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Physics > Astrophysics SL > Flashcards

Astrophysics SL Flashcards

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1
Q

apparent brightness (b)

A

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

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2
Q

astronomical unit (AU)

A

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

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3
Q

binary stars

A

two stars orbiting their common centre of mass

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4
Q

cepheid variable

A

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

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5
Q

Chandrasekhar limit

A

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

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6
Q

constellation

A

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

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7
Q

cosmic microwave
background (CMB) radiation

A

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

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8
Q

cosmic scale factor (R) (expansion)

A

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

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9
Q

dark energy

A

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

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10
Q

electron degeneracy
pressure

A

where electron repulsion prevents further gravitational collapse of a star

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11
Q

galactic cluster

A

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

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12
Q

galaxy

A

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

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13
Q

globular stellar cluster

A

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

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14
Q

Hertzsprung-Russell
diagram

A

graph plotting the luminosity of stars against their temperature

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15
Q

Hubble’s Law

A

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

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16
Q

L⊙ and M⊙

A

symbols for luminosity and mass of the Sun

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17
Q

light year (ly)

A

the distance light travels in one year

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18
Q

luminosity (L)

A

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

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19
Q

main sequence star

A

a “normal” star that is fusing hydrogen into helium

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20
Q

nebula

A

intergalactic cloud of dust and gas

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21
Q

neutron degeneracy
pressure

A

where neutron repulsion prevents further gravitational collapse of a star

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22
Q

Newton’s model of the
universe

A

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

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23
Q

open stellar cluster

A

irregular shaped stellar cluster of several hundred young stars

24
Q

Oppenheimer-Volkoff limit

A

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

25
Q

parsec

A

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

26
Q

planetary nebula

A

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

27
Q

planetary system

A

a group of planets orbiting a star

28
Q

pulsar

A

a rotating neutron star

29
Q

recession speed

A

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

30
Q

red giant (and supergiant)

A

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

31
Q

redshift

A

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

32
Q

redshift ratio (z)

A

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

33
Q

singularity

A

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

34
Q

stellar cluster

A

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

35
Q

stellar parallax

A

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

36
Q

supercluster

A

a large grouping of galactic clusters

37
Q

supernova

A

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

38
Q

type Ia supernova

A

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

39
Q

white dwarf

A

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

40
Q

cosmic scale factor (relative)

A

a measure of the relative size of the Universe

41
Q

accelerating universe outcome

A

expansion continues at an increasing rate due to dark energy

42
Q

type Ia supernovae (formation)

A

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

43
Q

closed universe outcome

A

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

44
Q

open universe outcome

A

gravity slows expansion but is not strong enough to stop it

45
Q

flat universe outcome

A

gravity slows expansion but takes an infinite time to do so

46
Q

MACHOS

A

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

47
Q

Jeans mass (Mj)

A

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

48
Q

r-process

A

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

49
Q

s-process

A

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

50
Q

CNO cycle

A

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

51
Q

proton-proton chain

A

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

52
Q

nucleosynthesis

A

process of forming different nuclides by nuclear fusion

53
Q

type II supernovae

A

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

54
Q

density parameter (Ωo)

A

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

55
Q

isotropic

A

the same in all directions

56
Q

WIMPS

A

Weakly Interacting Massive Particles - subatomic particles

57
Q

the Cosmological Principle

A

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

Physics (1 decks)

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