Recently, a paper titled “Largest structure in the nearby universe discovered: Discovery of the Quipu superstructure,” has generated considerable interest among astrophysicists. The paper has just been accepted and is yet to be published in the “Astronomy and Astrophysics” journal. A team of scientists headed by Hans Böhringer from the Max Planck Institute of Extraterrestrial Physics and the Max Planck Institute of Physics, has unveiled the most extensive supermassive structure in the universe – “Quipu”. Two researchers from Spain and South Africa were also involved in this project.
This cosmic superstructure with about 200 quadrillion solar masses was detected during the mapping from about 130 to 250 Mpc (megaparsecs) of the nearby universe by the German Aerospace Centre-led ROSAT X-ray satellite with the help of the cosmic large-scale structure in X-rays (CLASSIX) cluster survey. In 1990, this satellite mapped the sky using a high-resolution X-ray telescope.
What is a superstructure?
Superstructures are enormous galactic structures containing groups of galaxy clusters or superclusters of smaller galaxy clusters or galaxy groups. When galaxies come close to each other under the pull of gravity, they join together to form clusters. Under the influence of gravitational forces, these clusters coalesce to create superclusters or extensive galaxy clusters.
Over time, these superclusters emerge from more extensive formations. The “Sloan Great Wall,” spanning 1 billion light-years, and the “Laniakia,” spanning 520 million light-years, were formed this way.
Astronomy is one of the oldest branches of science, where scientists mainly study the structure and dynamics of celestial objects. However, researchers had not previously encountered such a large number as 200 quadrillion (fifteen zeros after 200). Both the mass and the size of Quipu is unbelievable.
According to astronomers’ observations, Quipu spans more than 400 Mpc. This gigantic structure is 13,000 times bigger than our Milky Way Galaxy! In astronomy, time is sometimes used instead of length to describe the size of cosmic objects. As such, it would take 13 million years for light to cross Quipu!
The enormity of this cosmic structure is reflected in project leader Böhringer’s explanation: “If you look at the distribution of galaxy clusters in the sky in a spherical shell with a distance of 416 to 826 million light years, you immediately notice a huge structure that stretches from high northern latitudes to almost the southern end of the sky.”.
It consists of 68 clusters of galaxies. Not only does this superstructure contain galaxies, but it also contains large amounts of dark matter.
Following the Incan Empire’s practice of using a system of knots on a cord to store numbers and other information depending on their colour, order, and numbers, scientists have termed their discovery as Quipu. Böhringer saw the cords in a museum near Santiago, Chile, while working at the European Southern Observatory.
Another reason for this nomenclature is that the distances of most galaxy clusters were measured at the Southern Observatory in Chile. Basically, a thick rope is wound around several narrow ropes in a Quipu shape, just like the ancient Inca script.
Apart from Quipu, scientists have found four other giant structures – Shapley, Serpens-Corona Borealis and Hercules, and Sculptor-Pegasus – around it at a distance of 130 to 250 Mpc. They found these massive structures by analysing data from his classic X-ray cluster, primarily using X-ray galaxy clusters.
There are 185 galaxy clusters within these five superstructures. Moreover, these five giants approximately contain 45% of galaxy clusters, 30% of galaxies, and 25% of matter, occupying about 13% of the universe’s volume.
Cosmological importance of the discovery
This finding is not only important for the mapping of the universe but also impacts fundamental cosmological measurements. The cosmic microwave background (CMB), the leftover microwave radiation from the Big Bang that permeates the universe, is impacted by their tremendous gravity as it travels through them.
Despite their expansion-induced separation, galaxies also exhibit local velocities known as unusual velocities or streaming movements. The Hubble constant, which measures the rate at which the universe is expanding, is distorted by the local expansion of the galaxies residing within the superstructures. This local velocity of the galaxies impacts measurements of the universe’s overall expansion. It is possible for supermassive objects to bend and distort the gravitational lensing of light from far away objects, which can lead to wrong distance measurements.
Scientists are also hopeful that future research on superstructures will help to improve conventional cosmological models.
“Even if these are only corrections of a few per cent, they become increasingly important as the accuracy of cosmological observations increases,” said Gayoung Chon, a principal investigator on the project from the Max Planck Institute for Physics.
Will Quipu last forever?
“In the future cosmic evolution, these superstructures are bound to break up into several collapsing units. They are thus transient configurations. But at present they are special physical entities with characteristic properties and special cosmic environments deserving special attention,” say researchers.
Shamim Haque Mondal is a researcher in the physics division, State Forensic Science Laboratory, Kolkata.