(via APOD: 2011 October 9 - Nobels for a Strange Universe)
The above image from the High-Z project was taken with Hubble back in 1994 of SN 1994D (a nearby Type Ia supernova). This was one of the earliest observed Type Ia supernovae used by three different teams of scientists to propose evidence for dark energy.
Over the last thirteen years, all three projects have continued to study supernovae around the visible universe, trying to confirm the existence of lambda, the universal constant that exists in some cosmological models, notably Einstein’s.
The existence and a source for lambda, however, have been contentious in astronomical circles. It seems, though, that the universe really is expanding a lot faster than we can account for with what we can “see” across the various spectra. And the rate of expansion would be very well explained by dark energy, some kind of energy that is tied to the fabric of space itself but unaccounted for in our current models.
This year’s Nobel Prize in Physics went to the heads of the three teams who’ve been meticulously doing this work to get a better and better idea about dark energy, even if we can’t observe it directly for now.