Lecture notes, lectures 1 - 2 PDF

Preview

Summary

Download Lecture notes, lectures 1 - 2 PDF

Description

Dark Matter and the Universe Topic 1 Dark Matter, Dark Energy and the Cosmology Revolution! What is the real structure of our Universe and how do we know it is so? !

Contents of Topic 1

This first Topic provides an introduction to the Dark Matter Problem, putting it in the context of current understanding of the composition of the Universe and covering some of the essential Cosmology and tools needed to study it.

‣ What do we mean by Dark Matter and why bother? ‣ Composition of the Universe & the Cosmology Revolution ‣ What could the Dark Matter be? ‣ Cosmology and tools for Dark Matter? ‣ The Cosmological Principle, Isotropy and Homogeneity ‣ The Big Bang ‣ Hubble’s Law and Redshift ‣ Critical Density ρc and the Density Parameter Ω0 ‣ The geometry of space and Inflation

What! is Dark Matter and Why Bother? ‣ The name Dark Matter attests to the fact it doesn’t give off light. Yet it provides the gravitational pull to hold together the galaxies and clusters we see in the Universe today.!

‣ We see the effects of Dark Matter everywhere – it bends light, it makes gas move at great velocity, without it galaxies would fly apart.!

‣ It must be something other than bright stars, but what?! !‣ So we should bother very much about ! Dark Matter. It is a dominant material in our Universe and yet we do not know what it is made of. It most likely will lead us to completely new physics.

‣ The term Dark Matter simply means material that is Non-Luminous.

! The Composition of the Universe

‣ In more detail current results give us the Mass-Energy

Composition of the Universe approximately as follows: !

!

‣ Note again! the

small fraction of visible atoms!

‣ Note how Dark Matter and Dark Energy dominate!

! The Composition of the Universe

‣ The little bit of the matter in the Universe we really know about can be broken down as follows: !

!

‣ Interesting fact: Neutrinos contribute about the same massenergy content to the Universe as do all the stars.

! The Composition of the Universe

more detail if we look at individual galaxies we see how ‣ In Dark Matter dominates galaxies but Dark Energy has the biggest influence in the Universe as a whole. !

!

Observable ! Universe

Galaxies

Ordinary Matter Dark Matter Dark Energy

Ordinary Matter Dark Matter Dark Energy

The Composition of the Universe ! ‣ These results are relatively recent - we are living through a period of cosmology and particle physics revolution.!

‣ For the first time in history we have a good picture of the

Universe - called the Inflationary Big Bang Model or the Standard Model of Cosmology.!

‣ We also have a good picture of the fundamental particles and forces - the Standard Model of Particle Physics.!

‣ The merging of these areas of science, Astrophysics,

Cosmology and Particle Physics, are giving us new and powerful insights, forged around the new disciplines of Particle Astrophysics and Particle Cosmology. !

‣ However, big questions remain…:! !

‣

The Cosmology Revolution!

So we have two important models but there are gaps.

Big Questions in Remain! ‣ A few of these questions are as follows: 1. How did the structure of the Universe we observe form?! 2. What is the Dark Matter?! 3. Could there be more than one kind of Dark Matter?! 4. Why is the Dark Matter distributed the way it is?! 5. Could the Dark Matter be new fundamental particles?! 6. What is the Dark Energy?!

!

What! does the Term Dark Matter Mean? ‣ “Dark Matter” means any Non-Luminous material that shows its presence by its gravitational influence.! ‣ Here’s an old example:! ! !

Calculate the Earth’s Mass two ways!

typical ! - 40,075 km! ‣ Earth’s circumference rock ‣ Typical rock density - 2.8 g/cm3! ‣ Use this to estimate the mass - ANS (1)………

gravity ‣ Newton says ‣ g = 9.8 m/sec2, G = 6.67 x 10-11m3/(kg sec2)! ‣ Use this to estimate the mass - ANS (2)………..

!

Dark Matter in the Universe !

‣ In the previous calculation we get a factor ~x2 discrepancy

due to the gravitational effect of the hidden high density “dark matter” core of the Earth. But how do we know there is hidden matter throughout the Universe? !

‣ Later Topics will cover many of the techniques used by Cosmologists, here is a summary:

1. Observation of Rotational Curves of Galaxies! 2. Observation of Gravitational Lensing! 3. Observation of Hot Gas in Galaxy Clusters ! 4. Computer simulations of Cluster Evolution! 5. Analysis of Large Scale Structure ! 6. Analysis of the Cosmic Microwave Background !

‣ All these show us that Dark Matter pervades the Universe

Dark Matter and Structure Formation !

‣ A particularly interesting

result comes from computer simulations which model Structure Formation in the Universe. It is impossible to get a match to the observed structure, with voids and clumps, without accounting for Dark Matter.!

‣ This example simulation is from the EAGLE group.

So What Could the Dark Matter be? !

‣ When considering Dark Matter it turns out we can think two ! broad classifications: Baryonic Dark Matter (normal matter but non-luminous) ! !

Some examples to be covered in later Topics are:! (1) Dim Stars (...