Void (astronomy)

Space has big empty spots.

These spots are called voids. They are very large. They have very few stars or galaxies. Most stars stay in groups.

Gravity pulls things together. This makes groups of stars. It leaves big gaps behind. These gaps are the voids.

Some voids are very, very big. We call these supervoids. Our own home is in a void, too. It has a special name.

Scientists study these empty spots. They help us learn about space.

Do you like looking at the stars?

Space is not just a random mix of stars. It has a pattern that looks like a web.

Most galaxies live in long arms called filaments. They also meet in big groups called clusters. These parts make up the walls of the web.

Between these walls are huge empty spaces. We call these spaces voids. Voids are mostly round and very big. They can be 30 to 300 million light-years wide. Most voids have very little matter in them. They have less than one-tenth of the average amount of matter in the universe.

How do voids form? It starts with tiny changes in the early universe. Gravity pulls matter into dense spots. These spots grow into galaxies and filaments. As matter moves into these groups, it leaves the empty spots behind. This makes the voids grow larger over time.

Scientists study voids to learn about dark energy. Dark energy is a force that makes the universe expand. Voids act like bubbles in space. Their shapes can change as the universe grows. Studying these changes helps us understand how the whole universe works.

The universe is not just a random cloud of stars. Instead, it looks like a giant cosmic web.

This web is made of long arms called filaments and thick walls called clusters. Most galaxies live in these crowded areas. However, there are huge gaps between these structures. These empty spaces are called cosmic voids. Voids are mostly round and very large. They can be 10 to 100 megaparsecs across. This is about 30 to 300 million light-years wide.

Voids are special because they have very little matter. They usually have less than one-tenth of the average density of the universe. Even the emptiest voids still hold about 15% of the average matter. This makes them look almost empty to anyone watching.

How do these massive gaps form? It all started with tiny changes in the very early universe. These changes are called quantum fluctuations. Over time, these small spots grew much larger. Gravity pulled matter into the densest areas. These areas collapsed and became galaxies and filaments. As matter moved into these groups, it left the other areas behind. This process created the large, foam-like structure we see today. The voids are the empty bubbles in this cosmic foam.

Scientists first discovered these voids in 1978. Two researchers named Stephen Gregory and Laird A. Thompson found them. They used the Kitt Peak National Observatory for their study. They looked at the areas around the Coma clusters. Before this, maps of the universe were often flat. New redshift surveys helped scientists make three-dimensional maps. These surveys used Hubble's law to find depth. This allowed astronomers to see the true shape of the web.

Many important things have happened in the study of voids. In 1981, a huge void was found in the Boötes region. It was about 34 megaparsecs wide. In 1989, a survey showed that voids and filaments dominate the universe. By 2009, the Sloan Digital Sky Survey gave us a very complete view. We even know that our own Milky Way galaxy lives in a void. It is called the KBC Void.

Studying voids helps us learn about dark energy. Dark energy is a force that makes the universe expand. Voids act like bubbles in space. Their shapes change as the universe grows. This happens because of the Sachs-Wolfe effect. This effect links voids to colder spots in the cosmic microwave background. By watching how voids change, scientists can study dark energy. This helps us understand how the whole universe works.

Cosmic voids are vast, largely spherical regions within the large-scale structure of the universe. They represent the empty spaces between the dense structures of the cosmic web. While they appear empty, they are essential components of the universe's architecture. These regions have a very low cosmic mean density. Most scientists define a void as having a density less than one-tenth of the universe's average. Even the emptiest voids contain about 15% of the average matter density.

The formation of these voids is a process driven by gravity and early cosmic events. It began with tiny anisotropies, or irregularities, from quantum fluctuations in the early universe. These fluctuations grew larger in scale over time. Regions with higher density collapsed more rapidly due to gravity. This caused matter to clump together into galaxies and filaments. As matter moved into these dense areas, it left behind large, underdense regions. This resulted in the foam-like structure of voids and filaments seen today.

The cosmic web consists of several distinct structural components. Voids are the massive, low-density bubbles. Surrounding these voids are walls, which contain the typical average density of matter. These walls are further divided into smaller features. Clusters are highly concentrated zones where different walls meet and intersect. Filaments are the branching arms of these walls. These filaments can stretch for tens of megaparsecs.

Astronomers began studying these structures in the mid-1970s. In 1978, Stephen Gregory and Laird A. Thompson published pioneering studies. They discovered voids in the foreground of the Coma/A1367 clusters using the Kitt Peak National Observatory. This era was revolutionized by redshift surveys. These surveys used Hubble's law to calculate depth from galaxy redshifts. This allowed for the first three-dimensional mapping of the universe. Since then, surveys like the Sloan Digital Sky Survey in 2009 have provided a complete view.

Scientists use different mathematical algorithms to locate these empty regions. The VoidFinder algorithm uses the Nearest Neighbor Approximation. It calculates density based on the distance to the third-closest galaxy. The ZOBOV algorithm uses a Voronoi tessellation technique. This method identifies regions based on high-density contrasting borders. Finally, the DIVA algorithm uses a dynamical approach. It defines voids as regions where matter is escaping. DIVA classifies voids into three morphological types: True voids, Pancake voids, and Filament voids.

Voids provide critical evidence for the existence of dark energy. The universe's expansion is believed to be accelerated by dark energy. Voids act like bubbles that are sensitive to these cosmological changes. Their shapes evolve as the universe expands. This relationship is linked to the Sachs-Wolfe effect. This effect causes voids to correlate with colder regions in the cosmic microwave background. Hotter regions correlate with filaments due to gravitational redshifting. This helps scientists constrain models like the ΛCDM model.

Studying voids also offers insights into other fundamental physics. For example, neutrinos have a very small mass and weak interactions. Because of this, they can free-stream in and out of voids. Furthermore, the existence of large voids and clusters requires that dark energy makes up about 70% of the universe. Even our own home is part of this structure. The Milky Way galaxy is located within a cosmic void known as the KBC Void.