How was it when the cosmic Web took shape?

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One of the strangest facts about the Universe is the way it has changed dramatically over time: a universe filled with large galaxies containing hundreds of billions of stars, agglomerated and clustered in a huge cosmic network, but everything was extremely smooth and uniform, with very few d & rsquo; Agglomeration or grouping to talk about it In fact, come back far enough and you will not find any galaxies or stars.

It makes sense from a qualitative point of view.The Universe was born with tiny imperfections , the gravitation grows them while the Univers expan As soon as, and according to how and where gravity wins, we get these huge galaxies and clusters of galaxies separated by regions containing nothing: the cosmic voids. But the structure was not formed at one time and the largest structures were formed last. This is the & nbsp; cosmic reason for which.

Imagine the universe as it was at these beginnings. It's full of matter and radiation that spread almost evenly everywhere you look. In the aftermath of the Big Bang, an average density of 100.003% was observed in a very dense region, while an average density of 99.997% was located in a very dense region. When we describe the primitive universe as being uniform, it is the level of uniformity we have achieved.

These overdensities and under-densities were almost exactly the same at all scales. Whether you're looking at an area a few kilometers or a few light-years away or a few million or billions of light-years away, this same one-third-to-one-third fluctuation describes over-sized and under-loaded regions in which the Universe has started.

But that will not stay long as well. Gravity immediately begins to preferentially attract mbad in the over-censored regions compared to all the others. The under-densified regions more easily give up their material to the surrounding areas, which are comparatively denser.

However, even though the law of gravity is universal and identical at all scales, the Universe does not form star clusters, galaxies, or clusters of galaxies all at once . In fact, it takes less than 100 million years for the first stars to form, but billions of years – more than ten times longer – before forming the huge clusters of galaxies populating the planet. 39; Universe.

This seems counter-intuitive, but there is a simple reason that appears in the first image of the nascent Universe: gravity is a force with infinite range, but does not not spread at infinite speeds. It only spreads at the speed of light, which means that if you want to have an impact on a region of space that puts you 100 million years to reach the speed of light, your presence will only be visible when 100 million years have pbaded. 19659003] This is why, in the cosmic microwave background chart above, the largest scales (left) show completely flat temperature fluctuations: gravitation has not yet impacted them. This first, mbadive peak is where gravitational contraction is occurring, but there has not been enough collapse to cause a decline in radiation. And the peaks-and-valleys beyond that represent a splash at scales smaller than the current cosmic horizon.

All of this translates into a detailed roadmap for scale structure in the forms of the universe. We can break it down into a few general rules.

• The structure will first be formed on smaller scales: stars before galaxies, galaxies before clusters, clusters before superclusters.
• This characteristic scale where the density fluctuations are greatest will correspond to a distance scale, today, where we are more likely to see correlations of galaxies than on shorter or longer scales.
• If there is a kind of phase of acceleration later in the Universe, this will cause a break in the formation of the structure: a maximum and maximum scale for the structure.
• And once you are gravitationally bound, you must remain so, even if the expansion of the Universe continues to infinity.

According to our observations of the distant Universe, all these predictions are:

The first stars as we understand them, appear when the Universe is between 50 and 100 million years old. It takes several million solar mbades (but less than a billion) to trigger the gravitational collapse of stars in the primordial material of the universe, which means that even the densest regions of all will not develop stars until several tens of millions of years ago.

It will take longer for these star clusters to merge to create galaxies, for these galaxies to unite to create galaxies and groups of evolved galaxies, and for these groups to unite to form galaxies. clusters of galaxies. This is what we mean by the cosmic web and the large-scale structure of the universe: it must be built, from small scales (where gravity acts first) to large ones.

how structures form in the Universe, giving rise to a network of filaments where clusters exist at the nexus level, the network appears first at smaller scales. Large scales do not have a structure until the Universe has aged yet, because of the extremely long time it takes a gravitational signal to travel hundreds of millions or billions of light years

. A universe of about 92 billion light years in diameter. And the scale at which we are more likely to see these galaxy correlations is about 500 million light years, which means that if you put your finger on a galaxy and look at a certain distance, you will have more Chances of Finding Another A galaxy lying 500 million light-years longer than you are between 400 and 600 million light-years away.

In addition, large-scale features that we recognize as clusters of galaxies should not be present in the early stages. For hundreds of millions of years, there should be no cluster of galaxies, and it would take billions of years to see large collections of galaxies clump together into a real cluster .

Those who appear at these beginnings should have a lower mbad than those who appear later. By and large, this is dramatically corroborated by the observations, the first clusters of known mbadive galaxies appearing well after the abundance of mbadive galaxies. Looking more closely, we find clusters of galaxies more mbadive and containing many more galaxies than the most distant

there appears to be a limit to the size and mbad of the structures. You may have heard about our local supercluster: Laniakea, which contains the Milky Way, the local group, the Virgin group and many other groups and groups that seem to be arranged in a lean web-like structure. If you had to map all this, you might be tempted to conclude that Laniakea is real and that this mbadive object is an even bigger structure than the large clusters of galaxies we see across the universe.

phantasy. Laniakea is only an apparent structure; it is not gravitationally related. On the largest cosmic scales, dark energy dominates the gravitational force for 6 billion years. If an object did not reach enough density to collapse by itself, it will never be.

Laniakea, like all the huge structures on the scale of the supercluster, is being torn apart by l & # 39; 39, expansion of the Universe. It takes an average of 2 to 3 billion years for these large clusters of galaxies to reach sufficient densities and allow gravitational collapse. The most mbadive ones may contain several thousand Milky Way Galaxy galaxies today, but there are not huge behemoths spanning tens of billions of light years or containing tens of thousands of Milky Way. The accelerated expansion of the Universe is simply too difficult to overcome for gravitation to be overcome.

Although the seeds needed for the cosmic structure were planted in the very early stages of the Universe, it takes time and the right resources for these seeds to grow to maturity. The seeds of the small-scale structure germinate first, because the gravitational force propagates at the speed of light, developing oversize regions in the first clusters of stars after only a few tens of millions of years. Over time, the seeds of galaxy scale structure are also developing, putting hundreds of millions of years to create galaxies in the Universe.

But clusters of galaxies, growing from seeds of the same magnitude over greater distances, take billions of dollars. years. At the time when the universe reached the age of 7.8 billion years, the accelerated expansion took over, which is why it does not. There are no larger bound structures than galaxy clusters. The cosmic web no longer grows as before, it is mainly torn by dark energy. Enjoy what we have while we have it; The universe will never be structured in this way!

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A simulation of the large-scale structure of the Universe.identify sufficiently dense and mbadive regions to match clusters of stars, galaxies, clusters of galaxies and determine when and under what conditions they form a challenge that cosmologists only raise. Zarija Lukic

One of the strangest facts about the Universe is the way in which it radically Changed over time, today we see a universe filled with large galaxies containing hundreds of billions of stars, clustered and grouped together in a huge cosmic network.Now closer to the Big Bang, however, everything was extremely smooth and uniform, with very little agglutination or agglomeration to speak of.In fact, go far enough and you will not find any galaxies or stars at all.

This seems logical from a qualitative point of view The universe is born with tiny imperfections, the gravitation grows them as the Universe zooms in and, depending on how and where gravity wins, we get these huge galaxies and clusters of galaxies separated by regions containing nothing: the cosmic voids. Mais la structure ne s&#39;est pas formée en une fois et les structures les plus grandes se sont formées en dernier. C&#39;est la raison cosmique pour laquelle.

L&#39;évolution de la structure à grande échelle dans l&#39;Univers, d&#39;un état précoce et uniforme à l&#39;Univers en cluster que nous connaissons aujourd&#39;hui. Le type et l&#39;abondance de matière noire produiraient un univers extrêmement différent si nous modifiions ce que notre univers possède. Notez le fait que la structure à petite échelle apparaît tôt dans tous les cas, tandis que la structure à grande échelle n&#39;apparaît que bien plus tard. Angulo et al. 2008, via l&#39;Université Durham

Imaginez l&#39;univers tel qu&#39;il était à ces débuts. C&#39;est plein de matière et de rayonnement qui se répartissent presque parfaitement de manière égale partout où vous regardez. Au lendemain du Big Bang, une densité moyenne de 100,003% était observée dans une région très dense, alors qu&#39;une densité moyenne de 99,997% était située dans une région très dense. Lorsque nous décrivons l&#39;Univers primitif comme étant uniforme, c&#39;est le niveau d&#39;uniformité que nous avons atteint.

Ces surdensité et sous-densité étaient presque exactement les mêmes à toutes les échelles. Que vous regardiez une région de quelques kilomètres ou quelques années-lumière ou de quelques millions à milliards d&#39;années-lumière, cette même fluctuation d&#39;un tiers sur 30 000 décrit les régions surdimensionnées et sous-tendues dans lesquelles l&#39;Univers a commencé.

les régions surdenses croissent et grandissent avec le temps, mais leur croissance est limitée par les petites magnitudes initiales des surdensité, l’échelle cosmique sur laquelle se trouvent les surdensité (et le temps nécessaire pour les traverser), ainsi que par présence de radiations qui sont toujours énergétiques, ce qui empêche la structure de se développer plus rapidement. Il faut des dizaines, des centaines de millions d&#39;années pour former les premières étoiles; Il existe toutefois des amas de matière à petite échelle bien avant cela. Aaron Smith / TACC / UT-Austin

Mais cela ne restera pas longtemps ainsi. La gravité commence immédiatement à attirer préférentiellement la mbade dans les régions surendensées par rapport à toutes les autres. Les régions sous-densifiées abandonnent plus facilement leur matière aux régions environnantes, comparativement plus denses.

Cependant, même si la loi de la gravité est universelle et identique à toutes les échelles, l&#39;Univers ne forme pas d&#39;amas d&#39;étoiles, de galaxies ni grappes de galaxies tout à la fois. En fait, il faut moins de 100 millions d&#39;années pour que les premières étoiles se forment, mais des milliards d&#39;années – plus de dix fois plus longtemps – avant que nous formions les énormes amas de galaxies peuplant l&#39;Univers.

Les fluctuations du fond diffus cosmologique, telles que mesurées par COBE (à grande échelle), WMAP (à échelle intermédiaire) et Planck (à petite échelle) correspondent toutes non seulement à un ensemble de fluctuations quantiques invariantes en échelle, mais aussi à une magnitude si faible que ils ne pourraient probablement pas provenir d&#39;un état arbitrairement chaud et dense. La ligne horizontale représente le spectre initial des fluctuations (dues à l&#39;inflation), tandis que la droite ondulée représente la manière dont les interactions gravité / rayonnement / matière ont modelé l&#39;Univers en expansion au début. Équipe scientifique NASA / WMAP

Cela semble contre-intuitif, mais il y a une raison simple qui apparaît dans la première image de l&#39;Univers naissant: la gravité est une force à portée infinie, mais ne se propage pas à des vitesses infinies. It propagates only at the speed of light, meaning that if you want to have an impact on a region of space that takes you 100 million years to reach at the speed of light, it cannot feel your presence until 100 million years have pbaded.

This is why, in the graph of the cosmic microwave background, above, the largest scales (at left) have temperature fluctuations that are completely flat: gravitation hasn&#39;t impacted them yet. That first, mbadive peak is where gravitational contraction is just taking place now, but there hasn&#39;t been enough collapse to trigger pushback on the part of radiation. And the peaks-and-valleys beyond that represent a splashing around on scales smaller than the current cosmic horizon.

The cosmic web is driven by dark matter, which could arise from particles created in the early stage of the Universe that do not decay away, but rather remain stable until the present day. The smallest scales collapse first, while larger scales require longer cosmic times to become overdense enough to form structure.Ralf Kaehler, Oliver Hahn and Tom Abel (KIPAC)

This all translates into a detailed roadmap for how the large-scale structure in the Universe forms. We can break it down into a few general rules.

• Structure will form on smaller scales first: stars before galaxies, galaxies before clusters, clusters before superclusters.
• That characteristic scale where the density fluctuations are the greatest will correspond to a distance scale, today, where we&#39;re more likely to see galaxy correlations than on either shorter or longer scales.
• If there&#39;s some sort of acceleration phase that arises later in the Universe, it will cause a cutoff in structure formation: a maximum, largest scale for structure.
• And once you become gravitationally bound, you should remain gravitationally bound even as the expansion of the Universe continues endlessly.

Based on our observations of the distant Universe, all of these predictions are borne out.

An illustration of the first stars turning on in the Universe. Without metals to cool down the stars, only the largest clumps within a large-mbad cloud can become stars. Until enough time has pbades for gravity to affect larger scales, only the small-scales can form structure early on.NASA

The first stars, as we understand them, appear when the Universe is between 50 and 100 million years old. It takes many millions of solar mbades (but under a billion) to initiate gravitational collapse down to stars for the primordial material in the Universe, which means that even the densest regions of all won&#39;t develop stars until many tens of millions of years have pbaded.

It will take additional time for these individual star clusters to merge together to create galaxies, for those galaxies to merge together to create evolved galaxies and galaxy groups, and for those groups to merge together to form galaxy clusters. This is what we mean when we talk about the cosmic web and the large-scale structure of the Universe: it has to build itself up, from small scales (where gravity takes action first) to large ones.

Even though this is how structure forms in the Universe, giving rise to a network of filaments where clusters exist at the nexuses, the network appears on smaller scales first. The larger scales don&#39;t exhibit structure until the Universe has aged further, owing to the extremely large amount of time it takes a gravitational signal to traverse hundreds of millions or billions of light years.

By the present, we have an observable Universe that&#39;s a whopping ~92 billion light years in diameter. And the scale at which we&#39;re more likely to see these galaxy correlations works out to about 500 million light years, which means if you put your finger down on any galaxy and look a certain distance away, you&#39;re more likely to find another galaxy 500 million light years away than you are 400 or 600 million light years away.

An illustration of clustering patterns due to Baryon Acoustic Oscillations, where the likelihood of finding a galaxy at a certain distance from any other galaxy is governed by the relationship between dark matter and normal matter. As the Universe expands, this characteristic distance expands as well, allowing us to measure the Hubble constant, the dark matter density, and even the scalar spectral index. The results agree with the CMB data, and a Universe made up of 27% dark matter, as opposed to 5% normal matter.ZOSIA ROSTOMIAN

Furthermore, the large-scale features we recognize as galaxy clusters shouldn&#39;t be present at the earliest stages. For many hundreds of millions of years, there should be no galaxy clusters at all, and it should take billions of years to see large collections of galaxies clumping together into bona fide galaxy clusters.

Moreover, the ones that appear at these early times should be lower in mbad than the ones that show up later. By and large, this is borne out spectacularly by observations, with the earliest mbadive galaxy clusters known appearing well after mbadive galaxies are plentiful. As we look close by, we find galaxy clusters that are more mbadive and contain far more galaxies than the more distant ones.

The giant, nearby galaxy cluster, Abell 2029, houses galaxy IC 1101 at its core. At 5.5 million light years across, over 100 trillion stars and the mbad of nearly a quadrillion suns, it&#39;s the largest known galaxy of all. The farther away we look, the lower in mbad galaxy clusters are, while the earliest proto-cluster we find is still more than a billion years after the Big Bang.Digitized Sky Survey 2, NASA

Most spectacularly of all, there seems to be a limit to the size and mbad of structures. You may have heard of our local supercluster: Laniakea, which contains the Milky Way, the local group, the Virgo cluster, and many other clusters and groups that appear to be arranged in a spindly, web-like structure. If you were to map it all out, you might be tempted to conclude that Laniakea is real, and that this mbadive object is an even larger structure than the big galaxy clusters we see across the Universe.

Yet it&#39;s nothing more than a phantasm. Laniakea is only an apparent structure; it isn&#39;t gravitationally bound. On the largest cosmic scales, dark energy dominates the gravitational force, and has been doing so for the past 6 billion years. If an object hadn&#39;t gravitationally grown to a sufficient density so that it would collapse under its own power by then, it never will.

The Laniakea supercluster, containing the Milky Way (red dot), on the outskirts of the Virgo Cluster (large white collection near the Milky Way). Despite the deceptive looks of the image, this isn&#39;t a real structure, as dark energy will drive most of these clumps apart, fragmenting them as time goes on.Tully, R. B., Courtois, H., Hoffman, Y & Pomarède, D. Nature 513, 71–73 (2014)

Laniakea, like all enormous supercluster-scale structures, is presently being torn apart by the expansion of the Universe. It takes, on average, about 2-to-3 billion years for these large galaxy clusters to grow to sufficient densities to gravitationally collapse. The most mbadive ones might contain many thousands of Milky Way-sized galaxies today, but there are no behemoths spanning tens of billions of light years or containing tens of thousands of Milky Ways inside them. The accelerated expansion of the Universe is simply too much for gravitation to overcome.

The cosmic web of dark matter and the large-scale structure it forms. Normal matter is present, but is only 1/6th of the total matter. The other 5/6ths is dark matter, and no amount of normal matter will get rid of that. If there were no dark energy in the Universe, structure would continue to grow-and-grow on larger-and-larger scales as time went on, but in its presence, there are no structures exceeding several billion light years in size.The Millenium Simulation, V. Springel et al.

Although the seeds necessary for cosmic structure were planted in the very earliest stages of the Universe, it takes time and the right resources for those seeds to grow to fruition. The seeds for small-scale structure germinate first, as the gravitational force propagates at the speed of light, growing overdense regions into the earliest star clusters after only a few tens of millions of years. As time goes on, the seeds for galaxy-scale structure grow too, taking hundreds of millions of years to bring about galaxies within the Universe.

But galaxy clusters, growing from the same magnitude seeds on larger distance scales, take billions of years. By time the Universe is 7.8 billion years old, the accelerated expansion has taken over, explaining why there are no larger bound structures than galaxy clusters. The cosmic web is no longer growing as it once was, but is primarily being torn apart by dark energy. Enjoy what we have while we have it; the Universe will never be this structured again!

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Further reading on what the Universe was like when: