At first, the sum total of the large, ordered structures in the universe appeared to fall into two categories. There were the clusters of galaxies—an unoriginal but descriptive name—each of which was a dense sphere containing a few dozen to a few hundred galaxies, all bound together by their mutual gravitational embrace. And then there were the field galaxies, lonely wanderers, severed and detached from the galaxy clusters, bound to no one but themselves. That was it: the galaxy clusters, the field galaxies, and the megaparsecs of the void enveloping them all.
But technology is technology and progress is progress. The telescopes became more powerful. The field of cosmology included more people. Techniques improved. The development of image intensification systems – the distant precursors of your smartphone camera – have allowed astronomers to see further and further into the darkness. With each new survey, the number of galaxies in our universe increased. With each night of observation, our window into the cosmos widened.
In the early 1960s, astronomers began to realize that there was more to the universe than just galaxies and galaxy clusters. There was something bigger – the supercluster. It took only a small sample of galaxies to reveal the shape of the first known supercluster, the Local Supercluster, with the galaxies themselves – each one the mass of a trillion suns – reduced to a tiny point of light, acting merely as tracers of huge ones Structure that stretched over a million parsecs per side. The faint sketches they were able to produce showed that galaxies aggregate into clusters and clusters into superclusters – the beginnings of our understanding of the large-scale structure of the Universe.
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Time passed. The observations continued, finding galaxy after galaxy and cluster after cluster. Until one day they didn’t. A mapping of the cosmos brought an unexpected result. This was yet another study of galaxies, clusters and superclusters. Once again, only a few galaxies were needed to reveal the grand structure of the cosmos. Once again astronomers strove to find the pattern, the hidden meaning of this magnificent design. Once again we wanted to map the sky and make it ours. But where a decent selection of galaxies should have revealed even more distant points of light was…nothing.
It was a cosmic accident. A plague in the universe. A Sahara too vast to describe except in astronomer’s reductive, almost meaningless jargon — an empty patch devoid of galaxies nearly 20 megaparsecs, or 65 million light-years across.
In 1978 we found a stillness between the stars: our first cosmic void.
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