Understanding Dark Energy

Yesterday I mentioned that the CFHTLS was using distant supernova to study the mysterious dark energy. The Supernova Legacy Survey (SNLS), as it is referred to, will detect hundreds of supernova out to a redhift of 1. SNLS uses Type Ia supernovae as standard candles to study the acceleration of the universe. Supernovae at high redshift are very faint.

SNLS detects supernovae by comparing the current image of a patch of sky with a template image taken previously. ? A computer program studies both images looking for new stars. Can you see the SN in the image to the far left which is not in the other image?

In order to use the SN to study dark energy we need to know the distance to the supernova. Since we (think) we know how bright the SN are intrinsically the measured peak brightness gives us a direct measurement of the distance. We also need to measure the reshift of the SN from a spectrum. This requires the largest optical telscopes in the world such as the 8-m Gemini. Some of the spectra from Gemini of detected SN are to the left. The measured spectra are the very squigly lines while the smoother line is the fit of a template SN spectrum.

The SNLS group published their results in late 2005 based on the first year (out of five) of SNLS data. These results already place the tightest constraints on the nature of dark energy when combined with the results from WMAP. SNLS is a good example at how astronomers are using data from several telescopes, both on the ground and in space, to tackle the challenges in understanding the Universe.