Ch19 - Stars Flashcards
(30 cards)
What are nebulae?
Clouds of dust and gas in outer space
What is the first stage of the formation of a star? (Nebulae)
Due to tiny variations in the nebula, denser regions begin to form. These regions pull in more dust and gas gaining mass and getting denser.
What is the second stage, after the tiny variations begin to form and it gains mass?
Gravitational energy is transferred into thermal energy and in one part of the cloud a protostar forms.
What is a protostar?
A protostar is a very hot, very dense sphere of dust and gas
What is need for a protostar turn into a star?
Nuclear fusion must take place producing a form of kinetic energy
The build up of mass and energy creates high pressures and temperatures inside the core. What does this cause?
The electrostatic forces of repulsion between hydrogen nuclei are overcome in order to fuse them together to form helium nuclei.
What does the formation of helium nuclei cause?
As hydrogen atoms fuse together to form helium, releasing huge amounts of energy. This energy pushes back against gravity, balancing the star. The star enters its main sequence stage.
what causes the outwards pressure to allow the star to remain in equilibrium?
Gravitational forces act to compress the star but the radiant pressure from the photons emitted during fusion and the gas pressure push the core outwards, maintaining equilibrium.
State 3 things that could be the reason as to why lower mass stars can remain in the main sequence for longer.
- Hydrogen fuel usage
- Core temperature and pressure
- Energy production
How may Hydrogen fuel usage be effected by a lower mass star and its duration in the main sequence.
Consume hydrogen fuel at a much slower rate compared to massive stars allowing the star to remain in equilibrium for longer as nuclear fission is taking place.
How may core temperatures and pressure effect a lower mass stars duration in the main sequence.
The core of a lower mass star does not reach extremely high temperature required for faster fusion processes, prolonging the hydrogen burning process.
How may energy production effect a lower mass stars duration in the main sequence.
The fusion process in smaller stars is more stable, allowing them to maintain a steady energy output over a longer period of time.
Stars of mass between __ and __ will evolve into a red giant
0.5M and 10M
(Main sequence -> Red giant)
What causes a main sequence star to lose its equilibrium?
There is a reduction in energy due to lack of hydrogen fuel will result in lack of outwards photon emission resulting in gravitational forces overcoming and the core begins to collapse.
(Main sequence -> Red giant)
As the core of a main sequence star begins to collapse what happens?
As the core of the star begins to collapse, the core shrinks and the pressure increases enough to start fusion in a shell around the core.
The shell around the core causes the star to expand as layers.
The layer expand and cool giving the star its red colour
The core itself is inert therefore fusion no longer takes place in the core.
Why do Red giants have inert cores?
As the core runs out of fuel, it cools down and is filled with helium. As Fusion takes place in a shell around the core, the core is too cool and not dense enough for fusion to take place. Therefore it is inert.
What are planetary nebulae?
How is a white dwarf born?
The layers of red giants around the core drift off into space as planetary nebulae. Leaving behind the hot core as a white dwarf?
What are the characteristics of a white dwarf?
It is very dense, often with a mass close to the suns
No fusion reactions take place
It emits energy only because it leaks photons created in its earlier evolution
What is electron degeneracy pressure and what does it do. Explain in context.
When the core of a star begins to collapse, electrons are squeezed together creating a pressure that prevents the core from further gravitational collapse. This pressure is known as electron degeneracy pressure.
For stars of what mass is electron degeneracy pressure sufficient to prevent collapse - Chandrasekhar limit
It is only sufficient to prevent collapse if the core ha a mass less than 1.44M
Explain what happens to main sequence stars of mass greater than 10M
when collapsing as the core is much hotter, the helium nuclei formed are moving fast enough to overcome electrostatic forces of repulsion, so fuse together into heavier elements. The process continues and expands building layers of different elements until the star develops an iron core. Iron nuclei cannot fuse together therefore no energy and star becomes unstable leading to the death of the star. This explosion is known as a supernova.
After the supernova, depending on the mass of the remaining core what will happen?
If the mass is less than 1.4M it will turn into a white dwarf.
If the mass is between 1.4M and 3M it will turn into a neutron star.
If the mass is greater than 3M, the gravitational forces will compress the core creating a black hole.
what does an emission line spectrum look like
Dark background with discrete lines
what does an absorption line spectrum look like
Rainbow background with dark lines
