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Astronomy > Unit 9: The lives of stars from birth through middle ages > Flashcards

Unit 9: The lives of stars from birth through middle ages Flashcards

1
Q

What do stars condense from

A

Interstellar gas and dust

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2
Q

What is the interstellar gas composition (in mass percentage)

A

74% - hydrogen
24%- helium
others 1%

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3
Q

How many chemical elements have been discovered

A

150

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4
Q

What is the origin or the universe

A

The big bang model

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5
Q

What was the first chemical element and how was it created

A

Hydrogen

The big bang theory

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6
Q

How are first generation stars made

A

various hydrogen atoms stick together due to gravity and form first generation stars

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7
Q

Are the stars we see in the sky alive or dead

A

Most of them are dead

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8
Q

What is the death of a star

A
  • The star sheds the remaining unused hydrogen into space instead of converting it into helium
  • After shedding off the hydrogen creates clouds and they begin to condense and form the second generation star
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9
Q

Is the sun a first or second generation star

A

second generation because of its age

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10
Q

What is interstellar reddening

A
  • Blue light scatters off dust in interstellar clouds, leaving the light we see from the stars redder than it would otherwise appear.
    Due to the reflected scattered blue light we see the dust cloud blue
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11
Q

Why is the sky blue?

A

sky appears blue because the scattered hydrogen is more blue than red

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12
Q

What colour does the sun appear

A

More yellow and green than it really is

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13
Q

How do we reveal regions of new stars formation

A

Clouds of interstellar dust glow
Clouds of hydrogen = red
Clouds of oxygen and hydrogen = red middle, blue ring around it

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14
Q

What are clouds of interstellar dust?

A

regions in space where second generation stars are being formed

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15
Q

Which constellations/regions are sites of intense CO emission and what does it mean

A

Region of orion and horsehead nebulae

This indicates that stars are forming in these regions.

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16
Q

The glowing gases in emission nebulae are excited by _____ from _________?

A

Ultraviolet radiation from young massive stars

  • Excited atoms absorb UV photons and omit photons of visible light
  • New hot stars emit UV photons
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17
Q

What is the horse head nebula

A

Dark nebula
ionized hydrogen in the constellation Orion
- Hot hydrogen rich cloud glowing red
- cold dark gas and dust

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18
Q

What is necessary for star formation?

A

Jeans instability (pressure and gravity)

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19
Q

What is Jeans Instability?

A

Jeans instability causes the collapse of interstellar gas clouds
- Sufficient density of gas surrounding dark core

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20
Q

What does it mean when the dark region developed a jean instability?

A

the density increased beyond the jeans limit

- low temp

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21
Q

In jeans instability the central gases are heating as they fall into _________

A

the newly forming protostar

- kinetic energy of molecules transforms into heat

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22
Q

What happens as the mass of a protostar increases?

A

the temperature also increases (it surface gets brighter while its core heats up more and more)

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23
Q

What do low temperatures do to molecules?

A

low molecular speed

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24
Q

What is a pre-main-sequence star?

A

Once little gas is left in the centre of the dark core and its accretion stops, the object becomes a pre-main-sequence star

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25
Q

How long does it take for a protostar to grow into a pre-main-sequence star

A

10^5 years

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26
Q

What does the protostar form from?

A

interstellar gas and dust

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27
Q

What is the size of a protostar compared to the Sun

A

a protostar of 1M is about 5 times larger in diameter than sun

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28
Q

Does a pre-main-sequence star contract slowly or rapidly

A

slowly

unlike the rapid collapse of a protostar

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29
Q

At what temperature does the core of a pre-main-sequence star need to reach for hydrogen fusion to happen

A

10^7K
- the energy emission makes pressure inside the star sufficient to halt in contraction. The balance between gravity and internal pressure defines the star’s diameter

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30
Q

What does the pre-main-sequence star evolution depend on and how long does it take

A

the initial mass

  • more massive stars just skip the pre-main-sequence star stage
  • few 10s million years for a sun like star to about 10^5 years for a 5M star
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31
Q

What is different about the core of pre-main-sequence stars

A

there is no thermonuclear reactions

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32
Q

What is the lower star mass limit

A

0.08M

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33
Q

What are brown dwarfs

A

lighter bodied stars, it is impossible for fusion reactions to happen, meaning it will be a failed star

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34
Q

What is the pistol

A

the brightest know star that formed nearly 3 million years ago and originally had 100-200 M

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35
Q

What are main-sequence stars

A

stars with nuclear reactions fusing hydrogen into helium at their cores at a constant rate
(stars spend most of their life cycles on the main sequence)

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36
Q

Explain main sequence lifetimes

A

larger the Mass in M the brighter and hotter it is, though the bigger it is the less time spent on the main sequence

37
Q

What is the mass of Red Dwarfs

A

0.08M - <0.4M

38
Q

What kind of fusion happens in red dwarfs core and how long do they stay on the main sequence

A
  • hydrogen fusion

- remains on the main sequences for hundreds of billions of years, none of them have yet left the main sequence

39
Q

Do Red Dwarfs have thermonuclear reactions after the main sequence?

A

No

40
Q

What is a Red Dwarfs terminating State

A

Helium body cooling t very low rate, moving down and the the right from the main sequence

41
Q

Why are Red Dwarfs living so long?

A
  1. Low rate of thermonuclear fusion (4H - He)
  2. They are completely convective
    They have a permanent supply of fresh hydrogen to helium thermonuclear core
42
Q

What Is the mass of low mass stars

A

0.4M < 8M

43
Q

How long do low mass stars stay on the main-sequence line

A

15 billion years to 1 billion years

44
Q

Do low mass stars have thermonuclear reactions after the main sequence

A

yes
4He + 4 He + 4 He ——> 12C + Y
12C + 4He —–> 16 O + Y
in a rich helium core, hydrogen fusion in a she

45
Q

What is a red giant

A

Hydrogen fusion in a shell

in rich helium core

46
Q

What is the terminal state of low mass stars

A

white dwarf- carbon oxygen body cooling at very low rate

- white drwafs occupy the centre of the H-R diagram

47
Q

Do red giants have thermonuclear reactions

A

no
-the outer layers of the red giants are hydrogen burning shells with a helium core (in main sequence star the hydrogen burning is in the core)

48
Q

What kind of star will the sun turn into

A

white dwarf?

we have carbon oxygen core, then helium fusion shell, than hydrogen fusing shell

49
Q

What rate does the luminosity of our sun increase at

A

10% per 1 billion years

50
Q

What is the life cycle of the sun

A

(0) - Birth
(4. 5 billion years)- now
(5. 5- 8.5)- gradual warming
(10) - red giant
(11) - planetary nebula
(14) - white dwarf

51
Q

What is the low mass star final

A
  • a planetary nebula and a white dwarf in its centre
52
Q

What is the matter inside a white dwarf called

A

degenerate state

53
Q

What is the average size of a white dwarf, density, and mass

A

about the size of the earth

  • density about 10^9 kg/m3
  • mass of one teaspoon of this matter is about 5 tons
54
Q

What kinda of star is sirius

A

white dwarf
very young and bright
-brightest star

55
Q

What is a nova star

A

the result of white dwarf

- shortly after peak brightness as a magnitude (-3 star)

56
Q

What is the variation in luminosity of nova stars

A

10^6

when a nova happens, the star become so bright that it can be seen without a telescope

57
Q

What does Nova mean

A

new

58
Q

What happens during a Nova

A

Occasionally, a star in the sky suddenly become between ten thousand and a million times brighter
- A hydrogen later compresses by the white dwarf gravitational forces (about 200 thousand times the gravitational force of earths surface). This enormous compression leads to the hydrogen fusion explosion . The explosion is the nova. In some binary systems the accretion explosion processes repeat periodically.

59
Q

How frequent do Novas happen in our galaxy

A

about 20 times a year

2 or three of them been observed

60
Q

What is an accretion ring

A

the hydrogen surface layer accumulated on the white dwarf , full of hydrogen
- this forms a companion star

61
Q

What is hydrogen fusion

A

when hydrogen is converted into helium

- this is an exothermic reaction cuz the mass of hydrogen is greater than the mass of helium

62
Q

What temperature does hydrogen need to get to be turn into helium? what happens after

A

100 million degrees

  • the helium can be made which creates carbon
  • this fusion helps the star to survive after main sequence
63
Q

What is helium fusion

A

helium- carbon

64
Q

What is carbon fusion

A

carbon- neon and magnesium

65
Q

What is neon fusion and oxygen fusion

A

these reactions produce the elements of sulphur, silicon, phosphorus, up to iron

66
Q

Which form of fusion is negative

A

only iron fusion

67
Q

What are intermediate -mass stars and high mass stars

A

Mass= 8 solar masses and 25 solar masses (high)

68
Q

What is the main sequence lifetime for intermediate and high mass stars

A

less massive = 500 million years or less

massive = few millions of years

69
Q

What thermonuclear reactions happen after the main sequence of intermediate and high mass stars

A

complete set of reactions

  • form hydrogen fusion to silicon to iron
  • iron does not fuse cuz requires more energy than what is produced
70
Q

What is the terminal state of intermediate and high mass stars

A
  • supernova explosion
  • can be seen from one end of the galaxy to the other
  • the luminosity is greater than the combined luminosity of the entire galaxy for a short period of time
71
Q

What happens after supernova explosion for intermediate and high mass stars

A

intermediate- neutron star

high mass- black hole

72
Q

What leads to luminous supegiants

A

a serious of fusion reactions in high mass stars
L=10^5L
- can be as big as jupiters orbit

73
Q

What is a supernova explosion

A

the death of a supermassive star
- the very last moments of a dying massive star
roughly 3000km in size
- the iron core collapses in about 1/10th second, the temp exceeds 5 billion L and the iron is converted back into protons, neutrons and electrons

74
Q

What happens to the nuclear density during supernova explosion

A

increases by alot

75
Q

What happens to the core during supernova explosion

A

becomes one huge stuff nucleus and the collapse stops

76
Q

What stage comes after supernova explosion

A

core bounce

77
Q

What factor does luminosity increase by inn supernova explosions

A

by a factor of up to 10^8

78
Q

How much energy is emitted by a supernova

A

as much as all 200 billion stars in the milky way combined

- for a few days the supernova shines as brightly as an entire galaxy

79
Q

What is a neutron star

A
  • roughly 20 km diameter
  • small
  • 2 solar masses
  • no thermonuclear reactions
80
Q

What is escape velocity

A

one half of the speed of light

81
Q

Who discovered pulsars and what are they

A

Jocelyn Bell and her professor anthony Hewish

- intense pulsating sources of radio energy known as pulsars

82
Q

What are pulsars an example of

A

examples of neutron stars

83
Q

Are neutron stars strong

A

yes very

84
Q

What are neutron stars surrounded by

A

Regions of charged particles

- this magnetic field makes particles accelerate, they create radiation (radio waves)

85
Q

What is the Crab Nebulal

A

the crab nebula and a pulsar are remains of 1054 AD supernova

  • this is from a supernova explosion
  • can be detected by radio, visible, UV, x rays and gamma rays
86
Q

What is beamed radiation?

A

this is a path of light beam that extends from the poles of a neutron star
- this is only visible in the beam of light is directly pointed at the earth

87
Q

Are neutron stars always visible

A

no because the beam of light is usually not facing the earth

88
Q

is a white dwarf a star

A

technically no

Astronomy (10 decks)

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