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Physics > P8 - Space > Flashcards

P8 - Space Flashcards

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1
Q

What is a main sequence star?

A

For a star to be on the main sequence it must have enough hydrogen to fuse into helium. Once the hydrogen runs out it leaves the main sequence.

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2
Q

Which last longer, stars with greater mass or lesser mass?

A

Lesser mass. Stars with greater mass have more fuel to burn, but they have higher luminosities so they run out quicker.

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3
Q

Why is a main sequence star sometimes said to pulse?

A

The energy released by fusion, produces an outwards force, causing star expansion.
However, the stars mass means that gravity acts in the opposite direction, forcing particles towards the core.

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4
Q

What does it mean when a star is said to be stable?

A

Both outward and inward forces are equal.
The star is in the main sequence phase.

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5
Q

How does a star form?

A
  1. A nebular starts to contract due to attraction between unstable particles.
  2. The clumps of matter have mass and are pulled together by gravity.
  3. Nebular collapses and forms an accretion disc, with a large gravitational pull.
  4. High pressure in the central mass, due to gravity, produces heat.
  5. The heat in the core became high enough for fusion. Forming a star.
  6. Planets began to form around the protostar, from material further out in the accretion disc.
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6
Q

What is a cloud of dust and gas called?

A

A nebular.

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7
Q

How does a nebular become a protostar?

A

Gravity pulls dust and gas together.
As the mass falls together it gets hot, hot enough for hydrogen to fuse into helium, forming a protostar.

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8
Q

What do nebulae mostly consist of?

A

Hydrogen.

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9
Q

How does the core remain hot in a protostar?

A

Nuclear fusion releases energy.

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10
Q

What is an accretion disc?

A

A rotating swirling disc, that forms from a nebular.

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11
Q

What is the gas model view of how temperature increases in the centre, during the birth of a star?

A

Gas temperature increases when it is compressed, so material at centre gets hotter and begins to glow.

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12
Q

What is the particle model view of how temperature increases at the centre of a star during it’s birth?

A

Speed of particles increase due to the gravitational force, therefore, temperature increases.

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13
Q

How does a red giant star form?

A

When all hydrogen has been used up in the fusion process, larger nuclei begin to form and star expands to form a red giant.

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14
Q

How does a white dwarf star form?

A

A small star, like the sun, may begin to contract under the pull of gravity and become a white dwarf which fades and changes colour as it cools.

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15
Q

How does a supernova form?

A

A larger star with more mass will go on making nuclear reactions, getting hotter and expanding until it explodes as a supernova.

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16
Q

What does an exploding supernova do?

A

Throws hot gas into space.

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17
Q

What does an exploded supernova leave behind?

A

A neutron star or black hole.

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18
Q

What is the life cycle for a star much bigger than the sun?

A

protostar -> main sequence star -> red super giant star -> supernova -> neutron star, or a black hole (depending on size)

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19
Q

What is the life cycle of a star the same size as the sun?

A

protostar -> main sequence star -> red giant star -> white dwarf -> black dwarf

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20
Q

Explain the first stage of the life cycle of stars.

A

Stars initially form from a cloud of dust and gas called a nebula. The force of gravity pulls the dust and gas together to form a protostar.

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21
Q

Explain the second stage of the life cycle of stars.

A

As the star gets denser, the temperature rises and more particles collide with each other. When the temperature gets high enough, hydrogen nuclei undergo nuclear fusion to form helium nuclei. This gives out huge amounts of energy, which keeps the core of the star hot. A star is born.

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22
Q

What is the life cycle of a star up to its collapse? 4 points

A
  1. gases and dust pulled together by gravity
  2. nuclear fusion begins as temperature and pressure increase
  3. when forces are balanced star is stable and remains in the phase for billions of years
  4. eventually star runs out of gas to fuse meaning it is not in equillibrium so collapses
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23
Q

What is red-shift?

A

An observed increase in the wavelength of light from distant galaxies (shifted towards red end of the spectrum).

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24
Q

What does red-shift tell us?

A

That the source of light is moving away from us.

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25
Q

What is the conclusion of red-shift?

A

That the universe is expanding.
Supports the Big Bang theory.

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26
Q

What is thought to be responsible for the accelerated expansion of the universe?

A

The existence of energy and mass that we can’t detect known as dark matter and dark energy.

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27
Q

What type of reactions take place at the start of a star’s life cycle as dust and gas is drawn together?

A

Fusion reactions.

28
Q

What factor determines the type of life cycle a star undergoes?

A

The size of the star.

29
Q

Which 2 phases do all the stars the same or greater size than the sun undergo?

A
  1. Protostar phase
  2. Main sequence phase
30
Q

What are produced during the fusion process of a star?

A

All the naturally occurring elements.

31
Q

What condition is required for fusion reactions to occur in a star?

A

Very high temperatures.

32
Q

How are elements heavier than iron produced?

A

In a supernova.

33
Q

How are elements distributed through the universe?

A

From a supernova explosion.

34
Q

What allows planets and satellites to maintain circular orbits?

A

Gravity provides the force that acts as the object’s centripetal force.
The presence of a centripetal force allows a planet to maintain it’s circular orbit.

35
Q

Why type of satellite can a planet’s moon be described as?

A

A natural satellite.

36
Q

Give 2 examples of artificial satellites.

A
  1. TV satellites.
  2. Satellites used for satellite imaging.
37
Q

Explain why for a stable orbit, the radius of the orbit must change if the speed changes.

A

At higher speeds, the object requires a greater centripetal force.
For a greater centripetal force the gravitational force must increase.
This is achieved by the radius of the force being decreased.

38
Q

What is the centripetal force?

A

Force, needed for circular motion, which acts towards the centre of the circle. It holds the planets in orbit around the sun.

39
Q

What can be said about the motion of a galaxy the further away it is?

A

The further away a galaxy is the faster it is moving.

40
Q

What does the Big Bang theory suggest?

A

That the entire universe started from a very small, hot, dense region in space.

41
Q

What did scientists observe to provide evidence that the universe is expanding at an ever faster rate?

A

Supernovae.

42
Q

Prior to observations of supernovae, what was believed about the rate of expansion of the universe and why?

A

Believed to be at an ever slower rate, because gravitational forces would slow it down.

43
Q

What is the Hertzprung - Russel diagram?

A

A scatter graph that compares the brightness of the star to the temperature.

44
Q

Why is the HR diagram useful?

A

It allows you to neatly put stars into categories - allowing you to predict the features of a newly discovered star.

45
Q

What is the trend of main sequence stars in an HR diagram?

A

As temperature increases, luminosity decreases.

46
Q

What did Isaac Newton discover that helps astronomers predict the orbits of planets?

A

Law of universal gravitation.

47
Q

What can be said about the orbital period of a planet if the radius is small?

A

Shorter orbital period.

48
Q

What are geostationary satellites?

A

They stay over the same place on Earth, they do this by orbiting the equator with a period of 24 hours.

49
Q

What height do all geostationary satellites orbit at?

A

3,600 km above surface of the Earth.

50
Q

What is blue shift?

A

The wavelength of light emitted from objects moving towards us.

51
Q

Why are different models used?

A

Different models are appropriate in different situations.

52
Q

What is a model?

A

An idea used to explain observations and data.

53
Q

Why does the gravitational force cause a planet to accelerate?

A

The gravitational force causes the planet to change direction constantly
This means the velocity is always changing.

54
Q

For a stable orbit, what happens when a planet moves closer to the sun?

A

Its orbital radius decreases, so the gravitational attraction increases.
Meaning force increases and therefore so does acceleration.
So orbital speed increases.

55
Q

What is the life cycle of a massive star after it’s collapse?

A

Increase in temp. and pressure, heavy elements can fuse.
It is too massive to be stable, so the star collapses, rebounds on its centre and produces a supernova.
Leaving a neutron star or black hole.

56
Q

What is the life cycle of a normal-sized star after it’s collapse?

A

Increase in temp. and pressure, heavy elements can fuse. (however less fusion than a massive star)
Produces a planetary nebular, lower scale supernova.
White-dwarf remains.

57
Q

Give 2 pieces of evidence for the Big Bang.

A

Red shift.
Cosmic Microwave Radiation

58
Q

What is CMR?

A

Background radiation that is present in space.

59
Q

How is CMR evidence for the Big Bang?

A

When the universe was young, it would have emitted lots of short-wave length radiation. As the universe expanded the radiation would have stretched to form microwaves.
Proving the hot young universe to have cooled and expanded since.

60
Q

Why do larger planets have rings?

A

There gravitational field is so strong it attracts debris.

61
Q

What are the smaller planets primarily made out of?

A

Rock.

62
Q

What are the larger planets primarily made out of?

A

Gas

63
Q

What was the initial model of the solar system?

A

Geocentric - earth central
Everything orbited around it in perfect circles.

64
Q

How many years after the geocentric model was the heliocentric model made?

A

600

65
Q

What is the heliocentric model?

A

Sun is centre.

66
Q

What did Galileo discover?

A

That moons orbited Jupiter, not everything orbited the Earth.

67
Q

What did Kepler discover?

A

That planets orbited in ellipses, and not circles

Physics (9 decks)

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