A single origin story for the Milky Way’s most mysterious stars

At the heart of the Milky Way, fractions of a parsec from Sagittarius A*, the supermassive black hole with a mass four million times that of the Sun, there exists a population of young, massive stars that has baffled astronomers for decades. They are freshly formed, energetically luminous objects racing through one of the most extreme gravitational environments in the galaxy — and their orbital motions have never quite made sense.

Three populations, one persistent puzzle

These young, massive stars near Sgr A* divide naturally into three distinct groups with very different behaviors. The innermost are the S-stars, moving along highly eccentric orbits with no preferred orientation. Farther out lies a structured disk of clockwise-rotating stars. And beyond that, a third population orbits at large angles to the disk plane. All three groups share a strikingly narrow age range — between roughly 6 and 15 million years — and all are massive objects of WR, O, or B spectral type. Their common youth, combined with their wildly divergent kinematics, is what makes this region of the sky so theoretically uncomfortable.

Previous models have tried to explain each group in isolation — through gas cloud encounters, in-situ star formation under extreme tidal conditions, or impulsive scattering by an unknown massive object — but none has ever succeeded in accounting for all three simultaneously.

A unified model and a hidden architect

A team led by Xiaochen Zheng at the Beijing Academy of Science and Technology has now proposed a unified dynamical model capable of explaining all three stellar populations within a single coherent framework, published as a preprint on arXiv (DOI: 10.48550/arxiv.2606.08971).

The central thesis is that all three populations formed together from a single primordial gas disk orbiting Sgr A*. Their diverse orbital properties emerged afterward, reshaped by the secular gravitational influence of an intermediate-mass companion with a mass of approximately 10,000 solar masses, acting together with mutual dynamical interactions among the stars themselves. The model quantitatively reproduces the observed orbital eccentricities, inclinations, disk geometry, and even a gap in the stellar distribution — all within the estimated stellar lifetimes.

IRS-13E as the likely culprit

The team identifies the compact cluster IRS-13E as the most probable candidate for this intermediate-mass perturber. Located at a projected separation of roughly 0.13 parsecs from Sgr A*, the cluster has long attracted attention because its total inferred mass substantially exceeds what its visible stars can account for — estimated at around 10,000 solar masses, possibly concentrated in an intermediate-mass black hole at its core. Prior ALMA observations detected ionized gas flowing along eccentric Keplerian streams around a point-mass potential at IRS-13E’s location, though the interpretation has remained debated.

Whether the hidden mass constitutes a genuine intermediate-mass black hole is still an open question. But if this model survives peer review, it would mark a significant step forward in understanding not only how stars can form in the immediate vicinity of a supermassive black hole — a process that seems physically improbable under standard star formation theory — but also how a secondary massive object can silently reshape an entire stellar population over millions of years. The gravitational choreography at the Milky Way’s center is far more structured, and far more consequential, than it has ever appeared.

© 2026 SKYCR.ORG | Homer Dávila Gutiérrez, FRAS. All rights reserved. Reproduction in whole or in part is prohibited without express authorization. More information: arXiv DOI: 10.48550/arxiv.2606.08971