Cosmic Background Data Caps Dark Matter Black Holes at 100 Billion Suns
Analysis of ancient light shows that supermassive black holes cannot constitute a large portion of the universe's invisible mass, narrowing the search for dark matter candidates.
By Tyler Khalil ·
100 billion solar masses marks the upper limit for black holes that could form a substantial portion of dark matter, according to a new study. The research determines that objects heavier than this threshold are too rare to account for the majority of the universe's missing mass. This finding narrows the range of viable candidates for the substance that holds galaxies together.
The study, led by theoretical physicists at the Mainz Institute for Theoretical Physics and New York University Abu Dhabi, focuses on "stupendously large black holes." These hypothetical objects would weigh between one million billion and ten million billion times the mass of the sun. Such masses would exceed that of entire galaxies, a condition that would make the universe appear "grainy" on large scales. Christopher Gerlach, a co-author at the Mainz Institute, noted that if dark matter were concentrated in these gigantic objects rather than spread as a fine dust, the irregularities would be detectable.
The team tested this hypothesis by analyzing the cosmic microwave background. This radiation is the light released from the early universe, approximately 380,000 years after the Big Bang. When the cosmos cooled enough for atoms to form, light began to travel freely, creating a snapshot of the infant universe that covers the entire sky. Antonio Iovino, a co-author at New York University Abu Dhabi, explained that the temperature of this background varies by about one part in 100,000 across different locations. These variations map how matter was distributed in the early cosmos.
The analysis revealed that the cosmic microwave background lacks the specific patterns of graininess that would be expected if stupendously large black holes were prevalent. Nicholas Leister, a theoretical physicist at the Mainz Institute, stated that the absence of this signal means such black holes cannot be a significant part of the dark matter. The result does not rule out the existence of these massive objects entirely, but it excludes them from being a major component of the universe's dark sector.
The findings suggest that the search for dark matter must continue with other candidates. The authors noted that relatively tiny black holes, roughly the size of asteroids, might still be possible constituents. The team is currently investigating whether those smaller objects can also be ruled out as a primary source of dark matter. The largest known black hole in the universe weighs about 36 billion solar masses, well below the 100 billion solar mass limit established by this study.
The study is scheduled for publication on October 26 in the journal Physical Review Letters. It provides a new constraint on the nature of dark matter, a substance estimated to account for about five-sixths of all matter in the cosmos. While dark matter was proposed decades ago to explain galactic rotation, its physical identity remains unconfirmed. The use of ancient light offers a direct method to test gravitational models against observational data.
