the accelerating universe the hubble diagramredshiftstandard candlescepheid variable...
TRANSCRIPT
The Accelerating Universe
The Hubble Diagram
Redshift
Standard Candles
Cepheid Variable Stars
Supernovae
Interpretation
2
The Hubble Diagram
CZ(km/s)
D (Mpc)
Δy
Δx
Slope = Δy/Δx = H0
3
Redshift
Redshift & Blueshift
when
λe
λo
4
Absorption lines can be blue-shifted (galaxy is moving toward us) or redshifted (galaxy is moving away). The velocity can be measured by the shift in the wavelength:
v = cz = (λo - λe)/λo
λo
λe
5
Standard Candles
Cepheids & Supernovae
A standard candle is an astrophysical object whose absolute magnitude is well known. By comparing the relative intensity of light observed from the object, with that based on its known absolute magnitude, the inverse square law for light intensity can be used to determine the distance to the object.
6
The Inverse Square Law of Light
… relates the absolute luminosity, M of an object to its apparent luminosity m by m = M / r^2 where r is the distance.
7
Cepheid Variable Stars
8
NGC 4526
Supernova 1994D
Supernovae
9
Original Hubble Diagram
CZ(km/s)
D
4
3
2
10
D1 D2
(Mpc)
D3 D4
Z4
Z3
Z2Z1Z0
D0
10
InterpretationH4 > H3 Decelerating
Universe
H3 > H2 Decelerating Universe
H2 < H1 Accelerating Universe
H1 < H0 Accelerating Universe
H = kilometres per second per Megaparsec
11
Cosmological constant or Quintessence?
What next?
12
Only one option!!!
13
The Big Rip
At last: proton decay