Download The Universe and Galactic Formation

ASTRONOMY
The Universe
Key Terms
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Astronomy: The scientific study of the universe; it includes the observation and
interpretation of celestial bodies and phenomenon
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Big Bang: The theory that proposes that the universe originated as a infinitely
small mass which sub sequentially began to expand
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Cosmology: The study of the origins of the universe
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Doppler Effect / Red Shift: the wavelength of an object lengthens and shifts
towards the red end of the spectrum as it recedes
from our position.
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Galaxy: A collection of stars, gas and dust held together by gravity
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Hubble’s Law: galaxies are receding from our galaxy at a speed that is
proportional to their distance
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Universe: All matter and energy, including the earth, the galaxies, and the
contents of intergalactic space, regarded as a whole
Origins
The Big Bang
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The universe formed approximately 12 – 14 billion years ago
Universe was condensed into an infinitesimally small point  SINGULARITY
For reasons still unknown, expansion of the singularity began
All matter and space were created at this instant.
In the first microseconds of expansion (Planck Era), the universe increased in
sized at a faster than light rate  Inflation theory: increased expansion rate
due to an unknown and unstable form of energy
– The universe went from the size of an atom to the size of a grapefruit in 10
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sec.
At 10 -32 sec. electrons, quarks and other subatomic particles formed
10 -6 sec. protons and neutrons form
300,000 years after the big bang the first atoms of H and He form  Light
1 billion years after the big bang  First Stars Form
BIG BANG
INFLATION AND BIG BANG EXPANSION
Evidence for the Big Bang Theory
The Big Bang Model is supported by a number of important observations.
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The expansion of the universe Edwin Hubble's 1929 observation that
galaxies were generally receding from us provided the first clue that the Big
Bang theory might be right.
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The abundance of the light elements H, He, Li The Big Bang theory predicts
that these light elements should have been fused from protons and
neutrons in the first few minutes after the Big Bang.
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The cosmic microwave background (CMB) radiation The early universe
should have been very hot. The cosmic microwave background radiation is
the remnant heat leftover from the Big Bang. (COBE and WMAP)
The COBE satellite was developed by NASA's Goddard Space Flight Center to
measure the diffuse infrared and microwave radiation from the early universe to the
limits set by our astrophysical environment.
Cosmic Background Explorer
The COBE satellite carried three instruments
1. Diffuse Infrared Background Experiment (DIRBE) to search for the cosmic infrared
background radiation (CIB).
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The CIB represents a "core sample" of the Universe; it contains the cumulative emissions of stars and galaxies
dating back to the epoch when these objects first began to form.
The COBE CIB measurements constrain models of the cosmological history of star formation and the buildup
over time of dust and elements heavier than hydrogen, including those of which living organisms are composed.
Dust has played an important role in star formation throughout much of cosmic history.
2. Differential Microwave Radiometer (DMR) to map the cosmic radiation sensitively
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The CMB was found to have intrinsic "anisotropy“ or fluctuations for the first time, at a level of a part in 100,000.
These tiny variations in the intensity of the CMB over the sky show how matter and energy was distributed when
the Universe was still very young.
Later, through a process still poorly understood, the early structures seen by DMR developed into galaxies,
galaxy clusters, and the large scale structure that we see in the Universe today.
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3. Far Infrared Absolute Spectrophotometer (FIRAS) to compare the spectrum of the
cosmic microwave background radiation with a precise blackbody.
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The cosmic microwave background (CMB) spectrum is that of a nearly perfect blackbody with a temperature of
2.725 +/- 0.002 K.
This observation matches the predictions of the hot Big Bang theory extraordinarily well, and indicates that
nearly all of the radiant energy of the Universe was released within the first year after the Big Bang.
• WMAP has mapped the Cosmic Microwave Background (CMB)
radiation (the oldest light in the universe) and produced the first fineresolution (0.2 degree) full-sky map of the microwave sky
• WMAP determined the age of the universe to be 13.73 billion years
old to within 1% (0.12 billion years)
WMAP (cont.)
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WMAP nailed down the curvature of space to within 1% of "flat" Euclidean,
improving on the precision of previous award-winning measurements by over
an order of magnitude
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WMAP's precision determination that ordinary atoms (also called baryons)
make up only 4.6% of the universe (to within 0.1%)
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WMAP's complete census of the universe finds that dark matter (not made up
of atoms) make up 23.3% (to within 1.3%)
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WMAP's accuracy and precision determined that dark energy makes up
72.1% of the universe (to within 1.5%), causing the expansion rate of the
universe to speed up.
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WMAP discovered that the universe was reionized earlier than previously
believed. By measuring the polarization in the CMB it is possible to look at
the amplitude of the fluctuations of density in the universe that produced the
first galaxies.
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WMAP has started to sort through the possibilities of what transpired in the
first trillionth of a trillionth of a second
Large Scale Structures
• Galactic Filaments
– Also known as Great walls , Supercluster
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complexes or Sheets
Not gravitationally bound and therefore take part
in
the Hubble expansion
Largest known cosmic structures in the universe
massive, thread-like structures with a typical length of 50
to 80 megaparsecs that form the boundaries between
large voids in the universe.
consist of gravitationally-bound galaxies; parts where a
large number of galaxies are very close to each other are
called superclusters.
• Voids
– the empty spaces between filaments
– contain very few, or no, galaxies
– have a diameter of 11 to 150 Megaparsecs
• Great Attractor
– a gravity anomaly in intergalactic space within the range of the
Centauries Supercluster that reveals the existence of a localized
concentration of mass equivalent to tens of thousands of Milky
Ways
– observable by its effect on the motion of galaxies and their
associated clusters over a region hundreds of millions of light years
across.
• Galactic cluster
– A system of galaxies containing from several
to thousands of member galaxies
• Galaxy
– A collection of stars, gas and dust held
together by gravity
Galactic Filaments of the Local Universe
11,000 Galaxies
with the Milky Way at the center
A Close up View of Home
It doesn’t add up.
• Data collected from COBE and WMAP indicates that the
universe is too large and “lumpy” in structure to have
formed in 13.7 billion years.
• More time was needed
– Inflation theory: microseconds after expansion of the
universe began there was an inflated increase in the
expansion rate of the early universe.
– This was due to the interaction of a mysterious form a
matter and energy which accounts for the majority of
matter and energy in the universe today
• Dark Matter
• Dark Energy
Dark Matter
• matter that is inferred to exist from gravitational effects on
visible matter and gravitational lensing of background
radiation
• neither emits nor scatters light or other electromagnetic
radiation (and so cannot be directly detected via optical or
radio astronomy).
• Its existence was hypothesized to account for discrepancies
between calculations of the mass of galaxies, clusters of
galaxies and the entire universe and calculations based on
the mass of the visible "luminous" matter these objects
contain
– stars and the gas and dust of the interstellar and intergalactic
medium.
• Evidence
– Galactic rotation curves: stars in galaxies move at different rates
– Velocity dispersions of galaxies: galaxies are being dispersed at
different velocities from one another
– Galaxy clusters and gravitational lensing: the structure of
clusters and the lensing effect of galaxies are caused by the
gravitational effect of dark matter that surrounds galaxies in halo
type structures
– Cosmic microwave background: CMB not uniform on a large
scale (lumpy); fluctuations in the radiation caused by
gravitational effect of dark matter
Dark Energy
• a hypothetical form of energy that permeates all of space and tends to
increase the rate of expansion of the universe.
• the most accepted theory to explain recent observations that the
universe appears to be expanding at an accelerating rate.
• Evidence
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Supernovae: rate at which light reaches us is increased
– Cosmic Microwave Background: universe in nearly flat therefore mass/energy =
critical density to have a flat universe; visible energy not enough
– Large Scale Structure: only accounts for 30% of total matter in universe
– Late-time Integrated Sachs-Wolfe Effect: Accelerated cosmic expansion causes
gravitational potential wells and hills to flatten as photons pass through them,
producing cold spots and hot spots on the CMB aligned with vast supervoids and
superclusters. This so-called late-time Integrated Sachs-Wolfe effect (ISW) is a direct
signal of dark energy in a flat universe
Composition of the Universe
Shape of the Universe
• Critical density ~ 6 H atoms/m3.
• Density of the Universe is close to this amount,
therefore the Universe is probably infinite.
GALAXIES
A galaxy is collection of stars, gas and dust held
together by gravity.
GALAXY FORMATION
STEP 1
• About 1 billion years after the “big bang” dark matter and cooling
gas condense and collapses under its own gravity to form a
PROTOGALAXY
STEP 2
• Gravity separates out the protogalaxy into a core and a halo.
STEP 3
• The subatomic particles that make up the gas interact to lose
energy and fall to the core of the protogalaxy.
STEP 4
• The dark matter which only weakly interacts, remains in the halo.
The Role of Dark Matter in Galactic Formation
Formation of Protogalaxy
Actual Image of a Protogalaxy
A protogalaxy candidate. The blue galaxy in the image is located approximately 10 billion light years away from us
and about four times farther away than the yellower galaxies in the image. The spectrum of the galaxy indicates it is
only about 10 million years old--a relative baby in terms of galaxy evolution.
PROTOGALAXY
Galaxy Evolution
Galaxy evolution is process of gravitational
interaction between dark and visible matter
and collisions between large galaxies.
1. Irregular galaxies condense to form globular clusters.
2. Globular cluster collide to form spirals which collide to form ellipticals.
Types of Galaxies
Galactic
Structure
ACTIVE GALACTIC NUCLEI
• Seyfret galaxies, Quasars and Blazars
1. All three are associated with super massive black holes.
2. Many astronomers think they are the same object viewed
from different angles.
3. They shine brighter than any other objects in the universe
4. They all emit great amounts of energy in the form of …
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Infrared radiation
Radio waves
UV radiation
X-ray radiation
Gamma radiation
Seyfert Galaxies
• Spiral shaped galaxies
• low-energy gamma-ray sources
• Rotating super massive black hole releases gamma
ray jets from either pole as matter is destroy
BLAZARS
• A class of active galaxy
characterized by strong,
compact, flat-spectrum
radio emission
• Extremely bright
• Strong gamma ray emissions
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Believed to be active galactic
nuclei whose jets are aligned
within 10° of our line of sight
QUASARS
• Quasi-stellar objects of small angular size and
immense power output.
• Strong radio sources
• Because they are so bright, quasars are some of
the most distant objects we can see in the
universe.
• Huge power output is believed to be fueled by
interactions between the central black hole and
a surrounding "accretion disk":
– a disk of matter that gathers around the black hole in
the galactic nucleus.
Infrared Imaging of Quasar Radio Jets
Infrared Imaging of
Quasar Radio Jets
QUASAR
THE FORMATION STARS
STAR FORMATION
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Stars form inside relatively dense concentrations of interstellar gas and
dust known as molecular clouds.
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These regions are extremely cold (temperature about 10 to 20K, just
above absolute zero). At these temperatures, gases become molecular
meaning that atoms bind together.
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CO and H2 are the most common molecules in interstellar gas clouds. The deep
cold also causes the gas to clump to high densities. When the density reaches a
certain point, stars form.
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Since the regions are dense, they are opaque to visible light and are
known as dark nebula. Since they don't shine by optical light, we must use
infrared radiation and radio telescopes to investigate them.
1. Star formation begins when the interstellar dust and gas is disturbed by some nearby
phenomenon (supernova, galactic collision, etc.)
2. The denser parts of the cloud core collapse under their own weight/gravity.
3. These cores typically have masses around 104 solar masses in the form of gas and dust.
4. The cores are denser than the outer cloud, so they collapse first. As the cores collapse they
fragment into clumps around 0.1 parsecs in size and 10 to 50 solar masses in mass.
5. These clumps then form into protostars and the whole process takes about 10 millions
years.
STAR FORMATION
Protostars:
• Once a clump has broken free from the other
parts of the cloud core, it has its own unique
gravity and identity and we call it a protostar.
1. As the protostar forms, loose gas falls into its center.
2. The infalling gas releases kinetic energy in the form of heat
and the temperature and pressure in the center of the
protostar goes up.
3. As its temperature approaches thousands of degrees, it
becomes a infrared radiation source.
STAR FORMATION
• During the initial collapse, the clump is transparent to radiation
and the collapse proceeds fairly quickly.
• As the clump becomes more dense, it becomes opaque.
1. Escaping infrared radiation is trapped, and the temperature and pressure in the center
begin to increase.
• At some point, the pressure stops the infall of more gas into the
core and the object becomes stable as a protostar.
• The protostar, at first, only has about 1% of its final mass. But the
envelope of the star continues to grow as infalling material is
accreted.
• After a few million years, thermonuclear fusion begins in its core,
then a strong stellar wind is produced which stops the infall of new
mass.
• The protostar is now considered a young star since its mass is
fixed, and its future evolution is now set.
PROTOSTAR