Bringing humanity one step closer to understanding the mysteries of dark matter, researchers at the Dark Energy Survey (DES) have today released the first in a series of dark matter maps. The map was presented at the April meeting of the American Physical Society in Baltimore, Maryland. Researchers hope that this work will allow them to understand the role played by dark matter in the formation of galaxies.
Combined, dark matter and dark energy make up roughly 85 percent of our universe, yet little is known about either. The map is the largest contiguous one to date at this level of detail. It was created with the Dark Energy Camera, which is a 570-megapixel imaging device, and one of the world's most powerful digital cameras. It is the primary imaging instrument for the Dark Energy Survey (DES), which is led by Fermilab in the US.
Making a dark matter map is no easy feat. A team at Manchester University, headed by astrophysicist Sarah Bridle, has spent the last two years meticulously capturing the data needed to make it.
"We took the 130 million images of the sky, which were then analysed," Bridle said over the phone. "We needed to analyse all the pixels in the image, then make a map of how the position of a pixel relates to the position of the sky. We then made a model for what we think the galaxy looks like based on this data."
The process of measuring galaxies is both complex and time consuming. According to a release from the researchers, some of the world's largest supercomputers are deployed to tackle the challenge, and "each time a new catalog is made it takes about as much computing power as running 500 ordinary desktop computers for two weeks."
Despite the mammoth task, the rewards are rich. Bridle commented that the map will allow researchers to look at where dark matter and where galaxies are, and allow them to try and find out how galaxies formed. "In general, even just looking at the dark matter itself is amazing because 85 percent of the mass in the universe is made up of it. We don't know what it is, and it's very hard to see it, so it's great to be able to see a map of it," she said. Bridle also noted that the map could help them gain more insights into dark energy.
Dark matter cannot be detected by astronomical instruments as it does not emit or absorb light, said Bridle. Nonetheless, she explained that "gravitational lensing is a way through which researchers can make a map of dark matter." This studies "the distortion that occurs when the gravitational pull of dark matter bends light around far-off galaxies."
"Dark matter could equally be called transparent matter—so it's just like if you've got a glass of water. The glass and water are transparent, but we can see that it's there because we can see that it's distorting the images of what's on the other side. In exactly the same way, we can look at the shapes of distant galaxies, and we can see that they're distorted by the effects of the gravitational lensing effects of dark matter," explained Bridle.
The Dark Energy Survey is set to run for five years in total, so the researchers will continue to compile data for the next three years.
"We're currently analysing a couple of thousand square degrees, so there will be more data. It took us two years to get to this point, so I'm not sure how long the next map will take," said Bridle, noting that she was aiming for some new results in the next year. "The total map will be 30 times bigger [than the first one]. It's going to cover one eighth of the whole sky."