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- no disk
- no spiral arms
- almost no gas, dust or new stars forming
- Usually have spiral arms, less or more prominent
- generally large amounts of gas and dust
- ongoing stellar formation
Irregular Shaped Galaxies
Gas, dust and star forming nebulae
Largest Elliptical galaxies are called ______ are how big, and smallest elliptical galaxies are called ______, and how big
- Giant, 5x bigger than Milky way
- Dwarf, 1% diameter of Milky way
Cosmological Distance Ladder from nearest to farthest
- Nearby Stars = Parallx
- Milky Way = Main Sequence Fitting
- Nearby Galaxies = Cepheids
- Galaxy Clusters = White Dwarf Supernovae, Tully Fisher relation
- Everything else = Hubble's Law
Apparent shift in a star's psition
Main Sequence Fitting
Apparent brightness of star cluster's main sequence tells us its distance
An object whose luminosity we can determine without measuring its distance
What are Standard Candles/Bulb's used for?
The measured apparent brightness of a Standard Candle can be used to determine its distance using the true luminosity and the inverse square law
How to get apparent brightness
Divide luminosity by area
Giant stars that pulse in size, temperature and luminosity over a regular period
Cepheid Variable stars with longer periods have
How to use Cepheid Variables to find distances
- 1. Measure period
- 2. Calculate Luminosity using period-Luminosity relationship
- 3. Measure apparent brightness (l)
- 4. Calculate distance from distance-luminosity relationship
Why are Supernovae Type Ia good standard candles?
- extremely bright
- easily detected, though rare
- uniform in brightness at maximum light
Entire galaxies can be used as standard candles because galaxy Luminosity is related to rotation speed.
What is Hubble's Law?
Relationship between a galaxy's velocity (redshift) and distance
What was Hubble's telescope built for and did Hubble build it?
- No, Hubble did not build it
- The telescope was made to pin down the line of best fit in Hubble's Law, ie the rate of universal expansion
What is the rotation curve method?
The most precise method for measuring the mass of a galaxy
What does the rotation curve method require knowing?
- true sizes of orbits of stars of gas clouds (thus distance of that galaxy)
- orbital speeds of the stars or gas clouds (using Doppler shift of spectral lines)
How much more dark matter is there than visible matter?
What is the evidence for Dark Matter in Spiral Galaxies?
Spiral Galaxies have flat rotation curves indicating large amounts of dark matter
Cosmology is... and is connected with...
the study of the structure and evolution of the universe and is connected with the study of galaxies
spiral galaxies are often found in
groups (< 50)
elliptical galaxies are much more common in
clusters (hundreds to thousands of galaxies)
How big is the Local Group? What galaxy does it contain?
Around 40 galaxies. Contains the Milky Way
In a group of galaxies like a cluster, the only important force acting between the galaxies is
velocities indicate what inside the cluster [of galaxies]
How much larger is the mass we find from galaxy motions in a cluster than the mass in stars?
Estimates of gravitational mass can be done most directly in what ways
- 1. Observing galaxies orbiting massive central elliptical galaxies
- 2. Gravitational Lensing
What are the possible solutions for the difference in observed and gravitational mass? Which do astronomers prefer and why?
- 1. Dark matter really exists and we are observing the effects of its gravitational attraction
- 2. Something is wrong with our understanding of gravity, causing us to mistakenly infer the existence of dark matter
Because gravity is so well tested, most astronomers prefer the dark matter explanation.
Ordinary matter is made up of what and called
- protons and neutrons
- baryonic matter
Nonbaryonic matter is what?
extraordinary matter or dark matter
What are MACHOs and where are they found
- Ordinary dark matter
- Massive Compact Halo Objects: dead or failed stars in halos of galaxies
What are WIMPs?
- Extraordinary dark matter
- Weakly Interacting Massive Particles: mysterious neutrino-like particles
MACHOs or WIMPs
WIMPs are the best bet. There is too little evidence of MACHOs
What do many nearby galaxies have at their centres?
What do the supermassive blackholes at the centre of most nearby galaxies seem to be?
dormant active galactic nuclei
The universe is consistent with what structure?
Soap bubble (as opposed to spaghetti)
What does it mean to say the universe is isotropic and homogenous
viewed on sufficiently large distance scales, there are no preferred directions (isotropic) or preferred places (homogenous) in the universe
Our sky is isotropic except for
the Milky Way, which is denser
Simply, the cosmological principle states that
Averaged over large enough distances, one part of the universe looks approximately like any other part.q
What is the Edge-centre problem?
Modern observations indicate the universe could be infinite and have no edge. If the universe has no edge, then it cannot have a centre
If the universe is infinite why don't you see the surface of a star in every direction you look? (Why does the sky get dark at night?)
The universe is infinite in size but not infinitely old- the night sky is dark because the universe had a beginning
Hubble discovered nearby galaxies have ___ redshifts, but more distant galaxies have ____ redshifts. This implies...
- nearby galaxies have small redshifts
- more distant galaxies have large redshifts
- This implies that the galaxies are receding from each other
What does the Hubble constant describe?
The universe's rate of expansion
What is 1/H0?
The age of the universe
What are the observable characteristics of the universe?
- 1) Redshift proportional to distance
- 2) Cosmological principle: universe is isotropic and homogenous
- 3) Content of universe is H and He changing into heavier elements inside stars
- 4) Gravity warps fabric of space-time
What determines the geometry of the universe?
The average density of matter
critical density of universe is
6 H atoms/m3
universe is closed, finite
universe is flat but still infinite
universe is open, infinite
What does low H0 imply?
Slower expanding universe (older universe)
What are the pillars of the Big Bang Theory?
- 1) the expansion of the universe
- 2) the primordial nucleosymthesis
- 3) cosmic background radiation
What elements were present at the Big Bang?
H, He, H2, Li
What is evidence for the Big Bang Theory?
- 1) The theory correctly predicts the abundance of helium and other light elements
- 2) CMB (cosmic microwave background radiation) we have detected the leftover radiation from the Big Bang
What era does CMB come from?
Era of atoms
What is CMB
stretched out photon wavelengths
The Big Bang was an explosion...
of space. Not in space
the number of galaxies should increase linearly
positive curvature [shape and description]
sphere, the number of galaxies increases with greater volume then decreases with very large volumes
negative curvature [shape and description]
saddle, number of galaxies increase more rapidly with ever greater volume than flat universe
What does the Big Bang explain
- observation of CMB
- predicts abundance of light elements
- predicts 3 types of neutrinos experimentally detected
What does the Big Bang not explain
- why matter>antimatter
- origin of density fluctuations that grew into galaxies
- uniformity of the universe
- why the density of matter in the universe is close to critical and curvature flat
What is the evidence for the Solar Nebula Hypothesis
- orbits of the planets lie nearly in a plane
- planets all revolve in the same direction
- planets mostly rotate in the same direction
What ended the era of planet formation?
Solar wind blew away the leftover gases
What is the dominant mass in our Solar System?
What is the difference between an asteroid, comet and meteorite?
- Asteroids are rocky formations inside the frost line
- Comets are icy formations outside the frost line beyond the orbit of Pluto (ie, Kuiper belt and Oort cloud)
- A meteorite is a speck of dust grains of sand or tiny pebbles that reach Earth's surface)
What is the reason for meteor showers?
Earth goes into the path of a variety of comet trails, causing a meteor shower
What is the definition of a planet?
Must dominate its own orbit
Where does Earth's water originate?
Water may have to to earth from icy planetesimals from outer solar system. Currently we pick up water when we pass through comet trails
How many times bigger is the Sun than the Moon?
How old is the universe?
13.8 billion years old
Planets and Solar system probably formed when? How do we know?
- 4.6 billion years ago
- radiometric dating of oldest meteorites
What theory best explains the features of our solar system?
Nebular theory states that the Solar System formed from a large interstellar gas cloud
How did terrestrial planets form?
- rock and metals collected into planetesimals
- planetesimals accreted into planets
How did jovian planets form?
- additional ice particles outside the frost line made planets more massive
- gravity of these massive planets drew in H, He gases
How do we explain the existence of Earth's moon?
Material torn from Earth crust by giant impact formed the moon
What is photometry and what is it used for?
- Photometry is measuring the brightness of a star and how much fainter it gets when a planet passes in front of it
- Photometry is used to detect planets and determine its size and mass
What is the Habitable zone?
Zone around star where we expect to find liquid water
What is called the morning and evening star and why?
Venus, because when we look at Venus we are looking towards the Sun
Why are big planets formed away from the Sun?
Gas close to the Sun is vapourized and can't be used for adding size to a planet
What is the composition of both Saturn and Jupiter?
Primordial solar nebula
What is special about how much energy Jupiter and Saturn radiate?
They both radiate more energy into space that they receive from the sun
What are some common properties of living organisms?
- obtain energy from surroundings
- adapting to surroundings to survive
- information storage
What are the necessities for life?
- nutrient source
- liquid water
What is the order of cosmic evolution?
- 1) origin of matter
- 2) formation of milky way
- 3) formation of Earth
- 4) origin of life on Earth
- 5) present
What is a bio indicator?
Nitrogen is a bio indicator because it is the exhaust of organic life
What is Europa and why is it a suspect for life after Mars?
- Moon of Jupter
- Criss cross lines indicate liquid water underneath
What happens when a star can no longer fuse H into He in its core?
Core shrinks and heats up
What happens as a star's inert helium core starts to shrink?
Hydrogen fuses in a shell around the core
What happens to a white dwarf when it accretes enough matter to reach 1.4 solar masses?
could there be neutron stars that appear as pulsars to other civilizations but not to us?
How does the radius of the event horizon change when you add mass to a black hole?
It increases (dropping a big rock makes a hole with a big radius)
What types of celestial object did Edwin Hubble observe to measure the distance to M31?
Cepheid variable stars
What evidence tells us that other galaxies contain dark matter?
their rotational speeds do not steadily decrease with distance form their centers
What do we assume when we use a standard candle to find distance?
- light intensity is inversely proportion to distance squared
- we know the luminosity of the standard bulb
Rotational velocity of a spiral galaxy is related to what other characteristic?
intrinsic luminosity (by Tully-Fisher relation)
Hubble's law describes what type of relationship?
What data on a galaxy is necessary to use Hubble's Law as a distance indicator?
redshift in galaxy's spectrum
what does the value of the Hubble constraint tell us?
expansion rate of the universe
How is the Hubble constant related to the age of the universe?
What effect does gravity have on the expansion rate of the universe?
gravity tends to decrease the rate of expansion
What evidence suggests that the universe's rate of expansion is increasing?
distance type IA supernova explosions are dimmer than expected
What is the fate of the universe based on the rate of expansion and changes in the rate of expansion?
the universe will expand forever at an increasing rate
How does the temperature and density of the early universe compare to these same conditions today?
the early universe was hotter and denser
What is the most abundant amount of matter and in what form?
What is the most matter in galaxy clusters?
In what form do we observe radiation left over from BB?
Where did the solar system come from?
cloud of gas through recycling of gas through many generations of stars
What was the solar nebula?
Piece of interstellar cloud from which Solar System was born
Rank sizes of planets from smallest to largest
Pluto, Mercury, Mars, Venus, Earth, Neptune, Uranus, Saturn and Jupiter
Where do we find asteroids and comets in our solar system?
- Asteroids: asteroid belt
- Comets: Kuipter belt and Oort cloud
What property of planets can be obtained from the study of moons and law of gravity?
Which two planets have nearly the same chemical make up as the Sun?
Saturn and Jupiter
Which method has been the most successful in locating planets orbiting other stars?
planet transit method
Which body in the outer solar system has the greatest possibility of harboring life?
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