In 1981, Robert Kirshner was working with other astronomers at the University of Michigan to calculate the redshifts – a measure of how fast something is moving away from Earth – of a large number of galaxies. Because of the way our Universe expands, the farther away a galaxy is, the faster it moves, meaning the redshift can be used as a measure of distance. Kirshner and his team took the opportunity to create a 3D map of the Universe.
As the map grew, something strange arose. 700 million light years from Earth, it was a vacuum. In a roughly spherical region about 330 million light years wide – an area the Milky Way could fit into billions of times – there were hardly any galaxies.
Initially, the region was called the Big Nothing, but later became known as Boötes Void, as it appears to be in the constellation of Boötes, the shepherd who drives the plow around the North Pole.
Since then, polls have succeeded in creating more detailed maps of our Universe. We now know that galaxies are arranged like a giant web. The majority of galaxies in our Universe are found in long structures, called filaments, that meander through the cosmos. When these meet, they create regions with a high concentration of galaxies, called clusters.
Between these threads, however, are huge voids with hardly any galaxies. Voids make up about 80% of the observable Universe, and most are between 30 and 300 million light years. Boötes is one of the greatest, which earned him the title of “supervide”. It is believed that Boötes is the product of small voids merging with each other.
It is believed that the cause of these voids lies in the origin of the Universe. In the early days of the cosmos, all matter in the Universe was tightly packed. Initially, it was thought to be a uniform soup, but random quantum fluctuations quickly created small differences in the distribution of matter.
Some areas were now slightly denser, meaning their gravitational pull was greater, so they pushed matter away from less dense areas. This made them even denser, again increasing their gravitational pull in order to attract more matter and so on. At the same time, the Universe was expanding rapidly and these fluctuations which started at a quantum level eventually spanned hundreds of millions of light years. During this time, smaller clusters of matter began to organize into galaxies.
By studying these large structures, astronomers can get a window into what the Universe looked like in its early days. Today, advances in telescope and imaging technology mean that they are able to create more detailed versions of Kirshner’s maps, such as the Dark Energy Investigation which mapped a quarter of the southern sky, examining approximately 300 million galaxies.
Meanwhile, supercomputers can now create detailed simulations of how the Universe developed from the earliest moments after the Big Bang to the cosmos we see today. By comparing these maps with the simulations, astronomers can begin to understand how our Universe came to look like it is today.
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