The recently proposed Black Hole Universe (BHU) model offers a bold rethinking of our cosmic origins. Rather than beginning with a singular “Big Bang,” this theory suggests that our universe may have emerged from the interior of a black hole formed within a larger parent universe. This idea provides fresh answers to long-standing puzzles in cosmology — such as what triggered cosmic inflation, why cosmic expansion is accelerating, and the small but non-zero value of the cosmological constant.
What makes this model especially compelling is that it leads to testable predictions — and this is where the ARRAKIHS mission could play a transformative role.
ARRAKIHS is uniquely designed to detect ultra-low surface brightness structures in the outskirts of galaxies — regions where the fossil record of galaxy formation and dark matter assembly is preserved. These faint features are essential for studying how galaxies grow and evolve, but may also hold clues to the nature of dark matter and the universe’s initial conditions, particularly if they differ from those predicted by the standard Big Bang model.
The BHU scenario envisions a finite, causally connected universe embedded in a larger space-time. This changes the global geometry and boundary conditions of the early universe, potentially affecting both the distribution and nature of dark matter. A key prediction of the BHU model is the existence of compact relics from the collapse and bounce phases — such as primordial black holes or neutron-star-like objects — which could contribute to the dark matter we observe today.
These compact relics would influence the structure and evolution of galaxy halos, with implications for both inside-out and outside-in formation scenarios. If relic dark matter accumulates in the outskirts or cores of galaxies, it could shift our understanding of where and how galaxies grow.
The ARRAKIHS satellite is equipped with four wide-angle telescopes: two using cutting-edge near-infrared technology, one optical, and one covering the near-ultraviolet. Together, they can detect signs of star formation and AGN activity — signatures of black hole accretion. These unique space-based capabilities will allow us to unveil the formation history of galaxies like our own Milky Way.
ARRAKIHS may not only deepen our understanding of galaxy evolution — it may help reveal where our universe came from.
Read the complete paper by Enrique Gaztañaga
et al. here.
