Lecture 21: The Formation of the Universe

Lecture 21: The Formation of the Universe
SCI238 W08 Lecture 21: The Formation of the Universe 2Mass survey shows rich structure in the distribution of galaxies L21 – Apr 1/08 Cosmology: the Early Universe

Cosmology: the Early Universe
This week’s events: the Moon: New Moon Apr. 5 (11:55 PM) Mercury: not visible Venus: difficult to see, visible in the morning Mars: high in southwest at sunset, sets in the middle of the night Jupiter: rises at midnight Saturn: perfect evening object - very high in the south at sunset, sets at 11pm. L21 – Apr 1/08 Cosmology: the Early Universe

Today’s Lecture the age of the Universe the Big Bang model micromave background: CMB chemical abundances: H, He… the early evolution of the Universe physical conditions in early Universe creation of matter, nucleosynthesis… problems: flatness, critical density, structure large scale structure of the Universe (clusters, superclusters, voids) the formation of galaxies L21 – Apr 1/08 Cosmology: the Early Universe

the Universe, past and future: what are the possibilities?... L21 – Apr 1/08 Cosmology: the Early Universe

the universe, past and future: some possibilities L21 – Apr 1/08 Cosmology: the Early Universe

Acceleration of the Universe also affects its age…
L21 – Apr 1/08 Cosmology: the Early Universe

How does the Hubble constant allow us to determine the Age of the Universe? the Hubble constant H0 = 71 ± 3.5 km/s∙Mpc in an empty Universe the age is 1/H0 = 13.8x109y (~14 Gy) note: units of Ho are inverse time how do we determine this age? since 1Mpc = 106pc = 3.09x1019 km then 71km/s∙Mpc = (70.4km/s)/(3.09x1019km) and 1/H0 = 4.35x1017s = 13.8x109y this calculation assumes H0 is constant – i.e. expansion rate has not slowed down over time… start here 1 April L21 – Apr 1/08 Cosmology: the Early Universe

the Hubble constant and the Age of the Universe
in an empty Universe the age is 1/H0 = 13.8Gy for H0=71 km/s∙Mpc in a flat Universe (at critical density) the age is 2/3 × 1/H0 = 9.2 billion years the age is lower because gravity has slowed the expansion rate note that this is less than the age of the oldest globular clusters = 12 billion years this discordance is a famous problem in astronomy that has been resolved only recently L21 – Apr 1/08 Cosmology: the Early Universe

Evidence for the Big Bang Model
a good scientific model should make predictions which can be verified. the Big Bang model makes two predictions which have been verified since the 1960s: the existence and characteristics of the cosmic microwave background – the leftover heat of the initial explosion was predicted (in the 1930’s!) to still be at a temperature of 3°K and appear as a blackbody would – emission strongest at microwave wavelengths the expected Helium abundance in the Universe L21 – Apr 1/08 Cosmology: the Early Universe

Arno Penzias and Robert Wilson: first observers of the Cosmic Microwave Background Radiation (CBR) L21 – Apr 1/08 Cosmology: the Early Universe

Cosmic Microwave Background
when the Universe had cooled enough, free electrons become bound into atoms of H & He the photons from that recombination were emitted without electrons to scatter them, photons were able to travel unhindered throughout the Universe the Universe became transparent (before that it was filled with particles that could absorb photons, or scatter them) the temperature of the Universe was 3,000 K at this time. L21 – Apr 1/08 Cosmology: the Early Universe

when the universe cooled enough it became transparent: radiation and matter went their own separate ways L21 – Apr 1/08 Cosmology: the Early Universe

the radiation in the universe has cooled from ~3000K to ~3K

the temperature of the Universe has cooled over time – and its BB spectrum has become redder now strongest in radio wavelengths L21 – Apr 1/08 Cosmology: the Early Universe

Cosmic Microwave Background (CMB)
The CMB, predicted in 1930s… accidentally discovered in 1965 by Penzias&Wilson appeared to come from every direction had a perfectly thermal spectrum with a temperature of 2.73 K this is the temperature expected after a Universe expansion of 1,000 times L21 – Apr 1/08 Cosmology: the Early Universe

More recently CMB observed by COBE and WMAP satellites

the density and rate of expansion also determine which elements are produced by primordial nucleosynthesis observed abundances agree with BB predictions + other constraints L21 – Apr 1/08 Cosmology: the Early Universe

Conditions in the Early Universe
The most distant galaxies we observe come from a time when the Universe was a few billion years old. The cosmic microwave background prevents us viewing light from before the Universe was 380,000 years old. So how do we know what conditions were like at the beginning of time? L21 – Apr 1/08 Cosmology: the Early Universe

We know the the conditions & expansion rate of the Universe today. running the expansion backwards: we can predict the temperature & density of the Universe at anytime in its history using basic physics in laboratory experiments we study how matter behaves at high temperatures & densities current experimental evidence provides info on conditions as early as 10–10 sec after the Big Bang L21 – Apr 1/08 Cosmology: the Early Universe

More recently CMB observed by COBE and WMAP satellites

Cosmic Microwave Background…radiation from the Universe at ~400,000yr old mapped over the whole sky by the COsmic Background Explorer (COBE) in 1990s CMB slightly hotter by ~0.003K in one direction of the sky than the other: due to Earth’s motion relative to it very smooth and uniform across the sky… L21 – Apr 1/08 Cosmology: the Early Universe

Cosmic Microwave Background: fluctuations
after subtraction of Earth’s motion …COBE did find slight temperature variations from place to place on the level of a few parts in 100,000. so any point on the sky is within ± of mean brightness fluctuations => early universe was not perfectly smooth – thank goodness! L21 – Apr 1/08 Cosmology: the Early Universe

WMAP (in the past few years) followed with higher resolution data
WMAP combined with other data; many cosmological parameters now well determined L21 – Apr 1/08 Cosmology: the Early Universe

we know the the conditions & expansion rate of the Universe today. running the expansion backwards: we can predict the temperature & density of the Universe at anytime in its history using basic physics in laboratory experiments we study how matter behaves at high temperatures & densities current experimental evidence provides info on conditions as early as 10–10 sec after the Big Bang L21 – Apr 1/08 Cosmology: the Early Universe

The Creation of Matter the early Universe was filled with radiation & subatomic particles. we’ve seen matter converted to energy… but Einstein’s famous equation is a two-way street! E = m c2 If T > 1012 K matter  p+ n e-  p- n e+ L21 – Apr 1/08 Cosmology: the Early Universe antimatter

particle creation and annihilation: two sides of the same coin… L21 – Apr 1/08 Cosmology: the Early Universe

The Destruction of Matter
when two identical particles of matter & antimatter collide… they annihilate each other and form gamma photons during the very first few moments of the Universe… matter and radiation (energy) were continually converting into each other the total amount of mass-energy remained constant L21 – Apr 1/08 Cosmology: the Early Universe

Chapters in the history of the Universe
era of galaxies era of atoms era of nuclei era of nucleosynthesis particle era electroweak era GUT era Planck era L21 – Apr 1/08 Cosmology: the Early Universe

Planck Era (t < 10–43 sec)
BANG! Planck Era (t < 10–43 sec) this era, the “first instant”, lasted for 10–43 sec. because we are as yet unable to link… quantum mechanics (our successful theory of the very small) general relativity (our successful theory of the very large) …we are powerless to describe what happened in this era. 10–43 sec after the Big Bang is as far back as our current science will allow us to go. we suppose that all four natural forces were unified during this era. L21 – Apr 1/08 Cosmology: the Early Universe

GUT Era (10–43 < t < 10–38 sec)
the Universe contained two natural forces: gravity Grand Unified Theory (GUT) force electromagnetic + strong (nuclear) + weak forces unified this lasted until the Universe was 10–38 sec old. at this time, the Universe had cooled to 1029 K the strong force “froze out” of the GUT force the energy released by this caused a sudden and dramatic inflation of the size of the Universe L21 – Apr 1/08 Cosmology: the Early Universe

Electroweak Era (10–38 < t < 10–10 sec)
the Universe contained three natural forces: gravity, strong, & electroweak this lasted until the Universe was 10–10 sec old. at this time, the Universe had cooled to 1015 K the electromagnetic & weak forces separated This was experimentally verified in 1983: discovery of W & Z bosons electroweak particles predicted to exist above 1015 K L21 – Apr 1/08 Cosmology: the Early Universe

Particle Era (10–10 < t < 10–3 sec)
The four natural forces were now distinct. Particles were as numerous as photons. When the Universe was 10–4 sec old… quarks combined to form protons, neutrons, & their anti-particles At 10–3 sec old, the Universe cooled to 1012 K. protons, antiprotons, neutrons, & antineutrons could no longer be created from two photons (radiation) the remaining particles & antiparticles annihilated each other into radiation slight imbalance in number of protons & neutrons allowed matter to remain Electrons & positrons are still being created from photons. L21 – Apr 1/08 Cosmology: the Early Universe

Era of Nucleosynthesis (10–3 sec < t < 3 min)
During this era, protons & neutrons started fusing… but new nuclei were also torn apart by the high temperatures When the Universe was 3 min old, it had cooled to 109 K. at this point, the fusion stopped and, the baryonic matter leftover in the Universe was: 75% Hydrogen nuclei (i.e. individual protons) 25% Helium nuclei trace amounts of Deuterium (H isotope) & Lithium nuclei L21 – Apr 1/08 Cosmology: the Early Universe

Cosmic Helium Abundance
In the Era of Nucleosynthesis, i.e. the first three minutes protons & neutrons roughly equal in number for T > 1011 K for T <1011 K, proton-to-neutron reactions no longer occur neutrons still decay into protons protons begin to outnumber neutrons At T < 1010 K, the products of fusion reactions no longer break up. helium, deuterium, & lithium remain stable At this time, Big Bang model predicts a 7-to-1 proton:neutron ratio. L21 – Apr 1/08 Cosmology: the Early Universe

Cosmic Helium Abundance
For every 2 n & 2 p+ which fused into a Helium nucleus… there are 12 p+ or Hydrogen nuclei Model predicts a 3-to-1 H:He This what we observe: minimum of 25% He in all galaxies L21 – Apr 1/08 Cosmology: the Early Universe

Abundances of Other Light Nuclei
By the time stable 4He formed… the Universe was too cool for He to fuse into C or other heavier nuclei 4He could fuse with 3H to form stable 7Li Deuterium (2H) is a “leftover” isotope. if densities had been greater, fusion would have gone faster, and more neutrons would have ended up in 4He instead of 2H nucleosynthesis models predict the amount of leftover 2H for each density L21 – Apr 1/08 Cosmology: the Early Universe

Abundances of Other Light Nuclei
measured abundance of 2H is one for every 40,000 H atoms compared to the model calculations the density of ordinary matter is 4% of the critical density. density of matter appears to be more like 30% of the critical density. majority of mass in the Universe is extraordinary, such as WIMPs. L21 – Apr 1/08 Cosmology: the Early Universe

Era of Nuclei (3 min < t < 3.8 x 105 yr)
The Universe was a hot plasma of H & He nuclei and electrons. photons bounced from electron to electron, not traveling very far the Universe was opaque When the Universe was 380,000 yrs old… it had cooled to a temperature of 3,000 K electrons combined with nuclei to form stable atoms of H & He the photons were free to stream across the Universe (later these become the CMB) the Universe became transparent L21 – Apr 1/08 Cosmology: the Early Universe

after the universe had cooled to 103K, it was transparent to radiation, and now dominated by matter L21 – Apr 1/08 Cosmology: the Early Universe

Era of Atoms (3.8 x 105 < t < 109 yr)
The Universe was filled with atomic gas. sometimes referred to as the “Cosmic Dark Ages” Density enhancements in the gas and gravitational attraction by dark matter… eventually form protogalactic clouds the first star formation lights up the Universe which provokes the formation of galaxies L21 – Apr 1/08 Cosmology: the Early Universe

Era of Galaxies ( t > 109 yr)
The first galaxies came into existence about 1 billion years after the Big Bang. This is the current era of the Universe. L21 – Apr 1/08 Cosmology: the Early Universe

Shortcomings of the Big Bang Model
So far, we have considered the evidence which supports the Big Bang theory. but, prior to 1980, cosmologists had identified three major questions which the theory was unable to answer: Where does structure come from? Why is the large-scale Universe so smooth? Why is the density of matter almost exactly the critical density? L21 – Apr 1/08 Cosmology: the Early Universe

A solution to shortcomings of the Big Bang Model? inflation…
In 1981, physicist Alan Guth realized that the Grand Unified Theories could hold the answers to these questions. When the strong force froze out of the GUT force… it should have released enough energy to expand the Universe by 1030 times in less than 10–36 sec we call this dramatic expansion inflation L21 – Apr 1/08 Cosmology: the Early Universe

Why is the Large-Scale Universe so Smooth?
in all directions, the Cosmic Microwave Background is uniform. traditional Big Bang model can not explain… how two disparate parts of the Universe, beyond each other’s cosmological horizon, can have the same temperature L21 – Apr 1/08 Cosmology: the Early Universe

Why is the Large-Scale Universe so Smooth?
inflation can solve this problem when the entire Universe was <10–38 light-second across… radiation signals could reach all points in the Universe temperatures were equalized then inflation expanded the Universe so quickly… that many points in the Universe went out of communication with each other L21 – Apr 1/08 Cosmology: the Early Universe

inflation in the young Universe may be the answer to questions about the Big Bang model L21 – Apr 1/08 Cosmology: the Early Universe

Why is the Density of Matter Almost Critical?
The gravitational pull of the Universe almost balances the kinetic energy of its expansion…Why? if matter were at least 10% denser, Universe would have already collapsed if matter were at least 10% less dense, galaxies would have never formed According to General Relativity, an imbalance of these energies imposes a curvature of spacetime. but when they balance, we say that spacetime is “flat” The effect of rapid inflation is to flatten spacetime. thus, inflation imposed the balance of these energies L21 – Apr 1/08 Cosmology: the Early Universe

a universe that starts out perfectly flat, stays perfectly flat
but a universe that starts out only slightly “not-flat” quickly diverges from flatness… L21 – Apr 1/08 Cosmology: the Early Universe

Rapid and large scale change (inflation) explains smoothness and flatness L21 – Apr 1/08 Cosmology: the Early Universe

Where Does Structure Come from?
The density of matter in the early Universe had to differ slightly from place to place. otherwise, galaxies would never have formed traditional Big Bang model does not tell what caused density enhancements Quantum Mechanics: energy fields must fluctuate at a given point. L21 – Apr 1/08 Cosmology: the Early Universe

Where Does Structure Come from?
CMB energy distribution is irregular… on microscopic spatial scales these quantum ripples would be greatly magnified by inflation. large ripples in energy are the seeds for the density enhancements. they imposed a pattern about which structure formed L21 – Apr 1/08 Cosmology: the Early Universe

New Evidence for Inflation
In 2002, Wilkinson Microwave Anisotropy Probe (WMAP) measured the Cosmic Microwave Background with much more precision than COBE. It detected far more subtle, small-scale temperature variations. these help explain structure L21 – Apr 1/08 Cosmology: the Early Universe

new evidence supporting the inflation model (WMAP + other data)
Overall geometry of the Universe is flat. Total matter density is 27% of the critical density. in agreement with M/L in clusters of galaxies Density of baryonic (ordinary) matter is 4.4% of critical density. in agreement with observed abundance of Deuterium Flat geometry + matter density < critical implies dark energy. – the remaining 74%! in agreement with accelerating expansion from white dwarf supernovae Age of the Universe is 13.7x109 y L21 – Apr 1/08 Cosmology: the Early Universe

Evolution of the Universe after the CMB…

Reminder: redshift, distance, and lookback time* z=Δλ/λ v/c distance (Mpc) (Mly) look-back time (Gy) 0.1 0.095 413 1,350 1.29 0.5 0.385 1,880 6,140 5.02 1.0 0.600 3,320 10,800 7.73 5.0 0.946 7,940 25,900 12.50 10.0 0.984 9,660 31,500 13.20 * Age of Universe = 13.9Gy L21 – Apr 1/08 Cosmology: the Early Universe

the distribution of galaxies on the sky is clumpy L21 – Apr 1/08 Cosmology: the Early Universe

the distribution of galaxies and clusters is also clumpy along the line of sight (3D) distances based on galaxy redshifts L21 – Apr 1/08 Cosmology: the Early Universe

Large Scale Structure of the Universe
slice of the Universe out to 109 pc slice of the Universe out to 2 x 108 pc On scales of 108 ly, galaxies are distributed in gigantic chains and sheets surrounding great voids. the chains come from the initial regions of density enhancement the voids come from the initial regions of density depletion On scales of several x 109 ly, galaxies appear evenly distributed. L21 – Apr 1/08 Cosmology: the Early Universe

Modeling Galaxy Formation
With our current telescope technology… we are unable to see back to the time when galaxies first formed we must rely on theoretical (computer) models to describe how galaxies formed The following assumptions are made when constructing these models: Universe was uniformly filled with H & He gas for the first million years after the Big Bang this uniformity was not quite perfect; some regions of the Universe were slightly denser than others L21 – Apr 1/08 Cosmology: the Early Universe

All of the H & He gas expanded with the Universe at first. after about 109 y, the denser regions slowed down and began to collapse under self-gravity the collapsing gas became protogalactic clouds clumping and collapse “aided” by presence of (cold) dark matter L21 – Apr 1/08 Cosmology: the Early Universe

Simulating the growth of structure in the Universe: I

Simulating the growth of structure in the Universe: II

Simulating the growth of structure in the Universe: III

Simulating the growth of structure in the Universe: IV

Simulating the growth of structure in the Universe: V

clumpy structure grows with time, building on original...

Simulating the growth of structure in the Universe
structure develops in many places, each appearing independently, and eventually merging. reminder: z = Δλ / λ L21 – Apr 1/08 Cosmology: the Early Universe

Simulation with dark matter...

What Determines Galaxy Type?
We can explore three options: the initial conditions of the protogalactic cloud; i.e. destined from birth later interactions with other galaxies – at any stage; i.e. a life-altering conversion or some combination… L21 – Apr 1/08 Cosmology: the Early Universe

Two factors to consider when modeling the birth properties of the protogalactic cloud: protogalactic spin …the initial angular momentum determines how fast the cloud will form a disk before it is completely turned into stars protogalactic cooling …the initial density determines how fast the cloud can form stars before it collapses into a disk L21 – Apr 1/08 Cosmology: the Early Universe

This giant elliptical provides evidence for the protogalactic cooling explanation. it is very distant (young) and very red, even accounting for redshift white and blue stars are missing star formation has ceased very early in the galaxy’s history no gas will be left to form a disk z=1.55 (lookback time: 8-10Gy?) L21 – Apr 1/08 Cosmology: the Early Universe

Galaxy Interactions when two spiral galaxies collide tidal forces randomize the orbits of stars gas either falls to the center to form stars or it is stripped out of the galaxies the disk is removed resulting galaxy becomes an elliptical. L21 – Apr 1/08 Cosmology: the Early Universe

merger simulations can help us understand galaxy evolution
the galaxy we see will depend on how long it has been since the merger event, our viewing angle, galaxy masses, encounter velocity etc… L21 – Apr 1/08 Cosmology: the Early Universe

a“ring” galaxy: AM galaxy collision: ring = gas shocked by the passage of an “intruder” L21 – Apr 1/08 Cosmology: the Early Universe

a “polar ring” galaxy: NGC 2685
a disc galaxy disrupted by capture of gas from a nearby galaxy? or?? L21 – Apr 1/08 Cosmology: the Early Universe

NGC 2442: a galaxy distorted by external interaction?
note that star formation seems concentrated in the upper arm L21 – Apr 1/08 Cosmology: the Early Universe

we observe that central black hole mass correlates with galaxy luminosity (mass) so initial gravitational potential well must also play a part L21 – Apr 1/08 Cosmology: the Early Universe

Models of Galaxy Formation
hierarchical lots of small galaxies form, then merge to make bigger ones problem: simulations leave far too many small ones around monolithic large clouds of inter-galactic gas collapse to form large galaxies problem: difficult to make such large clouds of gas in such a short time and combinations how long ago were merger events? how massive were merging galaxies? L21 – Apr 1/08 Cosmology: the Early Universe

Lecture 21: The Formation of the Universe

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