V404 Cygni, located 8,000 light years from Earth, is an exceptional subject of study for astrophysicists. This system hosts a black hole and two stars in an unexpected configuration.
Located in the constellation Cygnus, this cosmic trio is dominated by a black hole strongly pulling on a nearby star, while also exerting its influence on another more distant star. Such a combination puzzles scientists.
The star closest to the black hole, in fact, completes a revolution around it in only 6.5 days. In contrast, the second star, much more distant, completes a full orbit in 70,000 years, an exceptional astronomical cycle.
This type of system has never been observed before. Indeed, the forces generated by a supernova, an event that likely gave birth to this black hole, generally expel weakly bound stars. However, the distant star has remained gravitationally bound to the black hole.
What is a stellar-mass black hole?
A stellar-mass black hole is the result of the collapse of a massive star at the end of its life. When a star that is sufficiently heavy burns up all its fuel, its core collapses under the force of its own gravity, forming a black hole.
These black holes are often detected by their gravitational effects on nearby objects or by the X-ray emissions produced when the black hole "swallows" matter. This process emits intense energy, making these objects observable, despite their invisible nature.
In a triple system like V404 Cygni, the stellar-mass black hole acts not only on the nearby star, which it "devours", but also on a more distant star, illustrating complex gravitational interactions never observed before.
A direct collapse?
Direct collapse is a phenomenon in which a massive star collapses into a black hole without going through a supernova. Unlike supernova explosions, this collapse occurs without a massive release of energy, thus forming a black hole "silently."
This "gentle" process spares objects gravitationally bound to the star, allowing them to remain in orbit around the formed black hole. Direct collapse could explain why some stars remain close to black holes despite their powerful attraction.
Article author: Cédric DEPOND