Theoretical calculations published in Physical Review Letters suggest that ancient stochastic gravitational waves from the early universe could have partially converted into early fermions, offering a new mechanism that potentially explains the formation and modern distribution of dark matter.
Ever since Albert Einstein laid the groundwork with his 1905 introduction of spacetime and his 1915 theory of general relativity—which predicted that massive accelerating objects would create ripples across the cosmos—physicists have chased the invisible forces shaping our universe. While visible matter like stars, planets, and life on Earth accounts for roughly four percent of the cosmos, the vast majority remains unseen. Dark matter alone represents roughly 23 percent of the universe, with the remainder made up of dark energy. Despite its enormous gravitational influence in shaping galaxies and large-scale structures, its exact nature has remained a persistent mystery.
From Cosmic Ripples to Particle Formation
A new study led by Professor Joachim Kopp of Johannes Gutenberg University Mainz and the PRISMA++ Cluster of Excellence, in collaboration with Dr. Azadeh Maleknejad from Swansea University, approaches this puzzle from an unconventional angle according to research published in Physical Review Letters. Instead of focusing solely on modern astrophysical collisions, the researchers investigated stochastic gravitational waves generated during the earliest phases after the Big Bang, such as during cosmic phase transitions or from primordial magnetic fields.
These ancient background waves, far weaker and distinct from the energetic events detected by modern observatories, may have permeated the primordial universe. In this article, we investigate the possibility of gravitational waves — which are believed to have been ubiquitous in the early universe — being partially converted into dark matter particles,
Kopp explained. The researchers added that this leads to a new mechanism of dark matter production that has not been researched before
as detailed in the study’s findings.
How Gravitational-Wave Astronomy Matured
This theoretical leap builds upon a decade of transformation in gravitational-wave astronomy. On Sept. 14, 2015, at 5:51 a.m. EDT, the Laser Interferometer Gravitational-wave Observatory (LIGO) detected its first signal—cataloged as GW150914—originating from the merger of two massive black holes roughly 1.3 billion years ago. The Livingston, Louisiana detector registered the small chirp first, followed seven milliseconds later by the Hanford, Washington facility. That detection opened up an entirely new branch of astronomy where scientists essentially listen to space rather than just view it.
Operating as a Michelson interferometer, LIGO splits a single laser beam down two perpendicular arms measuring 2.5 miles (4 km) long, utilizing power-recycling mirrors to bounce the light roughly 300 times before recombination. As gravitational waves pass, they alter spacetime by stretching one arm while squeezing the other, shifting the light fringe patterns. In the years since that first run—which began just two days before making history—observatories have evolved from capturing isolated signals to conducting large-scale cosmic demographics.
Moving Beyond Analytical Estimates
The proposed conversion mechanism suggests that early stochastic gravitational waves could have produced fermions—a broad particle class encompassing electrons, protons, and neutrons—that initially possessed little or no mass. Over time, these fermions may have gained mass and evolved into the dark matter particles observed today.
Translating this theoretical framework into concrete cosmological models requires moving past current limits. Outlining the path forward, Kopp noted that the next step in developing this line of research is to go beyond our analytical estimates and conduct numerical calculations to improve the accuracy of our predictions
in comments shared regarding future study directions. Researchers also aim to explore whether similar gravitational-wave mechanisms might account for the difference between particles and antiparticles in the universe.
