The study of galaxies is thus intimately connected with:
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Cosmology
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Cosmology
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The study of the structure and evolution of the universe
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Range of Galaxy Sizes:
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From dwarf galaxies containing 100 million stars to giant galaxies containing more than 1 trillion stars
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Spiral Galaxies
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Contain hot, bright stars
The O and B type stars are most prominent so gives it a bluish tint
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Components of Spiral Galaxies
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Disk, bulge and halo
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Two main subcategories of Spiral Galaxies
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Normal Spiral
Barred Spiral
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Elliptical Galaxies
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Don't have a disk component
Red-yellow color indicates older star population
Contains very little gas & dust, so little star birth
Red Dwarfs
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Irregular Galaxies
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Contains mixture of star groups
Contains large amount of gas & dust
Has a blue/white color that indicates ongoing star formation
Small, faint & hard to detect
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Most common type of galaxy in the universe
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Dwarf elliptical galaxies
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What type of galaxy was more common when the universe was younger?
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Irregular Galaxies
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Which of the following is not one of the three major categories of galaxies?
-spiral galaxies
-globular galaxies
-irregular galaxies
-elliptical galaxies
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Globular Galaxies
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A standard candle is _________
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A light source of known luminosity
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What is a Cepheid variable?
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A type of very luminous star that makes an excellent standard candle
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What two observable properties of a Cepheid variable are directly related to one another?
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The period between its peaks of brightness and its luminosity
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What does Hubble's law tell us?
-The longer the period of a Cepheid variable, the greater its luminosity.
-The more distant a galaxy, the faster it is moving away from us.
-For every force, there is an equal and opposite reaction force.
-The faster a spiral galaxy's rotation speed, the more luminous it is
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The more distant a galaxy, the faster it is moving away from us
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Given that white dwarf supernovae are such good standard candles, why don't we use them to measure the distance to all galaxies?
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They are rare events, so we have observed them in only a tiny fraction of all galaxies.
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When we use an analogy that represents the expanding universe with the surface of an expanding balloon, what does the inside of the balloon represent?
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The inside of the balloon does not represent any part of our universe
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If we say that a galaxy has a lookback time of 1 billion years, we mean that _______________.
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Its light traveled through space for 1 billion years to reach us
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The "boundary" of our observable universe is called _____________.
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The cosmological horizon
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Cosmological redshift is the result of _____________.
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The expansion of the universe
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Telescopes designed to study the earliest stages in galactic lives should be optimized for observations in _______________
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Infrared light
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Which of the following is an important starting assumption in models of galaxy formation?
-All galaxies start out as spiral galaxies.
-Some regions in the universe start out denser than others.
-Galaxies form first, then black holes.
-Black holes form first, seeding the formation of galaxies.
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Some regions in the universe start out denser than others
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Collisions between galaxies typically unfold over a period of _______________.
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Hundreds of millions of years
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Current understanding holds that a galaxy's type may either be the result of _______________.
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Conditions in the protogalactic cloud that formed it or the result of later interactions with other galaxies
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Why are collisions between galaxies more likely than collisions between stars within a galaxy?
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Relative to their sizes, galaxies are closer together than stars
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Which of the following features is not a feature of central dominant galaxies?
-They are thought to form by the merger of several smaller galaxies.
-They often have multiple galactic nuclei near their centers.
-They are often spiral galaxies.
-They're found in clusters of galaxies
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They are often spiral galaxies
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Why should galaxy collisions have been more common in the past than they are today?
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Galaxies were closer together in the past because the universe was smaller
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The distinguishing feature of a starburst galaxy is ______________.
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A rate of star formation that may be 100 or more times greater than that in the Milky Way
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The unusually bright centers found in some galaxies are called ____________.
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Active galactic nuclei
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According to current understanding, what is a quasar?
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An active galactic nucleus that is particularly bright
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The mass of a supermassive black hole thought to power a typical bright active galactic nucleus is roughly _____________.
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1 billion solar masses
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Magellanic Clouds
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Two small, low mass irregular galaxies that are about 50-60 kph away
Can only see them when in the southern hemisphere
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Nearly all galaxies are found in ___________
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Clusters
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Clusters
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Groups of galaxies that are gravitationally bound to each other
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Local Group
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The Milky Way and the Andromeda Galaxy belong to a small cluster of about 30 galaxies
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Rich (Large) Clusters
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Largest groups of galaxies (100 to 1,000 of member galaxies)
Large gravity puts galaxies into spherical distribution
Contain mainly elliptical galaxies
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Poor (Small) Clusters (Groups)
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Only a dozen or so members
Ragged, irregular look
Mostly spirals & irregular galaxies
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True/False
Galaxy Clusters form differently from star clusters
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True
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Near Clusters
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Members fairly smoothly spread out
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Far Way Clusters
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Younger clusters
More ragged looking
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How Galaxy clusters form
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Clusters form by galaxies attracting each other into groups
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Superclusters
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Groups of clusters
Have a irregular shape
Contain 1/2 dozen to several dozen galaxy clusters spread over 10 million to 100 million of light years
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The standard candles are usually....
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Cepheid variables, supergiant stars, planetary nebulas, white dwarf supernovas, etc
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Variable Star
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Stars that change brightness in a periodic way
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A Cepheid variable can be used as a ____________
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Standard Candle
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A Cepheid variable can be used to measure __________
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The distance to a star
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Cepheid variable stars are very _________
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Luminous
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Cosmological Redshift
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As universe is expanding the wavelength of a photon traveling through it is also expanding
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Cosmological Principle
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The universe looks about the same no matter where you are within it
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Which of these galaxies would you most likely find at the center of a large cluster of galaxies?
- a large spiral galaxy
- a large elliptical galaxy
- a small irregular galaxy
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A large elliptical galaxy
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Which kind of object is the best standard candle for measuring distances to extremely distant galaxies?
- a white dwarf
- a Cepheid variable star
- a white dwarf supernova
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A white dwarf supernova
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Which of these galaxies is most likely to be oldest?
- a galaxy in the Local Group
- a galaxy observed at a distance of 5 billion light-years
- a galaxy observed at a distance of 10 billion light-years
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A galaxy in the Local Group
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When we observe a distant galaxy whose photons have traveled for 10 billion years before reaching Earth, we are seeing that galaxy as it was when the universe was:
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4 billion years old
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Which of these items is a key assumption in our most successful models for galaxy formation?
- The distribution of matter was perfectly uniform early in time.
- Some regions of the universe were slightly denser than others.
- Galaxies formed around supermassive black holes.
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Some regions of the universe were slightly denser than others
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The luminosity of a quasar is generated in a region the size of
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The solar system
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Observations indicate that galaxies with more massive central black holes tend to also have
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A greater mass of stars in their central bulges
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The primary source of a quasar's energy is
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Gravitational Potential Energy
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Which distance measurement technique is most suited to measuring objects at a distance of 10 million light-years?
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Cepheids
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Which distance measurement technique is most suited to measuring objects at a distance of 10 light-years?
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Parallax
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Which is more likely to collide - stars or galaxies?
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Galaxies are much more likely to collide than the individual stars
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Colliding spiral galaxies may result in:
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Elliptical galaxies
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Only ______ percent of galaxies are in close pairs now
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7
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There were many more ____________ galaxies and fewer _____________ galaxies than there are now
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- Spiral
- Elliptical
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Galactic Cannibalism
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Small galaxy losing itself to a larger galaxy
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Starburst Galaxies
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Galaxies that are "presently" forming stars so quickly that they will use up all their gas in less than a billion years.
They are filled with molecular clouds
Need a radio telescope to see whats going on in the center
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Galaxy collisions can trigger:
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Star formation
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Ring Galaxies
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Produced by one galaxy passing roughly perpendicularly through the disk of a larger galaxy
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Active Galaxies
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Galaxies that emit huge amounts of radio, infrared, ultraviolet and x-ray radiation from nucleus
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Radio Galaxies
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Galaxies that emit as much as 10 million times more energy from center than most galaxies
Usually elliptical galaxies
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AGN
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Active galactic nuclei
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Most of the energy emitted by Active Galaxies is coming from...
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The center (nuclei)
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What percentage of galaxies are active?
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10%
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Hot Spots
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Formed from high-speed particles pushing into the intergalactic gas
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Seyfert Galaxies are similar to...
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Radio Galaxies
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Unresolved nucleus
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A nucleus that looks like a star
A small, brilliant nucleus that has a strange EM spectrum
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Active size of a Quasar is...
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Less than the size of the solar system
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Quasar & Radio Galaxies
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Both can have radio lobes
Both have AGN surrounded by donut shaped rings of dark molecular clouds
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What are the brightest young galaxies with the brightest nucleus?
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Quasars
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Rotation Curve
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Plots the rotational velocity of stars or gas clouds VS. their distance from the center of galaxy
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