The Boötes Void, or the colossal void, is an immensely large spherical region of space with very few galaxies. It is situated in the vicinity of the Boötes constellation.
Since the time of the Big Bang, matter in the universe has been distributed throughout space and time. However, due to galaxies forming at different times with varying initial masses, the gravitational forces of galaxies differ.
If we were to investigate the distribution of galaxies in the universe, we would find that certain regions have a high concentration of galaxies, shining brightly, while others are scattered in galaxy groups, much like houses in the suburbs of a city.
In the observable universe with a diameter of 93 billion light-years, there are indeed regions that are not black holes, but these regions lack stars, planets, dark matter, and dark energy. They are often referred to as voids or cosmic voids.
Boötes Void is a nearly 250 million light-years wide region of space with very few galaxies. It is the largest known cosmic void. Image: ZME.
This region of no-time is called the cosmic void.
The nearest cosmic void to Earth at present is the Boötes Void, located 700 million light-years away from us. It is devoid of any stars, and everything inside it is submerged in darkness. The extent of this void is astonishingly vast, reaching 250 million light-years across, whereas the Milky Way’s diameter is just 180,000 light-years, and the Sun’s diameter is only 2 light-years. In other words, if the Sun were at the center of the Boötes Void, astronomers might feel as if there were only one galaxy in the universe: the Milky Way.
Illustration. Image: Zhihu.
Because matter is exceedingly scarce within the 250-million-light-year-wide Boötes Void, some science fiction enthusiasts might feel that it seems unnatural, as if some force compelled the removal of 250 million light-years of material. Conversely, conspiracy theorists suggest that this peculiar void is the result of an extraterrestrial war, perhaps a battle between ancient supercivilizations, ultimately creating this starless space.
Certainly, the scientific community is unlikely to endorse these unfounded speculations, and the study of the Boötes Void continues to rely on scientific discovery methods.
In the cosmic microwave background radiation map that reflects the entire universe, the Boötes Void is nearly devoid of any matter, so its temperature is significantly lower than the spacetime around it. This leaves a cold, blueish spot on the cosmic microwave background radiation map. In the future, if humanity’s spacecraft ventures into this region unintentionally, it will be akin to an ant falling into the Pacific Ocean. The crew on the spacecraft will lose all sources of light, making it impossible to reach stars that can replenish nuclear thermal propulsion.
The seemingly infinite night with a diameter of 250 million light-years resembles an insurmountable cosmic wall. For any civilization not yet mastering ultra-light spacecraft technology or traversing wormholes, this void could halt the expansion of most civilizations.
The formation of the Boötes Void: Cosmologists believe that the seeds of the Boötes Void may have formed at the very beginning of the Big Bang. As the universe underwent accelerated expansion, the Boötes Void grew larger over time, eventually reaching the diameter we observe today.
There is also a hypothesis that the 250-million-light-year-wide Boötes Void didn’t naturally form. Instead, it could be an amalgamation of many smaller voids during the universe’s expansion, much like black holes merging to form larger ones.
Currently, we are also situated within a void, although this void is so vast that it’s nearly imperceptible. The Milky Way is part of the Laniakea Supercluster, containing approximately 100,000 galaxies. While this may seem large, on a cosmic scale, the Laniakea Supercluster is just a dot surrounded by voids.
One thing is certain: over an extended period in the future, cosmic voids will become insurmountable barriers to humanity’s observation of the universe. These voids may conceal the true nature of what lies behind them, and there will be no means to cross these gaps – vast areas devoid of internal energy sources.