CMB Data Caps Dark Matter Black Holes at 100 Billion Suns

Black holes weighing more than 100 billion times the mass of the sun cannot constitute a major portion of dark matter, according to a new study. The research team concluded that if dark matter were composed primarily of such massive objects, the cosmic microwave background would show specific patterns that are not present in current data.

The investigation focused on what the authors term stupendously large black holes. These hypothetical objects would exceed the mass of entire galaxies, a range between 1 million and 10 million billion solar masses. While no such entity has been detected, with the largest known black hole estimated at 36 billion solar masses, scientists have long considered them a plausible candidate for the unseen mass that holds galaxies together.

Christopher Gerlach, a theoretical physicist at the Mainz Institute for Theoretical Physics in Germany, explained that dark matter is typically conceptualized as a fine dust spread throughout the universe. He noted that if the mass were instead concentrated in a few gigantic objects, the universe would appear grainy on very large scales. This distinction allows for a testable prediction based on the structure of the cosmos.

The team analyzed the cosmic microwave background, the light released from the early universe. This radiation dates back to the period when the universe cooled enough for atoms to form, roughly 380,000 years after the Big Bang. Antonio Iovino, a physicist at New York University Abu Dhabi, stated that the temperature of this background varies by about one part in 100,000 from place to place, providing a record of matter distribution in the infant cosmos.

The data revealed a smoothness that contradicts the presence of widespread, ultra-massive black holes. Nicholas Leister, also of the Mainz Institute, said the lack of expected graininess indicates that these objects are not a significant part of the dark matter total. The findings suggest that dark matter is more likely distributed in a finer form or composed of much smaller objects.

The researchers clarified that the result does not prove these enormous black holes do not exist. It only limits their abundance to a minor fraction of the total dark matter. The team is currently investigating whether smaller black holes, roughly the size of asteroids, might account for the missing mass, a question that remains open.

The study is scheduled for publication in the journal Physical Review Letters on Oct. 26.