Astronomers Stumble Upon First Triple Black Hole System, Defying Supernova Theories

Astronomers have discovered the first known triple black hole system in the Milky Way, challenging long-held theories of how black holes form. Located 8,000 light-years from Earth, the system involves a black hole feeding on a nearby star while a distant third star orbits the pair.

Portrait of Lydia Amazouz, a young woman with dark hair tied back, wearing glasses and a striped blue and white shirt, against a solid coral background.
By Lydia Amazouz Published on October 24, 2024 07:30
Astronomers Stumble Upon First Triple Black Hole System, Defying Supernova Theories
Astronomers Stumble Upon First Triple Black Hole System, Defying Supernova Theories - © The Daily Galaxy --Great Discoveries Channel

Astronomers have discovered the first known triple black hole system within our Milky Way galaxy, about 8,000 light-years from Earth.

This remarkable system, centered around V404 Cygni, consists of a black hole actively feeding on a companion star, while being orbited by a more distant third star. The discovery has raised significant questions about current models of black hole formation, specifically the assumption that they are born from violent supernova explosions.

V404 Cygni: A Unique Triple System in the Milky Way

The newly discovered system revolves around V404 Cygni, an X-ray binary that has been well-known to astronomers for decades. In this system, a black hole—approximately nine times the mass of the Sun—pulls material from a close companion star. This companion star, located very near the black hole, completes its orbit every 6.5 days, and as it spirals closer, it loses gas to the black hole, creating intense X-ray emissions.

The groundbreaking aspect of this discovery is the identification of a third star orbiting the black hole from a much greater distance. This outer star, only revealed through precise measurements from the Gaia space telescope, takes about 70,000 years to complete one orbit around the black hole. “This discovery was just a happy accident,” explained Kevin Burdge, the MIT astrophysicist who led the study. Burdge added, “I was just looking at a picture of V404 Cygni and noticed it was in a triple.” The discovery of this third star was surprising because it defies current understanding of how black hole systems form and maintain stability.

A Challenge to the Supernova Model of Black Hole Formation

Black holes are typically thought to form from the explosive death of massive stars, known as supernovae. These violent events generate immense amounts of energy, often resulting in a "natal kick"—a force that can fling nearby stars out of the system. This phenomenon has been well-documented in supernovae involving neutron stars, where companion stars are frequently expelled from the system. Stellar-mass black holes, being even more massive than neutron stars, would logically be expected to produce even stronger natal kicks, which should disrupt any nearby companions.

However, this new discovery suggests that not all black holes form in such a dramatic way. In the case of V404 Cygni, the presence of a third star at such a great distance suggests a more gentle birth process for the black hole. According to Burdge, “If you do anything dramatic to the inner binary, you’re going to lose the outer star.” Yet in this system, the outer star remains gravitationally bound, implying that the black hole likely formed through direct collapse, a process where a massive star collapses into a black hole without a supernova explosion. This process would result in much less disruption to the surrounding system.

Simulations run by Burdge and his team support this theory. These simulations involved modeling the birth of a black hole within a triple star system and introducing varying amounts of energy from hypothetical supernovae. Only simulations that eliminated the supernova and assumed a direct collapse scenario were able to replicate the observed structure of V404 Cygni. As Burdge explains, “The vast majority of simulations show that the easiest way to make this triple work is through direct collapse.”

Implications for Black Hole Evolution and Stellar Systems

The discovery of this triple black hole system opens up new possibilities for understanding the evolution of black holes and their role in the larger context of stellar systems. Triple star systems are rare but not unheard of, and they often involve complex gravitational interactions. The fact that a black hole can exist within such a system without disrupting its outer companion star suggests that other, yet undiscovered, triple black hole systems may exist. “This system is super exciting for black hole evolution, and it also raises questions of whether there are more triples out there,” Burdge remarked.

Another important aspect of this discovery is that the outer star in the V404 Cygni system is currently evolving into a red giant, which allows scientists to determine the age of the system. Based on this transformation, astronomers estimate that the system is around 4 billion years old. This is a significant achievement because it provides, for the first time, an accurate age for a black hole system. As Burdge noted, “We’ve never been able to do this before for an old black hole.”

This finding not only provides insight into the history of the V404 Cygni system but also offers a new way to understand the lifespan of black holes and their companion stars. The long orbital period of the third star, which is located over 3,500 times farther from the black hole than the Earth is from the Sun, emphasizes just how delicately balanced the gravitational forces in this system are.

Future Research and Unanswered Questions

While the discovery of V404 Cygni as a triple black hole system has answered many questions, it has also raised new ones. One of the key mysteries that astronomers are eager to investigate further is the precise nature of the outer star’s orbit. Specifically, scientists want to know whether the third star follows a circular orbit or if it is more eccentric, which could provide additional clues about how the system evolved over time. To answer this, the team plans to use the Very Large Telescope (VLT) to gather more data on the system's orbital dynamics.

As of now, V404 Cygni is the only known example of a stellar-mass black hole triple system. However, the ease with which it was discovered suggests that there may be many more out there, hidden within the vastness of our galaxy. According to Burdge, the chances of observing such a system increase significantly as technology improves and new instruments like Gaia continue to scan the sky for similar systems.

This discovery has also opened up a new frontier in the study of black hole formation and stellar death. The possibility that black holes can form through direct collapse rather than the widely accepted supernova model could significantly alter our understanding of how black holes are distributed throughout the universe. As Burdge concludes, “We think most black holes form from violent explosions of stars, but this discovery helps call that into question.”

In the coming years, further observations and simulations will be needed to explore these new questions, but for now, the discovery of V404 Cygni’s triple black hole system represents a significant leap forward in our understanding of the universe’s most enigmatic objects.

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