Researchers initially proposed supermassive black hole mergers as the cause. However, theoretical work published in Physical Review Letters<\/a> presented another possibility. Teams from CERN, King\u2019s College London, and the University of Warsaw outlined models showing that cosmic strings, relics from the universe\u2019s rapid inflation, could also produce gravitational radiation consistent with the observed signals.<\/p>\n Cosmic strings are predicted to form during symmetry-breaking phase transitions shortly after the Big Bang. These hypothetical filaments would be incredibly dense, yet thinner than a proton, and could span astronomical distances. Vibrations or collisions within a cosmic string network may generate gravitational wave patterns<\/a> across a wide range of frequencies.<\/p>\n Theoretical physicist Ken Olum and others revisited a concept first introduced by J. Richard Gott in 1991. Gott\u2019s model showed that if two infinite cosmic strings passed each other at relativistic speeds, their gravitational fields could bend space-time into a closed time-like curve. Such a loop would theoretically allow a traveler to return to a point in time before departure. The solution remains mathematically valid within Einstein\u2019s field equations, though practical implementation is viewed as implausible due to the requirement of infinite string length.<\/p>\n String Theory and Superstrings Enter the Discussion<\/p>\n Complementing the classical cosmic string hypothesis is the concept of cosmic superstrings, which emerge from string theory. This framework suggests that particles are not zero-dimensional points, but instead are one-dimensional strings vibrating across ten or more dimensions. Under early universe conditions, some of these quantum strings may have stretched to macroscopic scales, making them detectable today.<\/p>\n Olum stated in an interview with Popular Mechanics<\/a> that although cosmic superstrings are less likely to exist, they would be \u201crelatively easier to detect\u201d if they did. Their detection could serve as indirect evidence for string theory, which remains unconfirmed despite decades of mathematical development.<\/p>\n![\"Figure](\"https:\/\/physics.aps.org\/assets\/8297908e-6032-4057-bc79-cc6cc02c7cce\/e15_1_medium.png\")
<\/a>By monitoring the radio flashes from distant pulsars, astronomers have spotted a signal that could be the result of a background of gravitational waves. Credit: Tonia Klein\/NANOGrav<\/p>\n
![\"Figure](\"https:\/\/physics.aps.org\/assets\/efd5c393-1cdd-49a2-9cf4-a35940bdc38b\/e15_2_medium.png\")
<\/a>Cosmic strings that are closed into loops could produce gravitational waves at a wide range of frequencies, including those probed by NANOGrav. Credit: Daniel Dominguez\/CERN<\/p>\n