P8: Astronomy Flashcards

1
Q

Draw a diagram to show the stages that stars follow in their life cycles.

A
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2
Q

How are protostars formed?

A
  • A cloud of dust and gas, a nebula, is drawn inwards under the force of its gravity.
  • It begins to rotate increasingly rapidly.
  • The centre becomes hotter.
  • A hot, dense protostar is formed.
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3
Q

How do protostars develop into main sequence stars?

A
  • Protostar’s increasing force of gravity pulls in matter.
  • As the star’s volume increases, its density does too.
  • Pressure therefore increases, causing more collisions.
  • When the temperature gets high enough, hydrogen nuclei undergo nuclear fusion to form helium nuclei.
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4
Q

What event causes protostars to become main sequence stars?

A

When nuclear fusion starts to happen.

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5
Q

Main sequence stars typically last several million years, because they are stable. How are they stable?

A

There is an equilibrium between the gravitational collapse of a star and its expansion due to the outward pressure of fusion energy.

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6
Q

What eventually causes a main sequence star to become unstable and turn into a red [super]giant?

A

The hydrogen supply dwindles to less that 50%, causing the star to swell.

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7
Q

Small main sequence stars swell into ___ ___ and larger ones turn into ___ ___.

A

1) Red giants 2) Red supergiants

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8
Q

The colour of a star indicates what?

A

Its temperature.

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9
Q

List the colours of the hottest to coolest stars.

A
  • Blue
  • White
  • Yellow
  • Orange
  • Red
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10
Q

What happens to stars in the red giant stage?

A
  • Fusion of elements beyond helium produces less energy each time.
  • Eventually, the core will not have a high enough temperature or pressure to fuse the next element.
  • The star’s outer layers drift away (to form a new nebula)
  • The core remains very hot and dense, becoming a white dwarf.
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11
Q

What happens to a white dwarf after some time?

A

Eventually, it will emit less and less energy, and cool to a brown or black dwarf.

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12
Q

What do stars do in the red supergiant stage?

A
  • They glow brightly as they fuse elements up to iron.
  • Fusion of iron doesn’t produce any energy, removing the outward pressure.
  • The core collapses; protons and electrons fuse to produce neutrons.
  • Causes a shockwave through the outer layers of the star.
  • The star explodes into a supernova, forming all elements heavier than iron and ejecting them into the universe.
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13
Q

Where do all naturally occurring elements beyond iron come from?

A

Supernovas.

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14
Q

What happens once a red supergiant has become a supernova?

A
  • The supernova ejects its outer layers of dust and gas into space
  • Leaves a very dense core - a neutron star.
  • If this star is dense enough, it becomes a black hole.
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15
Q

What is a black hole?

A

An object with such a strong gravitational field that it can even act on photons - i.e. no light can escape.

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16
Q

How many planets are in our solar system?

A

8

17
Q

What do objects have to do in order to be classed as planets?

A
  • Orbit a star
  • Clear their neighbourhoods, i.e. have gravity strong enough to pull in nearby objects.
18
Q

What is the name given to an object orbiting a star which can’t clear its neighbourhood?

A

A dwarf planet.

19
Q

What are natural satellites?

A

Moons that orbit planets.

20
Q

Give an example of an artificial satellite.

A

The ISS.

21
Q

What are asteroids?

A

Objects made of metal and rock-like material, which orbit stars in highly elliptical orbits.

22
Q

What are comets?

A

Objects made of rocky material, dust and ice which vapourise as they approach stars.

23
Q

What galaxy is our solar system part of?

A

The Milky Way.

24
Q

Planets orbit stars in ___ orbits.

A

Circular (acually elliptical - but say circular).

25
Q

If an object moves in an [almost] circular orbit, it is constantly changing ___, and therefore also ___.

A

1) Direction 2) Velocity

26
Q

If an object moves in an [almost] circular orbit, it is constantly changing direction, and therefore also velocity. For this to happen while the object is at a certain speed, it must be ___. There must therefore be a __ __ acting on it, generated by __.

A

1) Accelerating. 2) Centripetal force. 3) Gravity.

27
Q

Explain how, for circular orbits, the force of gravity leads to changing velocity, but not changing speed.

A
  • If an object moves in a circular orbit, it is constantly changing direction, and therefore also velocity.
  • For this to happen while the object is at a certain speed, it must be accelerating.
  • There must therefore be a centripetal force acting on it, generated by gravity.
  • The object keeps accelerating to what it’s orbiting, but its instantaneous velocity (at a right angle to acceleration) keeps it in its elliptical orbit.
28
Q

Why do objects in closer orbits to a star/planet need to orbit it faster?

A

The closer an object is to a star/planet, the stronger the gravitational force it experiences, the faster the object needs to travel to remain in orbit (and not crash into what it’s orbiting).

29
Q

For an object in a stable orbit, if its __ changes, the __ of its orbit must do as well.

A

1) speed 2) radius

30
Q

What evidence do we have that the universe is expanding?

A

When we record light from distant galaxies, the wavelengths are longer than previously recorded; they are shifting towards the red end of the spectrum - called red-shift. Suggests the source of the light is moving away from us -the galaxies are receding quickly, from every direction.

31
Q

What evidence do we have that the universe is expanding at an accelerating rate?

A

More distant galaxies have greater red-shift than nearer ones, so are receding faster.

32
Q

The evidence that the universe is expanding gave rise to the Big Bang theory. Describe what this suggests.

A

Initially, all matter was concentrated in an extremely small, dense and therefore hot space. This then exploded, causing space to expand (as it still is now).

33
Q

What do scientists have to do when new evidence is discovered?

A

Adapt an existing theory or make a new one to explain it.

34
Q

What is dark matter?

A

An undetectable type of matter which holds the universe together but gives off no EM radiation. It is thought to be responsible for the accelerating expansion of the universe.

35
Q

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

A

Dark matter.