Since 2004, the Dark Energy Survey (DES) team have been delineating the distribution of dark matter and dark energy throughout the universe, and today they have released their most accurate survey to date. This is the strongest evidence yet for the theory that the majority of our universe is made up of matter and energy we can’t see.
DES is a worldwide collaboration made up of over 400 scientists from 26 institutions in seven countries, and their base is at the Fermilab in the Unites States. The United Kingdom has played a key role in this association, as the Science and Technology Facilities Council (STFC) has provided much funding and there are scientists from the UK’s most prestigious universities from Cambridge to University College London.
“The DES measurements support the simplest version of the dark matter/dark energy theory,” says Joe Zuntz, of the University of Edinburgh, who worked on the analysis. “This is a huge part of the picture showing how the cosmos has evolved over the last 14 billion years. It’s the dark universe made visible on an unprecedented scale.”
This theory states that the ordinary matter – the matter we can see – makes up only four per cent of the entire universe. Approximately 26 per cent of the universe is made up of cold dark matter, which is the hidden matter that pulls molecules together to eventually form galaxies. The remaining 70 per cent is dark energy, the force that’s causing our universe to expand at an accelerating rate for the last 14 billion years.
The primary instrument used by DES is the 570-megapixel Dark Energy Camera attached to the Blanco telescope in Chile, and is one of the most powerful cameras in the world. The collection of all this data, including other telescopes, resulted in a 1,300 square degrees survey of the sky, which is roughly the same size as 6,600 Full Moons in the night sky.
As dark matter cannot be directly measured, the DES scientists used two methods that indirectly measured this elusive form of matter. The first was by mapping the locations of galaxies and tracing their densities, while the other technique was to measure the shapes of 26 million galaxies over billions of light years away using gravitational lensing – an astronomical phenomenon in which the gravity of a large star can bend the path of light from our perspective on Earth.
“It is remarkable that dark energy, proposed in its simplest form by Einstein 100 years ago, is now measured so accurately by DES. However, the nature of dark energy is still a big mystery,” says Ofer Lahav of UCL, and chair of the DES. “This result is the culmination of 13 years of dedicated work.”
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