Astronomy and stars chap 19 Flashcards
Define Nebulae
Gigantic clouds of dust and gas, usually hundreds of times larger than our solar system
How are nebulae formed?
Over millions of years as tiny gravitational attraction between dust and gas particles pull towards each other forming clouds
How is a protostar formed?
As dust and gas get closer together gravitational collapse accelerates
Dense regions form
These regions pull in more dust/gas gaining mass and density
gravitational energy is transformed to thermal energy
These regions form protostars
What is a protostar?
A very hot dense sphere of dust and gas
What process is needed for a protostar to form a star?
Nuclear fusion
How does a protostar become a star?
Fusion reactions between hydrogen nuclei produce helium nuclei and kinetic energy
More and more mass is gained which increases the size and temperature of the protostar so electrostatic repulsion is over come
Why are very high temperatures and densities needed for nuclear fusion?
To overcome strong electrostatic repulsion between nuclei
What forces keep a main sequence star in equillibrium?
Gravity, radiation pressure and gas pressure
How are main sequence stars kept in equillibrium?
Gravitational forces compress the star
Radiation pressure from emitted photons and gas pressure from the nuclei counteract gravity
What decides how long a star stays stable for?
The size and mass of it’s core
Are bigger or smaller stars likely to stay stable for longer?
Smaller as they don’t burn as hot
Define Planet
An object in orbit around a star
Must have a mass large enough for it’s own gravity to give it a round shape
No fusion reactions occur in the body
It’s cleared its orbit of most other objects
What’s a dwarf planet?
Like a planet except they haven’t cleared their orbit of other objects
Define asteroid
Objects too small and uneven to be planets but have near circular orbits
No ice present
What is a planetary satellite?
A body in orbit round a planet
What’s a comet?
Small irregular bodies of ice, dust and pieces of rock
Between a few hundred metres to tens of kilometres across
All comets orbit the sun
Highly elliptical orbits
Some develop tails when approaching the sun
Define solar system
A system containing a large central star and all the objects that orbit it
What is a galaxy?
A collection of stars and interstellar dust and gas
Usually contain about 100 billion stars
What mass does a star that’s going to be a red giant have?
Between 0.5 solar masses and 10 solar masses
How does a star become a red giant?
Energy released via fusion is low
So gravitational force is greater than outward pressure
This causes the core to collapse
As the core shrinks pressure increases- fusion starts in a shell around the core
How does a red star become a white dwarf?
Red giants have inert cores
Fusion no longer takes place as the temperature is too low
A shell of helium nuclei has formed around the core
Layers start to move away from the core giving the star it’s red colour
Characteristics of a white dwarf
Very dense- volume of earth with the mass of the sun
Very hot but inert
Only emits photons that were created in earlier evolution
Surface temperature of up to 30 000K
What is the Pauli exclusion principle?
Two electrons cannot exists in the same energy state
How does Pauli apply to stars?
When the core of a star collapses electrons are squeezed together creating a pressure that prevents the core from further gravitational collapse
