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IB Physics HL > Option D: Astrophysics > Flashcards

Option D: Astrophysics Flashcards

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1
Q

What is a single star?

A

A luminous sphere of plasma held together by its own gravity.

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2
Q

What is a binary star system?

A

Two stars orbiting a common centre of mass.

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3
Q

What is a black hole?

A

A singularity in space-time.

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4
Q

What is a Cepheid variable star?

A

A star with a varying luminosity over a fixed period

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5
Q

What are clusters of galaxies?

A

Two or more galaxies that are close enough to each other to affect each other through gravitation.

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6
Q

What is a constellation?

A

A pattern of stars visible from Earth that are not gravitationally bound.

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7
Q

What is dark matter?

A

Matter unknown in structure that does not emit or absorb any radiation and makes up the around 20% of the universe.

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8
Q

What are galaxies?

A

Stars, gas, and dust held together by gravitational forces.

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9
Q

What is a main sequence star?

A

A normal star that is undergoing nuclear fusion of hydrogen into helium.

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10
Q

What is a neutron star?

A

A very dense star, consisting only of uncharged neutrons.

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11
Q

What is a nebula?

A

A giant cloud of interstellar dust and gas.

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12
Q

What is a planet?

A

A celestial body that orbits a star.

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13
Q

What is a planetary system?

A

Gravitationally bound, non-stellar objects in orbit around a star or star system.

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14
Q

What is a planetary nebula?

A

The ejection of mass from an exploding red giant star.

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15
Q

What are stellar clusters?

A

A group of similar age stars gravitationally bound together.

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16
Q

What is a parsec?

A

the distance when the mean radius of the Earth’s orbit subtends an angle of one arcsecond.

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17
Q

What is a light year?

A

The distance travelled by light in a year.

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18
Q

What is an astronomical unit (AU)?

A

The average distance between the Earth and the Sun.

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19
Q

What is hydrostatic equilibrium?

A

The condition when the gravitational force and the force due to pressure are balanced.

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20
Q

What is parallax?

A

The apparent displacement of an object because of a change in the observer’s point of view.

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21
Q

How can parallax angles be used to measure the distance to nearby stars?

A
  • As the Earth orbits the Sun, a nearby star will appear to move against the more distant background stars.
  • Astronomers can measure a star’s position once, and then again 6 months later and calculate the apparent change in position.
  • The star’s apparent motion is called stellar parallax.
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22
Q

What does each symbol mean and what are the units in the following equation:

d = 1 / p

A

d = distance from Earth to a star (parsec)
p = parallax angle (arcsecond)

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23
Q

What does each symbol mean and what are the units in the following equation:

L = σ A T^4

A

L = luminosity (W)
σ = Stefan-Boltzmann constant (W / m^2 K^4)
A = Area (m^2)
T = Temperature (K)

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24
Q

What does each symbol mean and what are the units in the following equation:

b = L / 4π d^2

A

b = apparent brightness (W / m^2)
L = luminosity (W)
d = distance to star (m)

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25
Q

What is this the relation between:

λ(max) T = 2.9 x 10^-3 mK

A

The relation between the wavelength of maximum intensity radiation of a star and its temperature.

λ = wavelength (m)
T = temperature (K)

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26
Q

What is this the relation between:

L ∝ M^3.5

A

The mass-luminosity relation for main sequence stars.

L = luminosity (W)
M = mass (kg)

27
Q

What does each symbol mean and what are the units in the following equation:

z = Δλ / λ(0) ≈ v / c

A

z = red shift (unitless)
λ = wavelength (m)
λ(0) = Emitted wavelength (m)
v = relative velocity of light source (m/s)
c = speed of light (m/s)

28
Q

What does each symbol mean and what are the units in the following equation:

z = R / R(0) - 1

A

z = red shift (unitless)
R = current cosmic scale factor
R(0) = cosmic scale factor at a point in time

29
Q

What does each symbol mean and what are the units in the following equation:

v = H(0) d

A

v = recession speed (km/s)
H(0) = Hubble constant (km / s Mpc)
d = distance to galaxy (Mpc)

30
Q

What is this the relation between:

Age of the universe ≈ 1 / H(0)

A

Relationship between age of the universe and Hubble constant

T = Age of the universe (s)
H(0) = Hubble constant (s-¹)

31
Q

What does each symbol mean and what are the units in the following equation:

ρ(c) = 3 H^2 / 8π G

A

ρ(c) = critical density (kg/m^3)
H = Hubble constant for a given cosmological time (km / s Mpc)
G = gravitational constant (Nm^2 / kg^2)

32
Q

What is the Jeans Criterion and the ideal conditions for formation of a protostar?

A

The Jeans Criterion is the minimum conditions for a nebula to form a protostar, this is when the gravitational potential energy is greater than the kinetic energy. Most likely to occur when:

  • The nebula is at a low temperature.
  • The nebula is extremely dense.
  • The mass is greater than the Jeans Mass
33
Q

What is the Chandrasekhar Limit?

A

The upper limit of mass for a white dwarf before it collapses into supernova (1.4 Solar Masses). This is due to electron degeneracy pressure preventing it from collapsing further.

34
Q

What is the Oppenheimer-Volkoff Limit?

A

The upper limit of mass for a neutron star before it collapses into a black hole (1.5-3 Solar Masses). This is due to neutron degeneracy pressure preventing it from collapsing further.

35
Q

What is luminosity?

A

The power radiated by a star (not dependent on temperature)

36
Q

What is apparent brightness?

A

The power per unit area received from a star (depends on distance)

37
Q

If a stars specific absorbed wavelengths are blue-shifted, what can we say about this star’s motion relative to Earth?

A

Moving towards Earth

38
Q

If a stars specific absorbed wavelengths are red-shifted, what can we say about this star’s motion relative to Earth?

A

Moving away from Earth

39
Q

Why do you become unable to use parallax angles to calculate the distance to further away stars?

A

The angle becomes too small to measure

40
Q

How can a Cepheid Variable star be used as a standard candle?

A
  • Measure the period of the star
  • Look up which luminosity corresponds to that period
  • Using the luminosity and apparent brightness, determine the distance of the star from Earth using b = L / 4π d^2
41
Q

How can redshift be used as evidence for the Big Bang Theory?

A
  • Light from distant galaxies is redshifted
  • Therefore it is moving away from us
  • If extrapolated back, the universe will have all started from one singular point
42
Q

List 3 characteristics of CMBR.

A
  • Highly isotropic
  • Homogenous
  • Peak temperature of 2.76K
43
Q

What is the critical density of the universe?

A

The density of the universe needed to completely stop expansion.

44
Q

List two problems with finding the mass of the universe.

A
  • Dark matter (WIMPs and MACHOs)
  • Dark energy
45
Q

What is a standard candle?

A

A star with a known luminosity that can be used to calculate the distance from said star to the Earth.

46
Q

Stars can be assumed to be perfect black body radiators, what is a black body?

A

A perfect emitter or absorber of radiation.

47
Q

Describe the evolutionary path of our Sun.

A
  • When all Hydrogen has fused into Helium, the Sun’s core will collapse
  • Outer layers will rapidly expand and cool, forming a red giant
  • Core becomes dense enough to fuse Helium into heavier elements
  • When it has run out of Helium, it’ll undergo a planetary nebula and become a white dwarf
48
Q

Describe the formation of a type 1a supernova.

A

Within a binary star system, a white dwarf accretes matter from a nearby companion star until it exceeds the Chandrasekhar limit and explodes.

49
Q

How can a type 1a supernova be used as a standard candle?

A
  • Has a known mass (1.4 Solar Masses)
  • Use the shape of the luminosity graph to determine luminosity
  • Using the luminosity and apparent brightness, determine the distance of the star from Earth using b = L / 4π d^2
50
Q

Use the expanding balloon analogy to explain receeding galaxies.

A

Galaxies are like points on a balloon and as it expands, they will spread apart but stay the same size.

51
Q

What is nucleosynthesis?

A

The process in which elements are formed.

52
Q

What does Jean’s Criterion state?

A

A cloud of Hydrogen gas can collapse under its own gravity if M > Mj.

53
Q

Where do stars spend the majority of their lifetime?

A

Main sequence

54
Q

Describe the processes that occur within a main sequence star.

A

Star converts hydrogen into helium through nuclear fusion. The outwards pressure of this fusion is equal to the inwards pressure due to gravity meaning the star is in hydrostatic equilibrium.

55
Q

What happens to a main sequence star after it runs out of Hydrogen in its core?

A

The core will collapse until it becomes dense enough to fuse helium into heavier elements. The outerparts of the star will expand and cool, forming a red giant.

56
Q

What happens when a red giant when it runs out of Helium in its core?

A

The core will collapse and fuse heavier and heavier elements. If there is enough mass, the core can become iron but cannot fuse any further and will collapse.

57
Q

Why can no elements heavier than iron be formed in the core of a red giant?

A

Iron has the peak binding energy per nucleon.

58
Q

Describe the r-process (rapid).

A
  • Vast numbers of neutrons means beta decay doesn’t occur quickly enough and more neutrons are captured instead.
  • Results in very large nuclei to be created.
  • Usually takes place during a supernova.
  • Large elements, such as uranium, can only be created in this way.
59
Q

Describe the s-process (slow).

A
  • As neutrons don’t have charge, they are not affected by electrostatic repulsion and can pass close to a nucleus.
  • It can be possible for this neutron to be “captured” as a result.
  • The newly formed nucleus will be excited and emit a gamma photon.
  • Also, this neutron may decay via beta decay resulting in a new element to be formed.
60
Q

What does the cosmological principle state?

A

The universe is both isotropic and homogenous

61
Q

What does isotropic mean?

A

Looks the same in all directions.

62
Q

What does homogenous mean?

A

Looks the same at every point.

63
Q

What is dark energy?

A

A mysterious force acting opposite to gravity, it cannot be seen and has no mass (as it repels and mass attracts)

64
Q

What is the relationship between cosmic scale factor and temperature?

A

Inverse

IB Physics HL (13 decks)

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