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Edexcel GCSE (9-1) Astronomy > 14 Stellar Evolution > Flashcards

14 Stellar Evolution Flashcards

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1
Q

What are Nebulae?

A

Nebulae are large interstellar clouds of dust and gas

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2
Q

What are open clusters?

A

Open clusters are a group of young stars that formed from the same giant molecular cloud. They all are roughly the same age

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3
Q

What are Globular Clusters?

A

Globular clusters a group of older stars

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4
Q

Where are open clusters found?

A

Open clusters are found on the spiral arms of the Galaxy

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5
Q

Where are globular clusters found?

A

Globular clusters are found in a ‘halo’ around the centre of the galaxy

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6
Q

What is the Messier Index?

A

The Messier Index is a catalogue of 110 astronomical objects that can be observed

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7
Q

How are all stars first originally formed?

A

All stars originate from the gravitational collapse of of a cool, dense molecular cloud of gas and dust that are found in the spiral arms of galaxies. As the cloud collapses, it becomes unstable and fragments into smaller clumps (protostars) that will form the cores of individual stars

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8
Q

What happens when a protostar collapses?

A

Gravitational potential energy is converted into kinetic energy and its temperature increases. It eventually becomes hot enough for the fusion of hydrogen into helium.

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9
Q

What is radiation pressure?

A

Radiation Pressure is the pressure that is exerted on a surface due to the exchange of momentum between an object and the electromagnetic field. The Radiation Pressure of stars is caused by the nuclear fusion of elements

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10
Q

What happens during the main sequence stage?

A

During the main sequence stage, radiation pressure and gravity balance. This stops any further gravitational collapse

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11
Q

How long is a star in the main sequence stage?

A

A star is in the main sequence stage for ~90% of its lifetime

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12
Q

What is the Chandrasekhar Limit?

A

The Chandrasekhar Limit is the maximum mass of a stable white dwarf

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13
Q

What is the accepted figure for the Chandrasekhar limit?

A

The maximum limit is a Sun with a core 1.4 times the mass of the Sun

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14
Q

How is a Red Giant formed?

A

When the generation of energy stops, the radiation pressure becomes zero and the star gravitationally collapses. This raises the temperature of the star and causes the fusion of hydrogen again but this time in a shell around the core. The helium core further contracts which increases the rate of energy generated. This makes the star expand and form a Red Giant

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15
Q

What happens if a Red Giant’s core becomes extremely hot?

A

If the core become’s hot enough, helium will fuse into carbon

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16
Q

What are Planetary Nebula?

A

A planetary nebula is a nebula that is formed by an expanding shell of gas from an ageing star

17
Q

Why does the core of a star eventually stop collapsing?

A

Electron Degeneracy Pressure

18
Q

What is Electron Degeneracy Pressure?

A

Electron Degeneracy Pressure is because the electrons cannot be squeezed together any closer and so resist any further compression

19
Q

What is formed after the Red Giant?

A

A White Dwarf

20
Q

What occurs after a White Dwarf?

A

A Black Dwarf

21
Q

Why do Black dwarfs form?

A

Black Dwarfs form after a white dwarf cools down and loses its energy

22
Q

What happens if a star has a core mass greater than the Chandrasekhar limit?

A

If a star has a core mass greater than the Chandrasekhar limit, the star will continue to collapse and will be able to fuse carbon into Neon. Fusion continues until iron is formed in the core

23
Q

What will happen if the core’s mass is greater than the Chandrasekhar limit but has a core mass less than 3x the mass of the Sun?

A

The collapse is stopped by the neutron degeneracy pressure

24
Q

What is the neutron degeneracy pressure?

A

The electrons are forced into protons to form a solid core of neutrons, and these neutrons prevent being compressed further

25
Q

What happens after the halt of collapse of a star due to the neutron degeneracy pressure?

A

The star becomes a neutron star

26
Q

What will happen if the core’s mass is greater than the Chandrasekhar limit and has a core mass greater than 3x the mass of the Sun?

A

The Star will turn into a red Supergiant after it is a main sequence. The neutron degeneracy pressure is insufficient to prevent the gravitational collapse after the supernova and the core collapses further to form a black hole

27
Q

What are Emission Nebulae?

A

An emission nebula is a cloud of ionized gas. The most common source for ionizations are high energy photons emitted from a nearby star.

28
Q

What are Reflection nebulae?

A

Reflection Nebulae are clouds of dust which are simply reflecting the light of a nearby star or stars. The nearby star or stars are not hot enough to cause ionization in the gas of the nebula like in emission nebulae but are bright enough to give sufficient scattering to make the dust visible.

29
Q

What are Absorption nebulae?

A

Absorption nebulae are nebulae that can be seen because they obscure, or absorb, the light coming from stars or bright nebulae behind them

30
Q

What is Averted vision?

A

Averted vision means looking slightly to the side of a faint, extended object so that light falls onto the rods (not the cones) of the eye’s retina
In dark conditions, the cones (which lie where the optical axis joins the retina) are not sensitised, but the rods (which lie adjacent to the optical axis) are.

31
Q

Which British astronomer published the Caldwell Catalogue?

A

Sir Patrick Moore

32
Q

What are diffraction spikes?

A

Diffraction spikes are when some stars appear to have crosses through them

33
Q

Which might initiate the collapse of a giant gas cloud that may eventually form stars?

A

Gravitational Waves and Supernovae

34
Q

What prevents the gravitational collapse of a white dwarf star?

A

Electron degeneracy Pressure

35
Q

How would you describe the main sequence stars that are at the bottom right on the H-R diagram as?

A

Old and Dim

36
Q

How would you describe the main sequence stars that are at the top left on the H-R diagram as?

A

Young and bright

37
Q

Why are neutron stars and black holes not found on the H-R diagram?

A

Neither emits enough radiation to be ‘bright’ enough to register on the luminosity/absolute magnitude/vertical axis

Edexcel GCSE (9-1) Astronomy (20 decks)

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