Local Void

The Local Void is a massive, relatively empty region of space. It sits right next to our own Local Group of galaxies. This region is significant because it contains far fewer galaxies than standard cosmology would predict. Astronomers have noted that the local universe is less dense than surrounding areas. This density is about 15% to 50% lower than what we see elsewhere. Some researchers call this region the Local Void or the Local Hole.

Gravity plays a major role in how the universe is structured. Gravity causes matter to clump together into clusters and long chains. These clumps of matter leave behind large gaps that are mostly empty. The Local Void is one of these enormous gaps. It is not one single open space. Instead, it is composed of three separate sectors. These sectors are separated from each other by thin, wispy filaments of matter.

We do not know the exact size of the Local Void. However, we know it is at least 45 megaparsecs across. A megaparsec is a unit used to measure vast distances in space. Some estimates suggest it could be much larger. It may reach 150 to 300 megaparsecs in width. The Milky Way sits in a flat array of galaxies called the Local Sheet. This sheet acts as a boundary for the void. The void begins at the very edge of the Local Group.

In 1987, astronomers Brent Tully and Rick Fisher discovered the Local Void. Since then, scientists have used different methods to study its properties. One method involved observing an isolated dwarf galaxy named ESO 461-36. This galaxy is located inside the void. Because the void is so empty, its gravity is very weak. This weak gravity should allow the dwarf galaxy to flee the void quickly. Scientists have observed this fast movement toward concentrations of matter. Some researchers suggest that dark energy might also explain this speedy expulsion.

Earlier models tried to explain our local surroundings differently. One model was called the Hubble Bubble. It was based on the measured velocities of Type 1a supernovae. This model proposed a void centered specifically on the Milky Way. However, recent analysis of that data changed our understanding. Scientists found that interstellar dust had caused misleading measurements. This shows how difficult it is to map the deep universe.

Even in this empty space, some galaxies exist. The Pisces A and Pisces B galaxies are two dwarf galaxies found there. Pisces A is 5.64 megaparsecs away in the Pisces constellation. Pisces B is 9.2 megaparsecs away. About 100 million years ago, these galaxies began moving out of the void. They moved toward a denser gaseous environment in the local filament zone. This change in environment caused their rate of star formation to double.

Other interesting galaxies reside near or within the void boundaries. NGC 7077 is a blue compact dwarf galaxy in the Aquarius constellation. It was discovered by Albert Marth in 1863. NGC 6503 is a colorful dwarf spiral galaxy in the Draco constellation. It is about 17 million light-years away. It features bright red gas regions and bright blue star-forming regions. NGC 6789 is another irregular galaxy in Draco. It was discovered by Lewis Swift in 1883. It is the closest blue compact dwarf galaxy to the Milky Way.

The Local Void is not a static place. Scientists believe the void is actually growing. This happens because matter pulls together into clumps in other areas. As matter moves into these clumps, the empty spaces expand. The Local Sheet is currently rushing away from the center of the void. This movement happens at a speed of 220 kilometers per second. The Milky Way is also being affected by this process. Our galaxy moves away from the Local Void at 250 kilometers per second.