14 Stellar Evolution 4th Flashcards

1
Q

Why is it difficult to classifying stars by their brightness?

A

The brightness they appear from Earth also depends on their distance from the Earth.

The closer the star, the brighter it appears.

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2
Q

What is the name of the long stable period a star enters when the outward pressure caused by thermal expansion balances the force of gravity pulling everything inward.

A

The main sequence

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3
Q

Which of the following is NOT evidence that supports the Big Bang Theory

A. Variation in gravitational field strength

B. The red-shift observed in light reaching Earth from distant galaxies.

C. Cosmic microwaves background radiation.

A

A. Variation in gravitational field strength

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4
Q

Describe the absolute magnitude scale.

A

-10 0 +10

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5
Q

Stellar evolution for a small mass star is…

Nebula –> Protostar –> Main sequence star –> Red giant –> white dwarf

What evolutionary stages does a large mass star go through?

A

Large mass star

Nebula –> Protostar –> Main sequence star –> Red super giant –> Supernova –> Neutron star

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6
Q

Stellar evolution for a low mass star is…

Nebula –> Protostar –> Main sequence star –> Red giant –> white dwarf

What evolutionary stages does a very large mass star go through?

A

Very large mass star

Nebula –> Protostar –> Main sequence star –> Red super giant –> Supernova –> Black hole

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7
Q

Where are the cool and dim stars found on the HR diagram?

A

Bottom right

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8
Q

Which of the following is not formed after a supernova?

A. a neutron star

B. a black hole

C. a red super giant

A

C. a red super giant.

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9
Q

On the Hertzsprung-Russell diagram, white dwarfs group together because they have…

A ..negative absolute magnitudes and high temperatures

B .. negative absolute magnitudes and low temperatures

C .. positive absolute magnitudes and high temperature

A

C .. positive absolute magnitude and high temperatures

White dwarfs are dim and hot!

NOTE: Confusingly, the low absolute magnitude, the brighter the star ( -4 is brighter than +5)

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10
Q

The absolute magnitude of a star is..

A. how bright the star would appear if it was at a standard distance from Earth

B. the brightest the star could appear to an observer

C. how bright the star appears from Earth

A

A. how bright the stat would appear if it was at a standadrd distance from Earth.

This allows us to compare the brightness of stars without worrying about their relative distances from Earth.

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11
Q

In general, the further away a galaxy is….

A. the smaller the observed increase in the wavelength of its light.

B. the slower it is moving away from us.

C. the bigger the observed increase in wavelength of its light.

A

C. the bigger the observed increase in wavelength of its light.

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12
Q

A hot star will emit most its visible light at the _____________ frequencies of visible light.

A

highest (blue)

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13
Q

Below is a description of how the universe started…

1) initially, all the matter in the universe occupied a single point
2) This tiny space was very dense and very hot

3) This single spot then exploded

4) Space started expanding, and the expansion is still going.

What is stage 3 called?

A

The Big Bang

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14
Q

Locate the white dwarf in the HR diagram below.

A

D

white dwarf stars are dim and cool

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15
Q

What is cosmic microwave background (CMB) radiation believed to be?

A. Energy from exploding supernovae.

B. Radiation given out by man-made objects in space, such as satellites and telescopes.

C. Leftover energy from the Big Bang explosion.

A

C. Leftover energy from the Big Bang explosion.

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16
Q

Eventually a star runs out of hydrogen in it core. The force of gravity inward is larger than the pressure of thermal expansion outward.

The star is compressed, until it is dense and hot enough that the energy (and so the pressure) created makes the outer layers of the star expand.

What is the name of this stage?

A

red giant (small mass star)

red supergiant (large mass star)

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17
Q

Where are the hot and dim stars found on the HR diagram?

A

Bottom left

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18
Q

A cool star will emit most its visible light at the _____________ frequencies of visible light.

A

lowest (orange and red)

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19
Q

Light from galaxies is red-shifted. What do measurements of the red-shift tell us?

A. All galaxies are moving away from us at the same speed

B. More distant galaxies are moving away faster than closer galaxies

C. Closer galaxies are moving away faster than distant galaxies.

A

B. More distant galaxies are moving away faster than closer galaxies

20
Q

The colour of a star is related to the star’s ____________ _____________

A

surface temperature

21
Q

The force of gravity pulls the dust and gas together to form a protostar. The temperature rises as the star gets denser and more particles collide with each other.

What occurs when the temperature gets hot enough (around 15 million K)

A

Hydrogen nuclei undergo nuclear fusion to form helium nuclei.

This gives out huge amounts of energy!!

22
Q

What is CMB or cosmic microwave background radiation?

A

It is the left over energy of the Big Bang.

23
Q

Which of the following will eventually become a supernova?

A stars with a similar mass to the Sun

B stars with a large mass than the Sun

C stars with a smaller mass than the Sun

A

B. stars with a larger mass than the Sun

24
Q

Absolute magnitude is a measure of how bright a given star would appear to be if it were…

A

a fixed distance from the Earth.

25
Q

True or False

’ A star that emits blue light will have a higher surface temperature than a star that emits red light’

A

True

26
Q

True or false

‘Our Sun is a yellow star and has a core temperature of around 5000K’

A

False- our Sun has a surface temperature of 5000K.

Its core temperature will be about 15 million K and therefore fusion can occur in its core.

27
Q

In a main sequence star, the outward pressure produced by nuclear fusion balances the force of gravity.

What causes this phase in the star’s life cycle to end?

A

The supply of hydrogen in the stars core, which is the fuel for nuclear fusion

Fusion ends when hydrogen runs out, meaning that the outward pressure no longer balances the gravitational force.

28
Q

Wavelength of light is commonly stated in nanometers.

What does the prefix nano represent?

e.g. 450 nm

A

450 nm = 450 x 10-9 m

29
Q

You need to be able to make calculations involving red-shift.

How is the amount the light from a galaxy is red-shifted (change in wavelength) related to the velocity of the galaxy?

A

This equation can be rearranged to find any of the variables.

30
Q

Where are the cool and bright stars found on the HR diagram?

A

Top right

31
Q

According to the Big Bang theory, when the universe began it was…

A. small, dense and hot.

B. identical to the current universe

C. much larger and cooler than the current universe.

A

A. small, dense and hot.

32
Q

Locate the red giants and red super giants in the HR diagram below.

A

C- red super giants - brighter than….

B- red giants

33
Q

How does the time a star spends on the main sequence vary with the mass of a star?

A

The more massive a star, the shorter the time it spends on the main sequence. (they burn hotter and faster!)

34
Q

Explain how red-shift provides evidence that the universe is expanding

A
  • red-shift suggests that the galaxy is moving away from us
  • red-shift measurements indicate that distant galaxies are moving away from us in all directions
  • more distant galaxies have greater red-shifts than closer galaxies. indicating that they are moving away faster than closer galaxies
  • this indicates that they whole universe is expanding.
35
Q

Different elements (such as hydrogen) absorb different frequencies of light.

When light, formed at the centre of star, passes through an outer atmosphere of hydrogen, a pattern of dark lines is produced.

These lines are found at exactly the same position that the hydrogen absorb.

What happens to these lines if the galaxy or star producing the light are moving away from us?

A

All the lines are shifted (the same amount) towards the red end of the spectrum - they are red-shifted.

36
Q

An observer measures the frequency of a passing ambulance’s siren with an oscilloscope. After the ambulance passes the observer, a decrease in the siren’s frequency is recorded. Name the effect that causes this change in frequency and explain why it happens.

A

Name of the effect: Doppler effect

Explanation: The relative motion of the ambulance away from the observer stretches the wavelength of the sound waves, which lowers their frequency.

37
Q

Different elements (such as hydrogen) absorb different frequencies of light.

When light, formed at the centre of star, passes through an outer atmosphere of hydrogen, a pattern of dark lines is produced.

These lines are found at exactly the same position that the hydrogen absorb.

What happens to these lines if the galaxy or star producing the light are moving towards from us?

A

All the lines are shifted (the same amount) towards the blue end of the spectrum - they are blue-shifted.

38
Q

The Sun is a yellow star. What colour would a lower surface temperature star be?

A

red

39
Q

True or False

The life cycle of a star depends on its mass

A

True

Very large mass stars end their lives as a black hole,

Low mass stars end their lives as a white dwarf

40
Q

Where are the hot and bright stars found on the HR diagram?

A

Top left

41
Q

The Sun is a yellow star. What colour would a higher surface temperature star be?

A

blue

42
Q

Why is the intense energy/light from the Big Bang that we now see all around us (Cosmic Microwave Radiation) in the microwave region of the spectrum?

A

After the Big Bang the energy was released in all direction and has cooled. The expansion of the universe since then means that this energy (light) has been red-shifted so far down the red end of the spectrum that it is now in the microwave region.

43
Q

Stars initially form from a cloud of dust and gas called a….

A

nebula

44
Q

Locate the main sequence in the HR diagram below.

A

A

Stars spend most of their life time on the main sequnce.

  • bright blue stars at the top left*
  • dim red stars at the bottom right.*
45
Q

Some of out local galaxies are blue-shifted. What does this mean?

A

These local galaxies have a relative motion which is towards us

46
Q

How is an expanding balloon with galaxies drawn on it a good analogy for what is happening to our universe?

Why is it a bad analogy?

A

Good analogy-

1) As you blow up the balloon, it stretches and the galaxies move further away from each other
2) the balloon represents the universe, as time goes on, space stretches and expands, moving the galaxies away from each other

Bad analogy-

1) the balloon only stretches so far
2) there would be galaxies inside the balloon as well

47
Q

Which process releases energy in stars?

A. Combustion

B. Nuclear fission

C. Nuclear fusion

A

C. Nuclear Fusion

This occurs in the core of a star which is at more than 15 million Kelvin.