How “dark” is the cosmic network?

Beijing time on March 18, according tomedia reports, every corner of the universe is a huge and invisible “net” penetration. Although everything we see in space is shaped by its tissues, the net itself is invisible because it is made up of dark matter. Dark matter exerts gravity on other matter, but does not release light and is therefore invisible to us.

Pictured is a visual image of the filaments of the cosmic web. The simulation was carried out by the “Evolution and Synthesis of Galaxies and Its Surroundings” (EAGLE) project.

But this is a thing of the past. For the first time ever, researchers have succeeded in “lighting up” some of the darkest corners of the universe.

Weaving web

Once upon a time, the universe was much hotter, much smaller, and much denser than it is today. The universe was also more boring than it is now, and the density was the same. Of course, space was much more crowded at the time than it is now, but wherever you go, there’s no difference everywhere.

But then the density of the universe also randomly appeared some small differences. Some small pieces have a slightly larger gravitational pull than the surroundings, so matter is often attracted to them. These groups of matter are growing, gravity is growing, attracting more and more material… Over the next few billion years, the process went back and forth. At the same time, the space between them is becoming more and more empty. “The rich are getting richer and the poor are getting poorer.” “Eventually, these dense masses gradually became the first stars, galaxies, and clusters, and the space between them became empty interstellar space.

Today, the huge “construction project” has been going on for 13.8 billion years, but it is not yet completed. Matter is still flowing out of these empty spaces and joining galaxies, which are also joining dense clusters. Today, the universe has formed a huge, complex network of silky matter, what we call the “cosmic network”.

A ray of light in the dark

Most of the matter in the universe is dark matter and does not interact with light, or “ordinary” matter such as stars or gas clouds. As a result, much of the cosmic web is completely invisible to us. Fortunately, where dark matter is concentrated in large quantities, other ordinary matter is attracted by its gravity and joins their “camp”.

In the densest regions of the universe, the gravitational pull of dark matter attracts large quantities of ordinary matter to gather. And these ordinary matter gradually transformed into stars. Like lighthouses on the dark beaches in the distance, these stars and galaxies can tell us where dark matter is hidden in the universe, faintly depicting the true structure of the cosmic web.

It’s easy to see where the clusters in the universe are, and they stand out as if they were on a night shift and a big city with bright lights on the ground. There must be a lot of dark matter in the structure of these objects, because there must be enough gravity to bring so many galaxies together.

And the open areas of the universe are easy to see. These areas must contain very little dark matter. Since no galaxies illuminate these areas, we can tell that most of these areas are empty.

But the grandeur of the cosmic network lies in the “filament” itself, which makes up the net. These tiny “rolls” of galaxies can be millions of light-years away, crossing the dark cosmic void and connecting a bright cluster of stars, the “city.”

Through the dim lens

And these “filaments” are also the most difficult part of the universe to study. There are some galaxies, but not many. And the length and direction of these filaments vary. By contrast, those clusters and voids are much simpler. So even though we learned about these filaments through computer simulations decades ago, we never really saw them.

However, a team of astronomers has recently made significant progress in mapping the Cosmic Web and published the results on January 29th on the paper’s preprint website arXiv. Their research process is as follows:

First, they identified a class of so-called “bright red galaxies” (LRGs) from data collected by the HEAVY-koon Oscillation Spectroscopic Survey (BOSS) mission. Bright red galaxies are extremely large galaxies, usually located in the center of dense dark matter regions. If bright red galaxies are located in the densest areas of dark matter, the lines that connect them should be made up of finer “filaments”.

But looking at the space between the two bright red galaxies, there is no sign of anything, after all, there is not much between them. So the team identified thousands of pairs of bright red galaxies from the data, recalibrated them, and then overlapped to produce a composite image.

Using this composite image, the scientists counted all the galaxies they could see and added all the light they emit. In this way, the researchers can measure how much ordinary matter makes up the filaments between bright red galaxies. Next, the researchers focused on the galaxies behind the filaments, especially their shape.

As the light emitted by these background galaxies passes through interwoven filaments, the gravitational pull of dark matter in the filaments causes the light to shift slightly, causing the images of these galaxies to shift slightly. By measuring its offset, the team managed to measure the amount of dark matter in the filament.

These estimates are consistent with theoretical predictions. Scientists have also confirmed that the filaments are not dark, and that each filament equivalent to 351 sun-mass escloses produces the equivalent of one sun.

This “filament” is still very primitive, but it is the first time such progress has been made. And this diagram clearly shows that while most of our cosmic network is dark, it is not a ray of light. (Leaf)