Astronomy: Galaxies (Unit 4) Flashcards
What happens to the matter of a star after its lifecycle has ended?
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
What do modern telescopes allow us to do, that helps us evaluate matter in space?
They allow us to take pictures of accumulated matter in space
In space, what does accumulated matter form?
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
Nebulae Definition
Clouds of interstellar gas and dust
Who was Sir William Herschel? What is he credited for?
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
Who was Caroline Herschel?
Caroline Herschel was a brilliant astronomer who was also William Herschel’s sister
What is “Nebula” Latin for?
“Cloud”
True or False: Emission Nebulae give off their own light and are hot
True
When would the Herschel siblings comprehend the temperature of nebulae?
The Herschel siblings would not comprehend the temperature of nebulae until years later when William discovered infrared light
What is a stellar nursery?
A type of nebula that is in an area where stars are forming
How does a “Cat Eye Nebula” look like?
An elliptical nebula with a single, very bright star visible in the middle is a “Cat’s Eye Nebula”
How can you identify a nebula through its layers?
You can identify nebula by outer layers of gas expanding into space
What is the only situation that can cause a “Cat’s Eye Nebula” to form?
A “Cat’s Eye Nebula” can only form when a star dies
How is a planetary nebula formed?
Planetary nebulae is formed when a star runs out of power and blows of its outer layers
How can temperature help identify planetary nebulae?
A planetary nebula can be identified by the warm glow left behind by a star
How was the term “planetary nebula” coined? Why did Sir William Herschel name it this way?
The term “planetary nebulae” is actually a misnomer; William thought that these nebulae resembled round gas planets
What are some features of nebulae the Herschels observed?
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
What force results in the formation of nebulae?
Gravity
What happens in a nebula in which stars are born?
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
How does gravity form supernovas?
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
Gravity Definition
Force that pulls matter together
What is Interstellar Space often referred to as? Despite this, what allows nebulae to form?
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
How does the observability of nebulae differ from Earth?
Some nebulae can be seen from Earth with the naked eye, but many others can only be seen with modern telescopes
How could one explain the behavior and composition of nebulae?
There is a wide variety in the behavior and composition of nebulae, and one nebula can have areas with different characteristics
Vacuum Definition
Area with no matter
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
What is light?
Radiation energy we can see
True or False: Modern telescopes can “see” radiation energy not visible with our eyes
True
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
Electromagnetic Radiation Definition
Energy carried by oscillating magnetic and electrical fields
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
True or False: Nebulae usually have overlapping attributes
True
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
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
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
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
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
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
What are Supernova Remnants?
Supernova remnants are nebulae that remain after a supernova. These nebulae are identified by their powerful radio emissions
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
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
How are nebulae classified?
By composition
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
What are the components of a galaxy held together by?
The stars and other components of a galaxy are bound together by gravity
What do galaxies vary in?
Shape and size
Galaxy Definition
A large group of stars, dust, dark matter, and gas
True or False: Galaxies are far from the largest structures in the universe
True
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
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
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
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
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
What is the estimated diameter of the Milky Way?
100,000 light years
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
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
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
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
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
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
What are galaxy clusters composed of?
Galaxy clusters are configured of thousands of galaxies held together by gravitational pull
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
True or False: the efforts of many astronomers over hundreds of years conclude that galaxies are in fact not all alike
True
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
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