Cracking open the 'dragon egg'. ALMA 1.3mm observations of a compact, young high-mass core candidate at 30mas resolution
Year: 2026
Type: article
Abstract: Massive pre-stellar cores are a central assumption of core-accretion models of high-mass star formation, yet convincing observational examples remain rare, with recent surveys generally finding widespread fragmentation in massive clumps. The `dragon egg' (C2c1a) core in the infrared-dark cloud G028.37+00.07 (the `dragon cloud') has been proposed as a promising compact high-mass core candidate . We present new ALMA Band 6 observations at 0.035''--0.078'' (sim175--400,au at 5,kpc) of C2c1, providing one of the most stringent high-resolution tests to date of a compact massive core candidate. The region resolves into multiple fragments, but the brightest component, C2c1a(a), remains a single compact continuum peak down to sim175,au, with a deconvolved radius of sim87,au and a nearest neighbouring fragment at a projected separation of sim2400,au . The continuum peak reaches a brightness temperature of sim40,K. This significantly exceeds the sim10,K gas temperatures inferred from lower-resolution NH_3 observations, indicating a strong radial temperature gradient. Continuum-based mass estimates for the compact component range from sim2, to sim30, . The data are also consistent with a strongly stratified structure in which a compact, warm inner component is embedded within a colder and more massive envelope, potentially tracing the earliest formation of (implying extreme densities of n_ > 10^9,cm-3) depending on the assumed temperature, while lower-resolution data indicate that it is embedded within a substantially larger mass reservoir of H2 on sim10^4,au scales. The spectrum towards the continuum peak shows no strong hot-core tracers and only weak, spatially extended H$_2CO and CO emission; no high-velocity outflow can be unambiguously associated with C2c1a(a). These properties are consistent with a very early evolutionary stage. We conclude that C2c1a(a) is an exceptionally compact core embedded within a massive cold reservoir, with no additional compact fragments detected within the present resolution and sensitivity limits a central protostellar `seed' within a still-dominant reservoir .
Source: Astronomy and Astrophysics
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
Awards: G1105844351, G1272900390, G1507096846, G1622782223, G1743472294, G302750986, G3715634343, G410571670, G4212894969, G451917667, G491712853, G5195188938, G5404395142, G5539308778, G5635532810, G593054264, G5967599077, G617610489, G624877701, G7097722406, G7805626310, G7863371703, G8284171658, G8497050386, G9000362223, G929308097
OpenAlex ID: W7216528612