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Astronomy > Midterm 2 > Flashcards

Midterm 2 Flashcards

Preparation

1
Q

How does Earth’s atmosphere affect observations?

A
  • The atmosphere transmits light at radio and optical wavelengths, but absorbs most light at other wavelengths
  • The atmosphere “blurs” our view of distant objects = decrease in angular resolution
  • Solution: Adaptive Optics
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2
Q

Adaptive optics

A

Using another star or creating an “artificial star” using a laser, to distinguish stars between one another in the sky

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3
Q

Where is the best location for a telescope?

A

On Earth:
- High sites(above the atmosphere)
- Dry(good weather)
- Dark(minimal light pollution)

In space:
- Required for most wavelengths
- High angular resolution and optical wavelength

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4
Q

What prevents Sun and other stars from collapsing under the weight of their own gravity?

A
  • Gas pressure opposes the weight of gravity
  • Equilibrium between gravity and pressure keeps the Sun from collapsing
  • Extremely high pressure in the center of the Sun results in extremely high density and temperature
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5
Q

Why does the Sun shine? How is energy produced in the Sun and other stars?

A
  • Nuclear fusion - the centre of the Sun is so hot and Dense that H can fuse into He
  • This provided the source of energy ( E = mc 2)
  • Verified by measurements of neutrinos in the Sun
  • Chemical and gravitational energy cannot explain the Sun’ luminosity = only enough for ~ 25 million years
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6
Q

How is energy transported outward from the center of the Sun?

A
  • Radiative diffusion : photons “scatter”(randomly bounce) outward through the radiation zone
  • Convection : rising hot plasma carries thermal energy through the convection zone, to the photosphere
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7
Q

What is the internal structure of the Sun?

A
  1. Core(where fusion happens)
  2. Radiation zone(where photons scatter)
  3. Convection zone(where hot gas rises and cool gas sinks)
  4. Photosphere(where light escapes and becomes visible)
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8
Q

How to measure properties of stars?

A
  • Luminosity(from flux and distance)
  • Temperature(from color and spectrum)
  • Radius(surface brightness and luminosity)
  • Mass(
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9
Q

How do star properties vary in different stars?

A
  1. Main sequence: most stars lie along the main sequence of Luminosity and Temperature. They all fuse H in their cores
    -More massive stars are more luminous, hotter and larger
  2. Red giants - low temperature, higher luminosity, larger radius
  3. White dwarfs - high temperature, lower luminosity, small radius
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10
Q

What causes the differences in stellar properties along the Main Sequence?

A
  • Mass of the star = core pressure, temperature, fusion rate(=luminosity)
  • More mass = hotter, larger, more luminous
  • More mass = shorter lifetime
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11
Q

How do properties of stars change with time?

A

Life-track of a Sun-like star:
1. Main Sequence
2. Red Giant
3. Planetary Nebula
4. White Dwarf

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12
Q

Why are Red Giants giant?

A

-Hydrogen fusion is occurring in a ‘shell’ outside of the core, producing pressure which pushes up on the material above
- Larger energy output acting on less mass = outer layer expands to a huge radius

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13
Q

What conditions are required for elements heavier than Hydrogen to fuse?

A

Higher core temperatures

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14
Q

Why can high-mass stars use more varieties of fuel throughout their life-spans, than low-mass stars?

A
  • More massive stars reach hotter core temperatures
  • They have more gravitational potential energy to convert into thermal energy
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15
Q

What is a white dwarf?

A

The “naked” core of a star after it lost most of it’s layers in the “stellar wind” during the red giant phase

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16
Q

What is a planetary nebula?

A

The outer layers of a star which have been ejected by the “stellar wind”, forming a shell of gas around the white dwarf(The surrounding gas is illuminated by the white dwarf)

17
Q

What are the life stages of a high-mass star?

A
  1. Main sequence
  2. Red giant
  3. Planetary nebula
  4. White dwarf
    +fuse heavier elements after leaving the main sequence
18
Q

How do high-mass stars die?

A
  • Iron core collapses since it cannot release any more energy from fusion
  • The core turns into a gigantic ball of neutrons
  • Leads to a core collapse SUPERNOVA
19
Q

What are the major ideas of General relativity?

A

Equivalence principle - effects of gravity = effects of acceleration
- Space + time = 4-dimensional spacetime

20
Q

What is Einstein’s view of gravity?

A
  • Gravity arises from “curvature” of spacetime
  • Mass causes spacetime to curve, curvature determines the motion of objects
  • Gravitational lensing - deflection of light when it travels near massive objects
21
Q

Gravitational lensing

A

Deflection of light when it travels near massive objects

22
Q

What is a black hole?

A

A region where spacetime curves so much that time appears to completely stop
- Nothing can escape, not even light
- Happens when large mass is packed into a small volume

23
Q

How can a White Dwarf explode?

A
  • Exceeds Chandrasekhar mass(whatever…)
  • Can happen if they gain mass from a binary companion
24
Q

What are the results of stellar evolution and how do the results depend on mass?

A
  1. Stars with mass > 8 MSun = > Burn all possible nuclear fuel => Core collapses into a NEUTRON star.
  2. Stars with mass < 8 MSun => Will not burn their fuel => Turn into a WHITE DWARF
  3. Stars with mass < 0.08 MSun => BROWN DWARFS
25
Q

What evidence do we have that neutron stars exist?

A
  • Pulsars: massive, rapidly spinning objects
  • Must be very small because of their rapid rotation
26
Q

What evidence do we have that black holes exist?

A
  • We observe massive objects orbiting in binary systems with visible stars
  • Masses are too large to be neutron stars
27
Q

What does the Milky Way look like?

A
  1. Disk - stars, gas and dust. Young stars are found in SPIRAL ARMS
  2. Bulge - spherical. Stars are located in the center
  3. Halo - surrounds the other 2, has the remaining stars
28
Q

How do stars orbit within our galaxy?

A
  1. Disk - orbit within the plane of the disk, moving in the same direction
  2. Bulge and halo - random directions
29
Q

What lies in the centre of our galaxy?

A

A large amount of invisible mass - a SUPERMASSIVE black hole

30
Q

What is the spectral sequence?

A

O - only
B - bad
A - astronomers
F - forget
G - gravity
K - kinetic energy
M - mass

L
T
Y

31
Q

Neutrinos

A

Neutrinos are produced by fusion reactions in the Sun’s core, and are observable from Earth, allowing us to “see” into the center of the Sun.

32
Q

End of life for low-mass stars

A
  1. Red Giant
  2. Stellar wind pushes masses from the outer shells into space
  3. The star can’t fuse heavier elements, because the core cools down
  4. Turns into a planetary nebula
  5. Turns into a white dwarf
  6. Cools down over time(Dark dwarf)
  7. IF mass surpasses the 1.4 because of a binary companion = explodes
  8. Thermonuclear(white dwarf) supernova
33
Q

End of life for high-mass stars

A
  1. Red Giant - fuses heavier elements
  2. Core fuses into Iron, no longer can generate energy from nuclear fusion
  3. Core collapses into a ball of neutrons = Neutron star(OR a Black Hole)
  4. Creates a core-collapse supernova

Astronomy (5 decks)

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