Spiral Arms & Galactic Center
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Size of the Milky Way
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The disk of the Milky Way galaxy is about 100,000 light years in diameter (one light year is about 9.5 x 1015 meters), but only about 1000 light years thick
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Number of Stars in the Milky Way
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200 billion stars
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How long does it take the sun to go around the Milky Way once?
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230 million years
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What are the shapes and regions of the Milky Way?
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Halo, Disk, Bulge
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Halo
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Contains Globular clusters, is spherical in shape, contains pop. II stars and very little interstellar gas and dust.
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Shapely used what to determine the size and position of the center of the Milky Way?
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Globular Clusters
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Density wave theory for spiral arm formation
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The spiral arms are regions where the gas and dust are slightly denser so when objects move slowly in it they get compressed like a traffic jam (stars are like the cars) the traffic jam will be there but they are different cars
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Self-Propagating star formation for spiral arm formation
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Need a gas cloud that starts to collapse on itself. SuperNova explosion causes the next supernova to form
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Pop I star
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Young stars, typically bright blue and in the disk. Around interstellar gas and dust. Formed relatively recently.
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Pop II star
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population of older stars, yellow and red, like globular clusters, with low metals, very little gas and dust.
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Elliptical galaxy
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A galaxy shaped like a round or flattened ball, generally containing only old stars. stars are distributed in an elliptical shape. pop II stars, hardly any gas or dust, smooth and elliptical in appearance, no disk, old stars only.
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Spiral/Barred Galaxy
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spiral galaxy in which a bar of material passes through the center of the galaxy, with the spiral arms beginning near the ends of the bar.
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Irregular Galaxy
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A galaxy that does not have a regular shape to fit Hubble's classification scheme. Pop I stars, young blue stars, gas and dust, galaxies in collision, no definite structure.
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Rich Cluster
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Contains thousands of individual galaxies
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Poor clusters
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loosely held together, local group
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Local group
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a new level of structure in the universe above the scale of our galaxy
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Virgo Cluster
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The closest cluster of galaxies to our local cluster. Contains roughly 2000 galaxies.
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'Rungs' in the Distance Ladder
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1. The radius of the Earth 2. Size, shape, and location of the moon 3. Size and location of the sun 4. Distances from the Sun to the planets 5. The speed of light 6. Distance to nearby stars 7. Distance to moderately distant stars 8. Distances to very distant stars 9. The shape of the universe
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Planck Epoch
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A mystery partly because we lack a quantum theory of gravity.
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The Grand Unification Epoch
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Forces except gravity are unified
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The inflationary Epoch
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Universe expands rapidly smaller than a proton to bigger than a melon - Supported experimentally
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Electroweak epoch
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Weak and electromagnetic forces act as one.
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The Quark, Hadron, and Lepton Epoch
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What we think of a "normal" elementary particle form and survive.
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Protons, Nucleosynthesis and the Cosmic Background Radiation
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Atoms form (Hydrogen and Helium) and Cosmic Background radiation 'decouples' form matter.
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Dark Ages
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Atoms exists but stars don't.
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"Modern" Era
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Stars form - Quantum fluctuations at the time of inflation determines the distribution of matter in the universe. Denser areas are where stars will form. Gravity is the major large-scale force
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Solar System
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Radar ranging
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Nearby Stars
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Parallax
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Milky Way
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Main-sequence fitting
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Nearby Galaxies
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Cepheids
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Galaxy Clusters
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White Dwarf Supernovae
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Tully-Fisher relation
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Distant standards
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Why are infrared and radio telescopes the instruments of choice for studying the galactic center?
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Dust in the plane of the Milky Way obscures observations at other wavelengths.
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Globular clusters trace out the structure of the Galactic disk. T/F
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False
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The Galactic halo contains as much gas and dust as the disk. T/F
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False
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Herschel's attempt to map the Milky Way by counting stars led to an inaccurate estimate of the Galaxy's size because he was unaware of absorption by interstellar dust. T/F
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True
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Cepheid variables can be used to determine the distances to the nearest galaxies. T/F
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True
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The Galactic halo contains only old stars. T/F
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True
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Stars and gas in the Galactic disk move in roughly circular orbits around the Galactic center. T/F
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True
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A telescope searching for newly formed stars would make the most discoveries if it were pointed
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Within a spiral arm
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What did a major discovery made by Harlow Shapley using RR Lyrae stars and globular clusters establish?
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The size of the Galaxy an the Sun's position in it.
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Which of the following is NOT a difference between the disk and the halo of the Galaxy?
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The halo population stars are primarily red in color, and there are no red stars in the disk.
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Which of the following best compares the motion of stars in the halo to the motion of the stars in the disk of the Galaxy?
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The stars in the halo move in randomly-oriented orbits, while the disk stars generally stay confined to moving in the disk.
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Which is the oldest component of the Galaxy?
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the halo
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Which type of star is common in the spiral arms of our Galaxy, and found almost nowhere else?
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High-mass O and B stars
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What effect does a spiral density wave have on the material it encounters?
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It slows the material down, causing it to compress and heat up, assisting gravity in forming stars.
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The orbit of the Solar System around the Galaxy is similar to that of a planet, almost circular and in the galactic plane. T/F
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True
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Most galaxies are spirals like the Milky Way. T/F
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False
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Most elliptical galaxies contain only young stars.T/F
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False
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Which of the following types of galaxies has experienced no significant star formation during the last 10 billion years?
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Elliptical
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Which of the following statements describes the orbits of stars within most elliptical galaxies?
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They have random orbits in three dimensions.
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Which type of galaxy exhibits the largest range of sizes and masses?
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elliptical
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Which of these standard candles has been used to determine distances to the most distant galaxies?
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Type I supernovae
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What is the criterion for a group of galaxies to be considered a cluster?
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Galaxies in a cluster are bound together by their mutual gravitational pull.
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Compared to the spirals, elliptical galaxies tend to be more dusty. T/F
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False
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Unlike spirals, elliptical galaxies do not contain a flattened disk. T/F
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True
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Most galaxies are spirals. T/F
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False
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Irr II galaxies may be the result of a collision, or close encounter, of two normal galaxies. T/F
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True
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Irregulars typically have very few blue stars. T/F
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False
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On average, elliptical galaxies are richer star forming regions than spirals. T/F
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False
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Irregular galaxies, although small, have large star-forming (HII) regions and much ongoing star formation for their size. T/F
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True
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M31 in Andromeda is a bigger version of our Galaxy, and the largest member of the Local Group. T/F
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True
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Which property is common to spiral galaxies?
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ongoing star formation and emission nebula in the arms
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The astronomer who originally classified galaxies into S, E, and Irr was
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Edwin Hubble.
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Compared to our own Galaxy, elliptical galaxies
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show no evidence of ongoing star formation.
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A galaxy with little cool gas or dust and no evidence of ongoing star formation is most likely a(n)
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Elliptical
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Which of the following is not one of Hubble's types of galaxies?
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Seyfert spirals
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Which of these would be made up of only Population II stars?
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elliptical galaxies
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DL: Solar System
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Radar Ranging
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DL: Nearby Stars
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Parallax
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DL: Milky Way
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Main-Sequence Fitting
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DL: Nearby Galaxies
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Cepheids
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DL: Galaxy Clusters
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Tully - Fisher Relation; distant standards
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DL: Further out
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Hubble's Law
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1. Planck Epoch
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A mystery partly because we lack a quantum theory of gravity
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2. The Grand Unification Epoch
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Forces except gravity are unified
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3. The Inflationary Epoch
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Universe expands rapidly smaller than a proton to bigger then a melon - supported experimentally
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4. Electroweak Epoch
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Weak and electromagnetic forces act as one
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5. The Quark, Hadron, and Lepton Epoch
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What we think of as "normal" elementary particle form and survive
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6. Photons, Nucleosynthesis and the Cosmic Background Radiation
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Atoms form (Hydrogen and Helium) and Cosmic Background Radiation 'decouples' from matter
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7. Dark Ages
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Atoms exist but stars don't
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8. Modern Era
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Stars form. Quantum fluctuations at the time of inflation determines the distribution of matter in the universe. Denser areas are where stars will form. Gravity is the major large-scale force.
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MW: Size
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100 thousand light years across
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MW: Stars
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200 billion stars
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MW: Sun's position
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2/3rds of the way out from the center (takes 230 million years for the sun to orbit the MW
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MW: Type of Galaxy
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Barred Spiral
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Galactic Disk
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flattened shape, spiral arms, both pop I and pop II stars, interstellar dust and gas, pop I stars associated with spiral arms
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Self Propagating Stars
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going super nova to make the next generation of stars
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Pop I
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contain young bright and blue stars; young lives; surrounded by interstellar dust
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Pop II
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older stars, long life, little gas and dust in the area
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Elliptical Galaxy
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random shaped
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Spiral Galaxy/ Barred Spiral Galaxy
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flat mix (Pop I) irregular in shape; mainly galaxies in collision
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Clusters
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where galaxies reside; MW is in the "local group" (a poor cluster); Rich clusters: Virgo cluster- big, a lot going on, giant elliptical galaxies
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How many stars are there in the milky way?
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200 billion
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Size of the milky way
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About 100,000 light years across
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What is the sun's position in the milky way?
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In the disk, about 2/3 out from the center
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How long does it take for the sun to go around the milky way once?
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230 million years
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What is the shape of the milky way?
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spiral galaxy
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Disk
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- flattened shape, spiral arms (pop I) - both population I and population II stars - interstellar gas and dust
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Bulge
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- center of the galaxy - football shape - population II stars - little gas and dust - supermassive black hole at the center
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Density Wave Theory
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traffic jam; cars = stars; stars move to denser regions; in and out, but spiral arm remains; young stars
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Self-propagating star formation
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one generation dies, new ones come; waves of stars; requires supernova explosions
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Population I Stars
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contain young stars, all colors including blue gas and dust present
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Population II Stars
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older stars, yellows and reds in color very little gas and dust
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Shapely methods
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globular clusters contain millions of stars, can be spotted at large distances and can help determine edge and center of galaxy
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Elliptical Galaxy
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population II stars low star formation, globular clusters, little gas or dust old stars, radial star motion
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Spiral Galaxy
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mix of stars halo, bulge, galactic disk
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Irregular Galaxy
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largest percentage of population I and gas and dust other galaxies colliding with each other low mass high gas content and high star formation
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Rich Clusters
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hundreds to thousands of galaxies large gravitational pull
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Poor Clusters
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only a handful of galaxies, low mass, irregular in shape
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Local Group
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poor cluster milky way galaxy is a part of
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Virgo Cluster
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closest rich cluster to us hundreds of galaxies irregular shape large gravitational pull
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Solar system
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radar ranging
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Nearby stars
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parallax
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Milky way
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main sequence fitting
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Nearby galaxies
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Cepheids
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Galaxy clusters
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tully fisher distant standards
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Farthest objects
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Hubble's law
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Planck Epoch
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A mystery partly because we lack a quantum theory of gravity
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The Grand Unification Epoch
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Forces except gravity are unified
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The inflationary Epoch
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Universe expands rapidly smaller than a proton to bigger than a melon - Supported experimentally
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Electroweak epoch
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Weak and electromagnetic forces act as one
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The Quark, Hadron and Lepton Epoch
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What we think of a "normal" elementary particle form and survive
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Photons, Nucleosynthesis and the Cosmic Background Radiation
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Atoms form (Hydrogen and Helium) and Cosmic Background radiation ' decouples ' from matter
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Dark Ages
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Atoms exists but stars don't
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"Modern" Era
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Stars form - Quantum fluctuations at the time of inflation determines the distribution of matter in the universe. Denser areas are where stars will form. Gravity is the major large-scale force
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what is our galaxy?
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the milky way
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what is the size of the milky way (in light years)?
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100,000 light years
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how many stars are in the milky way?
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hundreds of billions (200 billion)
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what is the sun's position in relation to the milky way?
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about 8kpc from center (in the disk, 2/3 of the way out from center)
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what is the shape of the milky way?
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barred spiral
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what is a barred spiral shape?
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spiral galaxy with a central bar shape
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what are the three regions of the milky way?
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bulge, disk, and halo
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what are the characteristics of a bulge?
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center of galaxy, supermassive black hole at center, football shape, population II stars, little gas/dust
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what are the characteristics of a disk?
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flat, spiral arms, population I and II stars, interstellar gas/dust
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what are the characteristics of a halo?
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spherical, globular clusters, population II stars, little gas/dust
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what is an elliptical galaxy
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3 dimensional, football shaped, very little gas and dust,
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population I stars
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young, bright blue, short lifetime stars
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population II stars
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older, yellow and red, long lifetime stars
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what kind of galaxy is made up of mainly population I stars?
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irregular
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what is used to measure distance to nearby stars?
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parallax
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a galaxy with very little or no interstellar gas and dust is _________
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elliptical
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how many years does it take the sun to orbit the milky way?
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230 million
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how do you determine position, or distance of the milky way?
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main sequence fitting
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what is density?
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a measure of compactness
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what could be considered similar to a traffic jam?
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density wave theory
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what is the density wave theory?
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the stars move to denser regions but the spiral arms remain (greater mass density and increased pressure)
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what is the self propagating star formation theory?
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creation & explosion of stars can create waves to trigger next round of star formation (possible spiral structure cause)
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what is a spiral arm?
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a distribution of material in a pinwheel shape design
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where does a spiral arm originate?
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the galaxy's center
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what kind of star can you associate a spiral arm with?
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population I
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what are the three types of galaxies?
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elliptical, spiral, irregular
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what kind of stars do elliptical galaxies have a lot of?
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yellow pop II
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what kind of stars do irregular galaxies have?
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young blue stars
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what kind of galaxy has a lot of gas/dust?
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irregular
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what kind of galaxy has a dense nucleus?
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spiral
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what kind of galaxy has a flattened disk?
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spiral (also has spiral arms)
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what kind of galaxy has spiral arms?
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spiral
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what kind of galaxy has an extended halo?
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spiral
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what kind of galaxy exhibits a large range of sizes/masses?
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elliptical
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what kind of galaxy has a lot of star production?
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irregular
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T/F elliptical galaxies contain a lot of old stars
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true
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T/F irregular galaxies are big
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false
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what kind of cluster has a lot of galaxies in it?
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rich
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what kind of cluster doesn't have as many galaxies in it?
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poor
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what kind of cluster has fewer galaxies because it has lower mass?
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poor
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what kind of cluster tends to be more irregularly shaped?
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poor
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what is the closest cluster to us?
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virgo
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what is the local group cluster?
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cluster that contains milky way
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what makes up the space between galaxies in a cluster?
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hot gas & dark matter
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what is the first rung on the distance ladder?
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radius of the earth
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what is the second rung on the distance ladder?
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moon
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what is the third rung on the distance ladder?
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sun
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what is the fourth rung on the distance ladder?
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distance between sun and planets
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what is the fifth rung on the distance ladder?
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speed of light
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what is the sixth rung on the distance ladder?
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distance between stars
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what is the seventh rung on the distance ladder?
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distance between moderately distant stars
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what is the eighth rung on the distance ladder?
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distance between very distant stars
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what is the ninth rung on the distance ladder?
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shape of the universe
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what was the distance ladder created for?
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relate distances on a variety of scales
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what is the oldest component of a galaxy?
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halo
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what epoch came first in the big bang?
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planck epoch
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what happened in the grand unification epoch?
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forces were unified
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what happened in the inflationary epoch?
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expansion. size of a proton -> size of a melon
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was the inflationary epoch proven?
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yes
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what was the electroweak epoch?
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weak and electromagnetic forces acting as one
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what was the dark ages?
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when atoms existed but stars did not
