Astrophysics SL

Question 1

apparent brightness (b)

Answer 1

amount of energy received per second per unit area by an observer (unit: Wm^-2)

Question 2

astronomical unit (AU)

Answer 2

the mean distance from the centre of the Earth to the centre of the Sun (1.50 x 10^11m)

Question 3

binary stars

Answer 3

two stars orbiting their common centre of mass

Question 4

cepheid variable

Answer 4

a star that undergoes a periodic expansion of its outer layers that gives a periodic variation in its luminosity

Question 5

Chandrasekhar limit

Answer 5

maximum star remnant mass (1.4M⊙) where electron degeneracy pressure prevents further gravitational collapse

Question 6

constellation

Answer 6

a group of stars that appear to make a pattern in the sky but they may not necessarily be close to each other in space

Question 7

cosmic microwave
background (CMB) radiation

Answer 7

radiation emitted by the universe consistent with a temperature of 2.7K

Question 8

cosmic scale factor (R) (expansion)

Answer 8

gives a measure of the expansion that has taken place in the universe

Question 9

dark energy

Answer 9

invisible energy source that may be accelerating the expansion of the universe

Question 10

electron degeneracy
pressure

Answer 10

where electron repulsion prevents further gravitational collapse of a star

Question 11

galactic cluster

Answer 11

a group of galaxies gravitationally bound together, orbiting around a common centre of gravity

Question 12

galaxy

Answer 12

a large scale collection of stars, gas and dust held together by gravity

Question 13

globular stellar cluster

Answer 13

symmetrically arranged stellar cluster of 10^4 - 10^5 old stars

Question 14

Hertzsprung-Russell
diagram

Answer 14

graph plotting the luminosity of stars against their temperature

Question 15

Hubble’s Law

Answer 15

the speed at which galaxies are moving away from Earth (recession speed) is directly proportional to their distance from Earth

Question 16

L⊙ and M⊙

Answer 16

symbols for luminosity and mass of the Sun

Question 17

light year (ly)

Answer 17

the distance light travels in one year

Question 18

luminosity (L)

Answer 18

total amount of energy emitted per second by a star (unit: W)

Question 19

main sequence star

Answer 19

a “normal” star that is fusing hydrogen into helium

Question 20

nebula

Answer 20

intergalactic cloud of dust and gas

Question 21

neutron degeneracy
pressure

Answer 21

where neutron repulsion prevents further gravitational collapse of a star

Question 22

Newton’s model of the
universe

Answer 22

the universe is infinite in space and time, uniform and static

Question 23

open stellar cluster

Answer 23

irregular shaped stellar cluster of several hundred young stars

Question 24

Oppenheimer-Volkoff limit

Answer 24

maximum star remnant mass (3M⊙) where neutron degeneracy pressure prevents further gravitational collapse

Question 25

parsec

Answer 25

distance at which the angle subtended by the radius of the Earth’s orbit is one arc-second

Question 26

planetary nebula

Answer 26

the ejection of the outer layers of a small star (< 8M⊙) once fusion has stopped

Question 27

planetary system

Answer 27

a group of planets orbiting a star

Question 28

pulsar

Answer 28

a rotating neutron star

Question 29

recession speed

Answer 29

the speed at which an object is moving away from an observer

Question 30

red giant (and supergiant)

Answer 30

large (mass & surface area), relatively cool star, red in colour

Question 31

redshift

Answer 31

apparent increase in the wavelength of light from distant galaxies due to their motion away from us

Question 32

redshift ratio (z)

Answer 32

ratio of change in wavelength due to cosmological redshift to original wavelength emitted by a galaxy moving relative to Earth

Question 33

singularity

Answer 33

point containing the entire universe at the start of the Big Bang

Question 34

stellar cluster

Answer 34

a close group of gravitationally bound stars, gas and dust (within a galaxy)

Question 35

stellar parallax

Answer 35

method used to measure distances to stars based on their apparent movement in position relative to distant background stars over a 6 month period

Question 36

supercluster

Answer 36

a large grouping of galactic clusters

Question 37

supernova

Answer 37

the ejection of the outer layers of a large star (> 8M⊙) once fusion has stopped

Question 38

type Ia supernova

Answer 38

type of supernova with a known luminosity that occurs in binary star systems where one of the stars is a white dwarf

Question 39

white dwarf

Answer 39

small (mass & surface area), relatively hot star, white in colour

Question 40

cosmic scale factor (relative)

Answer 40

a measure of the relative size of the Universe

Question 41

accelerating universe outcome

Answer 41

expansion continues at an increasing rate due to dark energy

Question 42

type Ia supernovae (formation)

Answer 42

formed when a white dwarf in a binary system gains mass from its companion star and explodes due to fusion restarting

Question 43

closed universe outcome

Answer 43

gravity causes the Universe to collapse back in on itself - the Big Crunch

Question 44

open universe outcome

Answer 44

gravity slows expansion but is not strong enough to stop it

Question 45

flat universe outcome

Answer 45

gravity slows expansion but takes an infinite time to do so

Question 46

MACHOS

Answer 46

Massive Compact Halo Objects - high density compact stars at the ends of their lives

Question 47

Jeans mass (Mj)

Answer 47

minimum mass required for a gas cloud to collapse and star formation to occur

Question 48

r-process

Answer 48

neutron capture where there is not time for beta decay to occur before further neutron capture

Question 49

s-process

Answer 49

neutron capture where there is time for newly formed nuclides to undergo beta decay and form a new element

Question 50

CNO cycle

Answer 50

process by which hydrogen undergoes fusion to create helium in stars with a mass greater than four solar masses

Question 51

proton-proton chain

Answer 51

process by which hydrogen undergoes fusion to create helium in the Sun

Question 52

nucleosynthesis

Answer 52

process of forming different nuclides by nuclear fusion

Question 53

type II supernovae

Answer 53

result from the rapid collapse and violent explosion of a massive star (> 8 solar masses)

Question 54

density parameter (Ωo)

Answer 54

the ratio of the actual density of the Universe (ρ) to the critical density (ρc)

Question 55

isotropic

Answer 55

the same in all directions

Question 56

WIMPS

Answer 56

Weakly Interacting Massive Particles - subatomic particles

Question 57

the Cosmological Principle

Answer 57

when viewed on a large scale, the Universe is homogenous and isotropic