G objects in the center of our galaxy. Credit: Jack Ciurlo/UCLA

Mystery Structure That Survived Encounter With Black Hole is Actually a Triplet of Stars

The VLT Ground Telescope has helped astronomers understand the nature of one of the mysterious G objects orbiting a black hole in the center of the Milky Way. Scientists have proven that object G2 is not an extended cloud of gas and dust, but consists of three young stars surrounded by dusty shells.


What is a G object?

G-objects are an unusual class of objects located in the immediate vicinity of the supermassive black hole at the center of the Milky Way. They were first discovered in 2005, and last year they were singled out as a separate category of astrophysical phenomena. They demonstrate the properties of both gas and dust clouds and star-like bodies, are large enough and may be the result of the merger of two stars.

Among the known G objects, G2 stands out, which came close to the black hole in 2014. Then it was assumed that this is a vast cloud of gas and dust, which will be stretched by tidal forces from the side of the black hole and cause a burst of its activity.


However, the scientists did not see the outburst, and later the model of a cloud without a dense core gave way to the model of a star enclosed in a dense shell of gas and dust.


Theories about G2

It is assumed that G2 may be a young stellar object surrounded by a highly dusty envelope, which fits into the scenario of star formation processes in the central zone of the galaxy. It also allows one to explain the observed compactness of the object and its other properties. However, this hypothesis needed to be confirmed by observational data.

Now, a team of astronomers led by Florian Peiβker of the University of Cologne published their analysis of near-infrared observations from 2005 to 2019 using the SINFONI spectrograph at the VLT complex in Chile.

The movement of the G2 object in its orbit around the black hole (marked with a cross) according to the VLT data. Credit: Florian Peißker et al. / The Astrophysical Journal, 2021
The movement of the G2 object in its orbit around the black hole (marked with a cross) according to the VLT data. Credit: Florian Peißker et al. / The Astrophysical Journal, 2021

The G object turned out to be three young stars

It turned out that the ionized gas that should have been associated with the tail of G2 is not actually associated with it, but is inside the S-star cluster. The G2 tail itself consists of two isolated and compact radiation sources.

Although the orbital elements for OS1 and OS2 are different, the first source shows similarities in inclination and periapsis argument to G2. G2 passed its pericenter in 2014, OS1 did it in 2020, and OS2 will do it in 2029.

The observed properties of objects can be described in terms of models of stars less than 10 7  years old, still accreting matter, and surrounded by non-spherical shells of gas and dust. In particular, G2 fits the T Tauri star model.


Thus, the second object from the G-body class is not an extended gas cloud, but three young stars (G2, OS1, and OS2), which are the remnants of a star cluster, the formation of which began in the circumnuclear disk around the black hole.

Join the discussion and participate in awesome giveaways in our mobile Telegram group. Join Curiosmos on Telegram Today. t.me/Curiosmos



Gillessen, S., Genzel, R., Fritz, T. K., Quataert, E., Alig, C., Burkert, A., Cuadra, J., Eisenhauer, F., Pfuhl, O., Dodds-Eden, K., Gammie, C. F., & Ott, T. (2011, December 14). A gas cloud on its way towards the supermassive black hole at the Galactic Centre. Nature News.
Kohler, S. (2017, July 24). The story of a boring encounter with a black hole. AAS Nova.
Peißker, F., Zajaček, M., & Eckart, A. (2018, December 4). The Apparent Tail of the Galactic Center Object G2/DSO. The Astrophysical Journal.
Starr, M. (n.d.). Mysterious object that survived a close encounter with a black hole is unmasked. ScienceAlert.


Written by Vladislav Tchakarov

Hello, my name is Vladislav and I am glad to have you here on Curiosmos. As a history student, I have a strong passion for history and science, and the opportunity to research and write in this field on a daily basis is a dream come true.

Write for us

We’re always looking for new guest authors and we welcome individual bloggers to contribute high-quality guest posts.

Get In Touch