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PH1600: Introductory Astronomy
Lecture 20: The Distant Universe
PH1600: Introductory Astronomy
Lecture 20: The Distant Universe
Next Lecture: Geometry of the Universe
School: Michigan Technological University
Professor: Robert Nemiroff
Online Course WebCT pages:
http://courses.mtu.edu/
This class can be taken online ONLY, class
attendance is not required!
You are responsible for…
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Lecture material
Listed wikipedia entries
 But not higher math
APODs posted during the semester
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APOD review every week during lecture
Completing the Quizzes
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Homework quizzes 1 - 9.
Homework 10 due later (Monday) by 5 pm
See WebCT at http://courses.mtu.edu/
Wikipedia entries:
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Olbers’ paradox
Cosmological principle
Hubble’s law
Metric expansion of space
Cosmic distance ladder
Considering Our Universe as a Whole
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The Cosmological Principle
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Homogeneous
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Universe Homogeneous & Isotropic
Smooth when averaged out
Example: jello, even fruity jello
Isotropic
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Same in every direction
Example: room with the lights out
Olber’s Paradox
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Why is the sky dark at night?
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Why is it bright during the day?
Assume the universe is infinite
Assume stars all have the same
surface brightness
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Surface brightness does not depend on
distance
Olber’s Paradox
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Point in any direction
That direction goes through empty
space but ends on a star
Every direction should be as bright
as the surface of a star
The sky should be bright at night
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What’s wrong with this picture?
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http://hyperphysics.phy-astr.gsu.edu/Hbase/astro/imgast/olbers.gif
http://commons.wikimedia.org/wiki/Image:Olber%27s_Paradox_-_All_Points.gif
Dense Forest Analogy
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Picture you are in a dense forest
Trees are found in every direction
Every direction you point ends on a
tree
Therefore, every direction is treebark brown
Olber’s Paradox: Possible Solutions
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Universe is finite in size
Universe is finite in age
Dust blocks out most light
Light gets too redshifted to see
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Which do you think is correct?
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Take a minute to think about it!
Olber’s Paradox: Solution
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All of those have some affect BUT
The finite age of the universe is the
most important factor
Light just can’t get to us from
distant stars
The Sky IS bright at night
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Background radiations in all energy
bands
The sky is never completely dark at
any wavelength
Olber was correct after all!
COBE All-Sky Map
Credit: COBE Project, DMR, NASA
APOD: 2006 October 7
The Cosmic Infrared Background
Credit: A. Kashlinsky (SSAI) & S. Odenwald (Raytheon), 2MASS, NSF, NASA
APOD: 2002 February 6
Our Dusty Universe
Credit: DIRBE Team, COBE, NASA
APOD: 2000 November 19
ROSAT Explores The X-Ray Sky
Credit: S. Digel and S. Snowden (USRA/ LHEA/ GSFC), ROSAT Project, MPE, NASA
APOD: 2000 August 19
The Expanding Universe: Hubble’s Law
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Our Universe is expanding!
Discovered by Edwin Hubble in
1930s
More distant galaxies are moving
away faster
Hubble’s Law: v = Ho d
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v is galaxy velocity, d is galaxy distance
and Ho is Hubble’s constant
http://hyperphysics.phy-astr.gsu.edu/hbase/astro/hubble.html
http://www.hk-phy.org/articles/univexpand/univexpand.jpg
(Courtesy of SLAC and Nicolle Rager)
http://www.interactions.org/imagebank/search_detail.php?image_no=SL0062
The Expanding Universe:
Where is the center?
In General Relativistic Cosmology:
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There is no center
There is no “Big Bang National Park”
The Universe is not an exploding golf ball
Every point can be considered the center
The expansion looks the same from every
point
The Expanding Universe:
What is expanding?
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Newtonian cosmology does have a
center
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You and I do not expand
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Would result in strange unseen forces
Anything held together does not
expand
The average space between
galaxies expands – almost drifts -apart
Expanding Universe:
Determining Hubble’s Constant
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What is Ho?
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Measure distance and redshift of nearby
galaxies
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Major astronomical quest of recent years
Hubble Space Telescope “Key Project”
Trouble: peculiar velocities
Today: Ho = 71 (+/- 5) km / sec / Mpc
d=v/Ho
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Say v = 7100 km/sec, then
D = 100 Mpc
Universe Expansion:
Cosmological Distance Ladder
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Sun
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Nearest stars
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How: parallax shift over six months
Open star clusters
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How: timing radar bounces
How: parallax, main sequence fitting
Cepheids
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How: found in star clusters
A Leonids Star Field
Credit & Copyright: Sherry Buttnor
APOD: 2001 November 20
The Cepheids of M100
Credit: NASA, HST, W. Freedman (CIW), et al.
APOD: 1996 January 10
Universe Expansion:
Cosmological Distance Ladder
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Nearest Galaxies
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Supernovas
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How: Cepheid variable stars
How: Inside galaxies with Cepheids
Distant Galaxies
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How: supernovas calibrate redshifts
M3: Inconstant Star Cluster
Credit & Copyright: J. Hartman & K. Stanek (Harvard CfA)
APOD: 2004 October 12
A Nearby Supernova in M51
Credit & Copyright: R Jay GaBany (Cosmotography.com)
APOD: 2005 July 19
Supernova Factory NGC 2770
Credit: A. de Ugarte Postigo (ESO) et al.,
Dark Cosmology Centre (NBI, KU),
Instituto de Astrofísica de Andalucía (CSIC),
University of Hertfordshire
APOD: 2008 January 18
Universe Expansion:
The Age of the Universe
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The universe must be older than things in it
Three old things:
Age of the Earth
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Age of the oldest white dwarf stars
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Oldest rocks are 3.5 billion years old
Faint white dwarfs: 12.5 +/- 1 billion years old
Age of the oldest globular star clusters
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14.6 +/- 1.7 billion years
White Dwarf Stars Cool
Credit: H. Richer (UBC) et al., WFPC2, HST, NASA
APOD: 2000 September 10
M55: Color Magnitude Diagram
B.J. Mochejska, J. Kaluzny (CAMK), 1m Swope Telescope
APOD: 2001 February 23
Universe Expansion:
New method: Microwave background
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Spot size and distribution on the
microwave background correlates
with universe age.
Universe age 13.7 +/- 0.1 billion
years old
A Year of Resolving Cosmology
Credit: WMAP Science Team, NASA
APOD: 2003 December 31