Astrophysics

Question 1

An astronomer claims to have discovered a white dwarf with a mass twice the size of our sun. Suggest why this claim is wrong.

Answer 1

The white dwarf can only have a maximum mass of 1.44 solar mass. (Chandrasekhar limit) therefore it cannot be twice the mass

Question 2

What is the mass of our sun in solar mass?

Answer 2

1 solar mass

Question 3

What does one solar mass equal to?

Answer 3

2.0 x 10^40 kg

Question 4

State two ways a black hole is different to a star

Answer 4

No fusion occurs
Black holes have smaller masses compared to stars

Question 5

State how emission lines is produced?

Answer 5

Electrons make transitions to lower energy levels which makes them lose energy and emitting a photon

Question 6

What is a nebula?

Answer 6

Giant clouds of dust and gas.

Question 7

How are nebulae formed?

Answer 7

Tiny gravitational attraction between particles of dust and gas pulls toward each other and eventually forms a cloud.

Question 8

How are protostars formed?

Answer 8

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.

Question 9

For a protostar to become a star what has to happen?

Answer 9

Nuclear fusion

Question 10

Why are many protostars not able to become a star?

Answer 10

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

Question 11

When hydrogen nuclei are forced together what do they form?

Answer 11

Helium nuclei

Question 12

How does a star remain in a stable equilibrium?

Answer 12

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.

Question 13

What is the stable phase of a star?

Answer 13

Main sequence star

Question 14

What affects how long a star is stable?

Answer 14

The mass and size of its core

Question 15

Are bigger stars or smaller stars likely to be stable for longer?

Answer 15

Smaller stars.

Question 16

Why are bigger stars stable less then smaller stars?

Answer 16

Larger stars are much hotter so release more power and convert the available hydrogen into helium in a much shorter time.

Question 17

What do main sequence stars with 0.5-10 solar masses turn into?

Answer 17

Red giants

Question 18

What happens at the start of a red giant?

Answer 18

The reduction in energy released by fusion results in the core of the star to start collapsing due to stronger gravitational force.

Question 19

As a red giant starts to collapse what happens next?

Answer 19

As the core shrinks the pressure increase for fusion to occur around the core.

Question 20

What happens after the red giant starts to collapse

Answer 20

As the pressure increases, the pressure increases to start fusion in a shell around the core.

Question 21

Why does fusion no longer occur in the core of a red giant?

Answer 21

The core is inert as there is very little hydrogen and the temperature isn’t high enough for helium to overcome its electrostatic repulsion.

Question 22

As fusion still occurs around the core of a red giant what happens?

Answer 22

The star starts to expand as the core slowly moves away from the core. The layers then cool and become red in colour.

Question 23

Once the layers around the core drift off into space what is left behind?

Answer 23

A planetary nebula and white dward

Question 24

Characteristics of a white dwarf?

Answer 24

Very dense
About the mass of our sun
No fusion occurs inside a white dwarf

Question 25

Why does a white dwarf emit energy if no fusion occurs?

Answer 25

As it leaks photons created in its earlier stages.

Question 26

What stops a white dward from further collapsing?

Answer 26

Two electrons cannot exist in the same energy state so when the core starts to collapse the electrons are squeezed. This created pressure that prevents it from collapsing further. (Electron degeneracy pressure)

Question 27

When does the electron degeneracy pressure not work?

Answer 27

When the mass is above a certain value

Question 28

What is Chandrasekhar limit?

Answer 28

This limit is the maximum mass of a stable white dwarf -1.44solar masses

Question 29

If a main sequence star has a mass greater then 10 solar masses what happens?

Answer 29

Red SUPER GIANT

Question 30

As the core of larger stars are hotter shattering happens?

Answer 30

The helium nuclei is moving fast enough to overcome electrostatic repulsion and form heavier elements.

Question 31

What happens to red super giants?

Answer 31

They have high temp and presure so can fuse to make heavier elements and shells. Eventually it will make an iron core which in inert. After this point it cannot produce any more energy. Lead to the DEATH of red super giant

Question 32

What can the remnant core of a supernova turn into?

Answer 32

Neutron star Or a black hole

Question 33

When does a supernova become a neutron star?

Answer 33

If the mass of the core is greater then Chandrasekhars limit it continue to collapse and eventually form a neutron star.

Question 34

Properties of a neutron star?

Answer 34

Entirely made up of neutrons Very small Mass of about 2 solar masses

Question 35

When are black holes formed?

Answer 35

When a supernova dies and the core has a mass greater the 3 solar masses it continues to collapse.

Question 36

Properties of black holes:

Answer 36

Has a such a strong gravitational file that in order to escape an object will need the escape velocity greater then the speed of light.

Question 37

What is a hertz-sprung Russell diagram?

Answer 37

A graph of stars in our galaxy showing the relationship between their luminosity and surface temperature.

Question 38

.

Question 39

Why are electron levels negative?

Answer 39

As external energy is required to remove an electron from the atom. It also indicates that the electrons are trapped within the atom or bound to the positive nuclei.

Question 40

When are electrons free from the atom

Answer 40

When they have zero energy

Question 41

What is the energy level with the most negative state known as?

Answer 41

The ground state

Question 42

When electrons move from a lower energy level to a higher one ?

Answer 42

It gets excited.

Question 43

When an electron moves from a higher energy level to a lower energy level what happens?

Answer 43

It loses energy

Question 44

When an electrons transitions between levels what is emitted?

Answer 44

A photon

Question 45

How do you find the change in energy?

Answer 45

Lower energy level minus higher energy level

Question 46

What does each element has a different set of?

Answer 46

Energy levels

Question 47

How can the starlight from a star help identify the elements within the star?

Answer 47

Using spectra’s

Question 48

What are the three types of spectras?

Answer 48

Emission line Continuous spectra Absorption line spectra

Question 49

How does an emission line spextra get produced?

Answer 49

When an elextron transition from a high energy ti a lower energy level it emits photons wirh a set frequency. Each line represents a photon with a specific wavelength. These can be observed from heater gases.

Question 50

How are absorption line spectra produced?

Answer 50

When a light from a source passes that would produce a continuous spectrum passes through a cooler gas. As the photon passes through the gas some are absorbed by the gas atoms raising the energy level of the electrons. Only photons that are exactly equal to the difference between energy levels are absorbed so specific wavelength are absorbed creating dark lines in the spectrum.

Question 51

What did the dark lines in an absorption spectrum show?

Answer 51

Which photons have ben absorbed by the gas atoms. Although the photons can be re emitted when the electrons drop back down they are emitted in all directions so the internist is reduced.

Question 52

What is a diffraction grating?

Answer 52

An optical component is regularly spaced slits or lines that diffract and split light into beams of different colour travelling in different direction.

Question 53

What is a black body?

Answer 53

An idealised object that absorbs all the electromagnetic radiation that shines onto it and when in thermal equilibrium emits a characteristic distribution of wavelengths at specific temperature

Question 54

What is wien’s law?

Answer 54

Wavelength max is inversely proportional to T

Question 55

What is the value for the constant?

Answer 55

2.90 x 10-3 mK

Question 56

What happens to the peak wavelength as the temperature increases?

Answer 56

Becomes sharper and taller. The wavelength decreases.

Question 57

Stefans law

Answer 57

Total power radiated per unit surface area of a black body us directly proportional to the fourth power of the surface temperature

Question 58

An objectaway from the wave source will experince what?

Answer 58

Longer wavelength with shorter frequency