stars and cosmology

Question 1

What are nebulae

Answer 1

Gigantic clouds of dust and gas

Question 2

how does a protostar form from a nebulae

Answer 2

Gravitational attraction pulls the dust together
As they get closer the collapse accelerates which creates denser regions which are hotter
Protostar forms (hot dense sphere of gas(

Question 3

How does a protostar become a star

Answer 3

Once the electrostatic repulsion between the hydrogen nuclei is overcome by extremely high temperatures and pressures (kinetic energy)
Hydrogen nuclei are fused to make helium nuclei, fusion begins

Question 4

What prevents a star from being compressed

Answer 4

The radiation pressure from photos emitted during fusion
The gas pressure from the nuclei in the core

Question 5

Low mass stars

Answer 5

Once run out of hydrogen
Red giants - core of star begins to collapse
- Pressure increases cause fusion into shell around core and layers of hydrogen forming other elements
Element layers float off into planetary nebula
Core remains as white dwarf

Question 6

Electron degeneracy pressure

Answer 6

Pressure created by electrons in the core of a white dwarf as they are being collapsed as they cannot exist in the same energy state

Question 7

What is the Chandrasekhar limit

Answer 7

1.44 solar masses
If the core of a star has a mass less than this then the electron degeneracy pressure is enough to prevent gravitational collapse

Question 8

Why do high mass stars have a different lifecycle

Answer 8

Mass is much greater therefore core is hotter
Consume hydrogen in much less time
Helium nuclei fuse into heavier elements

Question 9

Red supergiants

Answer 9

Protostar expands
Temp and pressure high enough to fuse even massive nuclei together —> forms a series of shells inside the star
UNTIL star has iron core, cannot fuse , makes it unstable
Supernova

Question 10

Supernova

Answer 10

Shockwave from a red super giant which ejects all the material into space

Question 11

Neutron star

Answer 11

If mass of star is greater than Chandrasekhars limit (1.44 solar masses) gravitational collapse continues into a neutron star

Question 12

Black hole

Answer 12

After supernova
If core has mass higher than 3M gravitational collapse continues
Results in gravitational field so strong nothing even photons can escape

Question 13

Hertz-sprung russel diagram
What are the axis

Answer 13

Y axis is luminosity
X axis is temperature but going right to left

Question 14

The astronomical unit (AU)

Answer 14

Average distance from Earth to the sun

Question 15

How many arc minutes in 1 degree
1 arc second is how many degrees?

Answer 15

60
(60 arc seconds in each minute)
1 arc second = 1/3600 degrees

Question 16

Parsec definition

Answer 16

The distance at which a radius of 1 AU subtends an angle of 1 arc second

Question 17

Stellar parallax

Answer 17

Technique used to determine the distance to stars which are relatively close to earth
Find the parallax angle as the earth orbits

Question 18

Describe the differences between absorbtion, continuous and emission line spectra

Answer 18

Emission: coloured lines on a black background corresponding to the wavelengths
Continuous: Conatins the complete spectrum of of vivible wavelengths and frequencies (heated solid metal)
Absorbtion: Continuous line passes through a cool gas, some electrons are absorbed as the gas gets excited (black lines on a continous spectrum)

Question 19

d = 1/p only if?

Answer 19

p is measured in arcseconds

Question 20

How is an absorbtion line spectrum formed

Answer 20

When the light from a continuous spectrum passes through a cool gas absorbs the same wavelengths of light as it would emit when it is hot. The wavelengths it absorbs appear black on the continous spectrum background

Question 21

A star is receeding when

Answer 21

Receeding
Redshift
Longer wavelength

Question 22

the cosmological principle

Answer 22

the universe is
1. isotropic
- (eye) looks the same to any observer at any point
2. homogenous
- matter is distributed evenly
3. The laws of physics are universal

Question 23

Hubbles Law observations

Answer 23

1. The light from galaxies was red shifted
2. Further away the galaxy is the faster it moves

Question 24

Evidence for big bang

Answer 24

1. Hubbles law
2. Microwave background radiation
   - universe first existed largely of high energy gamma photons, expansion of the universe stretched these high energy photons, now observe as microwaves