Planets & LifePlanets & LifePHYS 214PHYS 214

Dr Rob ThackerDr Rob ThackerDept of Physics (308A)Dept of Physics (308A)

thacker@astro.queensu.cathacker@astro.queensu.caPlease start all class related emails Please start all class related emails

with “214:”with “214:”

Today’s LectureToday’s Lecture

Cosmology continued…Cosmology continued… The Early Universe to GalaxiesThe Early Universe to Galaxies

Assignment 1 will be on the web Assignment 1 will be on the web tonighttonight

Due in two weeks timeDue in two weeks time

Origin of GalaxiesOrigin of Galaxies

The formation of galaxies is intimately The formation of galaxies is intimately tied to the earlier history of the Universetied to the earlier history of the Universe

Thus, to fully understand galaxy Thus, to fully understand galaxy formation, we must look at even earlier formation, we must look at even earlier epochs of the Universeepochs of the Universe

In fact, we must go almost all the way In fact, we must go almost all the way back to just after the Big Bang to back to just after the Big Bang to discover the first processes that discover the first processes that contribute to the formation of galaxiescontribute to the formation of galaxies

Galaxy formation in a Galaxy formation in a nutshellnutshell

Gravity is the driving force behind galaxy formationGravity is the driving force behind galaxy formation Any region of space that contains enough matter (is Any region of space that contains enough matter (is

at a high enough at a high enough densitydensity) to overcome the ) to overcome the expansion of the Universe will begin “gravitational expansion of the Universe will begin “gravitational collapse” and start to form a galaxy collapse” and start to form a galaxy Two competing effects: cosmic expansion versus the Two competing effects: cosmic expansion versus the

gravitational attraction of the mattergravitational attraction of the matter Any region that has enough density to contract is called Any region that has enough density to contract is called

overdense overdense relative to the average density of the Universerelative to the average density of the Universe The distribution of these regions is very variableThe distribution of these regions is very variable

There will be small regions that are overdense and large There will be small regions that are overdense and large onesones

Movie of gravitational Movie of gravitational collapsecollapse

But how do these overdense regions arise? What is the But how do these overdense regions arise? What is the perturbationperturbation that causes them? that causes them?

The Planck EpochThe Planck Epoch Before t=10Before t=10-43-43 s after the Big Bang the Universe s after the Big Bang the Universe

was governed by a single force “Superforce”was governed by a single force “Superforce” All the forces of Nature (Gravity, Electromagnetism, All the forces of Nature (Gravity, Electromagnetism,

Weak Nuclear Force, Strong Nuclear Force) were Weak Nuclear Force, Strong Nuclear Force) were merged into this Superforcemerged into this Superforce

Temperature is above 10Temperature is above 103232 K K This epoch is not open to scientific investigation This epoch is not open to scientific investigation

as we don’t have the theory we need as we don’t have the theory we need Could be string (or now “m-”) theoryCould be string (or now “m-”) theory Could be something elseCould be something else

The Epoch of Grand The Epoch of Grand UnificationUnification

Once gravity separates from the Once gravity separates from the Superforce we are left with Gravity + Superforce we are left with Gravity + the three other forces unified into a the three other forces unified into a Grand Unified TheoryGrand Unified Theory So two forces nowSo two forces now

Time is now just after 10Time is now just after 10-43-43 s s Temperature is around 10Temperature is around 103232 K K Universe is now full of various “GUT” Universe is now full of various “GUT”

particles particles

Inflation (Alan Guth, Inflation (Alan Guth, 1982)1982)

It is now widely believed that 10It is now widely believed that 10-35-35 s after s after the Big Bang the Universe went through a the Big Bang the Universe went through a period of period of accelerated expansionaccelerated expansion The Universe suddenly “inflated” in sizeThe Universe suddenly “inflated” in size Universe temperature was about 10Universe temperature was about 102727 K K

We measure the amount of expansion in We measure the amount of expansion in terms of the relative scale of the Universe terms of the relative scale of the Universe at one epoch to anotherat one epoch to another A simple function the A simple function the scale factor, a(t),scale factor, a(t), gives the gives the

relative size versus timerelative size versus time Normally the amount of expansion versus Normally the amount of expansion versus

time, time, t,t, is is a(t)a(t)tt2/32/3

During inflation, the amount of expansion is During inflation, the amount of expansion is proportional to proportional to a(t)a(t)eett

Growth of the scale factor Growth of the scale factor during Inflationary Epochduring Inflationary Epoch

Normal growth

Growth duringInflationary Epoch

(Relative scale)

Universe had expanded by an enormous amount (~1050) at the end of theInflationary Epoch (10-32 s after theBig Bang)

But what caused this But what caused this expansion?expansion?

Around 10Around 10-35-35 s after the Big Bang the Strong s after the Big Bang the Strong Nuclear force separates out of the Grand Unified Nuclear force separates out of the Grand Unified TheoryTheory So now have Gravity, Strong Force, but Weak Force So now have Gravity, Strong Force, but Weak Force

and electromagnetism are combined in the Electroweak and electromagnetism are combined in the Electroweak forceforce

It is believed this separation leads to the creation It is believed this separation leads to the creation of a very unusual energy state for the vacuum a of a very unusual energy state for the vacuum a ““false vacuumfalse vacuum”” This energy state essentially means This energy state essentially means space repels itselfspace repels itself

Once the Universe has a reached a certain point Once the Universe has a reached a certain point though this field “turns off” and the expansion though this field “turns off” and the expansion rate slows down enormouslyrate slows down enormously Exactly how this happens is still the subject of much Exactly how this happens is still the subject of much

researchresearch

What happens to average What happens to average density of space?density of space?

Things are really very very smooth early onThings are really very very smooth early on As inflation begins the energy of the universe As inflation begins the energy of the universe

is dominated by the quantum field that is dominated by the quantum field that makes up the “false vacuum”makes up the “false vacuum”

Due to quantum effects this field will be Due to quantum effects this field will be minutely different from one place to anotherminutely different from one place to another

There will be different energies in one place There will be different energies in one place to anotherto another

So there will be very small, but predictable, So there will be very small, but predictable, differences in density from one place to differences in density from one place to anotheranother

These differences in density will be the seeds These differences in density will be the seeds of galaxy formation later onof galaxy formation later on

At 10At 10-12-12 seconds… seconds…

The Electroweak force splits into the The Electroweak force splits into the weak nuclear force and electromagnetismweak nuclear force and electromagnetism

Temperature is now 10Temperature is now 101515 K K Still too hot to create atoms as protons Still too hot to create atoms as protons

and neutrons have not been formedand neutrons have not been formed At 10At 10-6-6 s, 10 s, 101313 K protons and neutrons are K protons and neutrons are

formedformed After 3 minutes, 10After 3 minutes, 1099 K, neutrons and K, neutrons and

protons combine to form nuclei of atoms - protons combine to form nuclei of atoms - nucleosynthesisnucleosynthesis

The Electroweak force splits into the The Electroweak force splits into the weak nuclear force and electromagnetismweak nuclear force and electromagnetism

Temperature is now 10Temperature is now 101515 K K Still too hot to create atoms as protons Still too hot to create atoms as protons

and neutrons have not been formedand neutrons have not been formed At 10At 10-6-6 s, 10 s, 101313 K protons and neutrons are K protons and neutrons are

formedformed After 3 minutes, 10After 3 minutes, 1099 K, neutrons and K, neutrons and

protons combine to form nuclei of atoms - protons combine to form nuclei of atoms - nucleosynthesisnucleosynthesis

Big BangBig Bang

NucleosynthesiNucleosynthesiss This is a triumph of This is a triumph of

modern nuclear theorymodern nuclear theory We can calculate - with We can calculate - with

exquisite precision - the exquisite precision - the primordial levels of primordial levels of Hydrogen, Helium, Hydrogen, Helium, Lithium (very little of Lithium (very little of anything else created)anything else created) One One HeHe for ten for ten HH

This composition This composition (predicted by nuclear (predicted by nuclear theory) is in excellent theory) is in excellent agreement with the agreement with the levels levels observed in the observed in the oldest stars oldest stars

Formation of atoms & the Formation of atoms & the Cosmic Microwave Cosmic Microwave

BackgroundBackground Even though the nuclei are formed, before Even though the nuclei are formed, before

about 300,000 years after the Big Bang it about 300,000 years after the Big Bang it is still too hot (above 3000 K) for electrons is still too hot (above 3000 K) for electrons to join with nuclei and form neutral atomsto join with nuclei and form neutral atoms

Up to this point we have a plasma of Up to this point we have a plasma of mostly protons and electronsmostly protons and electrons Remember there is 1/10Remember there is 1/10thth as many as many HeHe nuclei nuclei

When the electrons and protons combine When the electrons and protons combine to form to form HH a photon of light is released a photon of light is released

We detect these photons of light today as We detect these photons of light today as the the Cosmic Microwave BackgroundCosmic Microwave Background An echo of the Big BangAn echo of the Big Bang

We can associate We can associate a temperature a temperature with the photons with the photons arriving from the arriving from the Microwave Microwave backgroundbackground

For each For each direction on the direction on the sky we can then sky we can then make a map of make a map of those those temperature temperature fluctuationsfluctuations

The temperature The temperature turns out to beturns out to beT=2.735±0.060 KT=2.735±0.060 K

Less dense Less dense regions appear regions appear hotter, more hotter, more dense regions dense regions appear coolerappear cooler

COBE measurements(1996)

WMAP measurements(2003)

The CMB is still smooth to onepart in 105!

Cosmological Evolution Cosmological Evolution from the CMB onwardsfrom the CMB onwards

We’re now in the realm of star & galaxy We’re now in the realm of star & galaxy formationformation

Initially the universe is filled with neutral Initially the universe is filled with neutral Hydrogen which can absorb photons of light Hydrogen which can absorb photons of light above a certain frequency (the cosmic “Dark above a certain frequency (the cosmic “Dark Ages”)Ages”) This frequency corresponds to the ionization potential This frequency corresponds to the ionization potential

of H = 2.2of H = 2.21010-18-18 J, via the photon energy equation E=hf J, via the photon energy equation E=hf The formation of the first stars will be just before The formation of the first stars will be just before

the first galaxiesthe first galaxies Which will then merge to form larger galaxies….Which will then merge to form larger galaxies….

Summary of evidence for Summary of evidence for the Big Bangthe Big Bang

Hubble flow: recession of the galaxies, and expansion of the universe

The existence and nature of the Cosmic Microwave Background

The abundances of Helium, Lithium, Boron, Beryllium

Age of universe and oldest stars agree

Hubble’s deepest view of the Hubble’s deepest view of the UniverseUniverse

Formation of GalaxiesFormation of Galaxies

Because dark matter is the dominant Because dark matter is the dominant matter component of the Universe it matter component of the Universe it “drives” the galaxy formation process“drives” the galaxy formation process

Visible matter in galaxies (Visible matter in galaxies (i.e.i.e. stars) stars) will always be embedded within the will always be embedded within the larger dark matter “halo”larger dark matter “halo”

Mapping dark matter is extremely Mapping dark matter is extremely hard since it does not emit hard since it does not emit electromagnetic radiationelectromagnetic radiation We can only infer it’s presenceWe can only infer it’s presence

Types of GalaxiesTypes of Galaxies

This is NOT an evolutionarysequence – just a classificationscheme.The theory of galaxy formationmust explain all these differenttypes of galaxies.

Hierarchical Formation of Hierarchical Formation of GalaxiesGalaxies

The first movie of The first movie of galaxy formation I galaxy formation I showed clearly showed clearly demonstrates how demonstrates how important galaxy important galaxy mergers aremergers are

There were many There were many more mergers in the more mergers in the past than nowpast than now

Nonetheless, we can Nonetheless, we can still see these still see these mergers todaymergers today

Origin of spinOrigin of spin Galaxies spin partly Galaxies spin partly

because they collapse in because they collapse in an asymmetric fashionan asymmetric fashion

Material around them Material around them then exerts an unequal then exerts an unequal pull on the material as it pull on the material as it falls in falls in

This (really small) amount This (really small) amount of rotation is amplified of rotation is amplified greatly as the radius of greatly as the radius of the collapsing material the collapsing material reducesreduces

This is due to conservation This is due to conservation of angular momentumof angular momentum

Recall a skater spins faster Recall a skater spins faster as they pull their arms inas they pull their arms in

vmrL

Protogalaxy spinsslowly

Collapsing galaxyspeeds up spinas it gets smaller

Final spiral galaxy

Food for thought: the Food for thought: the fundamental constants of fundamental constants of

naturenature There are many (unexplained) constants There are many (unexplained) constants

used in the equations for the physical used in the equations for the physical forcesforces e.g.e.g. GG, Newtons gravitational constant, or , Newtons gravitational constant, or

the unit of charge on the electron, the unit of charge on the electron, ee If any of these values were changed - by If any of these values were changed - by

even a small amount - stars would not even a small amount - stars would not formform

Since the formation of stars is a Since the formation of stars is a precursor to the formation of life, precursor to the formation of life, is the is the Universe in fact tuned to form lifeUniverse in fact tuned to form life??

Summary of lecture 5Summary of lecture 5 There are 4 strong pieces of supporting There are 4 strong pieces of supporting

evidence for the Big Bangevidence for the Big Bang Big Bang NucleosynthesisBig Bang Nucleosynthesis Expansion of the UniverseExpansion of the Universe Age of the oldest stars versus estimated age of the Age of the oldest stars versus estimated age of the

UniverseUniverse The Cosmic Microwave BackgroundThe Cosmic Microwave Background

The origin of galaxies dates back to some of the The origin of galaxies dates back to some of the earliest moments after the Big Bangearliest moments after the Big Bang

Minute quantum fluctuations in the density of Minute quantum fluctuations in the density of space are eventually amplified to form galaxiesspace are eventually amplified to form galaxies

Galaxies form through the merger of smaller Galaxies form through the merger of smaller systems to form larger onessystems to form larger ones

Next lectureNext lecture

Questions of fine tuning & life: The Questions of fine tuning & life: The Cosmological Anthropic Principle(s)Cosmological Anthropic Principle(s)