Tag Archives: Dark Energy Survey

Ten areas in the sky were selected as “deep fields” that the Dark Energy Camera imaged several times during the survey, providing a glimpse of distant galaxies and helping determine their 3D distribution in the cosmos.

Astronomers map over 100 million galaxies to crack dark matter and dark energy puzzle

The Dark Energy Survey (DES) is an ambitious cosmological project that aims to map hundreds of millions of galaxies. In the process, the project will detail hundreds of millions of galaxies, observe thousands of supernovae, map the cosmic web that links galaxies, all with the aim of investigating the mysterious force that is causing the Universe to expand at an accelerating rate.

Using the 570-megapixel Dark Energy Camera on the National Science Foundation’s Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory (CTIO), Chile, the DES has observed a map of galaxy distribution and morphology that stretches 7 billion light-years and captures 1/8 of the sky over Earth.

Ten areas in the sky were selected as “deep fields” that the Dark Energy Camera imaged several times during the survey, providing a glimpse of distant galaxies and helping determine their 3D distribution in the cosmos.
Ten areas in the sky were selected as “deep fields” that the Dark Energy Camera imaged several times during the survey, providing a glimpse of distant galaxies and helping determine their 3D distribution in the cosmos. The image is teeming with galaxies — in fact, nearly every single object in this image is a galaxy. Some exceptions include a couple of dozen asteroids as well as a few handfuls of foreground stars in our own Milky Way. (Dark Energy Survey/DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA)



Now new results from the DES which collects the work of an international team of over 400 scientists from over 25 institutions from countries including the US, UK, France, Spain, Brazil, and Australia, are in. The findings are detailed in a ground-breaking series of 29 papers and comprises of data collected during the DES’ first three years of operation providing the most detailed description of the Universe’s composition and expansion to date.

The Víctor M. Blanco 4-meter Telescope is seen here at night at Cerro Tololo Inter-American Observatory, with trails of stars high above it. On this telescope is the 570-megapixel Dark Energy Camera — one of the most powerful digital cameras in the world. The Dark Energy Camera was designed specifically for the Dark Energy Survey. It was funded by the Department of Energy (DOE) and was built and tested at DOE’s Fermilab. (DOE/FNAL/DECam/R. Hahn/CTIO/NOIRLab/NSF/AURA)

The survey was conducted between 2013 to 2019 cataloging hundreds of millions of objects, with the three years of data covered in these papers alone containing observations of at least 226 million galaxies observed over 345 nights.

The fact that some of these galaxies are close to the Milky Way and others are much more distant–up to 7 billion light-years away– gives researchers an excellent picture of the evolution of the Universe over around half of its lifetime.

The results seem to confirm the standard model of cosmology, currently the best-evidenced theory of the Universe’s composition and evolution which suggests the Universe was created in a ‘Big Bang’ event and has a composition of 5% ordinary or baryonic matter, 27% dark matter, and 68% dark energy.

The snapshot of the Universe provided by the DES does seem to show that the Universe is less ‘clumpy’ than current cosmological models suggest, however.

Illuminating the Dark Universe

The fact that the ‘Dark Universe’ consists of 95% of the matter and energy in the known cosmos means that there are huge gaps in our understanding of the evolution of the Universe, its past, present, and its future.

These gaps include the nature of dark matter, whose gravitational influence holds galaxies together, and dark energy, the force that is expanding space between the galaxies driving them apart at an accelerating rate.

These effects seem to be in opposition, with one holding matter together and the other working upon space itself to drive matter apart. And it is this cosmic struggle that shapes the Universe which the DES aimed to investigate.

There are two key phenomena which the survey used to do this. Studying ‘the cosmic web’ that links galaxies together in clusters and loose associations gives hints at the distribution and influence of dark matter.

The Dark Energy Survey camera (DECam) at the SiDet clean room. The Dark Energy Camera was designed specifically for the Dark Energy Survey. It was funded by the Department of Energy (DOE) and was built and tested at DOE’s Fermilab. (DOE/FNAL/DECam/R. Hahn/CTIO/NOIRLab/NSF/AURA)



The second phenomenon used by the DES is the bending of light as it travels past curvatures in spacetime created by objects of tremendous mass like galaxies. This effect predicted by Einstein’s theory of gravity–general relativity–is known as ‘gravitational lensing.’

The DES relied on a form of this effect called ‘weak gravitational lensing’ to assess how dark matter is distributed across the Universe, thus inferring its ‘clumpiness.’

Weak graviational lensing was one ofthe phenomenna that teh DES took advantage of to investigation dark matter distributions (ESA)

The data collected by the DES was cross-referenced against measurements carried out by the European Space Agency (ESA) operated mission, the Planck observatory. The orbiting observatory, which operated between 2009 and 2013 and studied the cosmic background radiation (CMB)–an imprint leftover from an event shortly after the Big Bang in which electrons and protons connected thus allowing photons to travel freely for the first time.

Observing the CMB reveals conditions that were ‘frozen in’ to it at the time of this event known as the last scattering and thus gives a detailed picture of the Universe when it was just 400 thousand years old for the DES team to draw from.

Setting the Scene for Future Surveys

The DES intensely studied ten regions labeled as ‘deep fields’ which were repeatedly imaged during the course of the survey. These images were stacked which allowed astronomers to observe distant galaxies.

In addition to allowing researchers to see further into the Universe and thus further back in time, information regarding redshift– an increase in wavelength caused by objects receding which can arise as a result of the Universe’s expansion–taken from these deep fields was used to calibrate the rest of the survey. This constituted a major step forward for cosmic surveys providing the researchers with a picture of the Universe painted with stunning precision.

Whilst the DES was concluded in 2019, the sheer wealth of data collected by the survey requires a huge amount of computing power and time to assess. This is why we are only seeing the first three years of observations reported and likely means that the DES still has much more to deliver.

The Vera C Rubin Observatory currently under construction in Chile will pick up where the DES leaves off (LSST Collaboration)

This will ultimately set the scene for the Legacy Survey of Space and Time (LSST) which will be conducted at the Vera C Rubin observatory–currently under construction on the El Penon peak of Cerro Pachon in northern Chile.

Whereas the DES surveyed an inarguably impressive 1/8 of the sky over the earth, the wide-field camera that will conduct the LSST will capture the entire sky over the Southern hemisphere, meaning it will view half of the entire sky over our planet.

A major part of the LSST’s mission will be the investigation of dark matter and dark energy, meaning that when the data from the DES is finally exhausted and its secrets are revealed, a worthy successor will be waiting in the wings to assume its mission of discovery.

Researchers identify over 300 new minor planets in the Solar System

Our little corner of the universe just got a little bigger.

Pluto is arguably the most famous trans-Neptunian object.
Image via Wikimedia.

Data from the Dark Energy Survey (DES) helped researchers identify over 300 new trans-Neptunian objects (TNOs), minor planets located beyond the orbit of Neptune. A new study describes the methodology used, which the team hopes will be adapted in the search for the hypothetical Planet Nine and other undiscovered planets.

Worlds aplenty

“The number of TNOs you can find depends on how much of the sky you look at and what’s the faintest thing you can find,” says Gary Bernstein, a Chair Professor at the University of Notre Dame’s College of Engineering and paper co-author.

“Dedicated TNO surveys have a way of seeing the object move, and it’s easy to track them down. One of the key things we did in this paper was figure out a way to recover those movements.”

The DES, which completed six years of data collection in January, captures high-fidelity images of the southern skies in an effort to understand the nature of dark energy. However, researchers seem to have been intent on teaching it a few tricks, and used the data to look for TNOs.

While the DES was designed to take wide-angle, high-quality shots of galaxies and supernovas, the team had to adapt it to be able to track the movement of (tiny, by comparison) TNOs.

They started with a dataset comprising 7 billion “dots”, which are points of interest identified by automated software. These points were brighter than the background behind them, which could be indicative of a planet reflecting light. The next step was to remove any of them that were present on multiple nights — this signified that they were bodies such as stars or galaxies far, far away — slimming the list down to only 22 million points.

The last step involved trying to group these together into nearby pairs of triplets and check if these reappeared on several nights. By this point, the team was left with around 400 candidates. In order to establish whether these were TNOs, the team revisited the images they had for each object. Pedro Bernardinelli, a PhD candidate in physics & astronomy at the University of Pennsylvania and lead author of the paper, developed a way to stack multiple images to create a sharper view, which helped confirm whether a detected object was a real TNO. In order to verify their method, they applied it to known TNOs and introduced fake objects into the images — these were spotted as fake by the system.

After the months-long process, the team reported on 316 TNOs, including 245 discoveries made by DES and 139 new objects that were not previously published — this total represents 10% of all known TNOs. The objects orbit from around Pluto to nearly twice as far away.

The team now plans to re-run their system on the DES dataset using a lower detection threshold.

The paper “Trans-Neptunian Objects Found in the First Four Years of the Dark Energy Survey” has been published in The Astrophysical Journal Supplement Series.