what is the universe made of?
DESCRIPTION
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 Laws. All planets orbit in ellipses with the Sun at one focus - PowerPoint PPT PresentationTRANSCRIPT
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 Laws
1. All planets orbit in ellipses with the Sun at one focus
2. 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
r
va
2
2r
GMmF
maF
Moon Radius of Orbit
Period of Orbit
(km: all nearly circular)
(days)
Io 4.22 x 105 1.77
Europa 6.71 x 105 3.55
Ganymede 1.07 x 106 7.15
Callisto 1.88 x 106 16.69
r
GMv 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 = 2x1030
kg
– G = 6.67x10-11
m3 s
-2 kg
-1
– 1 light year = 1016
m
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
Planck Observations
All sky (visible)
www.chromoscope.net
DSS
All-sky (microwave)
Planck