Unit 9: Discoveries About Galaxies and the Universe Flashcards
(250 cards)
1
Q
Who were the main members of the Herschel family involved in nebula studies?
A
William Herschel, Caroline Herschel, and John Herschel.
2
Q
What was William Herschel’s main field of study?
A
Cosmology – the study of the organization and evolution of the universe.
3
Q
What was the largest mirror size of William Herschel’s telescope?
A
18 inches in diameter.
4
Q
How long did the Herschel family spend cataloging nebulae?
A
20 years.
5
Q
Who created the first nebula catalog and how many objects did it include?
A
Charles Messier; 110 objects.
6
Q
How many nebulae did William Herschel catalog?
A
About 2,500 nebulae.
7
Q
What did John Herschel do after William’s death?
A
He moved to the Cape of Good Hope to continue cataloging the southern sky.
8
Q
What was the total number of nebulae in the Herschels’ final catalog?
A
Over 5,000 nebulae.
9
Q
What was the major contribution of the Herschels’ nebula catalog?
A
It laid the foundation for the New General Catalog (NGC).
10
Q
What question could William Herschel not definitively answer?
A
Whether nebulae were all distant star systems or nearby gas clouds.
11
Q
Why was it hard for Herschel to determine nebulae composition?
A
Spectroscopy hadn’t been developed yet, so gas vs. stars wasn’t distinguishable.
12
Q
What was Herschel’s method to estimate star distances?
A
He judged distance by brightness.
13
Q
What did Herschel’s star map show?
A
That the stars are distributed in a flattened disk around the Sun.
14
Q
What analogy helps understand our galaxy’s shape from Earth?
A
The jelly donut – we are located on the edge, seeing the central bulge.
15
Q
What telescope did Lord Rosse build?
A
The Leviathan of Parsonstown with a 6-foot diameter mirror.
16
Q
What was Lord Rosse’s goal?
A
To determine whether nebulae are gas clouds or distant star systems.
17
Q
What was Lord Rosse famous for?
A
Detailed sketches of nebulae, especially spiral-shaped ones.
18
Q
What did the Whirlpool Galaxy sketch by Lord Rosse reveal?
A
It had spiral arms, confirming some nebulae were spiral galaxies.
19
Q
What did the bright object near the Whirlpool Galaxy turn out to be?
A
NGC 5195, a smaller galaxy being absorbed (galactic cannibalism).
20
Q
What term describes one galaxy consuming another?
A
Galactic cannibalism.
21
Q
Where did Henrietta Swan Leavitt work?
A
Harvard College Observatory.
22
Q
What was Leavitt’s job at the observatory?
A
Measuring apparent brightness (apparent magnitudes) of stars.
23
Q
What kind of stars did Leavitt discover thousands of?
A
Variable stars that pulse in brightness.
24
Q
What are variable stars?
A
Stars whose brightness changes over time.
25
What distinguishes Cepheid variable stars?
They are massive, luminous stars that pulsate regularly.
26
How were Cepheid variable stars named?
After Delta Cephei, the first discovered of its kind.
27
What causes the pulsation in Cepheid variables?
Changes in the opacity of their helium-rich atmospheres due to ionized helium.
28
What physical process leads to pulsation in Cepheid variables?
Trapped radiation builds pressure, inflates the star, then it cools and contracts again.
29
What is a light curve?
A graph of a star’s brightness over time.
30
What is the 'period' of a Cepheid variable?
The time it takes to go from bright to dim and back to bright.
31
What relationship did Leavitt discover?
The period-luminosity relationship of Cepheid variable stars.
32
What does the period-luminosity relationship state?
Longer period Cepheids are more luminous.
33
Where were Leavitt’s 25 Cepheid stars located?
In the Small Magellanic Cloud.
34
Why was Leavitt’s plot significant despite only showing apparent magnitude?
All Cepheids were at roughly the same distance, so relative luminosities were accurate.
35
What does the period of a Cepheid allow astronomers to calculate?
Its absolute magnitude or luminosity.
36
How can distance to a Cepheid be calculated?
By comparing its absolute magnitude with its apparent magnitude.
37
Why couldn't Leavitt directly convert to absolute magnitudes?
She didn’t know the distances to the Cepheids.
38
Why couldn’t parallax or spectra be used for Cepheids in Leavitt’s time?
They were too far away for either method to be applied.
39
What made Leavitt’s discovery so powerful for astronomy?
It enabled distance measurement to other star systems and galaxies.
40
Who was the first to use Cepheid variables as a distance method?
Harlow Shapley.
41
What major astronomical question was Shapley trying to answer?
Whether nebulae are within our galaxy or separate galaxies (island universes).
42
What two things were needed to answer the nebulae question?
Distances to nebulae and the size of our galaxy.
43
What key discovery did Shapley use to estimate distances?
The period-luminosity relationship of Cepheid variables.
44
How did Shapley build the period-luminosity relationship with luminosity?
By using nearby Cepheids with known distances from parallax measurements.
45
What type of star clusters did Shapley study?
Globular clusters.
46
Why were globular clusters important to Shapley's research?
They are some of the most distant objects in the galaxy, helping measure its size.
47
What did Shapley conclude about the Sun's location in the galaxy?
The Sun is not at the center but near the edge of the disk.
48
How large did Shapley estimate the Milky Way to be?
About 300,000 light years in diameter (an overestimate).
49
Why was Shapley's galaxy size estimate too large?
He didn’t account for interstellar dust dimming the light from globular clusters.
50
What is the actual diameter of the Milky Way?
About 100,000 light years.
51
What incorrect conclusion did Shapley make about the universe?
That all nebulae are within our galaxy and the Milky Way is the entire universe.
52
What did Shapley correctly determine about the galaxy’s structure?
It is disk-shaped with a central bulge and a spherical halo of globular clusters.
53
Where in the sky do we look to see the center of the galaxy?
Toward the Sagittarius constellation.
54
What feature blocks much of the light from the galactic center?
Interstellar dust.
55
What new understanding of the universe followed Shapley’s model?
That our galaxy is a single star system, later called the Milky Way galaxy.
56
What major shift in understanding occurred after Shapley's model?
Realization that our galaxy is just one of many in the universe.
57
What did late 1800s maps reveal about the distribution of spiral nebulae?
They were randomly distributed except for a gap along the Milky Way's disk.
58
What was Shapley's explanation for the 'zone of avoidance'?
That the Milky Way’s energy repelled spiral nebulae from its disk.
59
Who argued that spiral nebulae are galaxies like the Milky Way?
Heber Curtis.
60
What did Curtis observe in the spiral nebulae that supported his argument?
Dark patchiness similar to the dust in the Milky Way.
61
What conclusion did Curtis draw from this patchiness?
Spiral nebulae are other galaxies also containing dust.
62
What did Vesto Slipher contribute to the debate?
Spectra of spiral nebulae showing absorption lines and large redshifts.
63
What did Slipher's spectra prove?
Spiral nebulae are made of stars and are moving away at high speeds.
64
Why were Slipher’s velocity findings important?
The spirals' recessional speeds were far greater than typical stellar speeds, implying they were extragalactic.
65
What was the Shapley-Curtis debate?
A 1920 debate on whether spiral nebulae are inside or outside the Milky Way.
66
What did Shapley argue in the Great Debate?
That spiral nebulae are within our galaxy and the Milky Way is the entire universe.
67
What did Curtis argue in the Great Debate?
That spiral nebulae are distant galaxies and the Milky Way is one of many.
68
What observational point did Curtis use about novae in spirals?
They appeared fainter, suggesting the spirals are farther away.
69
What did Curtis say explained the zone of avoidance?
Dust in the Milky Way obscures distant spiral galaxies.
70
Why did the Shapley-Curtis debate end without resolution?
Neither side could conclusively disprove the other's arguments.
71
What object did Hubble study that helped prove the island universe theory?
The Andromeda Nebula (M31).
72
What type of star did Hubble discover in Andromeda?
A Cepheid variable star.
73
How did Hubble determine that M31 was outside the Milky Way?
By measuring the period of a Cepheid and calculating its luminosity and distance.
74
What was the calculated distance to M31 by Hubble?
About 1 million light years.
75
Why was Hubble’s Cepheid star in M31 significant?
It had a long period and was faint, indicating great distance and high luminosity.
76
How did Hubble inform Shapley of his findings?
Through a letter in February 1924.
77
What was Shapley’s reaction to Hubble’s discovery?
'Here is the letter that has destroyed my universe.'
78
What telescope was named in honor of Edwin Hubble?
The Hubble Space Telescope.
79
What is the Hubble Space Telescope known for?
Detecting galaxies near the edge of the known universe.
80
What is replacing the Hubble Space Telescope?
The James Webb Space Telescope (JWST).
81
What are two major features of the JWST?
A 6x larger mirror and an onboard spectroscope.
82
Why does JWST have a sunshield?
To block sunlight and allow clearer infrared observations.
83
What role did Canada play in the JWST?
Canada contributed funding and gets access to research time on the telescope.
84
What did Edwin Hubble do after proving spiral nebulae are galaxies?
He developed a classification system for galaxies based on their appearance.
85
How many major galaxy types are in Hubble's classification?
Four
86
What does 'S' stand for in galaxy classification?
Spiral galaxy
87
What features define a spiral galaxy?
A flattened disk, spiral arms, and possibly a central bulge
88
What percentage of galaxies are spirals?
About 30%
89
How are spirals further classified?
By lowercase letters (a, b, c, etc.) based on tightness of arms and bulge brightness
90
What is a barred spiral galaxy?
A spiral galaxy with a bar of stars through the center
91
What does 'SB' represent in galaxy classification?
Barred spiral galaxy
92
What type of galaxy is the Milky Way according to Hubble's system?
A barred spiral galaxy
93
What evidence supports the Milky Way being barred?
Infrared images show excess light on both sides of the bulge
94
What causes galaxy bars?
Possibly temporary phenomena or due to galaxy collisions
95
How do spiral galaxies likely form?
Through mergers of smaller galaxies
96
What are lenticular galaxies and their symbol?
Disk galaxies without spiral structure; denoted S0 or SB0
97
What percentage of galaxies are lenticular?
About 15%
98
What are elliptical galaxies and their symbol?
Egg or football shaped galaxies without a disk; denoted E
99
What percentage of galaxies are ellipticals?
About 5%
100
How are elliptical galaxies further classified?
By numbers E0 to E7 based on elongation
101
What causes elliptical galaxies?
Mergers of galaxies with similar mass
102
What does IRR stand for?
Irregular galaxies
103
What percentage of known galaxies are irregulars?
About 50%
104
What are dwarf irregulars?
Small irregular galaxies with only a few million to billion stars
105
Why are dwarf irregulars significant?
They are believed to be the building blocks of larger galaxies
106
What is the Hubble sequence?
A classification system for galaxies based on shape, also called the Hubble tuning fork
107
Does the Hubble tuning fork show galaxy evolution?
No, it's just a classification system
108
How many galaxies have been observed in the universe?
About 50 billion or more
109
What percentage of galaxies are spirals?
About 30%
110
Is the Milky Way unique in being a spiral galaxy?
No, spiral galaxies are common
111
What makes the Milky Way notable among spiral galaxies?
It's a giant spiral, among the largest of its type
112
What is the name of the Milky Way's galaxy group?
The Local Group
113
How many galaxies are in the Local Group?
About 30
114
What are the two largest galaxies in the Local Group?
The Milky Way and Andromeda (M31)
115
What is galactic cannibalism?
When a larger galaxy consumes a smaller one
116
What dwarf galaxy is the Milky Way currently consuming?
Sagittarius Dwarf Galaxy
117
What evidence do we have of the Milky Way's galactic cannibalism?
Streams of stars tracing the Sagittarius Dwarf's orbit
118
What happens to stars from a consumed galaxy?
They become part of the larger galaxy
119
What might happen between the Milky Way and Andromeda in the future?
They may merge into a giant galaxy
120
What is Abell 3827?
A galaxy cluster with a dominant supergiant elliptical consuming smaller galaxies
121
What is a supercluster?
A cluster of galaxy groups
122
What supercluster is the Local Group part of?
The Virgo Supercluster
123
Is the Local Group at the center of the Virgo Supercluster?
No, it's on the outskirts
124
What pattern do galaxies form in the universe?
A web-like or foam-like pattern
125
What causes this large-scale structure of the universe?
Dark matter's gravitational influence
126
What is the 2D Galaxy Redshift Survey?
A survey showing the distribution of galaxies across the universe
127
How do computer simulations of dark matter compare to galaxy maps?
They show similar web-like patterns
128
What does dark matter do?
Shapes the distribution of visible matter in the universe
129
What did Vesto Slipher discover about galaxies using their spectra?
Most galaxies are redshifted, meaning they are moving away from us
130
How fast were some galaxies receding according to Slipher?
Over 1000 km/s
131
What two major things did Hubble discover using redshift and Cepheid variables?
1) Most galaxies are receding from us, 2) The farther a galaxy is, the faster it recedes
132
What is Hubble’s Law?
The velocity of a galaxy's recession is proportional to its distance from us
133
What does Hubble's Law indicate about the universe?
That the universe is expanding
134
What is the Hubble constant?
The rate of expansion of the universe, represented as the slope of Hubble's Law
135
How can the age of the universe be estimated using the Hubble constant?
By taking the inverse of the Hubble constant (1/H₀)
136
What was Hubble’s original estimate for the age of the universe?
About 2 billion years
137
What is the modern estimated age of the universe?
About 13.7 billion years
138
Why did early calculations underestimate the age of the universe?
Due to less accurate distance measurements
139
Does the universe have a central point of expansion?
No, expansion appears the same from any galaxy
140
What analogy helps explain the expansion of the universe?
Galaxies on the surface of an expanding balloon
141
Why do all galaxies appear to recede from us?
Because space itself is expanding uniformly
142
Where is the center of the universe’s expansion in the balloon analogy?
Inside the balloon, in a higher spatial dimension
143
What might the center of our universe’s expansion exist in?
A fourth spatial dimension
144
Can we perceive the fourth spatial dimension?
No, but we can model it mathematically
145
What theoretical constructs might use the fourth dimension?
Wormholes
146
What is a wormhole?
A theoretical tunnel through space-time that could connect distant regions
147
Have wormholes been observed?
No, they remain theoretical
148
What does redshift in a galaxy’s light indicate?
That the galaxy is moving away from us
149
Who theoretically predicted an expanding universe before Hubble?
Albert Einstein
150
What modification did Einstein make to his equations to keep the universe static?
He added the cosmological constant
151
What does the cosmological constant (Lambda) do in Einstein's equations?
It counteracts expansion or contraction to keep the universe's size constant
152
What did Einstein call the cosmological constant after Hubble's discovery?
The biggest blunder of his career
153
Why might the cosmological constant actually be necessary?
To explain the rapid expansion of the universe
154
What does Hubble's discovery provide for Einstein's theory?
Observational evidence that the universe is expanding
155
What do Einstein’s field equations predict about the beginning of the universe?
That it started at zero size with all matter and energy in a single point
156
What are the two key unknowns that determine the universe’s fate?
The density of the universe (ρ) and the cosmological constant (Λ)
157
What is critical density?
The exact amount of density needed to halt expansion
158
What is the Big Freeze?
A universe that expands and then remains at a constant size forever
159
What is the Big Crunch?
A universe that halts expansion and contracts back to a point
160
What is the Big Chill?
A universe that expands forever at a steady rate
161
What is the Big Rip?
A universe with accelerating expansion that may tear all matter apart
162
What causes the Big Rip?
A positive cosmological constant causing accelerating expansion
163
What determines which cosmic fate our universe will follow?
The values of the density and cosmological constant
164
What era of the universe are we currently in?
The expansion era
165
What is outward momentum in the universe a result of?
The Big Bang
166
What is the role of gravity in the universe’s expansion?
To try to pull matter back together and slow expansion
167
What are today’s cosmologists trying to determine?
The exact values of density and the cosmological constant
168
What is the Big Bang theory?
The idea that the universe began from a single point and has been expanding ever since.
169
What happens to the density of the universe over time according to the Big Bang theory?
It decreases because mass is constant but volume increases.
170
What is the steady state theory?
A theory that suggests the universe has always existed and its density remains constant over time.
171
Why is Hubble’s Law inconsistent with the steady state theory?
Because it shows galaxies receding, implying decreasing density.
172
How did steady state theorists explain constant density despite expansion?
By proposing new galaxies continuously form between receding ones.
173
Who coined the term 'Big Bang'?
Fred Hoyle, as a mockery of the theory.
174
What observation first significantly challenged the steady state theory?
Martin Ryle's radio survey showing denser galaxy populations in the past.
175
What is the cosmic microwave background (CMB)?
Radiation left over from the Big Bang, stretched to microwave wavelengths.
176
At what wavelength does the CMB peak?
Around 2 millimeters (0.2 cm)
177
What event allowed light to travel freely through the universe?
The universe becoming transparent about 400,000 years after the Big Bang.
178
What is the inflation era?
A period in the early universe where it expanded rapidly from a tiny speck.
179
Who predicted the existence and wavelength of the CMB?
Robert Dicke and Jim Peebles
180
Who accidentally discovered the CMB?
Arno Penzias and Robert Wilson
181
What did Penzias and Wilson initially think was wrong with their equipment?
They thought it was picking up noise or interference.
182
Why is the CMB stretched to microwave wavelengths?
Because of the expansion of space over time.
183
What recognition did Penzias and Wilson receive for discovering the CMB?
They won the Nobel Prize in 1978.
184
When did the universe become transparent to light?
About 400,000 years after the Big Bang.
185
What makes radio astronomy ideal for studying distant galaxies?
Radio waves pass through dust and gas easily.
186
Why didn’t Peebles and Dicke win the Nobel Prize with Penzias and Wilson?
They predicted the CMB but didn’t detect it; Peebles later won a Nobel Prize in 2019.
187
What nationality is Jim Peebles?
Canadian
188
What did ancient Greeks observe in the night sky about 2500 years ago?
Cloudy patches referred to as nebulae (Latin for cloud or mist).
189
What are 'naked eye nebulae'?
Nebulae visible to the naked eye, without the use of telescopes.
190
Which nebulae are visible from the Northern and Southern Hemispheres?
One is visible from the north; two (Large and Small Magellanic Clouds) are visible from the south.
191
What ancient cultures recorded observations of nebulae?
Middle Eastern sky watchers and Aboriginal Australians.
192
Who are the Large and Small Magellanic Clouds named after?
Portuguese explorer Ferdinand Magellan.
193
What did the invention of the telescope reveal about nebulae?
That they come in various shapes: irregular, elliptical, and linear.
194
Who proposed that elliptical nebulae could be disk-shaped star systems?
Immanuel Kant.
195
What is the 'island universe theory'?
The idea that each elliptical nebula is its own universe (galaxy), and we live in one of many such galaxies.
196
Why did Kant believe we live in a disk-shaped star system?
Because the Milky Way appears as a bright band of light in the sky.
197
What does the word 'galaxy' mean?
It comes from the Greek word for 'milky', referencing the Milky Way.
198
What did Galileo observe about the Milky Way through his telescope?
It is made up of densely packed stars.
199
Why does the Milky Way appear as a band in the sky?
Because we are inside a disk of stars, and looking through the length of the disk shows more stars.
200
What causes the varying appearances of the Milky Way in the sky?
The Earth's position and orientation cause the band to appear vertical, horizontal, or at an angle.
201
How long did it take for the island universe theory to be accepted?
Over 300 years.
202
What was the dominant belief before the island universe theory was accepted?
That the Milky Way was the only galaxy in the universe.
203
What major event in the 1920s helped resolve the debate about the size of the universe?
A formal debate on whether there are multiple galaxies or just one.
204
Who definitively proved the island universe theory?
Edwin Hubble
205
Where did Edwin Hubble work?
Mount Wilson Observatory in Southern California
206
What was the largest telescope at the time Hubble worked?
100-inch Hooker telescope
207
What galaxy did Hubble study that contributed to proving the island universe theory?
Andromeda Galaxy (Messier 31)
208
What type of star did Hubble discover in the Andromeda Galaxy?
Cepheid variable star
209
What is the relationship between period and luminosity in Cepheid variables?
Longer period means higher luminosity
210
What did the faintness of the Cepheid variable in M31 imply?
It was much farther away than any star in the Milky Way
211
What distance did Hubble calculate for the Andromeda Galaxy?
About 1 million light years
212
What was Shapley's reaction to Hubble's discovery?
He said, 'Here is the letter that has destroyed my universe'
213
What telescope was named in honor of Edwin Hubble?
The Hubble Space Telescope
214
What is the name of the telescope intended to replace Hubble?
James Webb Space Telescope
215
What is a major feature of the James Webb Space Telescope?
A larger primary mirror and a spectroscope
216
What country significantly contributed to the James Webb Space Telescope?
Canada
217
What does the sunshield on the James Webb Telescope do?
Keeps sunlight away from the mirror to improve observations
218
What is the shape of the Cassiopeia constellation?
W-shaped
219
How can you find the Andromeda Galaxy using Cassiopeia?
Use the deeper part of the 'W' in Cassiopeia to point to the Andromeda Galaxy
220
What was the goal of the supernova survey started in the 1990s?
To measure the past rate of expansion of the universe using distant supernovae.
221
Why are supernovae good for measuring distances to faraway galaxies?
Because they have a known peak luminosity and are extremely bright.
222
Why are supernovae better than Cepheids for distant measurements?
Supernovae are more luminous and visible at greater distances.
223
How often does a supernova occur in a galaxy?
Roughly once every 300 years in spiral galaxies.
224
What did the supernova project reveal about the universe’s expansion?
The expansion of the universe is accelerating.
225
Which fates of the universe are associated with accelerating expansion?
The Big Chill and the Big Rip.
226
What provides observational evidence for the early universe's structure?
The Cosmic Microwave Background (CMB).
227
What does the CMB show us?
The distribution of matter in the universe 400,000 years after the Big Bang.
228
Which satellite created the highest resolution CMB map?
The Planck satellite.
229
What did the Planck telescope reveal about the universe's density?
It is equal to the critical density.
230
If the universe is accelerating but has critical density, what must be true?
Einstein’s cosmological constant must be greater than zero.
231
What is the name for the force believed to cause accelerating expansion?
Dark energy.
232
What percentage of the universe is dark energy?
Approximately 68%.
233
What percentage of the universe is normal matter?
About 30%.
234
How much of the universe is visible matter like stars and planets?
Only about 5%.
235
What is dark matter?
Matter that doesn’t emit light but has gravitational effects.
236
What are neutrinos?
Tiny, nearly massless particles created in nuclear reactions in stars.
237
What does the cosmological constant represent in Einstein’s equations?
An outward push on the universe’s expansion.
238
What is the ultimate fate of the universe if the Big Rip occurs?
All structures down to atoms are torn apart by accelerating expansion.
239
When might the Big Rip occur if it happens?
Tens of billions of years from now.
240
What did Edmond Halley discover about stars in the early 1700s?
He found that stars were moving through space, though their precise paths weren't yet known.
241
What did Jan Oort contribute in the 1930s?
He showed that stars in our galaxy orbit the center, like planets around the Sun.
242
According to Newtonian gravity, how should star speeds change with distance from a galaxy’s center?
Speeds should decrease with distance from the center (like planets in the Solar System).
243
What do rotation curves of galaxies actually show?
Star speeds remain constant or even increase at large distances from the center.
244
What does the discrepancy between predicted and observed rotation curves suggest?
There must be extra, invisible mass exerting gravity—this is dark matter.
245
What is dark matter?
A form of matter that doesn’t emit light but has gravity and affects the motion of visible matter.
246
What is gravitational lensing?
The bending of light from distant objects due to mass curving space between the object and the observer.
247
How does gravitational lensing provide evidence for dark matter?
Light from distant galaxies is distorted in ways that require more mass than visible matter accounts for.
248
What is an Einstein Cross?
A specific lensing configuration where a single background galaxy appears multiple times due to foreground mass.
249
What does lensing by galaxy clusters reveal?
That the space between galaxies (intra-cluster medium) contains large amounts of dark matter.
250
Do we know what dark matter is made of?
No, we don’t know its composition or detect it through any part of the electromagnetic spectrum—only through its gravitational effects.
