Dark energy is the mysterious force driving the universe’s accelerating expansion. In an effort to understand it, scientists are planning to make the largest 3D map of the universe to date. But before the galaxies can be plotted in three dimensions, researchers had to capture an enormous area in 2D. The result is the largest image of the night sky ever. And you can see the whole thing online.
It’s hard to overstate just how impressive this single image is. And the longer you look at it, the more you appreciate all of the work it must have taken to make the whole thing possible. It captures half of the sky and more than a billion galaxies, depicted through over 10 trillion pixels.
Do you take a lot of pictures on your phone? Are you always running out of space for selfies or cat photos? Well, in order to create a 10 trillion pixel image, you would have to stitch together 833,000 smartphone photos. Creating this map took more than 1,400 observing nights at three telescopes over the course of six years.
Completely covering half the sky was a huge logistical challenge for the 200 researchers involved in the project. For the telescopes to take the best images possible, the team had to consider hours of darkness, weather, exposure time, the paths of planets and satellites, the moon’s brightness and location — the list goes on. Even with all those variables factored in, there was still the matter of creating one homogeneous image.
It’s not as simple as just stitching them all together — the scientists needed a way to minimize distortions caused by weather and atmospheric turbulence.
To do this they used supercomputers to compare their images with past sky surveys and select the ones that most closely matched. Once they had the most accurate and uniform pictures possible, they put them together and this is the result.
Taking in the two billion objects sprinkled over such an enormous backdrop can be a bit overwhelming.
To make navigating the stars more user-friendly, the researchers adapted street-mapping software to suit their needs. They created a tool called the Legacy Sky Survey Viewer. Users can jump to an object if they know its name, or toggle filters to help find specific object types. They can also turn on overlays to see constellations, or which galaxies the researchers plan to further study for the 3D map.
While the navigation tool was originally designed to help researchers more easily find issues with their data, the scientists were surprised at how powerful it was. One said that suddenly the data just felt a lot more real and it changed the way the team interacted with it.
Another researcher figured that if it impacted them so much, maybe the public would want to see it too. So they made it available to all of us online, and that means that anyone could potentially discover new examples of rare objects, or even entirely new ones.
Considering how awe-inspiring this 2D map is, it’s amazing to think it’s a stepping stone to a bigger goal. It was created to identify which galaxies and quasars the Dark Energy Spectroscopic Instrument, or DESI, will survey. This instrument will be able to measure the distances to objects located up to 12 billion lightyears away. DESI will also measure the redshift of these objects to determine how fast they're moving away from us.
With this information, astronomers and cosmologists will be able to create a 3D map of a huge portion of the universe and tease out more information about how dark energy shapes the cosmos. If you’re like me and plan to set aside at least a full day to marvel at this image, just remember that the best may still be yet to come.