A study posted on arXiv suggests that about 300 years ago, a compact swarm of massive stars may have carved a nearly round hole in the glowing gas near the Milky Way’s central black hole. The target is the mini-cavity, a low-density pocket inside the ionized gas known as the mini-spiral around Sagittarius A*.
The paper points to the nearby IRS 13 cluster, a dense grouping of powerful stars close to the Galactic Center. According to the authors, winds from stars in that cluster may have swept through the gas and left behind a clean-looking cavity. A possible intermediate-mass black hole in IRS 13 may also have flared as it fed on the same material.
That combination gives astronomers a fresh way to read one of the Milky Way’s strangest small scars. The mini-cavity sits in a crowded region where gravity, gas, stellar winds and black holes all shape the same patch of space. Its shape looks simple. Its setting is anything but simple.
The strange mini-cavity near Sgr A*
The mini-cavity near Sgr A* lies inside the mini-spiral, a complex stream of ionized gas close to the supermassive black hole at the center of our galaxy. Sagittarius A*, often shortened to Sgr A*, sits about 27,000 light-years from Earth and contains roughly four million times the mass of the Sun.
The cavity itself is small by Galactic Center standards. The study describes it as having a radius of about 0.04 parsecs. That equals roughly 0.13 light-years, or about 760 billion miles. It sits only about 0.46 light-years away from Sgr A* in projected distance.
Its roundness is the puzzle. A near-circular gap in gas often points to a strong wind source sitting inside it. Such a star could blow material outward and clear a bubble around itself. In the mini-cavity, astronomers see the bubble more clearly than the culprit.
The paper’s abstract states that “the mini-cavity was formed by the winds of the IRS 13 cluster member stars about 300 years ago.” That short line carries a striking implication. The object that made the hole may have moved away, leaving a fossil-shaped mark in the gas.
IRS 13 moves into the frame
IRS 13 sits near the northwestern rim of the mini-cavity. It’s a compact cluster in one of the most extreme stellar neighborhoods in the Milky Way. In that region, stars orbit under the strong pull of Sgr A*, while streams of gas move through a changing gravitational landscape.
The study focuses on two IRS 13 members called E2 and E4. Both are Wolf-Rayet stars, a rare class of massive stars that lose material through intense winds. These stars are short-lived by stellar standards. They burn hot, shed mass violently and can shape the gas around them.
According to the authors’ model, E2 and E4 were positioned near the center of the mini-cavity roughly 300 years ago. Their current location beside the cavity then becomes part of the story. The stars could have passed through the region, blown open the gas and continued along their orbit.
That moving-source idea helps explain why the cavity lacks an obvious central star today. The Galactic Center changes on humanly invisible timescales, yet 300 years is a brief interval for astronomy. A fast star cluster can shift enough in that time to make an old imprint look strangely abandoned.
Wolf-Rayet winds as a cosmic drill
Stellar winds from Wolf-Rayet stars can act like invisible machinery. They carry gas outward at enormous speeds. When that outflow collides with surrounding material, it can sweep up a shell and excavate a pocket of lower density.
In the paper’s estimate, E4 plays the dominant role. Its terminal wind speed is about 1,367 miles per second. E2’s wind speed is lower, at about 466 miles per second. Both are extreme by everyday standards, yet E4 supplies the stronger blast.
The researchers estimate that the mini-cavity could have grown to its observed size in about 120 years. They describe this as an upper limit because the bubble may have continued expanding after the cluster moved on. That means the visible cavity could be the late-stage footprint of an earlier crossing.
The cavity’s expansion speed also matters. The study gives an average expansion speed of about 205 miles per second. That is more than three times the estimated relative speed between the stars and the surrounding gas. A fast-expanding bubble can keep a round shape even while the source travels through the region.
This is where the “drill” image becomes useful. The winds do the clearing. The cluster’s motion gives the process direction. The resulting mark can look like a clean hole punched through glowing gas near the central black hole.
A 300-year-old crossing
About three centuries ago, IRS 13 may have crossed the Bar region of the mini-spiral. The Bar is one part of the tangled gas structure close to Sgr A*. In the study’s scenario, this crossing placed the cluster’s strongest wind sources in the right spot to clear the mini-cavity.
The stars’ estimated motion is rapid. E2 and E4 move at about 124 miles per second, according to the values discussed in the paper. Their relative speed with respect to the surrounding gas may have been closer to 62 miles per second.
Those numbers let the researchers work backward. If the cluster is now beside the cavity, its earlier position can be traced along an orbital path. That backward motion places the stars near the cavity’s center around the time needed for the winds to carve the bubble.
The authors treat this as a model rather than a final reconstruction. The gas around Sgr A* is turbulent. The three-dimensional positions and motions of the stars are still difficult to pin down. A clean circle on the sky can come from a messy process in real space.
Even so, the timing is suggestive. A structure that seems oddly empty today may have been occupied by powerful stars only a few centuries ago. In Galactic Center terms, that’s recent history.
X-ray echoes from a hidden black hole
The same study also considers a more dramatic possibility. IRS 13 has been proposed as a possible home for an intermediate-mass black hole. Such an object would fall between stellar-mass black holes and supermassive black holes like Sgr A*.
If that proposed black hole passed through dense gas in the mini-spiral, it could have fed on some of that material. Accretion can heat gas to extreme temperatures. That process can produce X-rays, especially when matter falls into a compact object.
The paper estimates that this possible black hole may have produced X-ray flares with luminosities around 10^39 erg per second. That corresponds to about 10^32 watts. The flares would have happened centuries ago, yet their light could still matter today because of the layout of the Galactic Center.
X-rays can travel outward and strike molecular clouds, where they create delayed reflections. The study connects its flare estimate with X-ray reflections seen in the Sgr A, Sgr B and Sgr C cloud complexes. In this picture, the clouds act like distant screens lit by an earlier outburst.
The proposed black hole in IRS 13 remains uncertain. The flare connection also depends on the cluster’s path, the gas density and the timing of the light-travel delay. Still, the idea links a small cavity near Sgr A* to a broader mystery in the central Milky Way.
Why the Galactic Center keeps surprising astronomers
The Galactic Center is often described through Sgr A* and for good reason. The Event Horizon Telescope revealed the first image of the Milky Way’s central black hole in 2022. That image gave the public a direct view of the object anchoring our galaxy.
Yet the region around Sgr A* is packed with other actors. Massive stars blow winds into nearby gas. Clusters move on tight orbits. Molecular clouds preserve echoes from older high-energy events. Gravity pulls everything into complex paths around the central mass.
The mini-cavity sits at the intersection of these effects. Its shape may record the motion of a star cluster. Its gas may carry the imprint of Wolf-Rayet winds. Its surroundings may preserve X-ray echoes from a possible hidden black hole.
The authors emphasize the need for better measurements. More precise three-dimensional motions of IRS 13 stars would test the timing of the proposed crossing. The source known as E3, often linked with the possible intermediate-mass black hole, is especially important for future work.
More detailed gas modeling will also be needed. The mini-spiral is a moving, warped and turbulent environment. A stronger model could show whether the observed mini-cavity follows naturally from the IRS 13 crossing, or whether additional forces must be included.
For now, the study offers a vivid hypothesis. A star cluster may have swept through the glowing gas beside Sgr A*, opened a round pocket with ferocious winds and left behind a smoldering signature in X-ray-lit clouds. The Milky Way’s center still reads like an old crime scene, with stars, gas and black holes leaving clues in plain sight.
