Astronomy: Galaxies (Unit 4) Flashcards
1
Q
What happens to the matter of a star after its lifecycle has ended?
A
Because matter cannot be created or destroyed, the matter in a star, mostly helium and hydrogen from the early universe, remains after a star’s lifespan has ended
2
Q
What do modern telescopes allow us to do, that helps us evaluate matter in space?
A
They allow us to take pictures of accumulated matter in space
3
Q
In space, what does accumulated matter form?
A
In space, matter accumulates in clouds. Nebulae are either the beginnings of stars or the matter ejected when a dying star explodes, and are found in the space between stars
4
Q
Nebulae Definition
A
Clouds of interstellar gas and dust
5
Q
Who was Sir William Herschel? What is he credited for?
A
Sir William Herschel was a composer and astronomer who catalogued many nebulae. He is also credited with forming the theory of stellar evolution, or the life cycle of a star. He also built telescopes
6
Q
Who was Caroline Herschel?
A
Caroline Herschel was a brilliant astronomer who was also William Herschel’s sister
7
Q
What is “Nebula” Latin for?
A
“Cloud”
8
Q
True or False: Emission Nebulae give off their own light and are hot
A
True
9
Q
When would the Herschel siblings comprehend the temperature of nebulae?
A
The Herschel siblings would not comprehend the temperature of nebulae until years later when William discovered infrared light
10
Q
What is a stellar nursery?
A
A type of nebula that is in an area where stars are forming
11
Q
How does a “Cat Eye Nebula” look like?
A
An elliptical nebula with a single, very bright star visible in the middle is a “Cat’s Eye Nebula”
12
Q
How can you identify a nebula through its layers?
A
You can identify nebula by outer layers of gas expanding into space
13
Q
What is the only situation that can cause a “Cat’s Eye Nebula” to form?
A
A “Cat’s Eye Nebula” can only form when a star dies
14
Q
How is a planetary nebula formed?
A
Planetary nebulae is formed when a star runs out of power and blows of its outer layers
15
Q
How can temperature help identify planetary nebulae?
A
A planetary nebula can be identified by the warm glow left behind by a star
16
Q
How was the term “planetary nebula” coined? Why did Sir William Herschel name it this way?
A
The term “planetary nebulae” is actually a misnomer; William thought that these nebulae resembled round gas planets
17
Q
What are some features of nebulae the Herschels observed?
A
The Herschel’s observed that some nebulae gave off light, some nebulae are round and have outer layers of gas expanding into space, and they were able to understand the temperatures of novae
18
Q
What force results in the formation of nebulae?
A
Gravity
19
Q
What happens in a nebula in which stars are born?
A
In a nebula in which stars are born, atoms and bits of matter in interstellar space are pulled together by the force of gravity. When the mass becomes great enough, it collapses from the force of gravity. The matter in the center heats up and a star is born
20
Q
How does gravity form supernovas?
A
Gravity can cause a supernova in a massive, older star. When a star at least 5 times the size of the sun begins to run out of fuel, the pressure pushing outward is reduced, and gravity squeezes the star until it explodes. Matter form the star scatters, forming a nebula. Smaller stars can form planetary nebulae, in which the core of the star is surrounded by the expelled outer layers
21
Q
Gravity Definition
A
Force that pulls matter together
22
Q
What is Interstellar Space often referred to as? Despite this, what allows nebulae to form?
A
Interstellar space is often referred to as a vacuum, but this is not the case. The majority of space is approximately a vacuum, but space becomes denser to form nebulae
23
Q
How does the observability of nebulae differ from Earth?
A
Some nebulae can be seen from Earth with the naked eye, but many others can only be seen with modern telescopes
24
Q
How could one explain the behavior and composition of nebulae?
A
There is a wide variety in the behavior and composition of nebulae, and one nebula can have areas with different characteristics
25
Vacuum Definition
Area with no matter
26
Many types of nebula are categorized based on how they interact with what?
Many types of nebulae are categorized based on how they interact with electromagnetic radiation
27
What is light?
Radiation energy we can see
28
True or False: Modern telescopes can “see” radiation energy not visible with our eyes
True
29
Why are photos of nebulae and objects in space colorized?
Photos of nebulae, and many other objects in space, are often colorized to distinguish different wavelengths of radiation that we cannot see
30
Electromagnetic Radiation Definition
Energy carried by oscillating magnetic and electrical fields
31
What are nebulae made up of?
Nebulae are made up of interstellar dust, hydrogen, helium, and other gasses. The quantities of the components is how astronomers classify nebulae
32
True or False: Nebulae usually have overlapping attributes
True
33
What are HII (H2) nebulae?
HII (H2) nebulae have a high percentage of hydrogen. They come in several shapes and sizes, and can be found clustered together or stretched out in a thin line
34
What are Diffuse nebulae?
Diffuse nebulae are dispersed so that their edges are not hard lines, rather they appear to dissipate among the sky. They emit infrared light from their dust
35
What are Emission nebulae?
Emission nebulae are made of ionized gasses that emit light in an array of colors. Often they are found with a star nearby
36
What are Planetary nebulae?
Planetary nebulae appear more compact and in more of an elliptical form than other nebulae. They only last a few tens of thousands of years
37
What are Bipolar nebulae?
Nebulae classified as bipolar appear to have an hourglass shape, or in cases when their ends are wider, a shape like butterfly wings
38
What are Reflection nebulae?
Reflection nebulae are clouds of interstellar dust, revealed from transmitted light from nearby stars. Reflection nebulae appear appear mostly blueish because blue light reflects best off a nebula’s cloud of dust
39
What are Supernova Remnants?
Supernova remnants are nebulae that remain after a supernova. These nebulae are identified by their powerful radio emissions
40
What are Pulsar Wind Nebulae?
Pulsar wind nebulae, or plerions, are often found in the shells of supernova remnants. At times, they have been found around older pulsar wind nebulae, whose supernova remnants have decayed
41
What are Dark, or Absorption, Nebulae?
Dark, or absorption, nebulae have such thick interstellar clouds that they block out the light behind them. The dark spots among the Milky Way are the largest dark nebulae that have been found
42
How are nebulae classified?
By composition
43
How much space does a galaxy consume? How many stars does it have?
A single galaxy covers an enormous distance in space and can include millions or even many billions of stars
44
What are the components of a galaxy held together by?
The stars and other components of a galaxy are bound together by gravity
45
What do galaxies vary in?
Shape and size
46
Galaxy Definition
A large group of stars, dust, dark matter, and gas
47
True or False: Galaxies are far from the largest structures in the universe
True
48
How are galaxies organized?
Galaxies are bound together in groups. The Andromeda Galaxy is closest to and in the same group as the Milky Way. Galaxy groups are bound further into clusters. Galaxy clusters are the largest known components of the universe
49
How many stars do scientists believe the Milky Way consists of?
Every star visible to our naked eye on a clear night is part of the Milky Way. Scientists estimate that the Milky Way includes 100 billion stars
50
How do we know the shape of the Milky Way?
From Earth, the galaxy’s stars are seen to be focused in a bright band within a milky cloud. Astronomers figured out that the band indicated a disk shape
51
What is the shape of the Milky Way?
Astronomers examined many telescope images. They studied star ages and mapped star concentrations. Eventually, they were convinced that the stars forming the Milky Way are arranged in a relatively flat spiral. The visible band of stars is our view of the spiral-shaped disk from within
52
How far from the center of the Milky Way is our solar system?
Our solar system is an estimated 25,000 light years away from the galaxy’s center on an outward spiraling finger
53
What is the estimated diameter of the Milky Way?
100,000 light years
54
What is a similarity galaxies share that can lead to their grouping?
While the shapes of all galaxies are not the same, all galaxies share similar components and are similarly bound into larger groups and even larger clusters
55
How was the Milky Way given its name?
The Milky Way was given its name because it appears as a milky band of light when observed without light pollution
56
What is the composition of a galaxies mass? What makes up most of its mass?
Large groups of stars, gas, and dust make up 10% of a galaxy’s mass. The other 90% consists of dark matter, an unknown substance
57
What is at the center of most galaxies?
At the center of most, if not all, galaxies is thought to be a supermassive black hole with such a strong gravitational pull that it binds the galaxy together
58
How many galaxies are in the observable universe?
Astronomers estimate 100 billion galaxies are in the observable universe. The Milky Way is 1 of 4 galaxies observable without a telescope
59
What are Conglomerates of Galaxies called?
Conglomerates of galaxies are called galaxy groups. The Milky Way is part of the Local Group of Galaxies, which contains approximately 50 galaxies
60
What are galaxy clusters composed of?
Galaxy clusters are configured of thousands of galaxies held together by gravitational pull
61
What cluster is the Local Galaxy group, the one the Milky Way is in, a part of? How many galaxies are in this cluster?
It is a part of the Virgo Cluster, with about 2,000 galaxies
62
True or False: the efforts of many astronomers over hundreds of years conclude that galaxies are in fact not all alike
True
63
What did Edwin Hubble do?
The astronomer Edwin Hubble developed the major groups used to categorize galaxies. Based on distinctive differences in galaxy shapes, galaxies are classified as spiral, elliptical, or irregular. This classification system can be quite complex, with many additional subcategories and variations. However, most galaxies can be described within these 3 major groups
63
What did Edwin Hubble do?
The astronomer Edwin Hubble developed the major groups used to categorize galaxies. Based on distinctive differences in galaxy shapes, galaxies are classified as spiral, elliptical, or irregular. This classification system can be quite complex, with many additional subcategories and variations. However, most galaxies can be described within these 3 major groups
64
In addition to shape, what else do galaxies differ in?
In addition to shape, galaxies also differ in size, age of component stars, and composition. Typically, galaxies with relatively high amounts of dust and gas also have younger stars and active star formation
65
What may elliptical galaxies vary in?
Elliptical galaxies may vary in how elongated they are
66
What are the largest galaxy type?
Elliptical Galaxies
67
What are Elliptical Galaxies made up of?
Elliptical galaxies are made up of old stars and not much gas or dust
68
What two groups are spiral galaxies classified in?
Spiral and Barred
69
What are Barred Spiral Galaxies?
Barred Spiral Galaxies have a band of stars and materials that cut through the middle of the galaxy attaching to its spirals or arms
70
How do spiral galaxies vary?
The variation in spiral galaxies is the tightness of a spiral galaxy’s arms. The coil may range from tightly wound to quite loose
71
How does a spiral galaxy compare to an ellipt
72
How does a spiral galaxy compare to an elliptical galaxy?
Spiral galaxies have younger stars and are made up of more gas and dust than elliptical galaxies
73
How does the size of Irregular galaxies compare to others?
Irregular galaxies account for some of the smallest galaxies in the universe
74
How do irregular galaxies compare to elliptical and spiral galaxies?
Irregular galaxies have the youngest stars and have more gas and dust than both elliptical and spiral galaxies
75
What does each galaxy type—spiral, elliptical, or irregular—consist of?
Galaxies that share similar arrangements, compositions, and other characteristics
76
What is a galaxy called if it appears to be a mixture of a spiral and elliptical shape?
Lenticular
77
What is the most common type of galaxy?
Astronomers believe spiral galaxies are the most common type of galaxy, making up more than 2/3 of all galaxies
78
What is the largest galaxy in the Local Group of Galaxies?
The Andromeda Galaxy
79
How many stars are in Elliptical galaxies? What other form do they take?
Elliptical galaxies can be the universe’s giants, with up to 10 trillion stars. They can also be much smaller galaxies called dwarfs, which tend to be companions to other galaxies
80
How does electromagnetic radiation help with identifying the composition of nebulae?
The wavelengths of electromagnetic radiation from or blocked by a nebula says a lot about its composition.
81
What type of nebula is the Orion Nebula, and what does it emit? Which nebulae are stars born in?
The Orion Nebula, which is a diffuse nebula, emits infrared light that we cannot see along with light we can see. Stars are born in emission nebulae and often can be observed in the cloud. Wavelengths of radiation emitted by the stars in an emission nebula are different from the wavelengths emitted by ionized gases surrounding the stars.
82
What is a reflection nebula? What type of nebula is it?
A reflection nebula is a diffuse nebula that reflects light from a nearby star. This nebula can be the leftover matter surrounding a young star. The nebula scatters blue light from the star more efficiently than red light because dust grains in the cloud are similar in size to wavelengths of blue light.
83
What type of radiation do absorption nebula emit?
An absorption nebula is a dense area of dust grains and molecular gas known as molecular clouds. These nebulae can be the sites of star formation. Sometimes they are backed by bright emission or reflection nebula or are in an area with many stars, creating a distinctive shadow. They emit microwave and infrared radiation
84
What type of nebula is a Supernova remnant? What does it emit?
Supernova remnant nebulae are diffuse and expand carrying heavy elements with them. They emit X-rays when shock waves of the explosion interact with matter and radio waves, but they don’t always emit visible light. Radiation is emitted when heavier elements are formed in the nebula.
85
What do Planetary Nebulae emit?
Planetary nebulae also result from dying stars. They emit mostly blue-green light from ionized hydrogen and red or orange light from ionized oxygen, as well as X-rays. These nebulae are a source of matter in interstellar space. They are small and are illuminated and ionized by the star remnants in the center, which has strong ultraviolet emissions.
86
What is the second closest galaxy to the Milky Way?
The galaxy that is second closest to the Milky Way is an elliptical galaxy, the Sagittarius Dwarf. Some scientists believe that many elliptical galaxies remain unidentified.
87
What is the closest galaxy to the Milky Way? (Actually one)
Irregular galaxies are thought to compose 20 percent of all galaxies. As sites of active star formation, irregular galaxies are often under the gravitational pull of other galaxies. The closest galaxy to the Milky Way is the Canis Major Dwarf. It is an irregular galaxy that is a satellite of the Milky Way, orbiting its center. Two particularly well-known neighboring galaxies are the Large and Small Magellanic Clouds. These irregular galaxies are clearly visible from Earth’s Southern Hemisphere.
88
Black Hole Definition
An entity with gravity so strong that no light can escape it
89
Supernova Definition
A final, violent explosion of a star
90
What are the four main types of black holes?
Stellar Black Holes, Supermassive Black Holes, Intermediate-mass Black Hole, and Miniature Black Holes
91
How are Stellar Black Holes formed?
Stellar Black holes are formed when a star with great mass stops producing energy and rapidly collapses. This collapse, caused by an inward gravitational force, results in a supernova explosion. These types of black holes have 10 to 20 times the mass of our sun
92
How are Supermassive Black Holes formed?
Astrophysicists do not know exactly how supermassive black holes form, but evidence points to them being the byproduct of galaxy formation. Supermassive black holes can have a mass equal to billions of our sun’s. They may continue to grow because they continue to draw in more matter
93
What is a tidal disruption event?
A tidal disruption event happens when a star passes too close to a supermassive black hole
94
How are Intermediate-mass Black Holes formed?
Astrophysicists believe that intermediate-mass black holes form out of the collapse of some of the oldest stars that may of existed since the universe began. Another hypothesis states that they are created when black holes collide. The mass of intermediate-mass black holes is a few thousand masses our sun
95
How are Miniature, or primordial, black holes formed?
Miniature, also known as primordial, black holes may have formed shortly after the Big Bang. Scientists hypothesize that as the universe began rapidly expanding, some slow traveling matter may have compressed enough to collapse into black holes. Miniature black holes have masses less than or equal to that of Earth
96
When does the most common black hole form?
The most common type of black hole forms at the end of the life cycle of very massive stars, after a supernova
97
How do astronomers observe black holes indirectly?
Black holes don’t emit light, but astronomers can observe them indirectly. They observe the behavior of objects in space to determine whether a black hole is nearby. Stars that seem to be orbiting nothing are often orbiting a black hole. As the powerful gravity of a black hole sucks in gases and dust, the swirling gases become superheated. They give off x-rays and radio waves that telescopes can detect
98
When was the first image of a back hole created?
The 1st image of a black hole was created by a network of 8 radio telescopes on 4 continents: the Event Horizon Telescopes. The telescopes worked together as one planet-sized instrument. They collected data over several days in April 2017, and then worked almost two years to assemble them into the image that amazed the world
99
Radio Telescope Definition
An instrument that gathers radio waves from objects in space
100
What is the name of the black hole in the e center of the Milky Way?
A huge black hole named Sagittarius A is at the center of the Milky Way. It is 4 million times more massive than the sun
101
How massive are stars that form black holes?
At least 20 times the mass of the sun
102
True or False: the formation process that astronomers understand applies only to stellar blackouts holes
True
103
What type of black holes is usually at the center of galaxies?
Supermassive black holes
104
When do astronomers use the term “spaghettification”?
Astronomers use the term “spaghettification” when someone or something falls into a black hole and gets stretched to look like spaghetti
105
What is a star’s outward pressure caused by?
Radiation emissions
106
What are supernovas caused by? (Explosion or Implosion)
Implosions
107
What is the only way to see black holes?
The only way to see black holes is by the ring that encompasses them, called the event horizon
108
Singularity Definition
A mathematical point with essentially zero volume and infinite density
109
Event Horizon Definition
A theoretical boundary around a black hole that blocks the exit of light and matter
110
How do stars form black holes?
A star is balanced by the inward force of gravity and the outward force of emitted radiation. The radiation is released during energy-generating fusion. A dying, massive star becomes a black hole when this force balance is disrupted. The aging star first depletes its stores of hydrogen and helium. If the star is massive enough, it consumes progressively heavier elements on the periodic table, up to iron. But iron doesn’t undergo fusion, so the star ceases emitting radiation. Suddenly, the inward force of gravity is unchecked, and the star implodes. The star’s top layers explode outward as a bright, violent supernova. The remaining core collapses and compresses into increasingly smaller volumes. The small core of the star remaining after the supernova occurs forms a black hole. This formation happens when the core is crushed by the overwhelming force of gravity. Its contents are compressed to its singularity. A black hole can continue to gain mass only if it is surrounded by dust and gas. Those materials are drawn inside the boundary of the black hole’s surface, its event horizon. The velocity required to overcome the gravitational pull of the black hole’s interior is greater than the speed of light. Thus, neither matter nor radiation—including light—can escape a black hole once they have entered. Trapped contents are heated and stretched as they are incorporated into the black hole.
111
How did we find Messier 87?
In April 2019, the people of Earth got their first look at a black hole—or at least the first look at the light around a black hole. Scientists have known about black holes for several decades, yet no one had ever observed one before. It is impossible to see a black hole because its gravity is so strong that nothing can escape it, not even light. This recently observed black hole has been named Messier 87, and it is 6.5 billion times more massive than the sun. If not for the glowing gases around it, it would have remained hidden.
112
True or False: galaxies share stages of evolution
True
113
What are the starting components that all galaxies depend on?
All galaxies depend on the same starting components: gas and dust, merging matter, and tremendous gravity. As they evolve, galaxies continue to undergo similar forces and processes. They change in size, shape, and composition over very long periods of time
114
Evolution Definition
Gradual development, usually from simple to more complex
115
How are the structure and function of a galaxy related?
The structure of a galaxy affects its function. For example, the structure of irregular galaxies includes dust and other small particles. One major function of such a galaxy is to form new galaxies as the particles attract each other
116
How do galaxies evolve?
By colliding with other galaxies
117
What are the two theories of how galaxies formed?
There is two theories: first, galaxies formed from many small lumps of matter and dark matter that were already clumped together, and second, galaxies were born when vast clouds of gas and dust collapsed under their own gravitational pull
118
What happens after galaxies form?
From there, smaller galaxies collide and merge to form brand-new galaxies. Because these galaxies are so big, they attract other nearby galaxies with their gravitational force. This is how we ended up with elliptical galaxies and grand spiral galaxies, like the Milky Way, formed over billions of years ago
119
Due to the universe’s age, what can we conclude about massive galaxies?
Since the formation of the universe 13.8 billion years ago, nearly all massive galaxies in our universe have undergone at least one major collision. In fact, the Andromeda Galaxy is headed toward the Milky Way for a possible future collision—billions of years from now
120
What did NASA send to space in 2001?
In 2001, NASA launched into space the Wilkinson Microwave Anisotropy Probe (WMAP). The spacecraft had an important mission: to measure fluctuations in the temperature of the cosmic microwave background, the residual radiation of the Big Bang
121
Cosmic Microwave Background Definition
Radiation from the beginning of the universe
122
What data did WMAP provide by the time of its retirement in 2010?
By the time WMAP was retired in 2010, the data it provided had helped scientists refine humankind’s knowledge of basic facts about the universe, including its age, size, structure, contents, and origins. The WMAP data added to knowledge gained from studies conducted by other scientists and spacecrafts
123
What are some things WMAP confirmed about the universe?
Before WMAP’s mission, astronomers had used other data to estimate that the universe is flat and that it is between 12 and 14 billion years old. They also found that due to the momentum of the Big Bang, the universe was expanding, and doing so at an increasing rate. WMAP took measurements that allowed scientists to confirm the shape and expansion of the universe and to narrow the time frame of its age to 13.77 billion years old. It also confirmed that the CMB is much older the radiation emitted by stars, uniformly distributed across the universe, and of a uniform temperature of 2.725 degrees above absolute zero
124
What did WMAP confirm about the composition of the universe?
WMAP’s measurements also indicated that the composition of the universe is different than some scientists had expected. Only about 5% 9f the universe is made of ordinary matter, also called baryon in matter. Most baryonic matter is found in interstellar gases and stars. A tiny fraction of baryonic matter is found in planets, natural satellites, comets, asteroids, and other celestial objects
125
Baryonic Matter Definition
Matter that is made of atoms
126
What is the composition of the universe?
```
Dark matter — 25%
Dark Energy — 70%
Hydrogen and Helium gases — 4%
Stars — 0.5%
Neutrinos — 0.3%
Heavy Elements — 0.03%
```
127
What are examples of heavy elements in the universe?
Planets, just like Earth
128
What are neutrinos?
Neutrinos are electronically neutral particles, that have very little mass. They are created when nuclear particles collide. Neutrinos, hydrogen and helium gases, stars, and many heavy elements only make up 5% of our universe
129
What did astronomer Edwin Hubble do in 1929?
In 1929, the astronomer Edwin Hubble set out to measure the velocities of many galaxies. Edwin hypothesized that some galaxies would be moving away from us, while others would be moving toward us. However, to Edwin’s astonishment, he discovered that nearly all galaxies were moving away from us
130
Why are galaxies moving away from each other?
Since the universe is expanding
131
What do we know about dark matter through evidence?
Evidence shows that dark matter does not emit or absorb light, which is why it is invisible to human eyes. WMAP’s measurements show that the gravity of dark matter pulls baryonic matter into galaxies and galaxy clusters
132
What is dark energy thought to do and be?
Dark energy is thought to be the force behind the acceleration of the universe’s expansion
133
What are all the galaxies’ classifications?
A group contains about 50 or fewer galaxies, and a cluster contains 50 to 1,000 galaxies. Next are super-clusters, which are made up of solitary galaxies, groups, and clusters. Even larger are walls, sheets, and filaments of galaxies. Between the filaments are voids, large expanses of nearly empty space, populated by a few galaxies
134
What composes up most of the 5% of baryonic matter in the universe?
Interstellar gases compose most of the 5% of baryonic matter in the universe. The vast majority of these gases are hydrogen (including deuterium, an isotope of hydrogen) and helium, created by the Big Bang
135
How can astronomers find out which elements are present in stars?
By studying the electromagnetic spectrum it emits
136
What is the process of fusion like in stars?
Hydrogen —> Helium —> . . . Carbon —> Oxygen —> . . . Iron —> Supernova
137
How does the nuclear fusion of hydrogen to form helium work in stars?
Deuterium 2/1 H + Deuterium 2/1 H = helium 4/2 He + energy
138
What do we know about neutrinos?
Neutrinos have almost no mass, are electrically neutral, and travel at nearly the speed of light. They are formed during nuclear fusion in stars and interact only weakly with other particles. WMAP found evidence that neutrinos are abundant in the universe. They easily pass through nearly any kind of matter without harming or changing the matter at all. In fact, 100 million neutrinos pass through a human body every second. As they pass through matter, neutrinos form charged particles
139
What is the debate over neutrinos?
Some scientists that that the evidence collected by WMAP and by other sources, including the Ice Cube Neutrino Observatory in Antarctica, points to neutrinos being baryonic matter. Other scientists think that some dark matter is most likely composed of neutrinos. Still, others think neutrinos are neither baryonic matter nor dark matter, but a separate material. Scientists need more data in order to accurately classify neutrinos
140
How has technology enriched our knowledge on galaxy evolution?
Incredible technology allows astronomers to study distant galaxies by peeking back in time across a billion light years. Astronomers have learned that galaxies form initially from a starting point. The two theories of galaxy birth propose that galaxies either form from the merger of existing clumps of matter or from the collapse of gas and dust clouds. Either way, gravitational pull draws together the matter, forming new galaxies.
141
What happens to galaxies after formation? What happens as galaxies get more massive? Collisions?
Galaxies continue to grow, and their increased mass creates greater gravitational pull. This force in turn continues to draw in other matter surrounding a galaxy. One effect of gravitational attraction is galaxies merging with each other, forming groups and clusters. These mergers or collisions become more and more common as galaxies gain mass. A huge galaxy is most likely to draw in and consume smaller galaxies, especially those close to it. These mergers occur incredibly slowly, taking place over a few hundred million to a few billion years.
142
What happens at a galaxy’s death?
Galaxies eventually go through processes considered signs of galactic death. Over billions of years, galaxies deplete their gas and dust supply and stop forming stars. This marks a form of galaxy death. The image shows what the Milky Way (left) might look like compared to a dead spiral galaxy (right). Although it is smaller, the dead galaxy has three times the mass of the Milky Way. It is spinning twice as fast as the Milky Way, and its color shows no new star formation.
143
Why do scientists build neutrino observatories underground?
Neutrinos are formed when supernovas explode, when stars form, and when stars collide. They are also formed when nuclear bombs explode and in the reactions at nuclear power stations and particle accelerators. In order to study them, scientists had to find a way to distinguish them from the subatomic particles of cosmic rays. Because cosmic rays do not penetrate Earth’s surface, scientists have built IceCube and other observatories underground.
144
What does the IceCube Neutrino Observatory consist of?
The collaboration involves about 300 physicists from 12 countries. The observatory has IceTop, an aboveground component, as well as DeepCore, an underground component with hundreds of neutrino detectors inside a cubic kilometer of clear ice. The 5,160 digital optical modules in the ice detect the light emitted when charged particles crash into protons or neutrons in ice atoms. IceCube detects neutrinos that
are formed in extremely violent natural events, rather than at manmade events.
145
Why are neutrinos important?
Scientists find neutrinos useful because they aren’t changed in any way by the matter they pass through. They travel in straight lines and aren’t deflected by magnetic fields. Because of this, they can reveal much about how they were formed and the processes that formed them. Because most neutrinos were formed shortly after the Big Bang, they might carry important information about the beginning of the universe. Scientists hope that studying neutrinos might reveal fundamental information about dark matter and dark energy.
146
What are the three types of neutrinos?
In their research to date, scientists have discovered three types of neutrinos: ve, vμ, and vT. Each type of
neutrino relates to a type of charged particle. The ve neutrinos relate to electrons (e). The vμ neutrinos relate to muons (μ). The vT neutrinos relate to taus (T).
147
What are ways that galaxies are always in motion?
Galaxies are always in motion. They rotate around a center, usually a black hole, and speed through space
148
How fast does the Milky Way rotate around its center? How long does it take the Milky Way to complete on revolution?
The Milky Way Galaxy rotates around its center at more than 500,000 mph, taking 250 million years to complete just one revolution
149
What do galaxies do as they spin?
As they spin, galaxies also move through the universe. The Milky Way travels with a group of companion galaxies called the Local Group. The Milky Way is speeding toward the center of this small galactic group at about 25 miles per second—while the whole Local Group speeds toward a group of galaxies named the Virgo Cluster at about 375 miles per second
150
Do galaxies collide frequently?
Galaxies do not frequently collide because the universe is vast and there is so much space between galaxies that they usually remain a far distance from each other
151
What is the first way galaxies may react if they collide?
When galaxies meet, gravitational effects that result can pull stars into new paths. At times, one galaxy will tear the other apart, flinging gas, dust, and even stars out of place
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What is the second way galaxies may react if they collide?
There is a period of chaos, but eventually a new, stable galaxy is formed. When the two galaxies become one, black holes at the centers of the galaxies also merge and become larger. The process does not happen quickly. It takes hundreds of millions of years
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What is the third way galaxies may react if they collide?
When galaxies meet, they do not always merge or get pulled apart. They can also survive intact. There are several “dwarf galaxies” orbiting the Milky Way. Astronomers have studied the orbit of the Sagittarius Dwarf Galaxy, and they believe it has collided with the Milky Way several times in the past. Yet each time, it has emerged intact
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Dwarf Galaxy Definition
Small, dim galaxy of a few billion stars
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What happens when two stable galaxies collide?
When two stable galaxies collide, changes that the galaxies undergo make the galaxies unstable. However, over time, forces again become balanced, and the product of the collision becomes stable again
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What do we know about the future collision of the Milky Way and the Andromeda Galaxy?
Astronomers predict a very important galaxy collision about 4.5 billion years with the Milky Way Galaxy and the Andromeda Galaxy, but it will be more of a sideswipe than a straight-on collision. The collision will not happen quickly, taking millions of years
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How do the astronomers know the Milky Way and the Andromeda Galaxy will collide?
Astronomers know the galaxies will collide since they have been observing and measuring the movement of Andromeda carefully, first through the Hubble Space Telescope and then through the Gaia Space observatory. The data they collected and analyzed using computer simulations confirmed that Andromeda is moving toward the Milky Way at a speed of about 68 miles per second
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True or False: the collision of galaxies can cause stars to form
True
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What will happen when the Milky Way and Andromeda Galaxies collide?
Andromeda is now 2.5 million light years away from the Milky Way. Although both galaxies are speeding toward each other in space, they won’t meet for another four billion years. It will take an additional two billion years for the two spiral galaxies to merge into a new galaxy. The stars in each galaxy will not smash into each other. There is so much space between them that few, if any, will be destroyed. But the gravity of both galaxies will push and pull stars, gas, and dust out of their present positions. In time, all of the objects in both galaxies will organize themselves into a new elliptical galaxy. The stars will have new orbits around the new galaxy center. Computer simulations of the collision show that our solar system will end up farther toward the edge of the new galaxy than it currently is in the Milky Way.
