I'm having trouble deriving the amount of dimming expected of standard candles (eg. type 1a supernovae) as a result of dark energy.(adsbygoogle = window.adsbygoogle || []).push({});

Without the presence of dark energy, the standard GR solution (matter-only, at critical density) is that the absolute bolometric brightness of a standard candle varies with redshift z as 1/(1+z - [1+z]^{1/2})^{2}. This expression is the product of two terms: 1/D_{L}^{2}multiplied by 1/(1+z)^{2}. Here D_{L}is the "luminosity distance", which is the expected dimming of light due to geometry. As it turns out, D_{L}is a function of z so that the product simplifies to 1/(1+z - [1+z]^{1/2})^{2}.

Suppose that recent stretching of space due to dark energy is by a factor of b (b>1). Obviously this would change the redshift, replacing 1+z with b(1+z) for a given distant object. (This factor b is the extra stretch that occurred between the time when a given distant object emitted a photon and the present when the photon is received.) How would the factor b change the geometric distance term?

The observed luminosity at z=1 is only about half of the value 1/(1+z - [1+z]^{1/2})^{2}. If one simply replaces 1+z with b(1+z), luminosity vs. redshift curve remains the same instead of reducing to about half at z=1.

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Standard Candle Dimming Due to Extra Expansion

**Physics Forums | Science Articles, Homework Help, Discussion**