Did you know the Universe is full of voids? Areas where very few things exist. Boötes void
or the Great Nothing is such a place. When you look up at the night sky,
everything seems to be the same. Countless stars spread out in fairly uniform fashion.
But huge areas such as Boötes void are different and contain very few objects.
The Universe is a structure on its own: long filaments of dark matter threaded with galaxies
and clusters of galaxies punctuated by vast voids. These voids are just that; areas devoid of matter.
To truly understand the Universe, we may have to gaze into the abyss.
The largest known void in the Universe is Boötes void. This massive empty spherical region in space
is about 330 million light-years in diameter. It accounts for 0.27% of the diameter
of the entire Universe, which itself is a daunting 93 billion light-years across.
Boötes void is a massive expanse of empty space unlike any other ever observed.
This place lies about 700 million light-years near the Boötes constellation.
The American astronomer, Robert Kirshner, and his team discovered it back in 1981.
When we first observed the void, we found only one galaxy inside. Since then,
we’ve detected only a few dozen more.
The average distance from each galaxy would place one
every 10 million light-years. That’s four times the distance of the Andromeda Galaxy from Earth.
This is a big difference compared to our galactic neighborhood, the Virgo Super Cluster,
a much smaller region of space about 110 million light-years in diameter that’s home
to over 2000 galaxies including our Milky Way. When astronomer Greg Aldering once described the
scale of the Great Nothing, he said “if the Milky Way had been in the center of the Boötes void,
we wouldn’t have known there were other galaxies until the 1960s.”
Just for comparison, the Milky Way has about two dozen neighbors
in a region of space just 3 million light-years across.
Looking at the volume of the Boötes void, it should contain about 10,000
galaxies considering that the average distance between galaxies elsewhere in the Universe
is a few million light-years. Instead, we have only identified a total of 60 galaxies there.
The galaxies inside this vast emptiness are as lonely as they can be.
The Hubble telescope even brought us a photo of such a galaxy. MCG+01-02-015
is a spiral galaxy inside the Boötes void. The European Space Agency describes it as
"the loneliest of galaxies". How the galaxy got there, it is not known.
Included in this observation are 3 foreground stars, all from our own galaxy.
All other points of light are background galaxies floating like a swarm of
microbes in a drop of water. But how do such voids form?
Computer models have shown that smaller voids, which are more common,
come as a result of galaxies drawing closer to one another thanks to gravitational attraction.
This causes neighboring regions to deplete. But the big problem here is that this cannot
be the case for Boötes void. That’s because there just hasn’t been enough time since the beginning
of the Universe for mere gravitational forces to clear out a space of that size.
But as I mentioned earlier, the large-scale structure of the Universe is made up of long
filaments of dark matter threaded with galaxies and clusters of galaxies punctuated by vast voids.
This structure is expanding at an accelerating rate. Every day the
galaxies get farther apart from each other. The Universe is just like a sponge, or swiss
cheese, with empty areas inside. As the Universe keeps expanding,
cosmic voids such as the Boötes will keep growing even more. The filaments connecting
clusters of galaxies will stretch and break. The voids will merge and only gravitationally
bound galactic clusters will remain as islands, adrift in the expanding emptiness.