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physics content > Astrophysics > Flashcards

Astrophysics Flashcards

1
Q

What an astronomical unit

A

A measurement equivalent to 1.5*10^11m (the orbiting distance of the sun and earth)

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2
Q

What is apparent magnitude

A

The brightness of a star from earth

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3
Q

What is d

A

The distance from the nearby star and orbiting planet

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4
Q

How can you work out d (unit is parsec)

A

d (parsec) = AU / Arcsec

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5
Q

What is arcsec used for

A

The measure of the angle of parallax = 1/3600 degrees

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6
Q

What is 1 parsec in metres and light years

A

3.08 * 10^16 m

1pc = 3,26 ly

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7
Q

In Hippochus Apparent brightness scale which magnitude is visible to the naked eye

A

+6.00 (6th magnitude and lower)

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8
Q

What is the multiplier of change for each magnitude

A

2.51 times

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9
Q

Which apparent magnitude is brighter -26 or +6.0

A

-26

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10
Q

What is pagson’s law (ratio of intensity)

A

I2/I1 = 2.51^m1-m2

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11
Q

What is absolute magnitude?

A

It is equal to the apparent magnitude if it were placed at a distance of 10 parsecs from the earth

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12
Q

What is the equation for the ratio of intensity

A

I2/I1 = 2.51^m1-m2

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13
Q

What is a black body object

A

An object that absorbs all wavelengths of electromagnetic radiation and emits all wavelengths of electromagnetic radiation however does not exist in reality

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14
Q

What does the peak wavelength of an object help determine using wiens law?

A

The temperature

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15
Q

What is Wiens law on temperature

A

Max wavelength * temperature = weins constant

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16
Q

What is stefans formula

A

Power output of a star = stefans constant * surface area * temperature^4

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17
Q

What is the equation for intensity of light

A

intensity = p / 4pi * distance^2

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18
Q

What is luminousity?

A

The brightness of a star and the rate of light energy released by a star (power output)

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19
Q

Define parsec

A

The distance when the angle of parallax is 1 arcsec

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20
Q

What determines the luminosity of a star?

A

The average energy per photon
The amount of photons released per second

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21
Q

What does the colour of a star depend on?

A

The wavelength of light it does not absorb

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22
Q

In the Balmer series what do the absorption lines indicate?

A

Highlights any excitation or dexcitation involving n=2 and hydrogen, via visible light only

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23
Q

What are HR diagrams

A

Absolute magnitude (luminosity) against decreasing temperature (OBAFGKM)

involves main sequence stars, white dwarfs and red giants

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24
Q

What are protostars

A

These are baby stars formed from nebulas (compression of dust and gas), they’re not a part of the main sequence stars

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25
Q

What defines a star and allows protostars to be a part of the main sequence stars?

A
  • can conduct nuclear fusion
  • has a certain amount of mass
  • equilibrium of pressure (force from nuclear fusion) and gravity
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26
Q

Why do clouds of dust and gas gather

A

Due to gravity

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27
Q

What do main sequence stars fuse together for billions of years

A

Hydrogen into helium

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28
Q

What can main sequence stars become depending on their mass

A

High mass - red super giants
Low mass - red giants

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29
Q

What do red giants do?

A

They eventually run out of hydrogen to fuse, as temperature increases they begin to fuse helium to form heavier elements
- their outer layers expand and cool

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30
Q

How are white dwarfs formed?

A

When red giants are unable to conduct nuclear fusion due to running out of fuel, gravity becomes greater than pressure so the star contracts.
The core becomes dense only emitting light

31
Q

How are black dwarfs formed

A

When white dwarfs no longer emit light and are cooled down

32
Q

What are red super giants

A
  • They also continue to fuse helium atoms when hydrogen atoms however they can make elements up to iron
  • bigger than 3 times the solar mass
33
Q

What are supernovas?

A

A huge explosion of red super giants that occurs when all fuel runs out and gravity collapses in itself, as the outer layer falls inwards it rebounds of heat core launching them into space in a shockwave
This is where all elements heavier than iron is fused and flung into space

34
Q

What is a neutron star

A

When the gravity of a red super giant is so strong that it forces protons and electrons together to form neutrons (it is incredibly dense)

35
Q

What is black hole

A

When escape velocity becomes greater than the speed of light, gravity too strong where it forces neutrons to come together.

36
Q

What are the characteristics of a supernova

A
  • a great explosion of light
  • gravity condenses protons and electrons which forces electron capture which forms neutrons
  • shockwaves emit material and energy
37
Q

What is the range of absolute magnitude for supernovas?

A

-15 to -20

38
Q

How long do supernovas outshine the whole galaxy

A

24 hours

39
Q

What is the absolute magnitude of type 1a supernovas?

A

-19.3+-0.03

40
Q

What is scharzchild radius?

A

The radius of the event horizon of a black hole when you and light will not be able to escape the black hole

R = 2GM/c^2 (escape velocity with light)

41
Q

What is the range of absolute magnitude on the HR diagram

A

-10 to 15

42
Q

What is Hipparcos’ scale?

A

Classifies astronomical objects by their apparent brightness

43
Q

What is parallax

A

The apparent change of the position of a nearer star in comparison to distant stars

44
Q

Define stefans law

A

Power output of a black body radiator is proportion to surface area and absolute temperature^4

45
Q

Formula for intensity

A

P/(4pi d^2)

46
Q

What are spectral classes based on?

A

The strength of absorption lines

47
Q

What spectral classes are hydrogen balmer lines found in

A

O B A

48
Q

What causes hydrogen balmer lines

A

When stars are hot enough to excite hydrogen to n=2, if too hot it would excite to higher levels

49
Q

Which class has the strongest balmer lines?

A

A

50
Q

The direction of absolute magnitude on HR diagram

A

-10 to 15 top to bottom

51
Q

How does red giant become a white dwarf

A

Uses up all the helium in its core
it will eject its outer layers
Become hotter and dimmer

52
Q

What is in equilibrium in a main sequence star?

A

The outward press and inward gravity

53
Q

When does a star become a red giant?

A

When hydrogen runs out, helium is then fused to form outer layer which expands and cools

54
Q

How big are white dwarfs

A

1.4 solar mass

55
Q

How do you differentiate red giants and red super giants

A

red giants < 3 time solar mass
super red giant > 3 times solar mass

56
Q

What is a binary system

A

When two stars orbit a common mass

57
Q

What is a type 1 supernovae

A

When a star accumulates matter from its companion star in a binary system and explodes after reaching critical mass

58
Q

What is a type 2 supernovae

A

It is the death of a high mass star after it runs out of fuel

59
Q

What have scientist concluded is at the centre of our galaxies and why

A

Super massive black holes
As gas and stars near the centre appear to orbit quickly
Therefore there must be something with a strong gravitational field

60
Q

What is dark energy

A

The reason behind why the universe is accelerating

61
Q

What is the doppler effect

A

The compression or spreading out of waves that are emitted or reflected by a moving source

62
Q

What does the doppler effect do to lines of spectra

A

Shift them to blue end or red end (red/blue shift)
#

63
Q

What is blue shift and red shift in terms of spectra

A

Blue shift - when lines of spectra move towards earth
red shift - when lines of spectra move away from earth

64
Q

What is red shift used in evidence for?

A

An expanding universe

65
Q

What is the criteria of using red shift formula

A

When recessional velocity is much smaller than the speed of light

66
Q

What are the characteristics of quasars

A

Extremely large optical red-shifts
Very powerful light output
Not much bigger than a star

67
Q

How can you estimate the power output of a quasar?

A

Inverse square law for intensity

68
Q

What are exoplanets

A

Planets not within our solar system

69
Q

What are the two ways of detecting exoplanets

A

Radial velocity method
Transit method

70
Q

Explain the radial velocity method

A

In binary systems stars orbit a common centre of mass which causes them to wobble slightly

This causes a doppler shift in the light received from the star

This causes the line spectrum that are detected to be blue or red shifted

71
Q

Explain the transit method

A

Involves observing the intensity of light output, if the star intensity dips regularly this shows there is a another planet in orbit

72
Q

State the property of quasars that led to its discovery

A

High power

73
Q

Suggest why quasars stopped emitting radiation?

A

quasars are formed around black holes

black hole no longer has matter falling into it

physics content (19 decks)

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