Comprehensive 3D map of the universe fills 11-billion-year gap
A 20-year study of the night sky has allowed astronomers to produce a comprehensive 3D map of the universe, covering 11 billion years of expansion. A new analysis of this map has highlighted a mismatch in the Hubble Constant, and revealed when the expansion of the universe began to accelerate.
The Sloan Digital Sky Survey (SDSS) has been collecting data for over 20 years now, with each data release resulting in more and more detailed maps of the cosmos. Now, scientists have combined it all into one huge three-dimensional map that covers almost the entire history of the universe. Importantly, the team says that the new study fills in a massive gap in the middle that has long bothered astronomers.
“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 lead researcher on the project. “For five years, we have worked to fill in that gap, and we are using that information to provide some of the most substantial advances in cosmology in the last decade."
The new map uses data from different phases of the Sloan survey to chart objects at different distances from Earth – therefore representing different time periods in the universe’s history. In this map, Earth is the dot at the very center, and the differently colored rings represent different data sets, circulating outwards in ever greater distances in space and time.
The green section highlights galaxies closest to Earth, from data gathered during the first two SDSS runs. The pink and red circles cover the region up to about six billion light-years away, from observations of large, old, red galaxies. A little beyond that, the data comes from younger blue galaxies. To map even further out, to about 11 billion years ago, data was collected from quasars, which are bright galaxies with very active supermassive black holes at their centers.
The resulting map revealed a few new tidbits of information for astronomers. The researchers were able to use the map to measure the rate that the universe is expanding – a value known as the Hubble Constant. Strangely enough, they found the current value to be about 10 percent lower than when it’s calculated by measuring distances to nearby galaxies.
The team says that the data from the map is very precise, and made up of different data sets that all have the same conclusion. Exactly why there’s a mismatch for the Hubble Constant is a mystery that will require further study, the researchers say.
The study also showed that the expansion of the universe seemed to speed up about six billion years ago. It’s well known that the rate of expansion is accelerating, but nailing down when this began has been tricky in the past. Previous studies have suggested it started some four billion years ago, but the new data indicates it was earlier. A force dubbed "dark energy" is our current best guess for what is causing this acceleration.
And finally, since the study covers such a large section of space and time, it’s able to give one of the clearest pictures of what “shape” the universe is. Whether it’s flat or curved is the subject of ongoing argument for astrophysicists, but the new SDSS map adds evidence to it being flat.
The SDSS will continue to study the cosmos in ever more detail, with a new phase of operations due to begin later this year.
The research was published in a series of studies, as Sloan’s 16th data release. The team discusses the work in the video below.