When a star dies, a black hole is born, a classic origin story for most black holes. Recent research indicates that black holes can also originate from smaller black holes. MIT scientists analyzed data from the LIGO, Virgo, and KAGRA observatories, revealing that about 14% of merging black holes may actually be second-generation black holes formed from previous mergers of smaller black holes. This process, known as 'hierarchical merging,' suggests a more complex pathway for black hole formation than previously thought.
The study examined 155 pairs of binary black holes and identified significant spin differences among them, indicating that some may have originated from earlier mergers. Hierarchical mergers likely occur in dense stellar environments where stars are closely packed, allowing for repeated merging of black holes.
In 2024, scientists detected two lopsided merger signals from the observatories, indicating that at least one black hole originated from the collision of two previous black holes. The research team developed a model to analyze the gravitational wave signals for potential hierarchical merging patterns. Their analysis revealed that roughly 14% of merging black holes may have a history of repeated merging, with distinct mass characteristics compared to typical star-born black holes.
'We are finding that the formation of black holes is more diverse than we thought,' says Cailin Plunkett, the study's first author. This research provides new insights into black hole formation, potentially explaining the origins of some peculiar black holes observed today.
Blogger's Review: This study reveals the complexity of black hole formation, challenging traditional views and highlighting the potential of hierarchical merging. As gravitational wave detection technology advances, we may gain deeper insights into the origins and evolution of black holes in the universe.