Test 4 Flashcards
Why can we see a band of milky white clouds as part of the Milky Way?
We’re inside the galaxy’s pancake shape.
The Milky Way is a collection of ___#___ stars in a _____ shape.
a few hundred billion stars; pancake
What is the closest spiral galaxy to the Milky Way? How far away is it?
Andromeda; 2 million light years
What is the diameter of a typical galaxy?
100,000 light years
How many miles is a light year equal to?
6 trillion
What did William Hershall do?
He was an astronomer who tried to estimate where we are in the galaxy and its size.
How did Hershall attempt to measure the galaxy?
Star counts
What was Hershall’s conclusion?
The Milky Way isn’t very big and we are in the center.
star counts
Count stars to estimate distance
Ex. If a galaxy were to measure 10 stars by 1000 stars, it would extend farther to the right.
What did Harlow Shapley do?
He was an astronomer who counted globular clusters (rather than individual stars) to measure the galaxy.
What did Henrietta Levitt do?
She was a Harvard computer in the early 20th century. She discovered that cepheid variable stars have a relationship between luminosity and period.
Cepheid variable stars burn ____ in the core.
Helium
Define period of a variable star.
Time it takes to go bright, faint, then bright again
Luminosity allows us to find ____.
Distance
What did Shapley mistakenly study?
RR Lyrae Stars
What are the 5 parts of the Milky Way galaxy?
Nucleus, dust, gas lanes, disc, halo
Our galaxy used to be ____, but ___ ___ ___ happened.
spherical; Pizza Dough Physics
Where in the galaxy is the Sun located?
About 2/3 of the way between the center and the edge
How do we know how many stars are in the Milky Way?
Measure speed and orbital period.
1- Use Kepler’s Laws
2- Assume Sun is average mass
Formula: Mass of galaxy divided by mass of Sun
The galaxy is ____ massive than we thought.
more
Recent evidence suggests the Milky Way is a ____ spiral galaxy.
barred
How do we know the Milky Way has a spiral arm structure?
using H emitted radio waves, astronomers mapped it out
Which goes through dust easier: optical light or radio waves?
Radio waves
Spiral arms emit ____.
radio waves
Space between stars is filled with ___.
Hydrogen
What is the length of a radio wave emitted by H?
21 cm
H atoms in the ___ ___ of the galaxy emit ___ ___.
spiral arms; radio waves
Where does the Spiral Density Wave come from?
Center of Milky Way
What is the Spiral Density Wave’s pattern?
Compressed, spread out, compressed, etc.
What is Sagittarius A?
First radio source discovered in Sagittarius constellation
Sagittarius A is very ____.
bright
What is Sagittarius B?
Second radio source discovered in Sagittarius constellation
What drives the Spiral Density Wave?
No one knows
Why do we get radio waves coming from the center of the galaxy?
Magnetic field; Synchrotron Radiation
The most energetic source in the core of the Milky Way is the size of a ____ ____.
solar system
What do we suspect is spinning at the Milky Way’s core?
Super massive black hole
What makes a black hole super massive?
Small black holes merge
Who proved there were other galaxies?
Edwin Hubble
What is Extra-Galactic Astronomy?
Study of astronomy outside of the Milky Way
Edwin Hubble proved that the universe is ____.
expanding
Where did Edwin Hubble make his observations?
Telescope on Mt. Wilson
Who was Hubble’s assistant?
Milton Humison
Who discovered the Andromeda Galaxy? How?
Hubble; He found cepheid variable stars and figured out the period, luminosity, and distance. The distance is longer than the Milky Way’s diameter, proving it’s a galaxy outside of ours.
How far away is Andromeda?
2 million light years
What is the Milky Way’s approximate diameter?
100,000 light years
Hubble classified galaxies based on ____.
appearance
What are Hubble’s 2 broad categories for galaxies?
Elliptical & Spiral
There are ____ and Giant Elliptical galaxies.
dwarf
How many types of Elliptical galaxies are there? How do they vary?
8 (E0-E7). E0 is spherical like a basketball. E7 is elongated like a football.
What are the 2 types if spiral galaxies?
Normal/Ordinary (S or SA) and Barred (SB)
What is an S0 galaxy?
S0 galaxies are an intermediate type of galaxy between E7 and a “true” spiral Sa. They differ from ellipticals because they have a bulge and a thin disk, but are different from Sa because they have no spiral structure. S0 galaxies are also known as Lenticular galaxies.
What are the 3 components of a spiral galaxy?
Nucleus, disc, halo
Describe an Sa galaxy.
Spirals compressed, tightly wound around nucleus
Describe an S0 galaxy.
Disc with no spirals
Describe an Sc galaxy.
Spirals spread out, loosely wound
An Sb galaxy is characteristically between ___ and ___.
Sa, Sc
Galactic Cannibalism
how galaxies accrete mass; merging with other galaxies
Hubble’s Classes: Irregulars
galaxies that don’t fit any of Hubble’s classes; no shape
Hubble’s Classes: pec
peculiar; a galaxy that doesn’t perfectly fit a class
What are the 6 main properties of galaxies?
diameter, mass, luminosity, color, percentage of gas content, types of stars
How does a Giant Elliptical galaxy compare to the Milky Way?
bigger, brighter, more massive
How does a Dwarf Elliptical galaxy compare to the Milky Way?
smaller, less massive, fainter
What color is a sample of old stars?
Red
Describe the stars in an Irregular Galaxy.
young, blue, high percentage of gas
What color is a sample of young stars?
blue
What type of stars does an Elliptical Galaxy have?
old, red
What type of stars does a Spiral Galaxy, like the Milky Way, have?
mix of old and new, mix of red and blue
Elliptical Galaxies tend to be ___ with ___ gas content. They ___(are/ are not)___ forming new stars and appear ___ in color.
Elliptical Galaxies tend to be old with very little gas content. They are not forming new stars and appear red in color.
A cepheid variable star is a ___ indicator, sometimes called a ___.
distance; candle
The further away a galaxy is, the ___ it appears to be moving away from us.
faster
The Sun and similar stars can produce an HNK spectral line from ____.
Calcium
When did Hubble discover the universe was expanding?
1930s
What other scientist predicted the universe’s expansion before Hubble? Why isn’t he credited with the discovery?
Einstein, Theory of General Relativity in 1915; he didn’t believe it, so he altered the data to disprove expansion, he later admitted his mistake
What is the Local Group?
group of spiral galaxies (and some dwarf ellipticals) including the Milky Way, Andromeda, M-33, and others
What is the approximate diameter of our Local Supercluster?
130 million light years
What are the empty spaces between superclusters called?
voids
Active Galaxies use up a lot of ___.
energy
Where is the activity in an Active Galaxy usually located?
nucleus, Active Galactic Nuclei (AGN)
Quasars are a type of ____ ____.
Active Galaxy
Quasars emit huge amounts of ___.
radiowaves
What was the first Quasar discovered named? Where was it discovered?
3C 273; Cambridge
jet
material shot from the center of a galaxy
3C 273 is very ____ when viewed via radio wavelengths and emits huge amounts of ____.
bright; radiowaves
Ordinary stars are bright when viewed via ____ ___.
visible light
What is ‘Quasar’ short for?
Quasi-Stellar Radio Source
Most stars have ____ line spectrum, but 3C 273 has ___ line spectra.
absorption; emission
Why didn’t the emission lines from 3C 273 match any known element?
It was H with the largest redshift ever observed.
Why did H in 3C 273 have such a large redshift?
3C 273 is moving away very fast and is located very far away
What are the 8 characteristics of Quasars?
1- emit large amounts of radiowaves
2- very bright when observed through radio wavelengths
3- emission line spectrum
4- emission lines for H with the largest redshift ever observed
5- farthest objects in the universe
6- moving away from us very fast
7- incredibly luminous and energetic
8- vary in brightness significantly on various timescales
About how far away is a Quasar?
3 - 5 billion light years
Quasars are the most ____ and ___ things in the universe.
luminous; energetic
The energy output of a typical Quasar is comparable to ____ supernovas.
10,000
3C 273 varies in brightness on a timescale of approximately a few ___.
months
3C 273 is a ___(tame/wild)___ Quasar.
tame
What is the max size of a Quasar like 3C 273?
about a light month
Wilder Quasars will vary in brightness on timescales of about a ___. Their max size is about one light ___.
day; day
Quasars have extremely bright ___.
nuclei
What is the big mystery of Quasars and AGNs?
How do you get so much energy in such a small volume of space?
What is the most reasonable theory for the Quasar/AGN mystery?
Rotating Supermassive Black Holes are at the center. Objects could pick up the black hole’s energy in the ergosphere. The objects are then shot out (like a slingshot), explaining jets.
Galaxies near the Milky Way have settled down and may have ___ ___ ___ ___ in their centers. Why have they settled down?
rotating supermassive black holes; the black hole’s spinning has slowed down over time
If both Quasars/AGNs and regular galaxies have rotating supermassive black holes, what does that mean for Quasars/AGNs?
They will eventually settle down to form regular galaxies as the rotating slows.
What type of galaxy is M-87?
giant elliptical galaxy
M-87 is not a Quasar, but it is very ___. It has a ___ on one side and a ___ on the other, suggesting that the galaxy is orbiting its ___.
M-87 is not a Quasar, but it is very active. It has a redshift on one side and a blueshift on the other, suggesting that the galaxy is orbiting its nucleus.
Astronomers can use orbits like that of M-87 to determine ____.
distance (and other things)
M-87 has helped astronomers assume that galaxies ___ ___ as they get older.
settle down
What are the 2 major 20th century theories for the origin of the universe?
Big Bang Theory, Steady State Theory
What are the two sub-theories under the Big Bang Theory?
Closed Big Bang and Open Big Bang
What does the Big Bang Theory suggest?
there was a primeval fireball, the entire universe was compressed into a geometric point until it started expanding (raisin bread analogy)
What does the Open Big Bang Theory suggest?
the universe will continue expanding
What does the Closed Big Bang Theory suggest?
the fireball will expand to its max, then mass will cause it to collapse in on itself; this could end the universe
What is the sub-theory under the Closed Big Bang Theory? What does it suggest?
Oscillating Big Bang; it’s a cycle, the universe will expand -> collapse -> expand
What does the Steady State Theory suggest?
the universe (the average density or average distance between galaxies) does not change but the universe will continue expanding; H atoms will appear out of nothing every 500 million years, slowly forming new galaxies to keep the average distance between galaxies the same
Newton’s Infinite Static Universe
in any direction, if you go far enough, you will find a star
What is Olber’s Paradox?
If Newton’s Infinite Static Universe is true, how can the night sky be dark? It should be bright like the surface of a star.
The rate at which the universe is expanding is ___. When was this discovered?
increasing; the 1990s
Who discovered the Cosmic Background Spectrum? When?
Penzias and Wilson in the mid 1960s
How did Penzias and Wilson discover the Cosmic Background Spectrum?
The designed an antenna meant to minimize background noise (static). There was one bit of noise they couldn’t locate or eliminate.
What is the significance of the Cosmic Background Spectrum?
It is incredibly strong evidence confirming the Big Bang Theory, by confirming predictions made by the Theory. It also disproved the Steady State Theory.
What is the Cosmic Background Spectrum?
microwaves; radiation left over from an early stage in the development of the universe; thermal radiation assumed to be left over from the “Big Bang” of cosmology
What does the Cosmic Background Spectrum mimic?
black body 3º above absolute zero
Why would the universe be emitting microwaves at 3º above absolute zero?
The Big Bang would have been hot at first, then cooled off to about 3º above absolute zero.
The Big Bang stage of the history of the universe was the point of ___.
formation
What are the 7 stages of the history of the universe?
1- Big Bang 2- Inflationary 3- Hadron 4- Lepton 5- Radiation 6- Matter 7- Present
What did the Inflationary stage in the history of the universe involve?
very rapid expansion in a very short amount of time
During the Hadron stage in the history of the universe, ____ and similar particles came to be. There was ____ radiation and ___.
protons; electromagnetic; energy
During the Lepton stage in the history of the universe, ____ and similar matter came to be. There was ____ radiation and ___.
electrons; electromagnetic; energy
During the Radiation stage in the history of the universe, the temperature ___, forming ___ stars. __ is converted into He. The universe is __% He.
During the Radiation stage in the history of the universe, the temperature cools, forming cool stars. H is converted into He. The universe is 25% He.
Matter stage of the history of the universe: Matter + Anti-Matter = ?
large release of energy equal to E=mc^2
Why isn’t the Matter + Anti-Matter process a perfectly symmetrical process?
there is more matter than anti-matter
What is converted to create Carbon?
He
Why wasn’t Carbon formed prior to the present?
the universe was too cool to form C by the time He was formed
What is Hubble’s Law (2 observations)?
the observation that:
1- objects observed in deep space have a Doppler shift (redshift/blueshift), meaning they are moving away from Earth at a relative velocity
2- this Doppler-shift-measured velocity is approximately proportional to the objects’ distance from the Earth
What is the significance of Hubble’s Law?
It is a direct, physical observation of the expansion of the universe.
___ ___ are the brightest stars.
Red Giants
