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AS105 > Exam 3 > Flashcards

Exam 3 Flashcards

1
Q

Is there a minimum mass to a planet? A maximum mass?

A

Both

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2
Q

What provides pressure support for the Sun?

A

Nuclear fusion

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3
Q

Patterns in the stars tell us their

A

life stage

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4
Q

The mass of a star controls its rate of

A

core nuclear fusion

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5
Q

High-mass stars

A

live fast and die young

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6
Q

What do the bright blue stars in the Pleides tell us about their age?

A

They are high mass and young

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7
Q

Supernova

A

Stars born with >10x the Sun’s mass end their lives explosively

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8
Q

What mass of host star would be most likely to have a

planet with life?

A

0.3 Msun

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9
Q

“Planetary Nebula”

A

Eventually, stars shed their outer envelopes and only core remains

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10
Q

In a few billion years, the radius of the Sun will

A

increase

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11
Q

hydrostatic equilibrium

A

outward pressure must balance inward pull of gravity

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12
Q

Pressure in Sun comes from

A

H [hydrogen] to He [helium] fusion

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13
Q

4 H atoms

A

have a little less mass than 1 He atom, and that mass difference was converted directly into energy from fusion

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14
Q

Patterns in temperature vs. luminosity (intrinsic brightness) reveal

A

the life cycles of stars, where mass is the factor controls how fast star ages

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15
Q

When low-mass stars like the Sun run out of fuel for fusion its radius eventually expands into

A

red giant

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16
Q

When it is a giant, The Sun will have a radius extending to

A

Earth’s orbit

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17
Q

Earth is likely to be engulfed by the Sun then, in about

A

5-6 billion years

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18
Q

Eventually only the core (60% of Sun’s mass) will be left:

A

white dwarf

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19
Q

White dwarf

A

has about 60% the Sun’s mass packed into a volume the size of the Earth (1 teaspoon of white dwarf weighs more than a car)

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20
Q

All stars less than 8x the Sun’s mass

A

first become red giants than end their lives as white dwarfs when they run out of core H & He

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21
Q

In a few billion years, the surface temperature of Earth will

A

increase

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22
Q

What is the remnant white dwarf mostly composed of?

A

Carbon/Oxygen

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23
Q

Massive stars have

A

massive core temperatures

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24
Q

Heavier element fusion requires

A

hotter core temperatures

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25
Q

Why do we not expect the Sun to fuse Si à Fe

(silicon to iron) in its core?

A

The Sun is not massive enough to get core

temperatures hot enough for Si fusion.

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26
Q

Each advanced fusion reaction generates

A

less energy

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27
Q

Iron fusion

A

is the end of the line for massive stars.

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28
Q

What happens when a massive star runs out of pressure support?

A

It implodes and then explodes

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29
Q

Crab Pulsar

A

is the remnant of a supernova that went off in our
galaxy in 1054 AD
- at the center: a rapidly spinning neutron star

30
Q

Pulsar

A

a rapidly spinning neutron star
- Astronomers used pulsar as clock to see wobble from planets: this is how the very first exoplanets were discovered in 1992

31
Q

What are the pulses in a pulsar?

A

the rotation of the neutron star

32
Q

It is unclear if pulsar planets are first- or second-generation.

A

(1) Are they the small cores of giant planets that survived
the supernova explosion?
(2) Were they re-generated from the leftover debris from the exploded star?

33
Q

What has happened in this history of a planet around a pulsar?

A

It’s host star exploded

34
Q

What is a black hole?

A

Something so dense that not even light can escape

- the escape velocity exceeds the speed of light

35
Q

Special Relativity

A

Time and space are not absolute:

- They are relative and depend on your perspective (and motion)

36
Q

General Relativity

A

Gravity is explained by mass bending space

  • More massive objects bend space more
  • orbits are straight-line motion curved by the shape of space
37
Q

What happens to a planet’s orbit if the star it was orbiting disappears?

A

It keeps going in a straight line.

38
Q

If a star (or any mass) passes in front of a background star,

A

it can act as a lens to the background star’s light.

39
Q

If that star has a planet,

A

it will also lens the background star!

40
Q

Microlensing occurs

A

when any mass passes in front of a background light source!

41
Q

Could we find a black hole from gravitational microlensing?

A

Yes

42
Q

What happens if a black hole passes in front of a star?

A

A blip

43
Q

Dense stars like white dwarfs can actually create

A

“self-lensing binaries” when passing in front of another star

44
Q

What is at the heart of Einstein’s theory of general relativity?

A

Mass bends space

45
Q

Are we guaranteed to see the star that causes the microlensing event?

A

No

46
Q

Can we follow up on any planets found after the microlensing event

A

No

47
Q

In 2022, what method would you expect finds

the newest exoplanets?

A

Transits

48
Q

Can hot Jupiters have formed where we find them?

A

No
- We think hot Jupiters migrated in close to their host
star by drag in the disk in which they formed.
- They formed far out and moved in over time

49
Q

What is causing the gaps in the disks

A

Mass from young planets will shape the disk – mass interacts with mass to create resonances and thus gaps!

50
Q

“Nice Model”

A

explores the evolution of orbits in our Solar System

51
Q

After the orbits of the giant planets were rearranged

A

Our solar system likely went through instability 3.9 billion years ago (Late Heavy Bombardment)

52
Q

Orbital Resonances

A

can transfer energy and can often stabilize orbits: Galilean moons of Jupiter & TRAPPIST-1’s seven-planet chain

53
Q

What has today’s lecture said about the

orbits of giant planets?

A

Planetary orbits can be influenced by gravitational interactions with other planets or the disk they form in.

54
Q

How many planets did we know about in 1785?

A

7

55
Q

Uranus

A

discovered in 1781 by William Herschel, noting a

relatively bright object wandering against background stars.

56
Q

Neptune

A

discovered with a telescope in 1846,
- predictions of the orbit of Uranus using Kepler’s
laws were starting to fail. Something yet undiscovered was perturbing the orbit of Uranus
- gravitational influence was inferred before it was
directly discovered

57
Q

“Planet Nine”

A

In 2014, astronomers Konstantin Batygin and Michael
Brown suggested a ninth planet, yet undiscovered, may
exist in our solar system:
- Trans-Neptunian Objects (friends of Pluto, but futher out) have strange orbits that are most simply explained by a new planet not yet discovered
- might have >5x Earth’s mass, 400-800 au

58
Q

How many inhabited worlds do we know of in our Solar System?

A

One

59
Q

The Fermi Paradox: “Where is everybody?”

A
  • Hundreds of billions of stars in our Galaxy, many are likely habitable
  • Why do we have no evidence of past civilizations visiting Earth?
60
Q

Avi Loeb

A

white, Harvard professor who insists aliens have visited Earth

61
Q

‘Oumuamua

A

likely the first object with interstellar origins passing through our Solar System that humans have ever identified

  • It accelerated going out of the solar system but did not outgas, so isn’t a comet
  • Avi Loeb has claimed that this could be a thin solar sail built by extraterrestrial life, though few astronomers so far agree
62
Q

How could we make contact?

A

SETI has been listening for nearly 60 years around >1000 stars

63
Q

Arecibo Message

A

We have announced our presence by sending out a radio signal towards a cluster of stars roughly 25,000 lightyears away
- series of binary 1s & 0s, an extremely dense communique to inform about our chemistry, DNA, size & shape, Solar System, etc.

64
Q

Drake Equation

A

N is the number of civilizations with which communication is possible
(Still major uncertainties in some factors, so our expectation of the number of communicative civilizations in our Galaxy is still completely unknown)

65
Q

what is the chance that a random star in our Galaxy has a civilization that can communicate?

A

If there are 200 billion stars
in our Galaxy, then 15,750/200,000,000,000 = 0.00000008: there is a roughly
0.000008% chance that a random star in our Galaxy has a civilization that can communicate

66
Q

Fp

A

fraction of stars with planets: 1
This estimate was a large legacy of the Kepler mission, which found that on average roughly every star has 1 planet orbiting with a period <300 days.

67
Q

Ne

A

Number of planets that can develop life per star with planets: 0.15
A sensible value comes from the estimate from the Kepler mission that roughly 15% of stars host a planet in the habitable zone

68
Q

Fl

A

fraction of potentially habitable planets that develop life: 0.1/10%

69
Q

Fi

A

fraction of planets that develop intelligent life: 0.01 (differs)

70
Q

Fc

A

fraction of intelligent life that can develop interstellar communication

71
Q

L

A

lifetime of a communicative civilization
(value was perceived by scientists a bit lower during the Cold War when humans were near the brink of nuclear self-annihilation)

AS105 (3 decks)

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