If you think that space is a uniform carpet of stars and galaxies, prepare to be amazed. The Boötes void it's an area of space that seems to have forgotten to follow the rules.
Discovered almost by accident 40 years ago, this void is so large that it represents 2% of the diameter of the entire observable universe, yet it is… help me say… Empty. Let's try to understand better.
A cosmic enigma
There is a region of space that defies the laws of probability: it has a diameter between 250 and 330 million light years, it is so large that it contains over 2000 galaxies, but there are about 60 of them. one galaxy every 10 million light years. It's as if the universe forgot to fill this space.
Before diving into the mystery of the Boötes Void, it is useful to make a distinction. Also Barnard 68, a dark nebula located just 400 light-years away, has often been confused as a “void” in space. However, as explained byEuropean Southern Observatory (ESO), this nebula is actually full of stars, hidden by cosmic dust. So, don't be fooled by appearances. At the moment, there is only one Great Void: be wary of imitations.
The discovery of the “Great Void”
In 1981, astronomers published a paper with the provocative title: “One million empty cubic megaparsecs in Boötes?” The discovery was made by the astronomer Robert Kirshner together with his colleagues Augustus Oemler, Paul Schechter e Stephen Shectman during an investigation of the redshift of galaxies*.
Since then, the Boötes Void has become an enigma that has fascinated the scientific community. What could have caused such a large void?
Where are the “missing” galaxies?
There are several hypotheses about what the Boötes Void might have produced. Here are some of the most discussed theories:
- Fusion of smaller voids: One of the most accredited theories suggests that this huge region of space it could be the result of the fusion of multiple small voids. In this scenario, these smaller voids would have merged over time, creating a larger void.
- Expansion of the Universe: Another possibility is that the void is simply a product of the expansion of the universe. However, this theory does not fully explain why it is such a different region than others.
- Influence of Dark Matter: Some scientists speculate that dark matter could play a role in creating this void, perhaps influencing the distribution of galaxies so that they avoid this region.
- Anomalies in the Formation of Galaxies: A final theory suggests that there may be unknown factors that influenced the formation of galaxies, making this region particularly sparse.
Each of these hypotheses has its strengths and weaknesses, and at the moment none have been definitively confirmed. The Boötes Void therefore remains a fascinating mystery that continues to stimulate further research and debate in the scientific community.
On the other hand, only the 31% of the observed Universe contains material that we know about. Theories abound, but the truth is that we still have a lot to learn. If you want to know in detail the characteristics of the Boötes Void, I'll link you to a paper which contains valuable data on its structure.
* The redshift of galaxies is like the sound of a car moving away and getting quieter. If a galaxy moves away from us, its light becomes redder. Astronomers use it to understand the speed and direction of the galaxy.
