#large-scale structure

Did We Just Find The Largest Rotating ‘Thing’ In The Universe?

"Why are they rotating, however? Is it something that can truly be explained by tidal torques and nothing else? The early evidence points to “yes,” as the presence of large masses near the filaments — what cosmologists identify as “haloes” — seems to intensify the rotation. As the authors note, “the more massive the haloes that sit at either end of the filaments, the more rotation is detected,” consistent with gravitational torques inducing these motions. Nevertheless, more study is needed, as temperature and other physics may also play a role.

The big breakthrough is that we’ve finally detected rotation on these unprecedentedly large scales. If all goes well, we’ll not only figure out why, but we’ll be able to predict how quickly each filament that we see ought to be spinning, and for what reason. Until we can predict how every structure in the Universe forms, behaves, and evolves, theoretical astrophysicists will never run out of work to do."

We know that on small scales, everything rotates. We know that on the scale of the entire observable Universe, there's no rotation to be seen. Well, what are the largest structures, then, that do rotate? Galaxies? Galaxy clusters? Something even bigger? Yes, something bigger!

Did The Largest Galaxy Survey Ever Just Challenge Cosmology As We Know It?

"If you want to get headlines, eyeballs, and attention, just say those three magic words, “Einstein was wrong.” You won’t be right, of course; no one has been thus far. Relativity, both the special and general forms, have passed every test we’ve thrown at them for more than a century, and scientists have arguably tried harder to prove Einstein wrong than any other scientist in history. Now, within the framework of General Relativity and in the face of the largest galaxy survey ever, we’re going to claim “Einstein was wrong” instead of looking at the far more likely possibility: that we haven’t handled this unprecedented deluge of data properly in the one instance where a small but significant discrepancy manifests itself?

The truth is we have an enormous new set of valuable data, and we can extract a fantastic amount of information about the Universe from it. The nature and amount of dark matter and dark energy have been confirmed; the Universe’s expansion rate lines up with precisely what previous studies have said; and the clustering amplitude is slightly smaller than we expected it would be. It’s doubtful, however, that this is a sign of new physics; if anything, it’s an issue to investigate further and cross-check with other galaxy surveys. If it turns out to be something that’s actually worth a second look, more and better data will show us the way."

Ask Ethan: Can Dark Matter Really Explain The Universe’s Structure?

“If dark matter particles don’t interact and the only force that governs their motion is gravity, how do dark matter particles coalesce into a cloud? [In other words,] why aren’t all the particles hyperbolic?”

There’s a puzzling issue when it comes to the structure in our Universe: why does dark matter form bound structures at all? If you were to fall into our Solar System, for example, and were only affected by gravity, you’d make a hyperbolic orbit: you’d exit the Solar System, after being gravitationally redirected, on a different trajectory but at the same speed at which you entered. Gravity is a conservative force, and behaves identically on all cosmic scales. And dark matter, unlike normal matter, doesn’t interact in a collisional, dissipative way.

Did Our Universe’s Structure Grow From The Top-Down Or From The Bottom-Up?

“A century ago, we didn’t even know what our Universe looked like. We didn’t know where it came from, whether or when it began, how old it was, what it was made out of, whether it was expanding, what was present within it. Today, we have scientific answers to all of these questions to within about 1% accuracy, plus a whole lot more.

The Universe was born almost perfectly uniform, with 1-part-in-30,000 imperfections present on practically all scales. The largest cosmic scales have slightly larger imperfections than the smaller ones, but the smaller ones are also substantial and collapse first. We likely formed the first stars just 50-to-200 million years after the Big Bang; the first galaxies arose 200-to-550 million years after the Big Bang; the largest galaxy clusters took billions of years to get there.

The Universe is neither top-down nor bottom-up, but a combination of both that implies it was born with an almost scale-invariant spectrum. With future survey telescopes such as LSST, WFIRST, and the next-generation of 30-meter-class ground-based telescopes, we’re poised to measure galaxy clustering as never before. After a lifetime of uncertainty, we can finally give a scientific answer to understanding how our Universe’s large-scale structure came to be.”

In a top-down scenario, the Universe would form structures on large scales first, then fragment to form individual galaxies. In a bottom-up scenario, the Universe forms tiny structures first, which then collect and clump under their own gravity to bring about a Universe rich in large-scale structure. So, which one is the Universe we have? 

Cosmic superclusters, the Universe’s largest structures, don’t actually exist

“The idea of a supercluster and the name for ours, "Laniakea," will persist for a long time. But just because we named it doesn't make it real. Billions of years from now, all the different components will simply be strewn farther and farther apart from one another, and in the farthest futures of our imaginings, they'll disappear from our view and reach entirely.”

Galaxies don’t just exist in isolation in our Universe, but are often found bound together as a part of even grander structures. Our own Milky Way is bound in a galactic group (our local group), nearby are larger groups and galaxy clusters, and on still larger scales, cosmic superclusters appear to encompass as many as 100,000 individual galaxies. Yet it isn’t sufficient to simply see what appears to be a collection and draw an imaginary line around it. You can’t just give something a name and proclaim that it’s meaningful because you defined it. Instead, for a collection of objects in space, they need to be gravitationally bound together and connected. Thanks to dark energy, these superclusters aren’t.

In contemporary cosmology, the challenge is no longer simply observing the Universe — it is reconstructing what cannot be seen. As next-generation surveys generate unprecedented volumes of data, astrophysicists are developing increasingly sophisticated methods to map the invisible distribution of dark matter, control systematic uncertainties, and extract cosmological parameters with extraordinary…

The Milky Way’s place in the spacious heavens

Visualization of the local Universe based on detailed observations of nearby galaxies. The red line encloses Laniakea, a proposed supercluster of galaxies containing the Milky Way, which is represented by the black dot at the image center. [Credit: SDvision interactive visualization software by Daniel Pomarède at CEA/Saclay, France]

Finding our galaxy’s exact place in the vast structure of the…

For an even cooler look at large-scale structure of the cosmos, check out this movie of the entire visible universe.