07 universe mc neely

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Astronomy Topic 07 : The Universe http://www.pbs.org/faithandreason/media/bigbang.lg.j

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Page 1: 07 Universe Mc Neely

AstronomyTopic 07: The Universe

http://www.pbs.org/faithandreason/media/bigbang.lg.jpg

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Cosmology

Cosmology: The study of the origin, present structure, evolution, and destiny of the universe

Two basic modelsSteady stateEvolutionary

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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

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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

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Hubble Diagram

http://www.exo.net/~pauld/activities/astronomy/Hubblelawsn1a.gif

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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

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Raisin Bread Analogy

As bread expands, each raisin (galaxy) sees the others moving away

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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

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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

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Big Bang

http://www.theage.com.au/ffximage/2006/03/17/bigbangmain_wideweb__470x238,0.jpg

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Cartoon

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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

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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)

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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)

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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

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Steps in the Closed Universe

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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)

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Open or Closed?

http://www.astro.rug.nl/~ormel/article/open_closed.jpg

•Expand forever

•Expansion will halt

•Big Crunch, new Big Bang?

(critical)

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Oscillating?

http://astrosun2.astro.cornell.edu/academics/courses/astro201/images/open_closed.gif

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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”

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Accelerating Expansion

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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

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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

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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.

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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?

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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

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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

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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

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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

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Evidence for the Big Bang

Expanding UniverseGalaxy evolutionChemical elements in starsCosmic Background RadiationHydrogen and Helium

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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

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Expanding Universe: Redshifts

The farther away a galaxy is, the greater that its absorption lines are shifted towards the red-end of the spectrum

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Redshift

Note that the entire pattern of spectral lines is shifted to the right with the distant supercluster

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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

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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/

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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

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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

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Cosmic Background (COBE)

http://users.telenet.be/kosmonet/ruimtevaart/cobe.jpg

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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

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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

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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%

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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.

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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

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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.

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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/

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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

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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

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Big Bang Image

Just released-2008: Scientists have revealed image showing earliest moments of infant universe (next slide)…

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