BBC Sky at Night Magazine
A short history of dark energy
A puzzling observation 22 years ago led to today’s theories of dark energy
How do we know that the expansion of the Universe has been getting quicker of late? It’s based on a type of exploding star known as a Type Ia supernova. They detonate when a small, dead star called a white dwarf gorges on a nearby star until it becomes unstable. As this always happens at a similar stage, all supernovae of this type should explode with a similar brightness. This makes them great cosmic rulers, as dimmer ones must be further away.
In 1998, two teams of astronomers were racing to measure the distances to these stellar explosions. They found that Type Ia supernovae were consistently further away than they should be, suggesting the Universe had expanded more than we’d previously believed. The search for the culprit behind this accelerated expansion has remained one of cosmology’s hot topics.
Three of the astronomers behind the discovery shared the Nobel Prize in Physics in 2011, but others have called the results into question, pointing out that Type Ia supernovae aren’t quite the reliable yardsticks we’d thought they were.