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Enrique Gaztañaga | Physical review. D/Physical review. D. | (2026)
Abstract
We propose a new mechanism for generating cosmological relics -- black holes, gravitational waves (GWs), and possibly dark matter (DM) -- in a bouncing Universe. Relics arise through two channels: (i) compact objects and GWs produced during pre-bounce collapse that remain super-horizon and re-enter after the bounce, and (ii) dark-matter halos formed during collapse that exit the horizon and collapse into black holes upon re-entry. Unlike inflationary primordial black holes, these relic black holes originate from nonlinear structure formation during collapse. We derive the particle horizon and horizon-crossing conditions in bouncing cosmology and show that perturbations or compact objects larger than 90 m survive the bounce. The resulting population of relic black holes and GWs spans a wide mass range, offering a unified origin for dark matter, gravitational-wave backgrounds, and the early growth of supermassive black holes and galaxies.
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Plain English Takeaway
The paper explains how black holes and other cosmic leftovers could have formed before the Big Bang in a universe that bounces instead of starting from a single explosion. These leftovers might make up dark matter and help explain how galaxies and giant black holes formed so early.
Study Aim
The paper aims to introduce a new way that black holes, gravitational waves (ripples in space-time), and possibly dark matter (an invisible form of matter) could have formed in a universe that contracts and then bounces back into expansion, instead of beginning with a single Big Bang. The author wants to show that these cosmic relics can arise from structures created during the collapse before the bounce, and that this process could explain the origins of dark matter, gravitational waves, and the seeds of galaxies and supermassive black holes.
Simply put: The study wants to show that a bouncing universe could naturally create black holes and other cosmic leftovers that explain dark matter and early galaxies.
Study Design
The research uses theoretical models and mathematical calculations to describe how structures like dark matter halos and compact objects (such as black holes and neutron stars) form during a universe's collapse phase before a bounce. The author analyzes the conditions under which these objects can survive the bounce and reappear in the expanding universe. The study derives equations for the particle horizon (the maximum distance over which events can affect each other) and horizon crossing (when objects become too large to be influenced by their surroundings) in a bouncing cosmology. The analysis shows that objects larger than about 90 meters can survive the bounce.
Simply put: The study uses math and physics to figure out which cosmic objects could survive a universe that shrinks and then grows again.
Findings
The research demonstrates that in a bouncing universe, two main pathways can create relic black holes: (1) dark matter halos that become isolated during collapse and turn into black holes after the bounce, and (2) compact objects formed before the bounce that survive and reappear later. These relics can cover a wide range of masses, from small to supermassive, and could make up some or all of dark matter. The study suggests that this process could also explain the early appearance of supermassive black holes and galaxies. The author recommends looking for signs of these relics in gravitational wave detections and subtle effects in the cosmic microwave background (CMB), such as extra small-scale power or lensing effects, which future experiments might observe.
Simply put: The study finds that black holes and other objects from before the Big Bang could survive a cosmic bounce and help explain dark matter and early galaxies.
Just came across this paper Cosmological bounce relics: Black holes, gravitational waves, and dark matter that suggests that Dark Matter is actually black holes from another universe.