Institute of Astronomy

Dark Energy Survey publicly releases first three years of data

Published on 10/01/2018 

At a special session held during the American Astronomical Society meeting in Washington, D.C., scientists of the Dark Energy Survey (DES) announced  the public release of their first three years of data. This first major release of data from the Survey includes information on about 400 million astronomical objects, including distant galaxies billions of light years away as well as stars in our own galaxy.

DES scientists are using this data to learn more about dark energy, the mysterious force believed to be accelerating the expansion of the Universe. The rich dataset from the survey is also being used to understand the structure of our own Milky Way Galaxy as well as more distant, extreme galaxies known as quasars, which harbour enormous supermassive black holes at their centres. 

The public release of the first three years of DES data fulfills a commitment scientists on the survey made to share their findings with the astronomy community and the public. The data cover the full DES footprint – about 5,000 square degrees, or one eighth of the entire sky – and include roughly 40,000 exposures taken with the Dark Energy Camera. The images correspond to hundreds of terabytes of data and are being released along with catalogs of hundreds of millions of galaxies and stars. The DES data can be accessed online here:

Several members of staff and graduate students at the Institute of Astronomy (IoA) are part of the Dark Energy Survey Collaboration, and have been exploiting the new data from this experiment for a broad range of science. Dr. Manda Banerji and Prof. Richard McMahon are co-leads of the Galaxy and Quasars Science Working Group within DES. In a paper led by IoA graduate student, Clare Wethers, the Cambridge team used the deep images provided by DES to reveal, for the first time, lots of young stars forming in distant galaxies that contain powerful supermassive black-holes. Ordinarily the emission from a feeding black-hole or quasar is so bright that it dwarfs any emission from stars around it. “By looking at a special population of dust-enshrouded quasars where the light from the black-hole has been dimmed, we were able to exploit the unique sensitivity of DES to detect starlight in galaxies more than 10 billion light years away. This opens up a new observational window into our understanding of these mysterious and extreme, early galaxies” explains Dr. Banerji. 

Another discovery enabled by the data set is the detection of eleven new streams of stars around our Milky Way. Our home galaxy is surrounded by a massive halo of dark matter, which exerts a powerful gravitational pull on smaller, nearby galaxies. The Milky Way grows by pulling in, ripping apart and absorbing these smaller systems. As stars are torn away, they form streams across the sky that can be detected by the Dark Energy Survey.  Even so, stellar streams are extremely difficult to find since they are composed of relatively few stars spread out over a large area of sky.

Dr. Vasily Belokurov at the IoA is an expert on stellar streams and was involved in the study. “Stellar streams were once considered a rarity, a marvel of Nature. What we are witnessing today with the DES release is a transformation, when this niche science area becomes an established industry” he commented. Prior to the new discoveries by DES, only about two dozen stellar streams had been discovered. The growing numbers of these fragile star-trails now being mapped across the sky, are showing us how Gravity works and opening up the possibility of revealing the secrets of the mysterious dark matter that permeates our Universe. Since there is no universally accepted naming convention for stellar streams, the Dark Energy Survey has reached out to schools in Chile and Australia, asking young students to select names. Students and their teachers have worked together to name the streams after aquatic words in native languages from northern Chile and aboriginal Australia.

DES plans one more major public data release, after the survey is completed, which will include nearly twice as many exposures as in this release. IoA scientists continue to be involved in mining these ever-growing astronomical datasets to make new discoveries.

Based on the DES press release

Local IoA contacts: Dr. Manda Banerji (, Dr. Vasily Belokurov (, Prof. Richard McMahon (
Links: Read more about the young stars forming around distant quasars in DES here:
Read the papers drawn from the first years of DES data online here:

Figures: (click on each image to get higher-resolution version)

Colour composite image from the Dark Energy Survey showing four galaxies observed more than 10 billion years ago. Young, newly formed stars are represented by the blue colours in the images, and the dusty glow from the feeding supermassive black-holes can be seen in red. 

This image shows the entire Dark Energy Survey field of view – roughly one-eighth of the sky – captured by the Dark Energy Camera, with different colors corresponding to the distance of stars. (Blue is closer, green is further away, red is even further.) Several stellar streams are visible in this image as yellow, blue and red streaks across the sky. Image: Dark Energy Survey.

This image shows the full area of sky mapped by the Dark Energy Survey, and the eleven newly discovered stellar streams. Four of the streams in this diagram - ATLAS, Molonglo, Phoenix and Tucana III – were previously known. The others were discovered using the Dark Energy Camera, one of the most powerful astronomical cameras on earth. Image: Dark Energy Survey. Credit Fermlab



Page last updated: 10 January 2018 at 21:36