Paul M. Sutter writes:

The universe is permeated by a vast, invisible web, its tendrils weaving through space. But despite organizing the matter we see in space, this dark web is invisible. That’s because it is made up of dark matter, which exerts a gravitational pull but emits no light.

That is, the web was invisible until now. For the first time, researchers have illuminated some of the darkest corners of the universe.

A long time ago, the universe was hotter, smaller and denser than it is now. It was also, on average, much more boring. There wasn’t much variation in density from place to place. Sure, space was much more cramped overall, but in the young universe, no matter where you went, things were pretty much the same.

But there were tiny, random differences in density. Those nuggets had slightly more gravitational pull than their surrounding neighborhood, and so matter tended to flow into them. Growing bigger in this way, they developed an even stronger gravitational influence, pulling more matter in, causing them to be bigger, and so on and so on for billions of years. Simultaneously, as the nuggets grew, the spaces between them emptied out.

Over the course of cosmic time, the rich got richer and the poor got poorer.

Eventually, the dense patches grew to become the first stars, galaxies and clusters, while the spaces between them became the great cosmic voids.

Now, 13.8 billion years into this massive construction project, the job isn’t quite finished. Matter is still streaming out of the voids, joining groups of galaxies that are flowing into dense, rich clusters. What we have today is a vast, complex network of filaments of matter: the cosmic web. [Continue reading…]