The first double star system near the supermassive black hole at the center of the Milky Way has been discovered.

Within three light-years (one parsec) of the supermassive black hole Sagittarius A*, located at the center of the Milky Way, the environment is quite crowded. The nuclear star cluster situated there is one of the densest and most massive in the Galaxy. Its stars vary greatly in age, mass, size, and luminosity.

Over billions of years, some stars have predictably "fallen" even closer to the supermassive black hole, at distances of up to 0.13 light-years, or 8,200 astronomical units (the average distance from the Sun to the Earth). This group is sometimes referred to as the Sagittarius A* cluster or the "S-stars" (not to be confused with S-type stars). Notably, in addition to stars older than three billion years, there are also extremely young luminaries aged between four and six million years. Even more surprisingly, they all appear to be solitary, although observations and models suggest that most stars form in pairs and triplets.

The young age of the stars near the supermassive black hole and their solitary nature led scientists to hypothesize that many of these objects are the result of the merger of binary stars or separated pairs. Furthermore, the Sagittarius A* cluster includes unusual G-objects, resembling giant gas clouds, which may represent an intermediate stage in the merging of a binary star into a single entity.

The search for a binary star in the vicinity of the Galactic center has finally been successful. Using archival data from the SINFONI spectrograph on the VLT telescope and the near-infrared instrument NIRC2 on the Keck telescope, an international team of astronomers has discovered a binary star near the center of the Milky Way for the first time. The results of the study were published in the journal Nature Communications.

The age of the D9 pair is about 2.7 million years. It likely consists of a "main" Herbig star (Ae/Be) with a mass of approximately 2.8 solar masses and a T Tauri-type star with a mass of 0.73 solar masses. They orbit around their common center of mass every 372 Earth days, with a distance of only 1.59 astronomical units between them. According to scientists' calculations, the supermassive black hole would have "separated" them if the distance exceeded 42.4 astronomical units.

“In the D9 system, there are signs of gas and dust around the stars, indicating that it could be a very young stellar system that apparently formed near the supermassive black hole,” explained co-author Michal Zajacek, a researcher from Masaryk University (Czech Republic).

Based on its photometric parameters, D9 can be considered a representative of G-objects. Apparently, the G-object group indeed includes merged binaries surrounded by a debris cloud and binaries on the verge of merging. Estimates suggest that D9 will become a single entity in about a million years.

The presence of a companion, proximity to the supermassive black hole, and extreme conditions at the center of the Milky Way are factors that significantly influence the evolution of a star. The search for new pairs like D9 and a closer examination of stars at the Galactic center will help unravel the evolution of objects around supermassive black holes. Interestingly, there is even a hypothesis that the youth of the "S-stars" is explained by "reverse evolution" influenced by dark matter.