Final exam!!! Today we will discuss Cosmology and the Big Bang Wednesday we will finish the Big...
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Transcript of Final exam!!! Today we will discuss Cosmology and the Big Bang Wednesday we will finish the Big...
final exam!!! Today we will discuss Cosmology and the
Big Bang Wednesday we will finish the Big Bang,
have a short discussion of Life in the Universe, and review for the final exam
Remember:
“the Great Wall”
Earth
Virgo Cluster
Expanding UniverseToday’s Lecture: purpose & goals
Looking at an ‘empty patch of sky
AST 1002Planets, Stars and Galaxies
1) Hubble’s Law2) Expanding Universe3) Cosmology Assumptions4) The Origin of the
Universe “the Big Bang”5) Fate of the Universe
Galactic Clusters – II SuperClusters
On even greater scales the galaxy clusters themselves form clusters called superclusterssuperclusters that can be tens to hundreds of millions of light years across.
These superclusters resemble “…the froth on soap bubbles…”
in space. Between them lie great voidsgreat voids
containing relatively few galaxies.
Local Group
Virgo Cluster
Fornax Cluster
Ursa Major group
Canes group
Leo II group
Leo I
Virgo III group
10 million ly
Sculptor
Galaxy Collisions Occasionally galaxies collide
Happens most often in centers of rich galactic clusters
Stars that make up the galaxies don’t actually slam into each other
Passage of one galaxy through/near another causes major “stirring”
due to gravitational interaction Causes new activity such as
huge burst of star formation,
creation of AGNs,…
Think of walking around before or after a football
game
very little gas and dust
significant gas and dust – in arms
some gas and dust
Review
no new star formation!!
significant new star formation!! (in the spiral arms, spherical component older!!)
some new star formation (randomly throughout galaxy)
small, irregular, no rotation
fast rotation
slow rotation
Pop II
Pop II
Pop I
Measuring Distances Stereoscopic viewing (Parallax)
only “small” distances nearest few thousand stars in our galaxy
“Standard candles” objects which have ‘known’ luminosities Cepheid variables
variation tells luminosity – good to 65-100 million LY brightest stars in galaxy, size of HII regions, overall
brightness of galaxy – good in steps out to 1-2 billion LY Type Ia supernova
all have same luminosity good to 8-10 billion LY (a few measured
as far away as 12-13 billion LY)
Relies on Comparison to examples of the same type objects in nearby galaxies
History reminder – “Island Universes”
1924 – Edwin Hubble Measured the distances to
several galaxies using the Luminosity-Period relationship of Cepheid variables, discovered by Henrietta Leavitt (1912). (Cepheid variables)
This was conclusive proof that the
galaxy lay well beyond the Milky Way. 2 million l.y. away!
The universe was much larger than previously thought.
Andromeda galaxy
size of the Moon
Calculate the distance to the Andromeda Galaxy using Hubble’s method.
m - Mv = -5 + 5log10(d(parsecs))
Luminosity-Period Relation of Cepheid Variables
Andromeda galaxy
Distance Modulus Formula
Galactic Redshifts Edwin Hubble (1889-1953) and colleagues
measured the spectra (light) of many galaxies found nearly all galaxies are red-shifted
Redshift (Z)
From Ch. 2, (Doppler effect) Z = v/c
(for speeds approaching c, we’ll need a relativistic version
of this equation.)
rest
rest
-
= observed Z
Andromeda galaxy
Z = [(1+ v/c)/(1+ v/c)]1/2 - 1
Hubble’s Law Hubble found the amount of redshift depended
upon the distance the farther away, the greater the redshift
v = H0 x d
What is H0?Hubble’s data
distance to galaxy
Re
ce
ss
ion
al v
elo
cit
y
Bigger Structure Structure bigger than
galaxies Galaxy groups
2-30 galaxies Local Group – contains the
Milky Way Galaxy clusters
100s of galaxies – Virgo Cluster (rich cluster)
Superclusters groups and clusters combined
The Universe is filled with large scale structure
“walls” and “filaments” separated by great voids – (like froth on soap bubbles)
EarthVirgo Cluster
First detailed study done by Margaret Geller & John Hucra, Harvard-Smithsonian Center for Astrophysics
“th
e G
reat
Wall”
Hubble’s Law Holds for essentially all galaxies with measured
redshift and distance THEREFORE, measuring the redshift tells us the
distance redshifts up to 95% of the speed of light have been
measured!! ultraviolet wavelengths can be shifted into the visible, or
infrared
H0 is Hubble’s constant = 70 km/(s Mpc) Mpc = megaparsec
Consequences If everything is moving away from us and things
farther are moving faster Then the Universe is expanding!
This doesn’t mean what you are probably thinking . . . .
Expanding Universe Space itself is expanding, not matter
flying apart within space. Examples:
dots rubber band raisin bread ants on a balloon
It does not mean we are at the center of the Universe
every part of the Universe sees everything moving away from it
Cosmological Redshift
We now know 3 kinds of redshift
Doppler shift due to motion
Gravitational shift due to distortion of space-time by
mass Cosmological shift
due to stretching of space not due to relative motion
as space stretches, the wavelength stretches and becomes longer
rest
rest
-
= observed Z
Relativistic (near speed of light): Z = [(1+ v/c)/(1+ v/c)]1/2 - 1
Non-relativistic (<0.05c): Z = v/c
Looking Back in Time Remember it takes time for light
to reach us travels at 300,000 km/s So we see things “as they were” some
time ago The farther away, the further
back in time we are looking 1 billion LY means looking 1 billion
years back in time So the greater the redshift, the
further back in time redshift of 0.1 is 1.4 billion lightyears
which means we are looking 1.4 billion years into the past
Thinking Back in Time If all galaxies are moving away
from each, then in the past all galaxies were closer to each other.
Going all the way back, it would mean that everything started out at the same point
then began expanding This starting point is called the Big
Bang We can calculate the age of the
Universe using Hubble’s Lawv = H0 x
d d = v/H0
But distance = rate x time(the time here is how long the expansion has been going on The Age of the Universe)
thubble = 1/H0
Big Bang At the beginning of our
Universe, all matter was together in a very compact form
matter was nothing like it is now very “hot”
Then space started expanding things “cooled” eventually it was possible for
normal matter to “condense” out of the hooter form
Big Bang model makes a number of testable predictions….
…continued!
At the Beginning
Originally all the energy (and matter) of the Universe was condensed into an incredibly small
region MUCH smaller than the size of a proton
Energy, matter, space and time were all very different than today
need a new “theory of everything” to understand not yet possible 11-dimensional space??? (models are very weird)
During early expansion, space-time and gravity became separate from energy and mass
particles and antiparticles were being created from energy and annihilating into energy all the time
Glow of the Universe
The early Universe was very hot and dense
glowed with blackbody radiation
but so dense the light kept getting absorbed (opaque)
Eventually the Universe cooled enough to form hydrogen atoms
blackbody radiation could now travel freely That time called “recombination of the
Universe” Light from that time should be all around
us and be detectable. 3K background radiation
This light should be cosmologically redshifted
Mostly into microwave region CMB was first seen in 1960s
Pensias & Wilson (Bell Labs)
– won Nobel prize in physics for this
twenty years after prediction COBE satellite mapped the CMB
measured the spectrum wonderful match between theory and
data Temperature = 2.73K cooled glow from recombination
era. Incredibly uniform across sky.
Cosmic Microwave Background (CMB)
Composition of Light Elements
Helium
Big Bang model predicts the percentage of light elements
Hydrogen (1H), deuterium (heavy hydrogen, 2H), helium (4He), lithium (7Li), beryllium (9Be), boron (10B and 11B),…
elements formed before recombination (created out of light!)
percentages depend upon density and temperature of early Universe, and how fast it cooled.
Observed percentages agree with Big Bang model predictions
Almost all was created as hydrogen (1H) and helium (4He), with only trace amounts of anything else.
must have cooled from something very hot.
Fate of the Universe The Universe is expanding But gravity should be pulling it back in So what should the Universe’s fate be:
Continue expanding forever Have expansion keep getting slower forever and stop at
infinite time Expansion stops and eventually Universe collapses
upon itself These possibilities are called
open universe flat universe closed universe
Enough Matter? The amount of matter in the Universe helps
determine its fate if there is enough mass, gravity wins given H0 = 70 km/(s Mpc), critical mass density is 8x10-27
kg/m3
define MASS as the actual density of mass in the Universe divided by the critical density
MASS < 1 is an open universe MASS = 1 is a flat universe MASS > 1 is a closed universe
Enough Matter? Visible matter (stars in galaxies, & hot gas)
only 2% of critical density; MASS = 0.02 Dark matter in galaxies
(measured by galaxy rotation curves) about 10 times as much; MASS = 0.2
Dark matter between galaxies (measured by watching galaxies fall
inward in galactic clusters and from gravitational lensing)
raises total to 30% of critical density MASS = 0.3
We do not observe enough matter to cause the Universe to be closed
But it’s not the end of the story…
Is the Expansion Slowing Down?
Answer: Strangely enough…the rate of expansion is speeding up!
Use Type 1a supernovae a standard candle use brightness to determine
distance use redshift to determine
speed compare them data lies below prediction
(galaxies are speeding up!!)
Formation of Structure (early in the Universe) Normal matter was spread fairly
evenly due to interactions and radiation
Dark matter was not distributed smoothly
clumps remained Expansion spread things out
but gravity held large clumps of dark matter together
Dark matter attracted normal matter
source of galaxies and structure