Chapter 19 Stars

Question 1

How is a nebulae formed?

Answer 1

Tiny gravitational particles attract each other and form clouds of gas and dust. This is a nebulae

Question 2

How is a protostar formed?

Answer 2

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.

Question 3

How is a star formed from a protostar?

Answer 3

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.

Question 4

What are the 3 forces within a star and how do they act?

Answer 4

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

Question 5

What does main sequence say about the forces in a star?

Answer 5

The forces are balanced

Question 6

What is the difference between a planet and a dwarf planet?

Answer 6

A planet has cleared their orbit of any objects but a dwarf planet has not

Question 7

What is the difference between an asteroid and a comet?

Answer 7

A comet it made from ice and rock.

Question 8

What is a planetary satellite?

Answer 8

Is a body that is in orbit around a planet

Question 9

What happens to stars with lower mass?

Answer 9

They are cooler than more massive stars and so stay in their main sequence for longer.

Question 10

What is a red giant?

Answer 10

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

Question 11

What type of core does a red giant star have? and why?

Answer 11

Their cores are inert because fusion no longer happens

Question 12

What happens to the layers around the red giant star?

Answer 12

They start to move away from the core causing it to expand and as the layers cool off, it emits the red colour

Question 13

How is a white dwarf formed?

Answer 13

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

Question 14

What is electron degeneracy pressure?

Answer 14

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.

Question 15

What is the chandrasekhar limit?

Answer 15

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.

Question 16

What happens if a star is larger than 10M?

Answer 16

The star expands to form a red super giant and becomes much hotter allowing for more nuclei to fuse and form heavier elements

Question 17

Talk about the layers of a red super giant?

Answer 17

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

Question 18

What is a supernova?

Answer 18

This is when there is a huge implosion of the star and the layers bounce off the iron core and are thrown into space

Question 19

What are the two things that could happen to the core of a red giant after a super nova?

Answer 19

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

Question 20

What is created in a supernova?

Answer 20

Larger and heavier elements.

Question 21

What is a hertzsprung russell diagram?

Answer 21

It is a graph of surface temperature on the x axis and the luminocity on the y axis of stars

Question 22

What is a hertzsprung russell diagram used for?

Answer 22

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

Question 23

Name 4 facts about energy levels

Answer 23

• 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

Question 24

What is it called when an electron moves from a more negative energy level to a less negative energy level?

Answer 24

It is said to be excited

Question 25

How can an electron move energy levels?

Answer 25

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

Question 26

What is the equation for energy related to frequency?

Answer 26

E = hf

Question 27

How was helium discovered?

Answer 27

It was discovered looking at the emission and absorption spectrum from light from the sun.

Question 28

What is an emission line spectra?

Answer 28

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.

Question 29

What is a continuous line spectra?

Answer 29

All visible frequencies are present. This is often produced by atoms of heated solid metals

Question 30

What is absorption line spectra?

Answer 30

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.

Question 31

How are elements within stars detected?

Answer 31

When light from stars is analysed it can be seen as an absorption spectrum. Where the lines fall is specific to certain elements

Question 32

What is the defintion for a defraction grating?

Answer 32

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

Question 33

How is the zero order maxima produced?

Answer 33

It is produced when the angle of light passing through a diffraction grating is 0

Question 34

What is the equation used for diffraction gratings?

Answer 34

dSinθ = nλ
d = diffraction grating
θ = angle of maxima
n = maxima number
λ = wavelength

Question 35

How does temperature affect the light given off?

Answer 35

The frequency of light given off is affected by temperature

Question 36

What is a black body?

Answer 36

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

Question 37

What is weins displacement law?

Answer 37

It is a simple law that relates the absolute temperature of a black body and the wavelength (λmax) of an object

Question 38

What is the equation for weins displacement law? and what is weins constant?

Answer 38

λmax = k x 1/t
k = 2.9x10-3

Question 39

What is stefans law?

Answer 39

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

Question 40

What is the equation for stefans law?

Answer 40

L = 4πr^2σT^4

Question 41

How can weins law and stefans law be used?

Answer 41

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.