Hubble’s Law: Measuring the Age of the Universe Dr Lisa Jardine-Wright Cavendish Laboratory, University of Cambridge

Einstein 1915 • General Theory of Relativity: – Told astronomers that the Universe was either expanding or contracting depending on the amount of Mass and Energy in the Universe – Einstein didn’t like this idea so modified his theory to ensure that the Universe was static.

1926 29 Hubble’s Observations

Experiment • Using cutting edge data and images we are going to reproduce Edwin Hubble’s observations.

• To do this we need to measure the distance and velocity to a number of spiral galaxies and see if we observe a relation between these two quantities.

Part 1: Distance

Part 1: Distance

Galaxy

Size (mm)

Distance (Mpc)

λ CaK CaH

Z 1

=( λ - 3933.7) 3933.7

λ

Z 2

=( λ - 3968.5) 3968.5

Average z Z = z 1 +z 2 2

Velocity (km/s) v=cz

(c = 3x10 5 km/s)

NGC 1357 NGC 2276 NGC 2903 NGC 3627 NGC 4775 NGC 6181 NGC 6643 NGC 1832 NGC 5248

Part 1: Distance 120 110 100 90 80 70 60 50 40 30 20 10 0 0 20 40 60 80 100 120

Measured diameter in (mm)

140 160 180 200

Part 1: Distance

Galaxy NGC 1357 NGC 2276 NGC 2903 NGC 3627 NGC 4775 NGC 6181 NGC 6643 NGC 1832 NGC 5248

Size (mm)

Distance (Mpc)

λ CaK CaH

Z 1

=( λ - 3933.7) 3933.7

λ

Z 2

=( λ - 3968.5) 3968.5

Average z Z = z 1 +z 2 2

Velocity (km/s) v=cz

(c = 3x10 5 km/s)

Part 2: Velocities • White light can be split into its component colours or wavelengths – Spectrum

Part 2: Velocities • How do we measure the velocities of distant galaxies?

– Redshift The astronomical Doppler effect

Part 2: Velocities • Different chemicals absorb and emit light of different colours or wavelengths .

Part 2: Velocities • The wavelength of the emission and absorption lines from elements in our galaxy are

redshifted

due to their velocity away from us.

– If we can measure how much they are shifted we can calculate their velocity λ 0 galaxy and c

shift

 0  = speed of light v c = wavelength of line in the Lab, v = velocity of the

Example • λ = 3962, λ 0 = 3933.7, c = 3 x 10 5 km/s    0  0  v c 3962  3933 .

7 3933 .

7  v 3 x 10 5 v  2158 km/s

Part 2: Velocities

Galaxy Example NGC 2276

Size (mm)

Distance (Mpc)

CaK CaH λ 3962

Z 1

=( λ - 3933.7) 3933.7

0.007

λ 4000

Z 2

=( λ - 3968.5) 3968.5

0.008

Average z Z = z 1 +z 2 2 0.0075

Velocity (km/s) v=cz

(c = 3x10 5 km/s) 2250

NGC 2903 NGC 3627 NGC 4775 NGC 6181 NGC 6643 NGC 1832 NGC 5248

Hubble’s Law

Galaxy

Size (mm)

Distance (Mpc)

λ CaK

Z 1

=( λ - 3933.7) 3933.7

NGC 1316 NGC 2276 NGC 2903 NGC 3627 NGC 4775 NGC 6181 NGC 6643 NGC 1832 NGC 5248

λ CaH

Z 2

=( λ - 3968.5) 3968.5

Average z Z = z 1 +z 2 2

Velocity (km/s) v=cz

(c = 3x10 5 km/s)

Hubble’s Law

Hubble's Law Distance (Mpc)