Purple Mountain Observatory's August Triple: Milky Way's Mini-Vortex, an IMBH Candidate, and a Decade of CO Surveying

Forum topic · 小凯 · 2026-08-28

Summary

In August 2026, the Milky Way Imaging Scroll Painting (MWISP) team at the Purple Mountain Observatory of the Chinese Academy of Sciences announced three related discoveries from its long-term molecular-line survey using the 13.7 m millimeter-wave telescope in Delingha, Qinghai. First, the team reported the first known giant spiral-shaped molecular cloud spanning about 100 parsecs (roughly 300 light-years), named the Milky Way Scroll Vortex, whose quasi-sinusoidal radial velocity oscillations and near-rigid rotation match density-wave theory. Second, at its geometric center lies a bright nonthermal radio source driving a CO molecular outflow whose velocity-distance relation follows a 'Hubble law', making it an intermediate-mass black hole (IMBH) candidate inside the Milky Way. Third, the team catalogued 57 unusually narrow-line-width 'veil clouds' that appear dynamically quiet, sub/transonic, and may trace the atomic-to-molecular gas transition around the Local Bubble. Together with a Nature Astronomy paper on large-scale corrugation waves in the outer Galactic disk, these results show a self-built survey of over 30,000 molecular clouds shifting from filling observational gaps in the Western sky to exporting new physical mechanisms.

Purple Mountain Observatory's August Triple: A Mini-Vortex in the Milky Way and an IMBH Candidate

On August 28, 2026, the "Milky Way Imaging Scroll Painting" (MWISP) team at the Purple Mountain Observatory (PMO) of the Chinese Academy of Sciences announced the first discovery of a giant spiral-shaped molecular cloud at the ~100-parsec scale, named the Milky Way Scroll Vortex. At its geometric center sits a bright nonthermal radio source — an intermediate-mass black hole (IMBH) candidate — supported by a CO molecular outflow whose velocity–distance relation obeys a jet "Hubble law". Combined with the team's Nature Astronomy paper on outer-disk corrugations (Aug 7/22) and the identification of 57 "veil clouds" (Aug 24), these results mark a shift from filling observational blind spots to exporting new physical mechanisms, powered by over a decade of surveying with a 13.7 m millimeter-wave telescope in Delingha, Qinghai.

Key Points

A spiral within a spiral. The Scroll Vortex spans ~100 pc (~300+ light-years), far larger than typical molecular clouds (a few to tens of pc). Its radial velocity shows quasi-sinusoidal oscillations and slow, quasi-rigid rotation — features consistent with density-wave theory (Lin & Shu, 1960s), like a "mini spiral galaxy" inside the Milky Way.
An IMBH candidate at the center. A bright nonthermal radio source sits at the vortex's geometric center. A CO molecular jet with multiple redshifted and blueshifted lobes shows a velocity–distance relation matching the jet "Hubble law" — ballistic back-tracing that points to a single engine. A compact object capable of driving such a jet indicates an IMBH candidate (10²–10⁵ solar masses), the missing link between stellar-mass and supermassive black holes, and a possible "seed" needed to explain billion-solar-mass quasars at redshift z > 6.
The survey behind it. MWISP began in 2011 using the 13.7 m millimeter-wave telescope at Delingha with a superconducting spectrometer. Millimeter-wave CO lines penetrate dust that blocks visible light. By 2024 the team had catalogued 30,000+ molecular clouds, reaching ~26 kpc (~80,000 light-years) from the Galactic center — roughly half the outer disk's 3D skeleton in molecular gas, a coverage foreign projects (e.g., Gaia's stellar "Great Wave") did not provide.
Outer-disk corrugations (Nature Astronomy). After subtracting the known large-scale warp from the data, coherent red/blue vertical undulations emerge with radial wavelengths of 3.9–7.9 kpc and vertical amplitudes of 100–200 pc — likely "bending waves" excited by external gravitational perturbations (flying-by dwarf galaxies), possibly modulated by the Galaxy's own spiral arms and bar.
57 "veil clouds" (Aug 24). Found via Gaussian decomposition and hierarchical clustering: ¹²CO structures up to thousands of square arcminutes, low brightness (~3 K), velocity dispersion ~0.3 km/s, sizes 1–3 pc, thickness 0.1–0.3 pc, density ~300 cm⁻³. At ~10 K they move at 1–2 times the sound speed — dynamically quiet, unlike typical supersonic turbulent clouds. They align with the Gould Belt (~1,000 light-years around the Sun) and trace the boundary of the Local Bubble; HI narrow-line absorption suggests they may be transitioning from atomic to molecular gas — possibly "infancy photos" of molecular clouds, with non-ideal MHD dissipation timescales under 1 Myr.

Methodology: Subtract the Background, Read the Residuals

All three results share one approach: model and remove the large-scale background (warp, turbulence, noise), then examine residuals. The corrugations appeared after subtracting the disk warp; the vortex's quasi-sinusoidal velocity oscillation was isolated from turbulent noise; veil clouds were systematically screened by anomalous narrow line widths. A 13.7 m mid-size telescope plus 15 years of disciplined observations and careful data processing still delivered Nature Astronomy results — a lesson for "strong instruments, weak methods" gaps elsewhere.

Open Questions

1. IMBH mass measurement — high-resolution interferometry (ALMA, ngVLA) is needed to confirm it falls in the 10²–10⁵ M☉ range. 2. Origin of the corrugations — external perturbation vs. internal spiral/bar effects; combined multi-tracer simulations are planned. 3. Veil-cloud evolutionary stage — higher-sensitivity HI/CO observations and chemical clocks (HCO⁺, C¹⁸O) are needed to confirm the atomic-to-molecular transition.

From recording positions to understanding mechanisms: a survey that "painted" the Galaxy for over a decade is now surfacing physics — density waves at cloud scale, bending waves in the disk, turbulence dissipation in magnetic fields, and possibly a black hole jet engine.

References

1. China News Service, "Purple Mountain Observatory discovers giant spiral molecular cloud in the Milky Way," 2026-08-28, https://www.chinanews.com/gn/2026/08-28/10685905.shtml 2. Chinese Academy of Sciences, "The Milky Way not only warps but also corrugates," 2026-08-25, https://www.cas.cn/cm/202608/t20260825_5118992.shtml 3. Henan Association for Science and Technology, "MWISP survey discovers a new type of molecular cloud," 2026-08-24, https://www.hast.net.cn/2026/08-24/123738.html 4. Lin, C.C. & Shu, F.H., density-wave theory (1964–1966); Chen Xiaodian et al., 2019 Nature Astronomy 3D Galactic warp map 5. Poggio et al. 2025, "Great Wave" large-scale vertical oscillation in stellar samples