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Elliptical Galaxies
- no disk
- no spiral arms
- almost no gas, dust or new stars forming
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Disk-shaped Galaxies
- Usually have spiral arms, less or more prominent
- generally large amounts of gas and dust
- ongoing stellar formation
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Irregular Shaped Galaxies
Gas, dust and star forming nebulae
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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
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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
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Parallax
Apparent shift in a star's psition
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Main Sequence Fitting
Apparent brightness of star cluster's main sequence tells us its distance
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Standard Candle/Bulb
An object whose luminosity we can determine without measuring its distance
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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
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How to get apparent brightness
Divide luminosity by area
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Cepheid Variables
Giant stars that pulse in size, temperature and luminosity over a regular period
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Cepheid Variable stars with longer periods have
Greater luminosities
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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
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Why are Supernovae Type Ia good standard candles?
- extremely bright
- easily detected, though rare
- uniform in brightness at maximum light
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Tully-Fisher Relation
Entire galaxies can be used as standard candles because galaxy Luminosity is related to rotation speed.
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What is Hubble's Law?
Relationship between a galaxy's velocity (redshift) and distance
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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
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What is the rotation curve method?
The most precise method for measuring the mass of a galaxy
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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)
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How much more dark matter is there than visible matter?
10x
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What is the evidence for Dark Matter in Spiral Galaxies?
Spiral Galaxies have flat rotation curves indicating large amounts of dark matter
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Cosmology is... and is connected with...
the study of the structure and evolution of the universe and is connected with the study of galaxies
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spiral galaxies are often found in
groups (< 50)
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elliptical galaxies are much more common in
clusters (hundreds to thousands of galaxies)
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How big is the Local Group? What galaxy does it contain?
Around 40 galaxies. Contains the Milky Way
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In a group of galaxies like a cluster, the only important force acting between the galaxies is
gravitation
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velocities indicate what inside the cluster [of galaxies]
total mass
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How much larger is the mass we find from galaxy motions in a cluster than the mass in stars?
50x
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Estimates of gravitational mass can be done most directly in what ways
- 1. Observing galaxies orbiting massive central elliptical galaxies
- 2. Gravitational Lensing
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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.
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Ordinary matter is made up of what and called
- protons and neutrons
- baryonic matter
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Nonbaryonic matter is what?
extraordinary matter or dark matter
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What are MACHOs and where are they found
- Ordinary dark matter
- Massive Compact Halo Objects: dead or failed stars in halos of galaxies
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What are WIMPs?
- Extraordinary dark matter
- Weakly Interacting Massive Particles: mysterious neutrino-like particles
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MACHOs or WIMPs
WIMPs are the best bet. There is too little evidence of MACHOs
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What do many nearby galaxies have at their centres?
Supermassive Blackholes
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What do the supermassive blackholes at the centre of most nearby galaxies seem to be?
dormant active galactic nuclei
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The universe is consistent with what structure?
Soap bubble (as opposed to spaghetti)
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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
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Our sky is isotropic except for
the Milky Way, which is denser
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Simply, the cosmological principle states that
Averaged over large enough distances, one part of the universe looks approximately like any other part.q
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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
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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
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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
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What does the Hubble constant describe?
The universe's rate of expansion
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What is 1/H0?
The age of the universe
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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
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What determines the geometry of the universe?
The average density of matter
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critical density of universe is
6 H atoms/m3
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density>critical density
universe is closed, finite
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density=critical density
universe is flat but still infinite
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density<critical density
universe is open, infinite
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What does low H0 imply?
Slower expanding universe (older universe)
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What are the pillars of the Big Bang Theory?
- 1) the expansion of the universe
- 2) the primordial nucleosymthesis
- 3) cosmic background radiation
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What elements were present at the Big Bang?
H, He, H2, Li
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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
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What era does CMB come from?
Era of atoms
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What is CMB
stretched out photon wavelengths
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The Big Bang was an explosion...
of space. Not in space
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zero curvature
the number of galaxies should increase linearly
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positive curvature [shape and description]
sphere, the number of galaxies increases with greater volume then decreases with very large volumes
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negative curvature [shape and description]
saddle, number of galaxies increase more rapidly with ever greater volume than flat universe
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What does the Big Bang explain
- observation of CMB
- predicts abundance of light elements
- predicts 3 types of neutrinos experimentally detected
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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
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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
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What ended the era of planet formation?
Solar wind blew away the leftover gases
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What is the dominant mass in our Solar System?
the sun
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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)
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What is the reason for meteor showers?
Earth goes into the path of a variety of comet trails, causing a meteor shower
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What is the definition of a planet?
Must dominate its own orbit
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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
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How many times bigger is the Sun than the Moon?
100x
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How old is the universe?
13.8 billion years old
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Planets and Solar system probably formed when? How do we know?
- 4.6 billion years ago
- radiometric dating of oldest meteorites
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What theory best explains the features of our solar system?
Nebular theory states that the Solar System formed from a large interstellar gas cloud
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How did terrestrial planets form?
- rock and metals collected into planetesimals
- planetesimals accreted into planets
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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
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How do we explain the existence of Earth's moon?
Material torn from Earth crust by giant impact formed the moon
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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
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What is the Habitable zone?
Zone around star where we expect to find liquid water
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What is called the morning and evening star and why?
Venus, because when we look at Venus we are looking towards the Sun
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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
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What is the composition of both Saturn and Jupiter?
Primordial solar nebula
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What is special about how much energy Jupiter and Saturn radiate?
They both radiate more energy into space that they receive from the sun
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What are some common properties of living organisms?
- obtain energy from surroundings
- self-maintenance
- adapting to surroundings to survive
- information storage
- reproduction
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What are the necessities for life?
- nutrient source
- energy
- liquid water
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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
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What is a bio indicator?
Nitrogen is a bio indicator because it is the exhaust of organic life
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What is Europa and why is it a suspect for life after Mars?
- Moon of Jupter
- Criss cross lines indicate liquid water underneath
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What happens when a star can no longer fuse H into He in its core?
Core shrinks and heats up
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What happens as a star's inert helium core starts to shrink?
Hydrogen fuses in a shell around the core
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What happens to a white dwarf when it accretes enough matter to reach 1.4 solar masses?
it explodes
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could there be neutron stars that appear as pulsars to other civilizations but not to us?
yes
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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)
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What types of celestial object did Edwin Hubble observe to measure the distance to M31?
Cepheid variable stars
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What evidence tells us that other galaxies contain dark matter?
their rotational speeds do not steadily decrease with distance form their centers
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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
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Rotational velocity of a spiral galaxy is related to what other characteristic?
intrinsic luminosity (by Tully-Fisher relation)
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Hubble's law describes what type of relationship?
velocity-distance
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What data on a galaxy is necessary to use Hubble's Law as a distance indicator?
redshift in galaxy's spectrum
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what does the value of the Hubble constraint tell us?
expansion rate of the universe
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How is the Hubble constant related to the age of the universe?
inversely
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What effect does gravity have on the expansion rate of the universe?
gravity tends to decrease the rate of expansion
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What evidence suggests that the universe's rate of expansion is increasing?
distance type IA supernova explosions are dimmer than expected
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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
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How does the temperature and density of the early universe compare to these same conditions today?
the early universe was hotter and denser
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What is the most abundant amount of matter and in what form?
dark energy
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What is the most matter in galaxy clusters?
dark matter
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In what form do we observe radiation left over from BB?
radio
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Where did the solar system come from?
cloud of gas through recycling of gas through many generations of stars
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What was the solar nebula?
Piece of interstellar cloud from which Solar System was born
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Rank sizes of planets from smallest to largest
Pluto, Mercury, Mars, Venus, Earth, Neptune, Uranus, Saturn and Jupiter
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Where do we find asteroids and comets in our solar system?
- Asteroids: asteroid belt
- Comets: Kuipter belt and Oort cloud
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What property of planets can be obtained from the study of moons and law of gravity?
mass
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Which two planets have nearly the same chemical make up as the Sun?
Saturn and Jupiter
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Which method has been the most successful in locating planets orbiting other stars?
planet transit method
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Which body in the outer solar system has the greatest possibility of harboring life?
Europa
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