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Dark Energy Survey @TheDESurvey
2h
Here's the tea 🍵: past weak lensing experiments have had a tendency to report a smoother Universe than we'd expect… https://t.co/lTOQ4TOs0r

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Dark Energy Survey @TheDESurvey
23h
Weak lensing lets us put on special glasses that reveal where the invisible dark matter really is 😎! #ThisIsDES R… https://t.co/mM1U63RU5d

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Dark Energy Survey @TheDESurvey
Oct 24
How it started 👶how it's going🧓 Genious gif by @astroalexamon (using images from Dark Sky Simulations / SLAC & Pla… https://t.co/VP15jnHCIi

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Dark Energy Survey @TheDESurvey
Oct 23
The history of the Universe or how a cosmic soup grew up to be a cosmic web #ThisIsDES Full post at:… https://t.co/nqz1n4dFS6

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Dark Energy Survey @TheDESurvey
Oct 23
Interview with our Coordinator of the Transient & Moving Objects Group, Marcelle Soares-Santos! https://t.co/93eIIixWUl

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The Dark Energy Survey
3 hours ago
Day 9. The Cosmology Tea 🍵

Here’s the tea. Let’s look at a range of existing results (from galaxy weak lensing) of the amount of structure in the Universe. The grey bar is the best fit model to the Cosmic Microwave Background measured by the Planck satellite to stunning precision, and the coloured data points are all from previous weak lensing experiments. There’s something curious here; while none of these measurements disagree with each other to any real significance, statistics tell us that the measurements should fluctuate around the truth. 🤔

What we see is that lensing is persistently low: these late-time measurements predict a slightly smoother universe, compared to what the early Universe dictates. What’s really happening here? Either the CMB measurements are not quite right, the lensing measurements are biased, or we need some new physics to fill the cracks - like extension to Einstein’s theory of gravity. As lensing is a relatively new field, it’s fair to say that our results are under scrutiny! 🔍

📸 adapted from M. Kilbinger ... See MoreSee Less
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The Dark Energy Survey
1 day ago
Day 8 Distorted Galaxies 🔎

Imagine a galaxy far, far away 🔭 . The light it emits takes an adventurous path across the Universe, following distortions in the fabric of space-time generated by the gravitational influence of massive structures 💫 . That means that *every* image we take of the distant Universe is slightly distorted with the imprint of the cosmos between us and that galaxy📝. Nearby galaxies’ light travels past the same structures of the Universe to get to us on Earth 🌏 and so they acquire coherent distortions and alignments. If we can measure these shapes with extreme precision 📐, we gain an understanding of the chunk of the Universe that the light passed through ✨ .
Weak lensing measurements tell us where the dark matter is. Our eyes can only see the light emitted by the galaxies 👁 , but the lensing caused by the invisible dark matter lets us put on special glasses 👓 that reveals where it is 🤓!

In the movie you can see an exaggerated effect of lensing - pretty similar to the way a lens in your glasses work 🔎! As the lens moves across the page, the galaxies appear distorted. For weak lensing, the lens is the gravity due to massive structures in the Universe, and the effect is much more subtle.

#ThisIsDES
📸: @nasa ... See MoreSee Less
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The Dark Energy Survey
2 days ago
Day 7. A model describing 13.8 billion years ⏱

Now, it’s a particularly exciting time for cosmology: Technology has rapidly grown and with the most powerful telescopes in the world, there are several teams performing cosmology experiments independently. 🔭 With larger datasets than ever before, we have measurements of the large-scale structure of the Universe (including weak lensing measurements - more on those tomorrow!) that rival the precision of the Cosmic Microwave Background (CMB) experiments for the first time. That creates a pretty beautiful end-to-end test : does that model that so-well describes the seeds of the Universe, measured with the CMB, also fit measurements of the vast structures that formed billions of years later? 👀 Stay tuned in the coming weeks to find out!

📸 Dark Sky Simulations / SLAC & Planck Collaboration / gif by Alex Amon ... See MoreSee Less
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The Dark Energy Survey
3 days ago
In contrast to the smooth cosmic soup 🍲 that the CMB (see yesterday’s post!) provides a snapshot of, the Universe today is a web of structures with galaxies tracing out filaments of dark matter which meet in massive groups or clusters of galaxies. Using many different statistical measures, cosmologists aim to characterize these structures and uncover the physical model that explains their formation over the 13 billion years since the Big Bang.

A simple example is the number of galaxy clusters we can observe - in a Universe without dark matter these would be much rarer (without drastic modifications to the laws of gravity!). Another useful statistic is the number of galaxy pairs separated by a given distance - a Universe where dark matter clumps together more will have more close pairs of galaxies. While the underlying laws of physics which govern the growth of cosmic structure are beautiful in their simplicity, a stunning and complex variety of cosmic structure emerges over time, which we need to model with enormous simulations 🤯- we’ll come back to these in a week or two.

The picture shows a slice through our observable Universe, with each dot representing a galaxy observed by the Sloan Digital Sky Survey; you can see by eye the “cosmic web” traced out by the galaxies❄️🕸❄️🕸

image credit: M. Blanton / SDSS ... See MoreSee Less
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The Dark Energy Survey
4 days ago
Day 5. The Universe 13.8 billion years ago 🍼

Because the Universe is expanding, it is getting less dense and colder with time 🥶 So going back in time it was way more crammed and hotter: 13 billions years ago, the universe was completely different than today! 🥵 It was a very hot (around 3000°C!) soup of light, electrons and protons (what make up atoms) and nuclei of helium. 🍵Like in a fog, the light was constantly bouncing off the electrons and protons. 🌫 But 400 000 years after the Big Bang, the very first atoms of hydrogen and helium started to form, leaving the light free to travel indefinitely… 🧭 This primordial light is called the Cosmic Microwave Background. It fills the entire universe: you are living in a bath of light that travelled for 13 billions years! 🛁 The Cosmic Microwave Background (often shortened as CMB) was discovered in 1964 by Penzias and Wilson who were doing an unrelated experiment (with the first communication satellites!) using a horn antenna (see picture) 📡 and wanted to get rid of this annoying background radiation. Turns out they had discovered the radiation coming from the Big Bang!

Another big discovery about the CMB was made 30 years later: it has teeny fluctuations of intensity and temperature over the sky. It appears around 0.0006% (very teeny!) brighter in some directions than others! These fluctuations hold an incredible amount of information about our universe: they show how matter was distributed shortly after the Big Bang! The Planck satellite produced the most precise map of these fluctuations, swipe to see the map: the red blobs correspond to places where the CMB is hotter, and blue where it is colder. You are witnessing the universe 400 000 years after the Big Bang! 🕰 #thisisdes #cosmology #CosmicMicrowaveBackground #DarkEnergy #universe ... See MoreSee Less
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News

Scientists Leverage HPC and AI to Wrangle the ‘Galaxy Zoo’

July 8, 2019 12:00 pm

The research team developed a new approach to classifying these hundreds of millions of galaxies. Instead of relying on crowdsourced classification, the researchers used knowledge from the state-of-the-art Xception neural network, combined with the datasets generated by the Galaxy Zoo project, to train its deep learning models. They then applied the trained model to galactic images from the Dark Energy Survey (DES) – where it achieved a 99.6% accuracy in identifying spiral and elliptical galaxies.

Three sky surveys completed in preparation for Dark Energy Spectroscopic Instrument

July 8, 2019 12:00 pm

It took three sky surveys — conducted at telescopes in two continents, covering one-third of the visible sky, and requiring almost 1,000 observing nights – to prepare for a new project that will create the largest 3-D map of the universe’s galaxies and glean new insights about the universe’s accelerating expansion. This Dark Energy Spectroscopic Instrument (DESI) project will explore this expansion, driven by a mysterious property known as dark energy, in great detail. It could also make unexpected discoveries during its five-year mission.

Multiple Measurements close in on Dark Energy

May 6, 2019 12:00 pm

An extensive analysis of four different phenomena within the universe points the way to understanding the nature of dark energy, a collaboration between more than 100 scientists reveals. Dark energy – the force that propels the acceleration of the expanding universe – is a mysterious thing. It’s nature, write telescope scientist Timothy Abbott from the Cerro Tololo Inter-American Observatory, in Chile, and colleagues, “is unknown, and understanding its properties and origin is one of the principal challenges in modern physics”. Indeed, there is a lot at stake. Current measurements indicate that dark energy can be smoothly incorporated into the theory of general relativity as a cosmological constant; but, the researchers note, those measurements are far from precise and incorporate a wide range of potential variations.

Viewpoint: Dark Energy Faces Multiple Probes

May 1, 2019 12:00 pm

One of the top goals in cosmology today is understanding the dark energy that is responsible for the accelerated expansion of the Universe. Is the dark energy consistent with the cosmological constant of general relativity—representing a constant energy density filling space homogenously? Or can we find deviations from general relativity on cosmological scales that suggest a more complex nature for gravity? Questions like these motivate the current and next generations of surveys that aim to map out ever larger volumes of the Universe, using a wide variety of probes to constrain the properties of dark energy. The Dark Energy Survey (DES) has now derived such constraints from the combined analysis of four canonical observables related to dark energy: supernovae, baryon acoustic oscillations, gravitational lensing, and galaxy clustering [1]. The resulting bounds confirm what we knew from previous studies, which focused on single probes. But the results indicate that this multiprobe approach could allow surveys in the 2020s to improve such constraints by orders of magnitude, possibly bringing us close to solving the dark energy puzzle.

Supernovae, Dark Energy, and the Fate of Our Universe

April 5, 2019 12:00 pm

What’s the eventual fate of our universe? Is spacetime destined to continue to expand forever? Will it fly apart, tearing even atoms into bits? Or will it crunch back in on itself? New results from Dark Energy Survey supernovae address these and other questions. At present, the fabric of our universe is expanding — and not only that, but the its expansion is accelerating. To explain this phenomenon, we invoke what’s known as dark energy — an unknown form of energy that exists everywhere and exerts a negative pressure, driving the expansion. Since this idea was first proposed, we’ve conducted decades of research to better understand what dark energy is, how much of it there is, and how it influences our universe.

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