After five years of research, an international team over 100 astrophysicists from around 30 institutions worldwide has released the largest-ever 3D map of the universe.
The map is the result of an ongoing project known as the Sloan Digital Sky Survey (SDSS)- an ambitious project that aims to map out the expansion of the observable universe. At its current size, the project has surveyed over 4 million galaxies and quasars stretching from our own Milky Way to ancient objects over 11 billion light-years away.
"We know both the ancient history of the universe and its recent expansion history fairly well, but there's a troublesome gap in the middle 11 billion years," says Kyle Dawson, a cosmologist at the University of Utah and lead researcher of the project, "For five years, we have worked to fill in that gap."
Key to their efforts has been monitoring redshift- the phenomenon in which light is stretched by the expanding universe, increasing in wavelength towards the redder end of the light spectrum. The process is both what makes distant light sources appear redder, and those nearer to Earth seem bluer.
To calculate the rate of cosmic expansion 11 billion years ago, the researchers measured the redshift of millions of distant objects alongside their velocities. Their results, published among 23 new studies, show that the universe increased its rate of expansion after a brief period of deceleration, 6 billion years ago.
Why the universe is expanding, however, is a mystery. Some attribute it to 'dark energy', although whether or not it exists, and how it exists remains unknown. Astrophysicists thus hope that mapping the universe in this way may begin to yield clues about the properties of dark energy, something that, although it seems we are edging closer towards, is still some way away.