Astrophysics Flashcards
An astronomer claims to have discovered a white dwarf with a mass twice the size of our sun. Suggest why this claim is wrong.
The white dwarf can only have a maximum mass of 1.44 solar mass. (Chandrasekhar limit) therefore it cannot be twice the mass
What is the mass of our sun in solar mass?
1 solar mass
What does one solar mass equal to?
2.0 x 10^40 kg
State two ways a black hole is different to a star
No fusion occurs
Black holes have smaller masses compared to stars
State how emission lines is produced?
Electrons make transitions to lower energy levels which makes them lose energy and emitting a photon
What is a nebula?
Giant clouds of dust and gas.
How are nebulae formed?
Tiny gravitational attraction between particles of dust and gas pulls toward each other and eventually forms a cloud.
How are protostars formed?
Dust and gas get closer together and denser regions begin to form. These regions pull lore dust and gas and gain more mass becoming more denser. It becomes hotter as the gravitational energy converts to thermal energy.
For a protostar to become a star what has to happen?
Nuclear fusion
Why are many protostars not able to become a star?
In order for nuclear fusion to occur high pressure and temperature is required to overcome electrostatic repulsion between hydrogen nuclei. Hence they remain as protostars
When hydrogen nuclei are forced together what do they form?
Helium nuclei
How does a star remain in a stable equilibrium?
Gravitational forces compress the star, whilst the radiation pressure from the photons emitted during fusion and the gas pressure from the nuclei push outwards. The forces balance out and maintain equilibrium.
What is the stable phase of a star?
Main sequence star
What affects how long a star is stable?
The mass and size of its core
Are bigger stars or smaller stars likely to be stable for longer?
Smaller stars.
Why are bigger stars stable less then smaller stars?
Larger stars are much hotter so release more power and convert the available hydrogen into helium in a much shorter time.
What do main sequence stars with 0.5-10 solar masses turn into?
Red giants
What happens at the start of a red giant?
The reduction in energy released by fusion results in the core of the star to start collapsing due to stronger gravitational force.
As a red giant starts to collapse what happens next?
As the core shrinks the pressure increase for fusion to occur around the core.
What happens after the red giant starts to collapse
As the pressure increases, the pressure increases to start fusion in a shell around the core.
Why does fusion no longer occur in the core of a red giant?
The core is inert as there is very little hydrogen and the temperature isn’t high enough for helium to overcome its electrostatic repulsion.
As fusion still occurs around the core of a red giant what happens?
The star starts to expand as the core slowly moves away from the core. The layers then cool and become red in colour.
Once the layers around the core drift off into space what is left behind?
A planetary nebula and white dward
