Dark Bites

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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22h

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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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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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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Oct 23

Interview with our Coordinator of the Transient & Moving Objects Group, Marcelle Soares-Santos! https://t.co/93eIIixWUl

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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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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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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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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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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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