The cosmic web: from believing ourselves to be the center of the universe to knowing that we live in a gigantic galactic hole

Suppose we can leave home, and go not a little, but beyond the confines of our solar system, much beyond.

Let us leave behind the Orion arm, that part of the spiral structure of our galaxy that is closest to us.

We continue traveling and now leave the structure of billions of stars that revolve around a point close to Sagittarius A*, the monstrous black hole that inhabits the heart of the Milky Way.

If we get far enough away for all that structure to become a point, where would we go from there in search of other galaxies?

Would we find something just as close no matter which direction we travel?

The simple answer is no.

More information

Black holes: the mysterious 'gargantuans' that control our galaxies

Determining the large-scale structure of the universe is one of the fundamental questions in cosmology.

We know from sky maps that, by the way, it is increasingly difficult for us to build due to light pollution, that the matter of the universe on the largest scales is organized in intricate geometric patterns in the form of spider webs.

Yes, I said cobweb.

It is not uniform or random, it is in the form of a network, what we know as a cosmic network.

Matter in the Universe on the largest scales is organized into intricate geometric patterns in the form of a spider web, a cosmic web.

Our galaxy, for example, is gravitationally linked to a larger structure known as the Local Group, which in turn is immersed in the Local Supercluster, which is nothing more than an accumulation of more than one hundred individual groups and clusters of galaxies.

The universe on a large scale is not homogeneous, it has a structure, large walls, filaments, nodes and, above all, large voids.

The Milky Way is located in one of them, the largest, known as KBC (by the acronym of the astronomers who discovered it Keenan, Barger and Cowie).

KBC refers to the neighborhood of the Milky Way, whose average density of matter is considerably less than the average of the observable universe, has a diameter of about 2,000 million light years and even appears in the Guinness of records.

We live in that quasi-spherical void.

Thanks to the large maps of the sky, we have observed that the matter of the cosmos is concentrated in geometric patterns with a hierarchy of different structures.

On the one hand, there are the bubbles, at their intersection is where we see what we call the walls, and at the intersection of the walls the edges known as filaments are formed, with each structure described we go down one dimension.

The filaments are perhaps the most obvious at first glance, they are elongated and intersect at the nodes of the cosmic web.

The nodes are the places where most of the matter is concentrated.

But in this network, above all, there are holes, where there are almost no galaxies, huge empty bubbles.

The voids have typical diameters of between 30 and 300 million light-years.

Most of the cosmic volume turns out to be empty.

It is at the sites where two or more large filaments intersect that the density of matter becomes so high that massive galaxy clusters, containing hundreds or thousands of galaxies, can form.

The largest and most massive gravitationally bound objects in the universe, galaxy clusters represent the high-density “nodes” of the cosmic web.

Along the filaments, which can reach lengths of several hundred million light-years, the clumps accumulate new matter, which means that they are still growing, accreting material.

Most of the galaxies in the universe are found in small groups, such as the Local Group, located in a filament that connects the Fornax cluster with the Virgo cluster of galaxies.

In the cosmic web, there are mostly huge empty bubbles between 30 and 300 million light-years.

Most of the cosmic volume is empty

Network topology visualization of galaxy distribution.Kim Albrecht (Center for Complex Network Research)

The study of the cosmic web allows, for example, to understand how galaxies obtain their mass.

Galaxy formation is not isotropic, but rather has preferential directions that are marked by the existence of structure in the cosmic web.

If two galaxies are going to merge, in general they will not do it from any direction, but the probability is that they will do it in the direction of the filaments of this network.

The network therefore connects different scales, the size structure of about 300,000 light-years with sizes two orders of magnitude larger.

The unbearable weight of gravity given a set of initial conditions is responsible for building over time the intricate geometric pattern in the form of a spider web in which the matter of the universe is distributed.

Starting from some simple initial conditions, which we know thanks to the maps of the cosmic microwave background, it is possible to reproduce, with the simple assistance of the laws of physics, how these cosmic structures grow.

The seeds were already planted in the early universe, those random fluctuations that the universe presents in diapers that we have measured thanks to satellites such as COBE or PLANCK.

Everything is written, it seems, in those initial conditions.

Cosmic Void

You can follow