Is the universe undergoing an accelerated expansion?
One other study to determine the mass density had a surprising result. This was a study of type Ia supernovas.12,13 When a white dwarf star is in orbit with a normal giant companion star, the white dwarf can draw material off its companion. When a critical amount of accumulated mass is reached, the white dwarf collapses into a neutron star in a supernova explosion. Such explosions that lack hydrogen lines in their spectrum are known as type Ia’s. It is found that they have a characteristic brightness versus decay time. If we know the decay time of one, we then know its absolute brightness, and by comparing that to the relative brightness we can determine its distance independently from redshifts caused by the Hubble expansion of the universe. Type Ia’s show yet again that the universe has a low critical mass density, but they show something else as well. Distant type Ia’s are fainter than they ought to be under a Hubble expansion. No apparent observational or systematic errors can acco
