Cosmic strings: the mysterious scars of the universe

But what exactly are they, and why are scientists searching for them so intently? A recent study has led to a possible sighting of a cosmic string. Astronomers observed two galaxies in the region called CSc-1, discovering that they may not be two separate objects but a single galaxy “split” by the effect of a cosmic string. This phenomenon, known as gravitational lensing, could be caused by the massive density of the string, capable of bending light and creating duplicated images. Cosmic strings were first theorised in the 1970s by Tom W. B. Kibble. They are one-dimensional filaments, extremely thin but immensely dense, which may have formed in the first fractions of a second after the Big Bang. In that primordial era, the Universe was a chaotic sea of energy and particles, and during its expansion some imperfections may have given rise to these “scars” in space-time. Detecting a cosmic string would be revolutionary. These structures could reveal unprecedented details about the physics of the primordial Universe and about still-mysterious phenomena such as quantum gravity. In addition, studying them could confirm or refute fundamental theories such as string theory, which seeks to unify the laws of physics. Although cosmic strings are incredibly thin, they have enormous density. This makes them capable of generating observable effects. Among the most promising are:

• Gravitational lensing: extremely massive objects, such as cosmic strings, can curve space-time, creating a sort of natural lens that distorts and magnifies the light of distant objects. This effect could duplicate or distort the image of a distant galaxy.
• Gravitational waves: when a string breaks or forms a loop, it releases gravitational waves, ripples in space-time that can be detected by instruments such as LIGO and Virgo.
• Signatures in the cosmic microwave background (CMB): the CMB is a kind of “echo” of the Big Bang, and cosmic strings may leave traces in this residual radiation.

Using the Himalayan Chandra telescope, researchers analysed the spectra of the two galaxies and found them to be extraordinarily similar. This discovery, together with other geometric details, suggests that a cosmic string may be located precisely in that region. The study also identified a unique feature: an “isophote edge” in the collected images which, combined with the CMB data and spectroscopic observations, seems to strengthen the hypothesis of the presence of a cosmic string. However, scientists are aware that other phenomena, such as a rare type of gravitational lens, could explain the observations. Despite decades of research, cosmic strings have not yet been directly observed. Yet ever more advanced instruments and discoveries like the one at CSc-1 may bring us closer to definitive proof. Detecting a cosmic string would represent a fundamental milestone for cosmology, offering a glimpse into the physical laws that govern the Universe. Cosmic strings are more than a theoretical curiosity: they are a window into the remote past of our Universe and the fundamental laws that govern it. If one day we succeed in finding them, it could mark the beginning of a new era for physics, leading us to a deeper understanding of the origins of everything. Until then, they remain one of the most fascinating and promising mysteries of the cosmos.

By Lorenzo Cardia, 3L, Liceo Scientifico Vittorio Veneto – Milan