Tracing the Origins of Mysterious Gas Clouds near the Galactic Center
New observations and simulations by a team of researchers led by MPE reveal that a massive binary star near our Galaxy’s center is responsible for creating a series enigmatic gas clouds — compact gas clumps that help feed the supermassive black hole Sagittarius A*.
The center of our Milky Way is a remarkably dense and dynamic region. At its heart lies the supermassive black hole Sagittarius A* (Sgr A*), surrounded by stars, gas, and dust moving under extreme gravitational forces. These surroundings provide a natural laboratory for studying how matter behaves close to a black hole and how such objects are supplied with new material.
Over the last twenty years, astronomers have discovered several compact gas clouds near Sgr A* using infrared observations. These “clumps” are important clues to understanding how gas may eventually reach the black hole. Yet their exact origin and the physical processes that shape them have remained uncertain.
The G‑Clouds: A Growing Family
In 2012, astronomers identified a first, compact, ionized gas cloud named G2. It has a mass of a few Earths and emits light from hydrogen and helium, typical for hot, dusty gas. G2 follows an elongated orbit around Sgr A* and shows a faint trailing structure, G2t. Revisiting earlier observations revealed shortly after a similar object, G1, moving along a comparable orbit.
G1, G2, and G2t were proposed to be denser clumps within a common stream of gas. Moderate density fluctuations can lead to a clumpy appearance because a cloud’s brightness increases with the square of its density. Recently, researchers found that gas from G2’s tail has condensed into a third compact clump moving along a similar path, which one now could call G3, except that this name had by now already been given to a different object. Together, these objects form a coherent structure — the G1–2–3 streamer— tracing material that flows through the Galactic Center.
Calculations show that the infall of one such clump, roughly one Earth mass every decade, could provide enough material to sustain Sgr A*’s current activity. Understanding how these clumps form is therefore key to explaining how the black hole is fuelled.
Searching for the Source
Several origins have been proposed: stellar winds from massive stars, explosive events such as novae, or tidal stripping by Sgr A*. To test these ideas, an international team led by MPE used adaptive-optics-assisted spectrographs SINFONI and ERIS, which enable sharp infrared spectroscopy. Focusing on the hydrogen Brackett‑γ emission line, they reconstructed the orbits of the three clouds from their positions and velocities.
The analysis revealed that G1, G2, and G2t travel on orbits with almost identical orientation and shape. The chance that three unrelated objects share such specific orbital parameters is vanishingly small. This indicates a common origin for all three clumps.
A Binary Star as the Creator
By tracing the motions of the gas streamer backward in space and radial velocity, the researchers identified a viable source: the massive contact binary star IRS 16SW, located in the clockwise disk of young stars orbiting Sgr A*. The small differences between the G‑cloud orbits can be explained by the binary’s own orbital motion.
Hydrodynamical simulations further support this conclusion. They show that gas clumps can form where the stellar winds from the binary collide with the surrounding medium, producing a shock between the two stars. There, gas accumulates and becomes compressed, eventually detaching as individual clumps that travel inward — like what is observed in the G1–2–3 streamer.
What does it mean?
These findings suggest that stellar winds from massive stars in the Galactic Center can continually supply material to the black hole. The result connects stellar evolution, gas dynamics, and black‑hole feeding into one consistent picture — showing how star formation and black‑hole growth may be linked even in our own Galaxy.
