.5-10 sun masses
What star masses cause evolution into red supergiant?
10+ solar masses
After supernova what core mass causes a black hole
3 solar masses
What value is the Chandrasekhar limit?
1.44 solar masses
Where are white dwarfs in HR diagram?
Bottom left
Where are supergiants in HR diagram?
Along top
Energy level
A discrete amount of energy that an electron within an atom is permitted to possess
Ground state
The most negative value of energy level possible for an electron within an atom to possess-the most stable energy state of an electron
Excited
An atom with one or more electrons that have absorbed energy and been boosted into a higher energy level
Emission line spectrum
Set of specific frequencies of EM radiation (visible as bright lines in spectroscopy) emitted by excited atoms as their electrons move between energy states (losing the corresponding amount of energy in the form of photons as they do so)
Every element has a characteristic line spectrum
Absorption line spectrum
A set of specific frequencies for EM radiation (visible as dark lines in an otherwise continuous spectrum spectroscopy). They are absorbed by atoms as their electrons are excited between energy states by absorbing the corresponding amount of energy in the form of photons. Every element has a characteristic line spectrum
Spectral line
A line in an emission or absorption line spectrum at a specific wavelength
Photon
Quantum of electromagnetic energy
Continuous spectrum
A spectrum in which all visible frequencies or wavelengths are present
What are gas discharge tubes used for?
Observing spectra of a particular element
How does a gas discharge tube work?
- particular gas is trapped in the tube and a high voltage is applied across the tube
- electrons are emitted from the cathode and accelerate to wards the anode gaining KE
- electrons collide with gas atoms atoms causing them to get excited and gain energy
- gas atoms de-excited by emitting photons to lose the energy, causing the tube to light up
