Astrophysicists categorize black holes by mass into stellar-mass, intermediate-mass, and supermassive varieties. Theoretical cosmology posits additional types, including micro black holes and primordial black holes (PBHs), which likely formed in the Universe's earliest moments, well before the first stars ignited. Leading theories suggest PBHs could form a key component of dark matter. Researchers from the Kavli Institute for the Physics and Mathematics of the Universe recently outlined a formation mechanism tied to the inflationary multiverse, sparking new observations to test if these PBHs truly account for dark matter.
Primordial black holes hold exciting potential: they may constitute part of dark matter, generate some detected gravitational waves, seed supermassive black holes at galaxy centers, and drive heavy element synthesis by colliding with neutron stars, releasing neutron-rich material.
Dark matter, which dominates the Universe's mass, might partly consist of PBHs. The 2020 Nobel Prize in Physics recognized Roger Penrose for black hole theory and astronomers Reinhard Genzel and Andrea Ghez for confirming supermassive black holes.
To probe PBHs, the team examined the early Universe, where density fluctuations exceeding 50% could spawn black holes—far beyond the smaller perturbations that seeded galaxies. Various early-Universe processes could still foster PBH formation. Their study appears in the esteemed journal Physical Review Letters.
A compelling scenario links PBHs to "baby universes" spawned during cosmic inflation—the rapid expansion shaping today's galaxies and clusters. These baby universes can detach from our own. A tiny one collapses swiftly, its concentrated energy forming a black hole.
Larger baby universes have a fascinating fate: if surpassing a critical size, general relativity predicts differing perceptions. Inside, it expands like a universe; outside, it appears as a black hole.
In both cases, external observers detect primordial black holes, their event horizons—inescapable boundaries trapping even light—veiling multiverse structures within.
The researchers detailed their multiverse PBH scenario and demonstrated detection via the Hyper Suprime-Cam (HSC) on the 8.2-meter Subaru Telescope—a massive digital imager atop Hawaii's Mauna Kea at 4,200 meters. HSC data already imposes strict PBH limits.
HSC's edge: imaging the Andromeda Galaxy's stars every few minutes. A foreground PBH microlensing a star temporarily brightens it, with duration revealing mass. Monitoring 100 million stars opens vast detection windows.
Initial HSC data flagged a promising candidate matching a Moon-mass multiverse PBH. Buoyed by theory, the team now pursues deeper observations for a conclusive dark matter test.
