The Harvard-Smithsonian Center for Astrophysics is situated on a hill among chestnut and maple trees, a quarter of an hour’s walk from Harvard Square. The oldest part is a three-story U-shaped brick building at the top of the hill. There is the ancient original observatory, which is said to be haunted . Some claim to have seen the son of the observatory’s father, George Bond, who died of consumption and pneumonia in 1865 after spending a winter in the dome, unheated, photographing the Orion constellation area.
In 1981, in the corridor of the new building that abuts the south wall, there was a three-foot cube made of Plexiglas and illuminated with black light. Inside hung 2,400 balls of elderberry pith painted in black and blue. It was the diorama of two years of study mapping our cosmic neighborhood, “the largest scale model in the world,” one of its managers, Marc Davis, said proudly. One centimeter is equivalent to 630,000 light-years. In the center of the cube a small ball marked the position of the Milky Way. Beside it, a cloud of small spheres represented the Virgo cluster and a little further on, an even larger cloud symbolized the Coma cluster. A fleeting glance at the model taught us something very important about the universe: galaxies are grouped in an original way.
In fact, they are arranged in the same way that dust specks are placed on the surface of bubbles in a cauldron of soapy water: they are Hubble bubbles – in English Hubble Bubbles , a name that sounds like chewing gum. They don’t do it randomly, but in a row, like the pearls on a broken necklace or a bowed sheet of paper. Inside each bubble there is nothing, only emptiness. In the constellation of the Boyero, 500 million light-years from us, there is one of those monstrous wastes of space: a void of 300 million light-years where practically no galaxy has been found.
We owe another way of imagining the distribution of galaxies in space to Richard Gott and his colleagues at Princeton University: the cosmos is a sponge . In it, the matter is interconnected because otherwise it would not form a unit. Unexpectedly, the voids are also interconnected, something that is only possible in three-dimensional space. This is our universe.
A heresy turned into reality
This is a new vision. During the first half of the 20th century, thinking in this way was a heresy, since astronomy was governed by the dogma of the isotropy of the universe on a galactic scale. When Swedish astronomer Knut Lundmark pointed out in the 1920s that bright spiral galaxies seemed to ” huddle together in a belt perpendicular to the Milky Way ,” no one paid any attention to him. Those who, like him, mentioned this curious accumulation were ignored by the rest of the astronomical community and abandoned this line of research.
It was just a curious crowd. Thirty years later, a restless Frenchman named Gérard de Vaucouleurs was at the Mount Stromlo observatory in Australia with the aim of revising one of the bibles of astronomy, the Shapley-Ames catalog of bright galaxies. A tedious and boring job, but essential. While updating the galaxies in the southern hemisphere, de Vaucouleurs discovered that ours, along with its neighbors, lay at the edge of a much larger system that we see edge-on and where the galaxies appear to form a long band stretching across the sky from north to south; the location of the Milky Way in this tapestry recalls the marginal place that the Sun occupies in it. For him we were facing a new object in the universe that he called the Local Supergalaxy .
When he joined the astronomy department at the University of Texas at Austin in 1960, his suggestion “was met with thunderous silence. It was considered pure speculation, even nonsense.” It took more than a quarter of a century for his discovery to be accepted, fulfilling what the philosopher William James used to say about great discoveries: “First… it is attacked for absurdity; then it is admitted that it is true, but obviously and insignificant; finally, it comes to be considered so important that its opponents claim that it was they who discovered it”. Today no one doubts that the universe is structured hierarchically , like our own civilization.
A soapy cosmic structure
The Milky Way belongs to a small cluster with an uninspired name, the Local Group, which consists of about 30 galaxies scattered throughout a region of 3 to 4 million light-years. One side is anchored by the Milky Way, surrounded by a bevy of dwarf galaxies; the majestic Andromeda – the only spiral galaxy that can be seen with the naked eye and whose splendor can be glimpsed in the autumn sky – dominates the other end. The census has not yet been completed and it is safe to assume that new galaxies will continue to be discovered in our cosmic neighborhood. By cluster standards, our Local Group is nothing more than a small country town, a nice place to live away from the hustle and bustle of the big city.
Among the true megalopolises of the universe are the Virgo and Coma Berenices clusters, which can be compared to the cities of New York or Tokyo. Virgo’s is the closest to our little town. Located 50 million light-years away and with a population of the order of several thousand galaxies, its largest members can be seen with a modest amateur telescope. For its part, Coma is one of the most densely populated, with a census of 3 to 5 times that of Virgo and countless myriads of faint galaxies.
But not everything ends here. Cosmic cities do not have well-defined boundaries and are connected by “bridges” of galaxies . Three-dimensional maps of the universe have revealed that the Virgo cluster is nothing more than a “bump” in a very long filament formed by other groups of galaxies that, like the beads of a necklace, extend almost directly in the opposite direction to the galaxy. us across 300 million light-years to another galaxy-rich cluster, Abell 1367, in the constellation Leo.
Those maps have also revealed what the “fingers of God” look like: filaments of galaxies seem to point toward us, like the spokes of a bicycle. There is even one that looks like a stick figure drawing of a human being. Inside the Virgo cluster, its brightest galaxies are arranged along a long, narrow line 20 million light-years in size that points at us like a finger, but with a small deviation of 10 to 15º from our line of sight. Another filament pointing our way has also been discovered: the Aquarius Supercluster , a strand of 14 galaxy-rich clusters stretching 1 to 1.4 billion light-years from us.
All these observations of our nearby universe, the one that we can observe in a radius of 500 million light-years, show it with an undeniable foamy structure. “The local universe is like a sink full of dishwater,” Margaret Geller, an astrophysicist at Harvard, told Time magazine. The question that remains for the new generations of extragalactic astrophysicists is , how far does order go in the universe?
References:
Croswell, K. (2001) The universe at midnight, The Free Press
