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Physics > 8 Stellar and evolution > Flashcards

8 Stellar and evolution Flashcards

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1
Q

What is our nearest star?

A

It is the sun.

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2
Q

How far away is the sun?

A

It is approximately 150 million kilometers from the Earth.

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3
Q

What is the surface temperature of the sun?

A

It is approximately 6000*C.

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4
Q

What is the approximate temperature of the earths core?

A

15 000 000*C.

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5
Q

What is the star in the center of our solar system?

A

The sun.

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6
Q

What is a galaxy?

A

A ​galaxy ​is a large collection of billions of stars.

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7
Q

What causes galaxies to form?

A

Attractive gravitational forces between starts cause them to group together in enormous groups called galaxies.

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8
Q

What do galaxies consist of?

A

Billions of stars.

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9
Q

What kind of galaxy is our galaxy?

A

A spiral galaxy.

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10
Q

What is a spiral galaxy?

A

A very large group of stars that forms a
spring-like winding shape

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11
Q

What is our galaxy called?

A

The milkyway.

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12
Q

What is our approximate place in the galaxy?

A

We are approximately 2/3 of the way our from the center of our galaxy along one of the warms of the spiral.

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13
Q

What can we see within our galaxy?

A

A wide variety of stars.

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14
Q

Where is our solar system found?

A

In our galaxy.

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15
Q

How can we tell that stars are not all identical?

A

Looking up into a clear night sky, especially if we use a telescope, we can see that stars are not all identical.

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16
Q

What are the observable differences that we can see in stars?

A

They have different colours, different levels of brightness and appear to be different sizes.

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17
Q

What have scientists done in terms of stars so we can identify them easier?

A

Scientists who study the stars in detail have created classes or star groups based upon these similarities and differences.

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18
Q

Why are some stars white, some red, and others yellow?

A

Surprisingly we can find the answer to this question in a traditional blacksmiths. To shape a piece of iron without it breaking the iron must be very hot. A skilled blacksmith will know when the temperature of the iron is high enough simply by taking it out of the furnace (very hot oven) and looking at its colour.If it is glowing white or bright orange it is very hot. If it is a dull red it is much cooler and not ready to be shaped.

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19
Q

How do we know if a star is very hot by looking at its colour?

A

A very hot star emits more blue in its spectrum and therefore looks blue.

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20
Q

How do we know if a star is medium temperature by looking at its colour?

A

A medium star like our Sun looks yellow.

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21
Q

How do we know if a star is cool by looking at its colour?

A

Cooler stars appear red.

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22
Q

What is a picture of a table that shows the star classification, surface temperature, and colour?

A
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23
Q

What does the brightness of a star depend on?

A
  • The distance the star is from earth.
  • The luminosity of the star - that is, how much energy is transferred from the star each second.
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24
Q

What is a diagram which represents the birth of a solar system?

A
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25
Q

Where are stars formed?

A

From large clouds of dust and gas particles.

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26
Q

What do we call these large clouds of dust and gas particles?

A

Nebulae or stellar nebulae.

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27
Q

How are stellar nebulae formed (in terms of particles)?

A

These particles are drawn together over a very long period of time by gravitational forces.

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28
Q

What conditions are the particles under?

A

The particles are pulled together so tightly that there is a very large increase in temperature and pressure.

29
Q

What is the result of this increase in temperature and pressure?

A

As a result of this nuclear fusion reactions begin.

30
Q

Which nuclei are involved in this fusion?

A

Hydrogen nuclei join together to make larger nuclei.

31
Q

What happens to the amount of energy in this fusion?

A

Huge amounts of energy is transferred thermally and by radiation (light).

32
Q

What is formed?

A

An incredibly hot ball of gas.

33
Q

What is this incredibly hot ball of gas?

A

It is a very young star.

34
Q

What happens to the appearance of a star?

A

It changes gradually with time.

35
Q

What happens when a star first forms?

A

When a star first forms, gravitational forces are pulling particles together.

35
Q

What happens with these changes?

A

These changes follow a pattern.

36
Q

What happens when nuclear reactions begin?

A

The high temperatures create forces that try to push the particles apart - that is, make the gases expand.

37
Q

What happens when these two forces become balanced?

A

When these two forces are balanced, the star is said to be in its main stable period.

38
Q

What do we call this kind of star which is in its main stable period?

A

It is referred to as a main sequence star.

39
Q

How long does this period (main sequence star) last for?

A

This period can last for many millions of years.

40
Q

What is an example of a star that is a main sequence star?

A

At the moment our sun is in this stable period.

41
Q

What happens towards the end of this stable period in terms of nuclei and fusion?

A

Towards the end of this stable period, there are less hydrogen nuclei and eventually the hydrogen fusion reactions stop.

42
Q

What happens due to the fact that the fusion reactions stop?

A

Gravitational forces are now the largest forces.

43
Q

What happens due to the fact that gravitational forces are now the largest forces?

A

They compress the star.

44
Q

What happens as the star shrinks in size?

A

As the star shrinks in size there is a large increase in temperature.

45
Q

What happens as a result of these high temperatures?

A

The temperatures are so high that fusion reactions between helium nuclei begin.

46
Q

What is released from this fusion reaction?

A

Energy.

47
Q

What does this energy do to the star?

A

The energy released by these reactions causes the star to expand to many times its original size.

48
Q

What happens to its (light) energy as the star expands?

A

As it expands it becomes a little cooler and more of its light energy is emitted in the red part of the spectrum.

49
Q

What kind of period is the star now in?

A

The star is changing into a red giant.

50
Q

When does the next period for the star start?

A

Sometime later when most of the helium nuclei have fused (joined) together, new nuclear reactions begin.

51
Q

What is different about these nuclear reactions though?

A

Now the compressive or squashing forces are larger and the star begins to get smaller or contract.

52
Q

What does this contraction cause?

A

This contraction causes an increase in temperature so the star again changes colour.

53
Q

What colour is this star now after the contraction?

A

It now emits more blue and white light.

54
Q

What is the name given to the star that emits more blue and white light?

A

A white dwarf star.

55
Q

What is special about the matter in white dwarf stars?

A

The matter from which white dwarf stars are made is millions of times more dense than any matter found on the Earth.

56
Q

What is the final period after a white dwarf star?

A

A black dwarf star.

57
Q

When does the star change from a white dwarf star to a black dwarf star?

A

Finally as a white dwarf star cools it changes into a cold black dwarf star.

58
Q

What is an image of the life cycle of stars with a mass similar to that of our sun?

A
59
Q

Can this sequence be applied to all stars?

A

No, a star that is much larger than our sun may follow a slightly different path at the end of its life.

60
Q

What is the same about the periods gone through with stars smaller and bigger than the sun?

A

After the stable period they will both expand into large red supergiants.

61
Q

What happens after this stage (in a star with a mass much greater than our sun)?

A

At the end of this period, it contracts and becomes unstable.

62
Q

What happens to this star when it is unstable?

A

It explodes throwing dust and gas into space to form a new stellar nebula.

63
Q

What is this exploding star called?

A

It is called a supernova.

64
Q

What does any remaining matter form?

A

It will form a very dense neutron star.

65
Q

What could the star (with a mass much greater than our sun) create apart from a neutron star?

A

A black hole.

66
Q

When will the star create a black hole?

A

If the neutron star has a mass that is approximately five times greater than that of our sun or more, it collapses further to become a black hole.

67
Q

What is an image that shows the final stages for our stars with masses much greater than our sun?

A

Physics (24 decks)

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