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Dark Energy Survey @TheDESurvey
18h
We disguise our data before looking at the final results of our analysis🤡We indeed want to avoid adjusting our anal… https://t.co/nFXWatoI3k

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Dark Energy Survey @TheDESurvey
Nov 24
In case you missed the first one, tomorrow there is another 'virtual launch' event for the DES book! Several DEScie… https://t.co/jvPUvOVHV8

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Dark Energy Survey @TheDESurvey
Nov 23
Get into statistics. It'll change your life. #ThisIsDES full post at https://t.co/RxWjncU259 📸: Carles Sanchez https://t.co/qe6NH0d310

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Dark Energy Survey @TheDESurvey
Nov 21
Galaxies are like the visible tip of gigantic icebergs of dark matter 🧊 We measure galaxy clustering, not dark matt… https://t.co/D5T5uyfqeR

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Dark Energy Survey @TheDESurvey
Nov 19
Galaxies...it's complicated. In cosmology, we like to pretend we're above it all, working on the largest scales,… https://t.co/PMSKXTGyGb

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The Dark Energy Survey
18 hours ago
Day 32. Unbiased science 🎯

Let’s face it, humans are pretty biased creatures. This graph above shows the measurement of the neutron’s (one of the atom’s component) lifetime from different experiments at different time. See how in the 60's people independently measured it to be around 1010 seconds, and then in the 70's someone measured it to be around 940 seconds and people measured the same for years, although it is actually around 890 seconds! ❌This is because people knew about earlier results and when they got something not coherent with previous measurements, they would think they did something wrong and tried to obtain the same value as the previous result! 🧮 This is called confirmation bias.

In our analysis, we’d like this bias not to creep into our scientific experiments. 🔭Between our data and the model, there are many knobs to switch and dials to turn in our analysis choices. 🎛 To do this in the most scientifically resilient manner, we make our measurements and before anything is done with them - before they’re even accessible to the team, we disguise them. 🤡 That way, we can do our entire analysis based on reason, without knowing the results until the very end - ta da, Science! 👌🏾📏
#ThisIsDES

📸 : from K.A. Olive et al., 2014 ... See MoreSee Less
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The Dark Energy Survey
1 day ago
In case you missed the first one, tomorrow there is another 'virtual launch' event for the DES book! Several DEScientists will be on the panel.Join the editors and contributors of “The Dark Energy Survey – The Story of a Cosmological Experiment” to celebrate the release of this title which discusses the results and processes behind this project.

Find out how our Universe functions, why it is expanding and why this expansion is accelerating.

Register here: bit.ly/3n8lvhc ... See MoreSee Less
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The Dark Energy Survey
2 days ago
Day 31: Bayesian statistical analysis

Over the past 30 days we’ve described the various complex measurements that we make on the images of the sky taken by our telescope. We’ve also talked about the cosmological models that we think describe our Universe; in some sense these are beautifully simple, with a handful of simple ingredients 🍲 like the densities of dark matter and dark energy. We use Bayesian statistical analysis 📈📉to connect these two - to “constrain” i.e. estimate the values of these simple ingredients, which we call “parameters”, by using the information in our measurements.

In Bayesian analysis, we update whatever we knew before about the model parameters (this is called the prior), with whatever new information our data tells us. This lets us assign probabilities to possible ranges of parameters, for example, we can make probabilistic statements such as “there is an X% probability that the density of dark energy is not zero”. Here X is a number close to 100 - we are very confident that there is dark energy in the Universe, or something that acts like it. While we’ll never measure it’s density *exactly*, we can make statements about our confidence 👍👎 that it is in some range.

One crucial tool for Bayesian analysis is a sampler. A sampler is a Monte Carlo algorithm that explores the space of allowed parameters , which can then be used to generate a model to compare to the data. It’s super important to make a sampler very efficient, because the space of allowed parameters can be high dimensional, and the model can be slow to generate. The movie shows a sampler exploring a two-dimensional parameter space. As we get enough samples, we can see the region where there is a high probability or confidence that the true parameters reside. 🐛🐛

Thanks to Carles Sanchez for the cool video! ... See MoreSee Less
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The Dark Energy Survey
5 days ago
Day 30. Galaxy bias ➕

In the universe, galaxies are like the visible tip of gigantic icebergs of dark matter. 🧊 Imagine galaxies living in gigantic haloes of dark matter! ⚫️ The correspondence between these haloes of invisible dark matter and galaxies is called the galaxy bias. Why do we call it “bias”❓Because our measurements of how clustered galaxies are are “biased” compared to what one would get if we could measure how clustered dark matter is instead. Because galaxies form in regions where there’s a lot of dark matter, they actually are more clustered than the underlying dark matter. ➕The galaxy bias is just how much more clustered they are. By using galaxy-galaxy lensing (see few posts ago!), we can learn about this bias, and extract useful cosmological information from the galaxy clustering signal 💥

#ThisIsDES

📸: Andreas Weith ... See MoreSee Less
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The Dark Energy Survey
6 days ago
Day 29. Galaxies...it's complicated 🤯

It turns out galaxies are complicated! Galaxies aren’t just fuzzy blobs that move along dark matter filaments minding their own business. In cosmology, we usually work with such large scales that gravity is the only important force to consider.

But this assumption breaks down at galactic scales, where there are many complex interactions between the gas, stars and black holes that make up galaxies 💨💥🥘. Particularly spectacular are the powerful jets sometimes produced by the supermassive black holes at the center of galaxies, where huge amounts of gas and energy are spewed out of the galaxy at speeds close to the speed of light. ✈️✈️✈️🙀

This kind of behavior can even affect the distribution of dark matter in which the galaxy resides, which mean our gravitational lensing measurements are sensitive to it. So we need to be careful that we are modeling these effects correctly, or excluding the parts of our data that are affected.

The images today are from a study led by Vaidehi S. Paliya (ApJ 892, 133). They observed a jet which they believe resulted from the collision of two spiral galaxies; the first image is an artist’s impression, and the second is the actual data used, observed using the 8.2m Subaru telescope.

image credit: Vaidehi S. Paliya, NASA / ESA / Hubble / L. Calçada, ESO ... 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.

© 2020 The Dark Energy Survey