07 Universe Mc Neely
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Transcript of 07 Universe Mc Neely
AstronomyTopic 07: The Universe
http://www.pbs.org/faithandreason/media/bigbang.lg.jpg
Cosmology
Cosmology: The study of the origin, present structure, evolution, and destiny of the universe
Two basic modelsSteady stateEvolutionary
Expanding Universe
Any model of the universe must explain its expansion
The universe appears to be expandingThe light from distant galaxies appears to
be red shifted due to this expansionHubble’s Law: The further away a galaxy
is, the greater its redshift is and the faster it is flying away from us
Hubble’s Law
The (linear) relationship between a galaxies velocity of recession and its distance
Hubble’s Law:v = Hd
Where v=velocity, d=distance, and H=Hubble constant
In a graph of distance vs. recessional velocity, H becomes the slope of the line
Hubble Diagram
http://www.exo.net/~pauld/activities/astronomy/Hubblelawsn1a.gif
We are not the center
Galaxies appear to be flying away from our position
Observers in other parts of the universe would make similar observations
Our corner of space isn’t special, and the laws of nature are the same everywhere in the universe
Raisin Bread Analogy
As bread expands, each raisin (galaxy) sees the others moving away
Big Bang Theory
BB states that the universe exploded violently into existence 13.7 billion years ago and has been expanding ever since
At the Big Bang, all of the matter in the universe was packed together into an infinitely small area
Evolutionary Model:The universe had a beginning, will have an end,
and has evolved or changed over time
Big Bang Events
The infant universe rapidly expanded (inflation) One-millionth of a second: Four forces emerge (gravity,
electromagnetism, strong and weak) In the first few seconds electrons, protons, and neutrons formed Within minutes, the first hydrogen formed. Hydrogen was the
original element. Some helium and other trace elements were also created
300,000 years: Cosmic Background Radiation emerges 300 million years later, matter sprung from energy (decoupled)
forming stars and galaxies The universe has been expanding ever since The universe consists of 74% hydrogen, 24% helium, and 2% trace
elements The velocity of the universe’s expansion is increasing due to dark
energy
Big Bang
http://www.theage.com.au/ffximage/2006/03/17/bigbangmain_wideweb__470x238,0.jpg
Cartoon
Open or Closed Universe
Two variations of the Big Bang exist, the open and closed universe
The determinant for closure is the amount of matter in the universe
The gravity exerted by matter can halt the universe’s expansion
This is one reason why dark matter is an important topic
Open Universe?
Open Universe: The universe will expand outward forever. Eventually the universe will fade away into a cold, dark voidFlat Universe: Universe will neither expand
forever or collapse. Eventually expansion will stop (critical density)
Steps in the Open Universe
A. Big Bang explosion took placeB. Galaxies formedC. Galaxies are still recedingD. Original hydrogen used up, the resulting cold, black
universe will continue expanding indefinitely
Diagrams courtesy Moché, Astronomy, a Self-Teaching Guide, Wiley (1993)
Closed Universe?
Closed Universe: In the closed universe, the universe will eventually stop expanding and begin to contract. The universe will fall back together into a Big CrunchOscillating Universe: Idea that a new universe
is created after each Big Bang and Crunch. The universe may expand and contract eternally creating new universes each time
Steps in the Closed Universe
Steps…
A. Big Bang occurred
B. Galaxies formed and continued to recede
C. We live in an expanding universe; galaxies are racing away from one another today
D. Galaxies will stop
E. The universe will contract; galaxies will fall back inward
F. Matter will be crunched together again (Big Crunch)
Open or Closed?
http://www.astro.rug.nl/~ormel/article/open_closed.jpg
•Expand forever
•Expansion will halt
•Big Crunch, new Big Bang?
(critical)
Oscillating?
http://astrosun2.astro.cornell.edu/academics/courses/astro201/images/open_closed.gif
Open Universe and Dark Energy
The study of distant white dwarf supernovae indicate that the universe is open, and that its rate of expansion is accelerating
Evidently a repulse force (dark energy) exists in the universe that acts contrary to gravity
Einstein had originally predicted a repulsive force in the universe but considered it a “blunder”
Accelerating Expansion
Exploding White Dwarfs
White dwarf supernovas (type 1A) occur when a white dwarf is present in a binary star system
The white dwarf pulls material from its companion star eventually causing either a nova (temporary brightening) or supernova (exploding star)
These supernovas make good standard candles as they achieve a similar brightness
Observations of type 1A supernova led to the discovery of the acceleration of the universe’s expansion
Supernova 1994D
This photo from the Hubble Space Telescope is of a supernova discovered in 1994
The supernova appeared in NGC 4526, a galaxy in the constellation Virgo
http://antwrp.gsfc.nasa.gov/apod/ap981230.html
Dimmer Distant Supernova
•These HST images show the galaxy in which the supernova SN 1997ff occurred. •This supernova was dimmer than expected. •The distance to such galaxies was greater than previously thought •An outward force, named dark energy, seems to be acting over vast distances in the universe.
Steady State Theory
Rival of Big BangStates that the universe is eternal and
unchangingThe universe does not evolve over time and has
no beginning or endTo explain expansion, the SS theory claims that
new hydrogen is created in empty space when needed
SS theory is rejected because it violates conservation of energy law that prohibits the creation of new matter
God is a Steady Stater?
Steps in the Steady State Universe
a) Galaxies are receding, the universe is expanding, new matter is being created, new galaxies are being formed
b) The same pattern will occur. The universe maintains the same average density forever
Sir Fred Hoyle (1915-2001)
Despite being known for coining the term “Big Bang”, Fred Hoyle was the major supporter of the Steady State theory, and he held this position until his death in 2001
Hoyle, an atheist, felt that the Big Bang theory was too religious, and that it implied a creator
Hoyle was also known for discovering the mechanism by which elements are created in stars (nucleosynthesis)
Always an iconoclast, he also proposed that life came from space in the form of free-floating bacteria. This theory is known as panspermia
Big Bang vs. Steady State
Big Bang The universe had a
beginning and will have an end
The universe has a concrete age
Objects in the universe can change over time—older & more distant galaxies are different
Expansion resulted from an original explosion
Resembles biblical creation Main proponent: Hubble
Steady State The universe is eternal
without beginning or end The universe is ageless Objects in the universe do
not change over time—galaxies should appear the same regardless of distance or age
Expansion results from the creation of new matter
Resembles eastern religious beliefs found in Buddhism and Hinduism
Main proponent: Hoyle
Big Bang Pioneers
In 1927, the Belgian priest Georges Lemaître proposed that the universe began with the explosion of a primeval atom
Lemaître’s proposal came after astronomers discovered the redshifts of distant galaxies
In 1929, American astronomer Edwin Hubble found experimental evidence to support Lemaître's theory
Hubble matched his distance measurements of galaxies with redshift data to discover that distant galaxies in every direction are going away from us with speeds proportional to their distance
http://en.wikipedia.org/wiki/Edwin_Hubble#Biography
Lemaître & Hubble
Evidence for the Big Bang
Expanding UniverseGalaxy evolutionChemical elements in starsCosmic Background RadiationHydrogen and Helium
Expanding Universe
Universe appears to be expanding due to the observation of redshifts in distant galaxies
This implies that the entire universe was together at one time and then exploded outward
Expanding Universe: Redshifts
The farther away a galaxy is, the greater that its absorption lines are shifted towards the red-end of the spectrum
Redshift
Note that the entire pattern of spectral lines is shifted to the right with the distant supercluster
Changing Galaxies (Galactic Evolution)
Galaxies in the original Hubble Deep Field, the deepest image of distant galaxies, appear different than closer galaxies
This indicates that the galaxies have evolved over time
In a steady state universe, galaxies should look the same at any age or distance from earth
Hubble Deep Field (1996)
The Hubble Deep Field is a 10-day long exposure of a tiny, apparently blank portion of the sky 1/30 of the full moon’s diameter
Released in 1996, the Deep Field represented views of the most distant galaxies yet obtained
Click: Hubble Ultra Deep Field
http://hubblesite.org/newscenter/archive/releases/1996/01/image/a/
Creation of Elements
The oldest known stars consist of mainly hydrogen and helium and lack heavier elements
New stars contain heavy elements recycled from older generations of stars that died and ejected their contents into space during supernova explosions
In a steady state universe, all stars would display similar amounts of chemical elements
Cosmic Background Radiation
In 1965, Penzias and Wilson detected microwave radiation coming equally from all directions in space, day and night, all year. They later won the Nobel Prize for this discovery
This radiation indicates that space is filled with a slight amount of heat equal to 2.7 K
This heat is apparently the leftover fireball radiation of the Big Bang itself. The energy is extremely redshifted into the microwave region of the electromagnetic spectrum due to the universal expansion
In 1989, the Cosmic Background Explorer (COBE) satellite returned images of the cosmic background.
http://bustard.phys.nd.edu/Phys171/lectures/cmbr.0.html
Cosmic Background (COBE)
http://users.telenet.be/kosmonet/ruimtevaart/cobe.jpg
Cosmic Background (WMAP)
The Microwave SkyThe detailed, all-sky picture of the infant universe from three years of WMAP data. The image reveals 13.7 billion year old temperature fluctuations (shown as color differences) that correspond to the seeds that grew to become the galaxies. http://map.gsfc.nasa.gov/m_or.html
Hydrogen and Helium
Most stars and galaxies contain from 25-28% heliumStars produce helium from hydrogen during nuclear
fusion reactionsYet the amount of helium in stars is greater than
would be produce in this mannerThe majority of helium in stars was likely present
from the start and was created during the Big Bang itself
Just after the Big Bang, the universe was temporarily hot enough to fuse hydrogen into helium which explains the extra helium in stars
What is the Universe Made of?
Regular matter-5% (chemical elements)
Dark matter-25%Dark energy-70%
The Universe
Dark Energy,
70%
Dark Matter, 25%
Regular Matter, 5%
Age of the Universe
Original estimates were based on the Bible
For example, using Biblical chronology, Bishop Ussher dated the creation at October 23, 4004 BC
Modern estimates based upon WMAP observation of the CBR
Currently accepted age = 13.7 b.y.
Edge of the Universe
Estimates of the radius of the universe are equal to the speed of light (c) divided by the Hubble Constant, c/H
This would equal the distance to the edge of the observable universe, the Hubble Radius
The edge of the universe is the Big Bang itself, this is as far back as we could ever look
Observable Universe
The Hubble Radius today is about 13.7 billion light-years away in all directions. Inset: This HST Deep Field Telescope image shows some of the most distant galaxies we have seen.
Slice of Universe?
This shows the slice of the universe surveyed by the 2dF Galaxy Redshift Survey. Every dot is a galaxy, with the Milky Way at the centre; distance from the centre is redshift and angle around the circumference is angle on the sky. There are 221,283 galaxies in this slice, which shows the highly-structured nature of the galaxy distribution. http://msowww.anu.edu.au/news/archive/2003/03_mar/
Olber’s Paradox
Proposed by Heinrich Olbers in the 1800s, it questions why the sky is dark at night?
In an infinite universe, the sky wouldn’t be dark at night
The sky would be as bright as the surface of a star because every line of sight outward would eventually come to the surface of a star
Paradox Solved?
With the Big Bang, the universe is not infinite, it had a definite origin in the distant past
Light from more distant stars had not had time to reach us yet, and the expansion of the universe will prevent this from ever happening
In an infinite universe, every line of sight from earth would
encounter a star—the sky should be bright at night, as bright as a
star’s surface
Big Bang Image
Just released-2008: Scientists have revealed image showing earliest moments of infant universe (next slide)…