astro physics and cosmology

Question 1

planet

Answer 1

objects with mass sufficient for their own gravity to force them to take a spherical shape, no nuclear fusion occurs, cleared orbit of other objects

Question 2

dwarf planets

Answer 2

planet where the orbit has not been cleared of other objects

Question 3

planetary satellite

Answer 3

Bodie that orbits a planet

Question 4

asteroid

Answer 4

objects which are too small and uneven to be planets, near circular orbit around the sun

Question 5

comets

Answer 5

small, irregularly sized balls of rock, dust and ice. they orbit the sun in an elliptical orbit

Question 6

solar system

Answer 6

systems containing stars and orbiting objects like planets

Question 7

galaxy

Answer 7

collection of stars, dust and gas

Question 8

nebulae

Answer 8

gigantic clouds of dust and gas

Question 9

protostar formation

Answer 9

• nebulae with dense regions of dust and gas
• gas pulls dust and gas together causing it to collapse
• as cloud collapses, its starts to spin and forms a rotating disk (angular momentum causes the spin)
• centre of disk, a dense core forms
• gpe is converted to thermal which heats up centre
• sphere of very hot, dense, dust and gas which os called a protostar

Question 10

how are main sequence stars formed from protostars

Answer 10

• when protostar formed from a cloud of gas and dust, gravity pulls the material inward
• as material gets closer togther it becomes denser and hotter
• the increase in denisty and temperature leads to an increase in pressure
• pressure comes from gas particles colliding and pushing outwards
• the temp and pressure must then be high enough for hydrogen to overcome elcatrostatic forces of repulsion and undergo nuclear fusion where hydrogen is fused to helium
• fusion will occur when the pressure outward pressure balances the inward force of gravity

Question 11

how does a low mass main sequence star become a red giant

Answer 11

• core mass of 0.5 solar masses
• smaller cooler core they remain in main sequence longer
• hydrogen supplies low g forces inwards overcome radiation and gas pressures
• core collapses and outer layers expand and cool
• core of red giant becomes hotter as gpe becomes thermal energy and it fuses helium into heavier elements up to carbon as hydrogen continues to be fused in the layers around the core

Question 12

red giant to white dwarf

Answer 12

• star runs out of fuel it expels its outer layers resting planetary nebulae
• core contracts further becoming dense white dwarf
• no fusion occurs
• photon which were produced earlier leak out dissipating heat
• star core collapses electron degeneracy pressure prevents the. core form collapsing, as long as core mass is below 1.44 then the white dwarf is stable this is the Chandrasekhar limit

Question 13

high mass main sequence into red supergiant

Answer 13

• mass exceeds 10 solar masses
• hydrogen supplies deplete
• core contracts
• as mass is greater when gpe is converted to thermal energy the core gets hotter than red giant allowing helium fusion into heavier elements than carbon up to iron
• outer layers expand and cool forming red supergiant

Question 14

death of high mass star

Answer 14

• fuel in red supergiant used up fusion stops
• gravity becomes greater than outward pressure due to fusion
• core collapses in on itself and becomes rigid
• outer layers fall inwards and rebound off the core launching them into space as a shockwave
• remaining core of a supernova is either a neutron star or black hole depending on mass

Question 15

red supergiant into neutron star or black hole

Answer 15

• core greater than 1.44 gravity forces protons and electrons to combine and form neutrons this produces small dense neutron star
• core greater than 3 the gravitational forces are so strong that the escape velocity of the core becomes greater than the speed of light this is a black hole

Question 16

hertzprung - russel diagram

Answer 16

• top supergiants
• middle right giants
• negative linear line main sequence
• bottom left white dwarf

Question 17

Chandrasekhar limit

Answer 17

the maximum mass that a white dwarf can have whilst remaining stable

Question 18

x and y axis of hertzprung russel diagram

Answer 18

y axis is luminosity
x axis is temperature (increases to the left)

Question 19

rules for energy levels

Answer 19

• electron cannot have an energy level between states
• negative as external energy os requires for an electron to escape
• lowest most negative energy level is the ground state

Question 20

emission line spectra

Answer 20

• series of colour lines on a black background
• light passes through outer layers of a star, electrons in atom absorb photons and become excited
• they then de excite releasing photons of specific wavelengths
• these are detected on earth and have wavelengths characteristic of the elements in the outer layers, shown as emission line spectra

Question 21

continues line spectra

Answer 21

all visible wavelengths of light are present, they are produced by atoms of solid heated metals

Question 22

absorption line spectra

Answer 22

• dark spectral lines on coloured background
• each line corresponds to wavelength of light absorbed by atoms in outer layers of a star
• dark lines are at wavelengths that are characteristic of the elements in the outer layers

Question 23

what happens when an electron is de-excited

Answer 23

releases energy as a photon with specific wavelength
- energy released is the difference between the initial and final energy level of photon

Question 24

diffraction gratings

Answer 24

components with regularly spaced slits that can diffract light. different colours of light have different wavelengths and so will be diffracted at different angles

Question 25

weins displacement law

Answer 25

wavelength of emitted radiation at peak intensity is inversely proportional to the temperature of the black body

Question 26

stefans law

Answer 26

power output of a star is directly proportional to its surface area and to its (absolute temperature)^4

Question 27

light year

Answer 27

distance travelled by light in vacuum in one year

Question 28

doppler effect

Answer 28

change in wavelength and frequency of a wave as the source moves away from or towards the observer

Question 29

stellar parallax

Answer 29

apparent shift imposition of object against backdrop of distant objects due to the orbit of the earth

Question 30

parsec

Answer 30

the distance from which 1 AU subtends an angle of 1 arc second (1/3600 of a degree)

Question 31

cosmological principle

Answer 31

universe is isotropic and homogenous and the laws of physics are universal

Question 32

isotropic

Answer 32

universe is the same in all directions to envy observer and it has no centre or edge

Question 33

homogenous

Answer 33

matter is uniformly distributed for a large volume of the universe the density is the same

Question 34

red shift

Answer 34

shut in wavelength and frequency of waves from a retreating source towards/beyond the red end of the spectrum it is evidence of the Big Bang

Question 35

Hubbles law

Answer 35

velocity of receding objects is directly proportional to their distance from earth

Question 36

big bang theory

Answer 36

universe exploded from a extremely hot dense point and is still expanding

cosmic background microwave radiation is the heat signature left behind from the Big Bang

em radiation released in the explosion shifted from extremely high energy waves into the microwave region as the universe expanded stretching out the waves

Question 37

dark energy

Answer 37

• energy that has an overall repulsive effect through out the universe

Question 38

big bang times

Answer 38

• time and space created
• universe expand and cools in period of inflation
• fundamental particles gain mass, quarks and leptons
• quarks bind to form hadrons (protons and neutrons)
• expanding and cooling
• cools enough for atoms to form

Question 39

cosmic background microwave radiation

Answer 39

• main observation of big bang
• radiation was released as gamma rays but now stretched to microwaves
• accounts fro temp of 2.7K