What is the Universe Made

of?

Scales in The Universe• If the Earth were the size of a golf

ball, how far away would the Sun be?

• How far away would Neptune be?

• How far away would the nearest star be?

Kepler’s Laws1. All planets orbit in ellipses with the

Sun at one focus2. The orbit draws out equal areas in

equal times.3. The square of the period is

proportional to the cube of the radius

These apply to all orbiting bodies, not just planets...

Circular Orbits

• Centripetal acceleration

• Gravitational force

• Newton’s 2nd Law

rva2

2rGMmF

maF

Moon Radius of Orbit

Period of Orbit

(km: all nearly circular)

(days)

Io 4.22 x 105 1.77Europa 6.71 x 105 3.55

Ganymede 1.07 x 106 7.15Callisto 1.88 x 106 16.69

rGMv 2

Finding Dark Matter• Use Kepler’s 3rd Law to predict the

velocities of stars around the centre of a galaxy:

– Mass of Galaxy = 28 billion solar masses– 1 solar mass = 2x10

30 kg– G = 6.67x10-11 m3 s-2 kg-1

– 1 light year = 1016m

Measured velocities• Here are the measured velocities

– Do they look like what you predicted?

• Use Kepler’s 3rd Law to estimate the mass of the galaxy

What is Dark Matter?• It’s matter that’s not visible, but can

only be detected by its gravitational effects– Best theory is that it is an exotic particle– If it is what we think it is, we might be

close to finding it!

Here are some other examples…

Expansion of the Universe• In 1929 Edwin Hubble found link

between distances to galaxies and their radial velocities

• Plot Hubble's data

Hubble's DataObject Distance (Mpc) Velocity

(km/s)Object Distance

(Mpc)Velocity (km/s)

S. Mag.

0.032 170 3627 0.9 650

L. Mag.

0.034 290 4826 0.9 150

N.G.C.6822

0.214 -130 5236 0.9 500

598 0.263 -70 1068 1 920

221 0.275 -185 5055 1.1 450

224 0.275 -220 7331 1.1 500

5457 0.45 200 4258 1.4 500

4736 0.5 290 4151 1.7 960

5194 0.5 270 4382 2 500

4449 0.63 200 4472 2 850

4214 0.8 300 4486 2 800

3031 0.9 -30 4649 2 1090

The Hubble Space Telescope

The Hubble Space Telescope

The Cosmic Microwave Background

The contents of the Universe

• We currently think the Universe is composed of three constituents:– Normal matter (“atoms”)– Dark Matter– Dark Energy

• To find out how much of each, we need to look at the evidence

Heavens’ Kitchen• Choose your ingredients

– Total Matter, Normal Matter, Dark Energy

• How does the Cosmic Microwave Background Compare?

• When did Galaxies form?• How to the galaxies compare?

What is the Universe made of?

• We think the Universe is made of:– 5% Normal matter– 27% Dark Matter– 68% Dark Energy

The Planck Satellite

• 4x4x4m• 2 tonnes on launch• 2m mirror• Cooled to 0.1K• 2 instruments• 300-10000 microns

All sky (visible)

www.chromoscope.net

DSS

All-sky (microwave)

Planck