Indian astronomers have discovered a huge new supercluster of galaxies 4 billion light-years away in the constellation of Pisces. The object, known as the Saraswati supercluster, stretches for 600 million light-years across and has a mass of 20 million billion Suns, or about 20,000 Milky Ways.
The discovery, reported in the Astrophysical Journal, throws a spanner in the works of the current cosmological model. The supercluster is too big to be already in place 10 billion years after the Big Bang (which is when we are seeing it). It contains 43 clusters of galaxies, and according to the current model, shouldn't have had time to accumulate to this size.
“Our work will help to shed light on the perplexing question; how such extreme large scale, prominent matter-density enhancements had formed billions of years in the past when the mysterious Dark Energy had just started to dominate structure formation,” the authors of the paper from the Inter University Centre for Astronomy & Astrophysics and the Indian Institute of Science Education and Research, said in a statement.
“Previously only a few comparatively large superclusters have been reported, for example, the ‘Shapley Concentration’ or the ‘Sloan Great Wall’ in the nearby universe, while the ‘Saraswati’ supercluster is far more distant one.”
Saraswati is the name of the Indian goddess of knowledge, music, art, wisdom, and nature – the muse of all creativity. Her name is also associated with real and celestial rivers, a good symbolism for such a large supercluster.
Looking at galaxies with a telescope, it’s not automatically clear if they are near or far. Objects might appear near to each other but they might be separated by billions of light-years. Working out distances requires a lot more work and precise measurements of the light (spectrum) of each galaxy.
“We were very surprised to spot this giant wall-like supercluster of galaxies, visible in a large spectroscopic survey of distant galaxies, known as the Sloan Digital Sky Survey. This supercluster is clearly embedded in a large network of cosmic filaments traced by clusters and large voids,” that authors added.
Galaxies are not randomly spread out in the universe, they are distributed in a filamentary structure called the cosmic web. The cosmic web is one of the predictions of the cosmological model that requires the presence of dark matter and dark energy, the two mysterious components of the universe.
Dark matter is a type of matter that only interacts with gravity and not light and dark energy, and is the supposed cause of the accelerated expansion of the universe. The cosmological model had successfully predicted several features we have observed in the universe, but since we still don’t know what dark matter and dark energy are, it will likely have to be rethought to incorporate new findings like the formation of the Saraswati supercluster.