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We spoke with Dr Rita Tojeiro, an advanced research fellow at St Andrew’s University and co-leader of the decade-long project, who told us more about the map.
“People have been trying to map the universe since the 1970s, and the reason we want to do this is because the three-dimensional structure of the universe can tell us a lot about its composition and dynamics.”
“Imagine there’s a sort-of dark skeleton to the universe, primarily made of dark matter that we can’t see. Where there is more dark matter there are more galaxies, so if you can map the three-dimensional positions of the galaxies, by inference you can map dark matter, which can tell us a huge amount about the universe.”
With contributions from hundreds of astronomers, Rita and her team were able to measure the positions of over one million galaxies over one quarter of the sky, mapping the three-dimensional structure of the universe over 650 cubic billion light-years.
What, though, was the team looking for? Rita explains:
“We had two primary goals with this project. One, was to map the expansion rate of the universe. We have known for some time that the universe is expanding, but we also know that its expansion is accelerating. We call whatever is causing this acceleration dark energy, but the problem has always been that we know so little about dark energy. So we begin by mapping out its effect, and we use our measurements to distinguish between different possibilities for what dark energy might be.”
“We needed to see how fast the Universe’s expansion was accelerating, and for how long. We found that the universe’s expansion has been accelerating for the past 5 or 6 billion years, and the influence of dark energy has had to remain constant throughout this time. This is information that theorists can now work with.”
The project’s second goal was to monitor the effect of general relativity on an enormous section of the universe. Rita adds: “These maps allow us to test Einstein’s theory of general relativity. By mapping this many galaxies in 3D we can see how they are moving. General relativity predicts how large their motion should be, so by measuring it we can directly test this theory. Additionally, by creating a data set this large and by making it accessible, people can use it for any number of things.
Rita, who during her PhD used data from maps to study how galaxies have evolved, told us about how maps are now better equipped for a task of this magnitude:
“The improvement in our ability to map the universe comes from being able to monitor certain regions far more quickly, and speed is of the element when it comes to areas of this size.”
“We now have the tech available to look at a wider region of the sky and identify a few thousand galaxies, and very quickly establish the distance of each of them. A combination of factors – from wider field cameras to multi-object spectrographs – have helped contribute to this development.”
Indeed, while universe mapping has been attempted since the 1970s, technological limitations have posed a significant challenge. Rita explains:
“To make a 3D map you need three coordinates. In our case that’s two coordinates on the sky – like longitude and latitude – and the third coordinate is a distance. In the 1970s you’d identify the position of a galaxy in the sky, but take a very very long time acquiring the data needed to compute a distance to it. Now, technology has evolved, and we can take more of these positions in a shorter space of time.”
While mapping may now be smoother than in the 1970s, some challenges still remain. Rita tells us more:
“The major challenge we found was visualizing this data. All of these maps are numbers, and we struggled to work this data into something visually important that people can use.”
When asked what was next for Rita, her team, and the project, she said, “We are finished with the project, and will move onto our next one. It’s publically available, so people can dig into the data, expand the map and find their own conclusions and findings. There’s always more to find out.”
Have you seen the map of the universe? Let us know what you think in the comments below.
Main image credit: NASA