19.1 - 19.7

Question 1

what are nebulae

Answer 1

clouds of dust and gas (mostly hydrogen). often larger than our solar system

Question 2

how are nebulae formed?

Answer 2

over millions of years, the tiny gravitational attraction between dust and gas pulls the particles towards each other

Question 3

how is a protostar formed

Answer 3

tiny variations in nebulae cause denser regions. these regions pull in more dust/gas getting even denser. the GPE turns into thermal energy forming a protostar

Question 4

what is a protostar

Answer 4

a very hot and dense sphere of dust and gas.

Question 5

how is a star formed?

Answer 5

when the core of a protostar becomes hot/dense enough to cause nuclear fusion. high temp/pressure is needed

Question 6

why do stars not collapse under their own gravity?

Answer 6

the compressing force of gravity is equal to the radiation pressure and gas pressure pushing outwards

Question 7

define ‘main sequence star’

Answer 7

the main period of a stars life during which it is stable

Question 8

what characterises a planet

Answer 8

1. its mass is large enough that its own gravity gives it a round shape
2. it has no fusion reactions
3. it cleared its orbit of most other objects

Question 9

what’s the difference between a dwarf planet and a planet

Answer 9

the main difference is that dwarf planets have not cleared their orbits of other objects. (e.g. pluto has many similar sized objects near its orbit)

Question 10

what are asteroids

Answer 10

objects that are too small and uneven to be planets. usually in near-circular orbits around the sun and without the ice that comets have

Question 11

what are satellites

Answer 11

an object in orbit around a planet (natural or man-made)

Question 12

what are comets

Answer 12

small, very irregular objects made of dust, rock and ice. many orbit the sun in highly eccentric, elliptical orbits

Question 13

what are galaxies

Answer 13

a collection of stars and interstellar dust/gas. on average they contain 100Billion stars

Question 14

what is a ‘red giant’ star

Answer 14

an expanding star at the end of its life. its core is inert and fusion only takes place in a shell around the core

Question 15

what happens when a star runs out of hydrogen

Answer 15

when a star runs low on hydrogen the energy released from fusion is much less. gravity is stronger so the star shrinks.

Question 16

what happens when a star shrinks at the end of its ‘main sequence’

Answer 16

The increase in pressure is enough to start fusion in the shell around the core. this causes the periphery around the star to expand as layers slowly move away

Question 17

why is a red giant red

Answer 17

as the star expands its outer layers cool so they glow red

Question 18

how is a white dwarf formed

Answer 18

the outer layers of a red giant drift off into space forming a planetary nebula. this leaves the hot core as a small white dwarf

Question 19

what is electron degeneracy pressure

Answer 19

a quantum-mechanical pressure created by electrons in the core of a collapsing star due to the Pauli exclusion principle

Question 20

why do white dwarfs not collapse under their own gravity

Answer 20

electron degeneracy pressure

Question 21

what is the Chandrasekhar limit

Answer 21

the mass of a star’s core, beneath which the electron degeneracy pressure is strong enough to prevent gravitational collapse

Question 22

what happens when massive stars run out of hydrogen

Answer 22

the energy released from fission decreases so it shrinks. the core is so hot that the fusion of helium starts. this causes it to expand into a red supergiant.

Question 23

what happens to a red supergiant

Answer 23

it fuses elements into iron, forming a stable core. Iron nuclei cant fuse so the star implodes due to its own gravity. the outer layers bounce off the core ejecting them into space (a type II supernova)

Question 24

whats a neutron star

Answer 24

the remanent core of a massive star after it goes supernova. the core collapsed under its own gravity causing a very high density. It’s made almost entirely of neutrons

Question 25

whats a black hole

Answer 25

the remanent core of a massive star after it goes supernova. the core has collapsed so far that the escape velocity is greater than the speed of light

Question 26

what’s a Hertzsprung-Russel diagram

Answer 26

a graph showing the relationship between the luminosity and average surface temperature of stars in our galaxy

Question 27

what is the luminosity of a star

Answer 27

the total radiant power output, measured in Watts

Question 28

energy levels in atoms

Answer 28

an electron cant have a quantity of energy between two levels

energy levels are negative since energy is needed to remove them from the atom

electrons with zero energy are free from the atom

each element has unique energy levels

Question 29

define ‘ground state’

Answer 29

the energy level with the most negative value possible for an electron. its the most stable energy state

Question 30

what is meant by an ‘excited atom’

Answer 30

an atom containing an electron or electrons that have absorbed energy, moving to a higher energy level

Question 31

what is de-excitation

Answer 31

when an electron moves from a higher energy level to a lower one. it emits energy in the form of a photon

Question 32

define ‘spectroscopy’

Answer 32

a technique in which spectral lines are measured to identify elements within stars

Question 33

define ‘spectral lines’

Answer 33

a line in an emission or absorption line spectrum at a specific wavelength

Question 34

what’s an emission line spectrum

Answer 34

a set of specific frequencies of EM waves emitted as excited electrons move back to lower energy levels

Question 35

what’s a continuous spectrum

Answer 35

a spectrum in which all visible frequencies/wavelengths are present

Question 36

what’s an absorption line spectrum

Answer 36

a set of specific frequencies shown as dark lines on a continuous spectrum. they were absorbed by atoms to excite electrons

Question 37

how can elements in a star be analysed

Answer 37

when the light they emit is analysed it looks like an absorption line spectrum. this is checked against elements emission line spectrum to see if they are present in the star

Question 38

what’s a black body

Answer 38

an ideal object that absorbs all of the EM radiation incidents on it. when in thermal equilibrium it then emits a distribution of wavelengths for a specific temperature

Question 39

what is Wiens displacement law

Answer 39

the maximum wavelength at which the intensity of radiation emitted by a black body is at a maximum is inversely proportional to the absolute temperature of the body