Download Linking Asteroids and Meteorites through Reflectance Spectroscopy

Astronomy 100
Tuesday, Thursday 2:30 - 3:45 pm
Tom Burbine
[email protected]
www.xanga.com/astronomy100
Scores
• The highest score in the class currently is a 97%
• The lowest score in the class currently is a 33%
• (Assuming their test grades remain the same for
the rest of the class and actually calculating their
HW and PRS scores)
Class Average
• The exam average for the class is 72.2%.
• If I assume everybody gets 100% for HW and
PRS scores and that this exam average does not
change for the remaining tests:
• Class average = 80% x 72.2% + 20% x 100%
• Class average = 77.8%
• After all the exams, this class average should rise
to above 80%
Schedule
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Today (Quasars, Dark Matter)
Thursday (end and beginning of the universe)
May 3 (Does Life Exist Elsewhere in the Universe)
May 5 (Review)
May 10 (Exam 4)
May 12 (Exam 5) (optional)
May 20 (Final) (optional)
Exam 4
• Know the class notes
• Know all the definitions on the website
• Know the Summary of Key Concepts at the end
of every chapter
Exam 5 and Final
• Know the class notes
• Know how to do every question on the 1st 4
exams
• Know the Summary of Key Concepts at the end
of every chapter
OWL assignment (Due Thursday)
• There is be an OWL assignment due on Thursday
April 28 at 11:59 pm.
• There are 15 questions and a perfect score will
give you 2 homework points.
Homework Assignment
(Due by May 3)
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Make up a test question for next test
Multiple Choice
A-E possible answers
1 point for handing it in
1 point for me using it on test
The question needs to be on material that will be
on the 4th exam
Homework Assignment
(Due by May 5)
• I have placed 40 terms on the website
• You get 0.1 of a HW point for each of these you
define and hand in to me
• Definitions need to be hand-written or hand-typed
• A lot of these definitions will be on next test
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Drake Equation
Dark Energy
Tully-Fisher Relation
ALH84001
Cepheid Variable
White Dwarf
Jocelyn Bell
Viking Mission
Hubble’s Law
SETI
Big Bang
COBE
Standard Candle
Quasar
Planck Time
Inflation in the Early Universe
Olber’s Paradox
Cosmic Microwave Background
Isotope
Baryon
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Percival Lowell
Redshift
Dark Matter
MACHO
Critical Density
Radio Galaxy
Main Sequence Fitting
Cosmological Horizon
White Dwarf Supernova
Interstellar Medium
Supercluster
WIMPS
Pulsar
Habitable Zone
Maunder Minimum
Convection Zone
Radiation Zone
Hubble’s Constant
Starburst Galaxy
Europa
Astronomy Help Desk
• There is an Astronomy Help Desk in Hasbrouck
205.
• It is open Monday through Thursday from 7-9
pm.
Hubble’s Constant
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v = d x Ho
d = v/Ho
d = distance the galaxy is from you
v = velocity the galaxy is moving away from us
Example
• A galaxy is moving away from us at a speed of
6,000 km/s
• How far is it away from us?
• Ho = 71 km/s/megaparsec
• d = v/Ho
• d = (6,000 km/s)/(71 km/s/megaparsec)
• D = 84.5 megaparsecs
Active Galactic Nuclei
• Active Galactic Nuclei are the unusually bright
centers found in some galaxies
M87
Elliptical Galaxy
Quasars
• Quasars are the brightest active galactic nuclei
• Emit immense amounts of radiation
• Some are brighter than 1,000 Milky Ways
Quasars
• Look like stars
• But have huge redshifts
Radio Galaxies
• A galaxy that emits unusually large quantities of
radio waves
• Thought to contain an active galactic nuclei
Power
• Active Galactic Nuclei, Quasars, and Radio
Galaxies are thought to be powered by
supermassive black holes
• They can exceed 1 billion solar masses
Energy
• Energy from the black holes comes from its
gravity
• Gravity converts potential into kinetic
• Collisions convert kinetic into thermal energy
• Photons carry this thermal energy away
Very Efficient
• E=mc2
• 10-40% of the energy of the accreting material is
released as radiation before the matter crosses the
event horizon
• More efficient than fusion, which turns less than
1% of the mass of the material into energy
Dark Matter
• Matter we infer to exist from its gravitational
affects but from what we detect no light
• Dark matter dominates the mass of the Universe
Rotation curve
Plot showing orbital velocities
Of gas and stars
Milky Way Galaxy
• The mass of dark matter may be 10 times the
mass of visible matter
• Visible matter is stars
Spiral Galaxies
Why is Dark Matter Important?
• The Universe is believed to proceed along two
paths
• It may continue to expand forever
• Or it may stop expanding and collapse
• Its fate is dependent on the density of matter
Elliptical Galaxies
• The orbits of stars in elliptical galaxies are
disorganized
Elliptical Galaxies
• Since some stars are moving towards us and some
are moving away from us
• Spectral lines are broadened
Elliptical Galaxies
• Velocities of stars stay relatively constant as you
move from galactic center
• Ellipticals contain dark matter
However
• We can’t determine the amount of dark matter in
an elliptical galaxy
• Because we can’t measure their masses as far
from their centers
Mass-to-Light Ratio
• You can compare the measured mass to the
luminosity of a galaxy
Milky Way
• Milky Way contains 90 billion solar masses of
material within the Sun’s orbit
• Luminosity of Milky Way at this orbit is 15
billion solar luminosities
• Mass-to-Light ratio of our Galaxy at this orbit is
6 solar masses per solar luminosities
This tells us that …
• The value of 6 solar masses per solar luminosity
tells us that most of the matter is dimmer than the
Sun out to the Sun’s orbit
• Mass-to-Light ratio of our Sun is 1 solar mass per
solar luminosity
• So most matter is dimmer than the Sun
For some ..
• For some galaxies, they have mass-to-light ratios
of 50 solar masses to solar luminosity
• This is too high to be accounted for by stars alone
Fritz Zwicky (1898-1974)
• Was among the first to suggest that there is a
relationship between supernovae and neutron stars
• Suggested in the 1930s that dark matter was
found in Galactic Clusters
Cluster
• Cluster is a collection of galaxies (that can
number dozens to thousands) that are
gravitationally bound
Zwicky
• By calculating the speed of galaxies as the rotate
around in a cluster
• He found that galaxies in the clusters had huge
mass-to-light ratios
Types of Dark Matter
• MACHOs
• WIMPS
MACHOs
• Massive Compact Halo Objects
• Includes
– Brown Dwarfs – failed stars
– Faint red stars
– Jupiter-sized objects
WIMPs
• Weakly interacting massive particles
– No electrical charge
– Do not emit electromagnetic radiation
– Have mass so do interact some with matter
Neutrinos
• Dark matter in galaxies can’t be neutrinos because
neutrinos escape from galaxies with enormous
speeds
WIMPS
• Have to have masses larger than neutrinos
• Have not been discovered yet
Questions