In a groundbreaking study published in Nature, physicists from MIT and Caltech have revealed the first observed “black hole triple” system, prompting new questions about the formation of black holes. This unique system features a central black hole that is actively consuming a small star every 6.5 days, while a second, more distant star orbits the black hole every 70,000 years.
Traditionally, black holes are believed to form from the explosive deaths of massive stars in a process known as supernovae. However, the presence of the outer star raises significant questions about this narrative. If the central black hole had formed through a typical supernova, it would have expelled nearby objects due to the immense energy released. The fact that this second star remains in orbit suggests a different origin: a more gentle “direct collapse,” where a star collapses under its own gravity without a violent explosion.
Kevin Burdge, a Pappalardo Fellow at MIT and co-author of the study, noted, “We think most black holes form from violent explosions of stars, but this discovery helps call that into question.” The research team, which also includes several MIT physicists, emphasizes that this could be the first evidence of a black hole born from direct collapse.
The discovery of the triple system was somewhat serendipitous. While searching for new black holes in the Milky Way, Burdge examined images of V404 Cygni, a well-studied black hole about 8,000 light years away. Upon inspection, he identified two distinct sources of light, leading to the realization that they belonged to the central black hole and its inner star, with the second light coming from a distant companion.
Using data from the Gaia satellite, the researchers confirmed that the two stars are gravitationally bound, as they moved in tandem over the past decade. Burdge calculated the odds of this alignment as approximately one in ten million, solidifying the existence of a triple system.
To understand how this configuration could arise, the team conducted simulations of various scenarios for the black hole’s formation. Their results overwhelmingly favored the direct collapse model, as most simulations indicated this method would retain the outer star, unlike the supernova scenario.
Additionally, the outer star is nearing the end of its life cycle, transitioning into a red giant phase, which allowed the researchers to estimate the age of the entire system at around 4 billion years. This insight not only provides a timeline for the black hole’s formation but also offers a rare glimpse into the evolution of such celestial bodies.
The discovery of this black hole triple system is a significant advancement in astrophysics, challenging existing paradigms of black hole formation and suggesting that there may be more such systems waiting to be discovered. As Burdge aptly put it, “This system is super exciting for black hole evolution, and it also raises questions of whether there are more triples out there.”