Midterm 3 Flashcards
(174 cards)
1
Q
What is in our solar system?
A
Early astronomers knew Moon, stars, Mercury, Venus, Mars, Jupiter, Saturn, comets, and meteors. Now: ● 1 star ● 8 planets (add Uranus & Neptune) ● 166 moons ● >660,000 asteroids ● comets, meteoroids ● ~50 dwarf planets, ● Kuiper Belt objects
2
Q
What are terrestrial planets?
A
Close to the Sun. Made of rocks (silicon) and iron.
High density
Small (10000 km in diameter)
3
Q
What are Jovian Planets?
A
Farther from the Sun. Made of gases (H, He, methane, water, ammonia), lower density, large
4
Q
How do the planets orbit the Sun?
A
The planets orbit the sun from W to E along the plane of the ecliptic – looking down from the Earth’s North pole, planets orbit counterclockwise
5
Q
Can we develop a model for the formation of the solar system that explains these properties?
A
The nebular hypothesis suggests that the planets formed from a gas cloud which collapsed into a disk.
This gas cloud has roughly the same composition as the Sun (mostly hydrogen, helium, + a trace of carbon, oxygen, nitrogen, iron etc)
6
Q
The idea that the planets form from a disk is called
A
The nebular hypothesis.
This idea was proposed by
many people, one of which
was Pierre Simon Laplace, a mathematician in 18th century France
However, this was not the only idea
7
Q
Alternatives to the nebular hypotheses
A
Tidal model: a passing star ripped material from the Sun and that material collapsed to form the planets
Capture model: The sun and planets formed separately, but the planets were captured later by the Sun
Accretion model: The sun moved through a gas cloud, got some gas and that gas formed the planets
8
Q
What should we remember about the mass of our solar system?
A
Remember that most of the mass of the solar system is in the Sun. So the formation of the solar system is a footnote to the formation of the Sun.
Recall that stars form from molecular clouds.
9
Q
What is a protostar
A
The collapse of a molecular cloud from a star forms a protostar and the disk of gas that surrounds it
10
Q
What is Disk Formation
A
As the cloud collapses, the angular momentum in the gas makes it spin faster and faster until the the gas moves fast enough to orbit the protostar.
This is a general principle in astronomy. Collapse of stuff leads to the formation of a disk due to angular momentum
11
Q
What is the concept of angular Momentum?
Hint: think of an ice skater
A
Angular momentum: spinning things keep spinning, and in the same direction Conservation of angular momentum says that product of radius and rotation rate must be constant.
→ Therefore, as a dust cloud collapses, its rate of
rotation will increase.
12
Q
What is the condensation of the planets?
A
● Gas does not condense (because it remains gas), but dust can gather – tiny chunks of rocky and icy matter, with sizes of about 10-5 m
● Dust grains form in cool atmospheres of old stars, are ejected, grow by accumulating molecules from interstellar gas
● Dust collects into larger bodies: dust bunnies!
13
Q
What is the process of clumps of dust growing larger?
A
accretion
14
Q
What is happens when objects get large enough to create gravity strong enough to affect their neighbors?
A
Planetesimals
15
Q
Eventually nearly all material is wept up into ________?
A
Protoplanets
16
Q
What happens to the stuff that escapes capture and is left over?
A
Asteroids and Comets
17
Q
How did the Moon form
A
During the formation of the Earth, the young Earth suffered a collision with a Mars-sized body that threw up material into orbit that condensed to form the Moon.
This is a rare event, and Earth is the only terrestrial planet with a large moon
18
Q
How are Jovians formed?
A
To form the Jovian planets, we need one more stage of planet formation in which the gas accretes onto these rocky cores
However, to accrete gas we need a big core!
Bigger cores are possible if you can gather more material. In regions where the gas is so cold that ices form – beyond the snow line or frost line – we have the extra stuff to make this possible.
19
Q
What is Scattering and Ejection
A
The larger pieces of this debris in the early solar system are called planetesimals. The ejection and scattering of planetesimals allowed the planets to change their orbits.
Generally Neptune, Uranus and Saturn move outward at the expense of Jupiter, which moves inward.
Jupiter being the biggest planet tends to fling stuff out of the solar system, causing it to move inward, while the other three planets tend to move planetesimals inward – so they move outward.
20
Q
The Nebular Hypothesis and the Solar System
A
● Planets form in a rotating disk
○ Planets are all (nearly) in a plane to about 1%
○ All orbit in a counterclockwise direction and nearly all
rotate in the same direction as well.
○ Orbits are nearly circular
● Planets are relatively isolated – far away from their neighbors
○ Planets accrete all the material in their neighboring orbits
21
Q
What are good indicators of the past composition?
A
The small bodies that have the best clues are asteroids, comets, meteoroids (coming from asteroids and comets) and plutoids.
The age and chemical composition of these things can tell us about the early solar system
22
Q
What are Asteroids?
A
● Rocky bodies that are held together by gravity and internal forces
● Most live in a belt between Mars and Jupiter at 2.8 A.U. called the asteroid belt
● about 100,000 rocky objects bigger than 1 km exist
● Ceres is the largest asteroid with a diameter of ~1000 km
● A few thousand have orbits that cross Earth’s orbit –
called near-Earth asteroids (NEAs)
● Some are near Jupiter (60 degrees ahead and behind)
and are called Trojans
23
Q
Why do we care about Asteroids?
A
● Asteroids are left-over material from formation of the solar system
→ ideal laboratory to study formation of earth and other planets
● Potential source of water on earth
24
Q
What are Meteors, Meteorids, and Meteorites
A
Although these terms sounds very similar, they describe different phenomena that can be arranged by time:
A meteoroid is a piece of interplanetary matter that is smaller than a kilometer and frequently only millimeters in size.
Most meteoroids that enter the Earth’s atmosphere are so small that they vaporize completely and never reach the planet’s surface.
The flash of light we see while they burn up in the atmosphere is what we call a meteor (or fireball, for the brightest ones)
Whatever is left once it hits the ground (anywhere between the size of a sand grain to a giant boulder) is a meteorite.
25
What is a widely accepted hypothesis about the dinosaurs?
A widely accepted hypothesis is that an impact of a 10 km asteroid hit the Earth 65 million years ago and killed off the dinosaurs.
26
What are Comets?
● Icy bodies – called “dirty snowballs” – made of rocks, water ice, frozen methane, frozen ammonia, and frozen carbon dioxide
● ~1 – 10 km in size.
● When they pass close to the sun, the ices sublimate: solid
→ gas. Blows out a halo of gas and rocks (pebbles),
which is called a coma
● Sunlight and the solar wind push on the gas and dust
blowing the tail away from the sun
● Comet tails point away from the sun, NOT opposite of
direction of motion
27
What is the diffuse halo of gas and dust around the nucleus of the comet
coma
28
How do comet's tail point?
Comet tails point away from the sun due to the solar wind and the light from the Sun.
29
What are meteor showers
Meteor showers are associated with comets – they are the debris left over when a comet breaks up.
30
What are defining factors of EARTH?
Radius is 6400 km
Density ~ 5000 kg/m3 – five times density of water
● Has a thick atmosphere of mostly nitrogen and oxygen
● Has active volcanoes
● Has a magnetic field
● Has known life
31
What are defining factors of MERCURY?
Radius ~ 2400 km
mass ~ 5% of Earth Density 5400 kg/m3 – about the same as Earth No atmosphere
No volcanoes
Has a magnetic field Covered in craters similar to Earth's moon
32
What is the temperature on Mercury?
Temperature on Mercury varies drastically! On the day side it is hot, 700K, but on the night side it is cold, 100 K (-200 F)
● Wide variation in temperature because there is no atmosphere to trap heat and moderate temperatures
● Because Mercury has no atmosphere and no water, there is no erosion, so the surface is heavily cratered like the Moon
33
What does Mercury have that the Moon doesn't?
Mercury has one feature unique to it and not found on the Moon. It has scarps or cliffs.
These scarps result from the cooling (and shrinking) of Mercury, which resulted in compression and cracking of the surface.
34
What are the defining factors of Venus?
● Radius ~ 6100 km
● Mass ~ 82% of Earth
Density ~ 5300 kg/m3 – about the same as Earth
● Very thick atmosphere
● Many volcanic features, indirect evidence of current volcanic activity
● No magnetic field
35
What type of atmosphere does Venus have?
Venus has a large, thick atmosphere which covers the entire surface with clouds of sulfuric acid.
Its atmosphere is 90x thicker than the Earth’s: pressure on the surface is 90 times higher than on Earth
36
What is the temperature on Venus?
Venus is HOT! Its average temperature is 730 K – hotter than Mercury and hot enough to melt lead.
● This is because the atmosphere traps heat via the greenhouse effect
● Sunlight strikes surface and is converted to heat, which is absorbed and re-radiated by carbon dioxide in the atmosphere instead of radiating out into space
37
What is the greenhouse effect on Earth?
```
Greenhouses gases (carbon dioxide, water vapor, methane) in the atmosphere trap heat Sunlight strikes surface and is converted to heat, which is absorbed and re-radiated in the atmosphere instead of radiating out into space
An increase in the amount of greenhouse gases in the atmosphere increases the heat trapped
```
38
Why is Mars red?
Called the red planet because of its red color – due to rust, iron oxide
● Has nearly a 24 hour day – very similar to earth
● Atmosphere is made mainly of carbon dioxide, but it is very thin – 1/150 that of earth. Remember Venus is 90x that of earth
39
Does Mars have seasons?
Mars has seasons – the tilt of Mars is close to that of earth.
40
What is the Atmosphere of Mars?
Atmosphere is mainly CO2 (carbon dioxide) with some nitrogen and argon.
It is so cold that the atmosphere freezes onto the poles as frozen CO2 depending on the season
41
What are the bands and what is the that prominent feature on Jupiter?
Multicolored bands in atmosphere
● Bands are caused by convective cells that are stretched by rotation
● Most prominent feature is the Great Red Spot – a hurricane that has persisted for at least 300 years
42
Why do Jupiters belts stretch around Jupiter?
These belts are high and low pressure regions, as we also have on Earth
However, because of the Jupiter’s rapid rotation and thick atmosphere, these belts stretch around the planet rather than being localized
43
What is the structure of Jupiter?
Inner core rocky, like Earth Mantle is liquid metallic hydrogen: under very high pressures, hydrogen becomes liquid and acts like a metal – able to conduct electricity
Outer mantle is molecular hydrogen
Atmosphere very convective with large, persistent weather features
44
What is Europa?
It is the smallest of the four Galilean moons orbiting Jupiter, and the sixth-closest to the planet of all the 79 known moons of Jupiter. It is also the sixth-largest moon in the Solar System. Europa was discovered in 1610 by Galileo Galilei[1] and was named after Europa, the Phoenician mother of King Minos of Crete and lover of Zeus (the Greek equivalent of the Roman god Jupiter).
45
What are defining factors of SATURN?
Radius ~ 10 times Earth, mass ~ 100 times Earth
Density ~ 700 kg/m3 – less than water, Saturn would float!
● Composed of mainly hydrogen and helium
● No surface - Strong magnetic field
46
What are Saturns Rings made of?
Made of icy particles from 1 cm to a few meters in size
The many divisions in the rings are due to tiny moons between the divisions known as shepherd moons
47
What is Titan?
Saturn’s largest moon – 2nd largest in solar system (Jupiter’s Ganymede is largest)
● Only other body in solar system with stable surface liquid: seas and lakes of methane
● Nitrogen-rich (98%) atmosphere, thicker and denser than Earth’s
Evidence for methane rain
48
What are the defining factors of URANUS?
Radius
~ 4 times Earth Mass
~ 15 times Earth Nearly featureless
Rotation axis is tilted 98 degrees!
The tilt may be result of a giant impact (?)
49
What are the defining factors of NEPTUNE?
Radius ~ 4x bigger than Earth.
Mass ~ 17x Earth Has bands of clouds unlike Uranus
Has a large storm on it called the Great Dark Spot.
50
What can fit inbetween our Earth and Moon?
The distance between earth and moon is large enough to fit all planets in the solar system between them.
51
What is NOT a characteristic of the early solar system, based on current observations?
The initial composition of the solar nebula varied between its inner and outer regions
52
What is a planetesimal
Bodies of ice and rock 100 meters or more in diameter
53
Whether or not a planet is composed mostly of rock or gas is set by
its mass
its temperature
its distance from the star when it formed
random chance
a combination of A, B, and C
a combination of A, B, and C
54
What is the best description of a moon
Any natural satellite of a planet or asteroid
55
Why do the outer giant planets have massive gaseous atmospheres of hydrogen and helium whereas the inner planets do not?
The outer planets grew massive quickly enough to gravitationally hold on to these gases before the solar wind dispersed the accretion disk
56
What are Asteroids and comets?
material left over from the formation of the planets
57
The moon probably formed
out of the collision between Earth and a Mars-sized object
58
Which of the following is NOT considered evidence of cataclysmic impacts in the history of our Solar System?
Uranus is "tipped over" so that it rotates on its side
Correct!
Valles Marineris on Mars is a huge scar, many times deeper than the Grand Canyon, which spans one-fourth the circumference of the planet
Mercury has a crust that has buckled on the opposite side of an impact crater
Mimas has a crated whose diameter is roughly one-third size on the Moon's size
Mercury, Earth's Moon, and many other small bodies are covered with many impact craters
Valles Marineris on Mars is a huge scar, many times deeper than the Grand Canyon, which spans one-fourth the circumference of the planet
59
Was it ever possible (or is it currently possible) for Jupiter to become a star?
No, it would have to be at least 13 times more massive
60
Why do the terrestrial planets have a much higher fraction of their mass in heavy chemical elements (as opposed to lighter chemical elements) than the giant planets?
Terrestrial planets are low in mass and high in temperature, thus their lighter chemical elements eventually escaped to the outer reaches of the Solar System
61
Because of the greenhouse effect, this planet has the hottest surface temperature in the Solar System
Venus
62
What are pulsar planets?
The first planets that were found using pulsar PSR
They found 3 planets from looking at the timeing irregularities of the pulsar.
As planets orbit the pulsar, they exert tiny tugs on the pulsar which move it slightly out of place.
63
What is the first technique for finding planets?
Technique 1: Radial Velocity
So as you look at a star which has an orbiting planet, the light of the star is redshifted as it moves away from you and blue-shifted as it moves toward you
This reveals the presence of a hidden body that pulls on the star, i.e., the planet
Instead of looking for the planet directly, we look for the wobble it causes in the star
64
What is technique 2 - transits
Watching for eclipses, when planets pass in front of their parent star.
Look for a very small drop in the amount of light received.
This can tell us the radius of the planet, since we know how uch of the light of the star is blocked.
65
Technique 3 is direct imaging
This is done by blocking out the light of a star using a coronagraph
This has been done for the Sun for years in order to study the corona – hence the name coronagraph
But stars are so small
that it is very hard to block out their light
66
Technique 4: Microlensing
The curvature of space-time bends both matter and light
So light will bend as it moves around a massive ody like a star or galaxy.
67
What are the four ways of finding planets
●Radial velocity – gives mass
● Transits – gives size
● Direct imaging – it might give size, but it’s always good to actually see the planet
● Microlensing – gives mass, and for a long time was the only way to detect Earth-mass planets
68
What is the most powerful technique?
The combination of radial velocity and transits is the most powerful technique now
69
What are 3-day orbits and what size are the planets in 3 day orbits?
When astronomers began look for extrasolar planets, they found many planets with about 3-day orbits. This is called the 3-day pileup.
For the most part, these planets are all Jupiter-mass or bigger.
So these are known as the hot Jupiters
70
What do you need to form Jupiter size planets?
Recall that you need big cores to form Jupiter. Bigger cores are possible if you can gather more material. In regions where the gas is so cold that ices form – the snow line or frost line – you have the extra stuff.
71
What is planetary migration?
Planetary Migration
If a giant planet forms while the gas disk is still around, the planet may sink inward toward the star.
This is called
planetary migration and might explain the hot Jupiters.
72
Is our solar system special?
Most planets that are found are really close to their star – totally unlike our solar system
This is because they are much easier to find in radial velocity and transit surveys
This is called a selection effect. Accounting for this to figure out the real distribution is HARD But this is now changing with the Kepler satellite
73
How would we find Earth type planets
One of the main goals of planet searchers is to find a planet about the size of Earth in a region around a star where it is not too hot nor too cold
This is called the habitable zone, and it’s defined as the range of distances from the star at which the temperature is right for liquid water to exist on the surface of a planet
This will depend on the temperature of the star, and the temperature of a planet will also depend on its atmosphere Planets in the habitable zone are sometimes known as “Goldilocks planets”
74
What is the Kepler satellite?
Space observatory, launched 2009, mission extended to 2016 but recently modified due to failure of reaction wheels on spacecraft
● Continuously monitors brightness of 150,000 stars in a fixed field of view, looking for planetary transits
● Earth-like transit produces a brightness change of 84 parts per million and lasts for 13 hours
75
What is the TESS satielite?
● Follow-up mission to Kepler
● Similar science goals and strategy as Kepler
● Wider instantaneous field of view
⇒ Cover more sky area
● (Almost) full sky coverage
● Limited to relatively bright stars
⇒ better chance to find host stars that are nearby
76
What is planetary migration?
If a giant planet forms while the gas disk is still around, the planet may sink inward toward the star.
This is called
planetary migration and might explain the hot Jupiters.
77
The transit method of detecting exoplanets involves
| Correct!
looking for a variation in a star's radial velocity caused by its motion around the center of mass of the planetary system
78
When an exoplanet is detected by the Doppler or radial velocity method, what is measured is the
shift in position on the sky of the star it is orbiting around (astrometry)
79
The term "hot jupiters" refers to
jovian-type exoplanets orbiting extremely close to their respective stars
80
One of the surprising results that has already come out of the discoveries of exoplanets is the large number of exoplanets like Jupiter but bigger that are quite close to their respective stars. The idea put forward to explain this difference from the Solar System is
planetary migration -- interaction between the nebula (planetary disk) and the planet shifting the planet inward or outward
81
The Milky Way appears as ____________ in the night sky because _____________.
a faint band of light sprinkled with dark clouds; the Sun lies in the disk
82
Globular clusters are found in which part of the Galaxy?
both the halo and the disk
83
Studying standard candles in globular clusters offered the first conclusive proof that our galaxy was much _______ than originally believed.
larger
84
The Sun is located approximately
halfway out in the disk
85
Why is 21-cm radiation one of the best ways to map the spiral arms of the Milky Way?
These photons, which are produced by atomic hydrogen, are not blocked by the dense clouds of gas and dust in the disk
86
Which of the following statements about the formation of spiral structure in dis galaxies is NOT true?
Spiral arms can be produced by the gravitational interaction with other galaxies
Spiral structure can be triggered by bursts of star formation
Bars can disturb the disk and initiate the formation of spiral arms
A single disturbance in the disk would suffice in forming and maintaining stable, long-lived spiral arms
Elongated bulges can contribute to the formation
A single disturbance in the disk would suffice in forming and maintaining stable, long-lived spiral arms
87
Halo stars near the Sun are distinguished from disk stars by what characteristic?
low heavy element abundances and high relative velocities
88
A spiral galaxy contains
upper and lower main sequence stars
89
Hubbles constant, Ho represents?
The rate of expansion of the universe
90
a spiral structure can be triggered in a disk galaxy by
any disturbance to the disk
91
the hubble classification scheme for galaxies sorts them by?
their visual appearance
92
What did Edwin Hubble study in the andromeda galaxy that proved it was an individual galaxy and not part of our own milky way?
cepheid stars
93
The oldest stars in the galaxy are usually _____ in heavy elements because ________
low, they were formed before much chemical enrichment had taken place
94
How many years does it take the sun to complete an orbit around the milky way?
230 million years
95
Galaxies move away from us in all directions because
space is expanding
96
Astronomers use galactic redshift as a measure of
distance
97
What type of standard candle is used to determine distances to globular clusters?
RR lyrae stars
98
Why do rotation curves of galaxies imply that dark matter exists?
The velocity of stars stays approx constant at distances well beyond the visible edges of galaxies, implying that galaxies contain much more matter than what we observe in stars and gas.
99
Active star formation does not occur in elliptical galaxies because they
contain little molecular hydrogen.
100
What makes up the majority of the mass of an individual spiral galaxy?
dark matter
101
In spiral galaxies, the size of the central bulge is correlated with the
tightness of the spiral arms
102
Why do we know that at least one generation of stars formed and died before the milky ways globular clusters formed
All globular cluster stars have some amount of heavy elements.
103
What is the galactic bulge?
The Galactic Bulge contains a mix of old and young stars
more old stars at greater distances form the center
contains gas and dust, especially in inner regions
yellow-white
104
What is the galactic disk?
The Galactic Disk is home to most of the young stars in the Galaxy and has old stars as well,
and contains most of the dust and gas in the Galaxy
highly flattened
white coloration with blue spiral arms
105
What is the galactic halo?
The Galactic Halo has mainly old stars and is home to many globular clusters
contains no gas and dust
roughly spherical-mildly flattened
no star formation
reddish in color
106
What is the galactic center?
the Galactic Center contains a supermassive black hole
The orbital speed of an object depends only on the amount of mass between it and the galactic center.
107
What is a planetesimal?
bodies of ice and rock 100 meters or more in diameter
108
Whether or not a planet is composed mostly of rock or gas is set by
its mass, temperature, and distance from the star when it formed
109
Which is the best description of a moon?
any small icy body in the solar system
any small rocky body in the
solar system
any natural satellite of a planet or asteroid
a captured asteroid
a captured comet
any natural satellite of a planet or asteroid
110
Why do the outer giant planets have massive gaseous atmospheres of hydrogen and helium whereas the inner planets do not?
The outer planets grew massive quickly enough to gravitationally hold on to these gases before the solar wind dispersed the accretion disk
111
Which of the following is NOT considered evidence of cataclysmic impacts in the history of our Solar System?
Uranus is "tipped over" so that it rotates on its side
Valles Marineris on Mars is a huge scar, many times deeper than the Grand Canyon, which spans one-fourth the circumference of the planet
Mercury has a crust that has buckled on the opposite side of an impact crater
Mimas has a crated whose diameter is roughly one-third size on the Moon's size
Mercury, Earth's Moon, and many other small bodies are covered with many impact craters
Valles Marineris on Mars is a huge scar, many times deeper than the Grand Canyon, which spans one-fourth the
112
Why do the terrestrial planets have a much higher fraction of their mass in heavy chemical elements (as opposed to lighter chemical elements) than the giant planets?
Terrestrial planets are low in mass and high in temperature, thus their lighter chemical elements eventually escaped to the outer reaches of the Solar System
113
What is a galaxy?
A galaxy is a huge collection of stars that is isolated in space and held together by gravity.
We happen to live in one called the Milky Way Galaxy or just the Galaxy (with a capital “G”)
114
How do we know what the galaxy looks like?
Recall that the distance ladder is our collection of methods for measuring distances to astronomical objects: ladder because each step builds on the one before
115
Do stars oscillate?
All stars oscillate. Oscillations are long sound waves, and the oscillation time is the time it takes sound to cross the star.
Large stars, like large bells, oscillate more slowly than small stars. Late in their evolution, bright stars have, for a short time, unusually large oscillations.
116
What stars take between 1-100 days to pulsate?
Cepheids
117
What stars take less than 1 day?
RR Lyrae stars
118
What stars take longer than 100 days?
Mira variables
119
What are Miras?
Variable Stars: Miras
Late in a star’s evolution, its oscillations can become unstable, growing enormously, and greatly changing the brightness of the star each oscillation
The larger a star is, the longer its period of oscillation
Shown on the right is a Mira variable star at its faintest and at its brightest.
120
With variable stars as _________, the size of the milky way can be found
the standard candle
121
What does the milky way galaxy consists of?
● The Galactic disk
● The Galactic bulge
● The Galactic halo
● The Galactic Center
Each of these parts differs greatly in terms of stellar populations, chemical abundances, kinematics (motion) of stars
122
What is Hydrogen 21cm emission?
The electron and proton in an atom of neutral hydrogen have spin. Their spins can be aligned, or they can point in opposite directions. Sometimes the spin of the electron flips, and when this happens a photon is emitted with wavelength 21 cm. This can be observed in the radio, and is used to map neutral hydrogen gas.
123
What is the winding problem
Spiral arms are not material formed into a spiral by the rotation of the galaxy –if this were the case, the arms would wind up until they disappeared
124
What are the three spiral structures?
```
Spiral Structure
The Spiral structure can vary from galaxy to galaxy:
● Sa – weak spiral (but prominent bulge)
● Sb – visible spiral
● Sc – prominent spiral (with just a small bulge)
Sa
Sb
Sc
```
125
What are elliptical galaxies?
The other major type of galaxy is elliptical
● These are spherical(ish) distributions of old stars
● Smooth – no distinct features and no disk
● Have older stars and little to no current star formation
● Similar to bulges of spiral galaxies, but larger
126
What are the largest most massive gallaxies?
Elliptical
127
Hubbles classification scheme
Classification is based on a galaxy’s appearance Three main categories:
● Ellipticals
● Spirals: normal (S)
and barred (Sb)
● Irregular (there’s a whole complicated
zoo of irregulars alone)
A galaxy’s classification is called its Hubble type
Hubbles "tuning fork diagram"
128
Classification of spiral galaxies?
● Bulge-to-disk ratio (B/D) - What fraction of light from each component
● Smoothness of stellar distribution
● Tightness of winding of spiral arms
129
What are dwarf ellipticals
Dwarf ellipticals and Dwarf Spheroidals
Dwarf ellipticals are the most common type of galaxies in galaxy clusters. Dwarf Spheroidals are even lower mass, more spread out and thus harder to find. They dominate the Local Group by number, but are virtually negligible in terms of stellar mass.
130
What are the colors of spirals and ellipticals?
Spirals blue ⇔ ellipticals red
Spirals have more gas and dust than ellipticals
These are related!
131
Three types of nearby galaxies?
Ellipticals -- No new stars
Wide range of sizes, little gas or dust.
Spirals -- gas or dust in disk,
New stars in spiral arms,
some in nucleus, Medium size
Irregulars -- Usually small sizes
new stars throughout gas and dust throughout
132
Difference between groups and clusters
Galaxies are not distributed randomly throughout the universe – they are usually found in associations of galaxies called groups and clusters
● Groups are smaller associations, with usually less than 50 galaxies
● Clusters are larger and can contain thousands of galaxies – galaxy clusters are the most massive gravitationally bound objects in the universe
133
What is the Local group, virgo cluster and the local supercluster
● The Milky Way, Andromeda, and several other smaller galaxies form the Local Group
● The nearest large galaxy cluster to the Local Group is the
Virgo Cluster
● Galaxy clusters themselves tend to clump together into superclusters. The Virgo Cluster, the Local Group, and several other nearby clusters form the Local Supercluster
134
What is Hubbles law
v = H × d is called the Hubble Law and H is the Hubble constant.
To determine it, we need to measure the velocity of many many galaxies, and their distances
135
What does hubbles constant rely on?
The value of Hubble’s constant relies on using Cepheids to obtain the distance to the Virgo Cluster (50 Mly or 18 Mpc) and to other galaxies within 100 Mly
136
Why is hubbles law so important?
In addition to converting redshifts into distances, the Hubble constant also gives an estimate for the age of the universe.
Assuming all galaxies originate in a single point (the Big Bang, more later), faster galaxies are now located at larger distances. We can use this to calculate the time since they started expanding:
Time = distance / velocity = (velocity / H) / velocity = 1 / H
Using H = 72 km/s/Mpc (make sure to convert units first!)
⇒ age of universe = 13.6 billion years
137
What is most of the galaxys mass?
Most of the Galaxy's mass is dark matter, matter too dim to see at any wavelength, that lies in the halo. We do not yet know what it is.
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What to remember about the Milky Way?
● A galaxy is stellar and interstellar matter bound by its own gravity
● Our Galaxy is a spiral galaxy
● Variable stars (Cepheids, RR-Lyrae) can be
used for distance measurement, through the
period–luminosity relationship
● True extent of a galaxy can be mapped out
using globular clusters
● Star formation occurs primarily in the disk, but
not in halo or bulge
The Milky Way: Summary
● Spiral arms may be density waves.
● Galactic rotation curve shows large amounts
of undetectable mass at large radii
● This is called dark matter and makes up most
of the mass of the Galaxy
● Activity near galactic center suggests
presence of a 3.7-million-solar-mass black
hole
● Mass is measured from the orbits of stars near
the center
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What is a barred spiral galaxy
Barred Spiral Galaxies
More than half of all spiral galaxies also have a central bar in the bulge. The Milky Way is believed to have a bar.
These bars can connect to the spiral arms, but do not always
140
What are spiral arms?
Leading theory is that they are density waves – regions of higher density that stars and gas move through
141
A pulsar is a
a) oscillating white dwarf
b) oscillating neutron star
c) rotating white dwarf
d) rotating neutron star
e) none of the above
rotating neutron star
142
A black hole is likely to be the end of stellar evolution for what type of main sequence star?
a) O
b) M
c) G
d) A
a) O
143
What can escape from within a black hole?
a) Neither light nor matter
b) Light only
c) Both light and matter
d) Matter only
a) Neither light nor matter
144
The mass of a black hole candidate can befound by
a) measuring its luminosity and distance
b) measuring the speed of an orbiting companion and the radius of its orbit
c) measuring the radius of its event horizononly
d) measuring its luminosity and the radius or its event horizon
b) measuring the speed of an orbiting companion and the radius of its orbit
145
Which of the following is not a terrestrial planet?
a) Mars
b) Earth
c) Neptune
d) Mercury
e) Venus
c) Neptune
146
Which of the following is not a Jovian planet?
a) Venus
b) Jupiter
c) Neptune
d) Saturn
e) Uranus
a) Venus
147
Compared to terrestrial planets, Jovian planets are
a) larger and denser
b) smaller and denser
c) larger and less dense
d) smaller and less dense
C) larger and less dense
148
Most of the solar system’s mass is in
a) the Sun
b) comets
c) asteroids
d) meteoroids
e) planets
The Sun
149
When a rotating cloud contracts, it
a) spins slower and flattens
b) spins faster and flattens
c) spins slower and heats up
d) spins faster and heats up
b) spins faster and flattens
150
Why do all of the planets have orbits that lie in nearly the same plane and that are in the same direction – counterclockwise looking down on the solar system from far above the Earth’sNorth Pole?
a) When they were captured by the Sun, theSun was moving past a cluster of planets, and all of those planets were on one side of its path.
b) Shortly after they formed, the planets were moving in random directions. In the4 1/2 billion years since then, the Sun’s gravity has pulled them into the same plane.
c) The planets and Sun all formed from a cloud of gas and dust that contracted as it cooled. As the cloud contracted, its spin increased and it flattened. By the time the planets formed, the cloud was a flat spinning disk.
c)The planets and Sun all formed from a cloud of gas and dust that contracted as it cooled. As the cloud contracted, its spin increased and it flattened. By the time the planets formed, the cloud was a flat spinning disk.
151
They often pass the Sun once and then leave the solar system.
a) comets
b) meteoroids
c) asteroids
a)comets
152
What is the reason for the difference between typical meteors and typical meteorites?
a) The only meteors that do not burn up in the atmosphere are the large ones. These are all asteroid fragments.
b) The only meteors that do not burn up in the atmosphere are the rocky ones.These all come from comets.
c) Meteorites are the meteors that burn up in the atmosphere.
d) Meteors are ice balls, while meteorites are great balls of fire.
a)The only meteors that do not burn up in the atmosphere are the large ones. These are all asteroid fragments.
153
Comet tails extend from the comet in what direction?
a) away from the Sun
b) away from the Sun when the comet is approaching the Sun and toward the Sun when the comet is moving away
c) toward the Sun
a) away from the Sun
154
This planet has no liquid water on its surface, but does have channels which are probably the stream beds of ancient rivers.
a) Jupiter
b) Mercury
c) Mars
d) Venus
e) Uranus
c) Mars
155
The Earth’s atmosphere is primarily
a) carbon dioxide and oxygen
b) water vapor and carbon dioxide
c) nitrogen and oxygen
d) methane and ammonia
e) nitrogen and water vapor
c) nitrogen and oxygen
156
What are the main constituents of Mars?
a) hydrogen and rock
b) rock and ice
c) water, methane and ammonia
d) hydrogen and helium
e) rock and iron
e )rock and iron
157
The crater-covered surface of this terrestrial planet resembles the surface of the Moon.
a) Mars
b) Mercury
c) Earth
d) Venus
e) Jupiter
b)Mercury
158
Dry ice (frozen carbon dioxide) vastly enlarges this planet’s polar caps in the winter for each cap.
a) Mars
b) Mercury
c) Earth
d) Venus
e) Jupiter
a) Mars
159
The Great Red Spot is
a) a desert on Mars
b) a crater on the moon
c) a persistent storm on Jupiter
c) a persistent storm on Jupiter
160
Compared to Population I stars, Population II stars are
a) older, with a smaller fraction of heavy elements
b) younger, with a larger fraction of heavy elements
c) older, with a larger fraction of heavy elements
d) younger, with a smaller fraction of heavy elements
a) older, with a smaller fraction of heavy elements.
161
What population of stars are found in globular clusters?
a) Population I only
b) Population II only
c) both Population I and Population II
d) neither
b) Population II only
162
Each method of finding distances (or distance indicator) listed below is used to find the distance to a set of objects. Match the indicators to the objects.
1 radar bouncing
2 parallax
3 main-sequence matching ("spectroscopic parallax")
4 Cepheid variables
A distances to planets
B distances to the nearest stars
C distances to nearby galaxies
D distances to stars in the Milky Way more than 2,000 ly away
a) A and 2, B and 3, C and 1, D and 4
b) A and 3, B and 1, C and 4, D and 2
c) A and 1, B and 2, C and 4, D and 3
d) A and 4, B and 3, C and 1, D and 2
c)A and 1, B and 2, C and 4, D and 3
163
he Milky Way is
a) a spiral galaxy
b) an elliptical galaxy
c) a globular cluster
d) an irregular galaxy
a) a spiral galaxy
164
In which part of the Milky Way galaxy is theSun?
a) halo
b) disk
c) central bulge
d) none of these
b) disk
165
Most of the mass of the Milky Way galaxy is
a) in the spiral arms
b) in the disk, but not in the spiral arms
c) in the nuclear bulge
d) invisible and in the halo
e) in the brightest, most massive stars of halo
d) invisible and in the halo
166
The strongest evidence for a black hole in the center of the Milky Way is
a) Observed orbits of stars show nearly 4million times the mass of the Sun is in a region less than 6 light-hours across.
b) Doppler shifts of 21-cm radiation from the galactic center imply that roughly 50 mil-lion times the mass of the Sun lies withina region 3 light-years across,
c) Observed orbits of stars show nearly 30million times the mass of the Sun is in aregion less than 8 light-seconds across.
d) Doppler shifts of 21-cm radiation from the galactic center imply that over one billion times the mass of the Sun lies within a region 3 light-years across.
e) None of these is thought to be evidence for a central black hole.
a)
Observed orbits of stars show nearly 4million times the mass of the Sun is in a region less than 6 light-hours across.
167
Why is 21 cm radio emission useful for studying the structure of the Milky Way
a) The waves penetrate dusty cocoons to re-veal star formation
b) The waves are not absorbed by Galacticblack holes
c) It can be used to map the hydrogen gas in the spiral arms
d) Radio waves provide a distance measurement like parallax
c) It can be used to map the hydrogen gas in the spiral arms
168
What convincing evidence do we have for the presence of a relatively dense halo of invisible“dark matter” permeating the Milky Way?
a) Light from distant stars is blocked by someunseen effect
b) Much of the matter making up the MilkyWay is far colder than it should be
c) Many of the stars in the Milky Way are los-ing energy, as though passing through a dense cloud of material
d) Stars further out in the galactic disk seem to be moving at about the same speed as those that are further in, when they should be moving slower.
d) Stars further out in the galactic disk seem to be moving at about the same speed as those that are further in, when they should be moving slower.
169
What is the rough proportion (by total mass) in the universe of well-understood visible matter to poorly understood “dark” matter?
a) The amount of dark matter is about one percent the amount of visible matter
b) The amount of dark matter is about one fifth the amount of visible matter
c) The amount of dark matter is about equal to the amount of visible matter
d) The amount of dark matter is about five times the amount of visible matter
e) The amount of dark matter is about one hundred times the amount of visible matter
d)The amount of dark matter is about five times the amount of visible matter
170
How are galaxies spread out throughout the universe
a) They are grouped into clusters that are spread more-or-less evenly through out space
b) They are grouped into clusters that in turn are clumped into superclusters
c) Galaxies are densest near us, and be-come more spread out as we look furtherout
d) Galaxies are densest near a distant point in space, which can be interpreted as the center of the universe, and are ore spread out as one looks way from that point.
b)They are grouped into clusters that in turn are clumped into superclusters
171
What is Hubble’s Law based on
a) More distant galaxies showing greater blue shifts
b) Distant galaxies appearing proportionally dimmer
c) More distant galaxies showing greater redshifts
d) Slowly varying Cepheid variables appearing brighter
c)More distant galaxies showing greater redshifts
172
What is the Hubble classification for the galaxy shown in Figure 1 (see page between Instructions and Questions)?
a) E
b) Sa
c) Sc
d) Irregular
e) Quasar
b)Sa
173
What is the Hubble classification for the galaxyshown in Figure 2?
a) E
b) Sa
c) Sc
d) Irregular
e) Quasar
c) Sc
174
Most of the galaxies shown in Figure 3 have what Hubble classification?
a) E
b) Sa
c) Sc
d) Irregular
e) Quasar
a) E
