Centrally concentrated star formation in young clusters

¹ Department of Astronomy, Columbia University, 538 W 120th St., New York, NY 10027, USA
² Department of Astrophysics, American Museum of Natural History, 200 Central Park W., New York, NY 10024, USA
³ Gumarbek Daukeyev Almaty University of Power Engineering and Telecommunications, 126/1 Baytursynuli St., Almaty 050000, Kazakhstan
⁴ Heriot-Watt University Aktobe Campus, K. Zhubanov Aktobe Regional University, 263 Zhubanov Brothers St., Aktobe 030000, Kazakhstan
⁵ Physics Department, Nazarbayev University, 53 Kabanbay Batyr Ave., Astana 010000, Kazakhstan
⁶ Energetic Cosmos Laboratory, Nazarbayev University, 53 Kabanbay Batyr Ave., Astana 010000, Kazakhstan
⁷ Max Planck Institute for Astrophysics, Karl-Schwarzschild-Straße 1, 85748 Garching bei München, Germany
⁸ Department of Physics and Astronomy, McMaster University, 1280 Main St. W., Hamilton, ON L8S 4M1, Canada
⁹ Department of Physics, Drexel University, 3141 Chestnut St., Philadelphia, PA 19104, USA
¹⁰ Fesenkov Astrophysical Institute, 23 Observatory St., 050020 Almaty, Kazakhstan
¹¹ Al-Farabi Kazakh National University, 71 Al-Farabi ave., 050040 Almaty, Kazakhstan

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Received: 4 July 2025
Accepted: 10 November 2025

Abstract

The study of star cluster evolution necessitates modeling how their density profiles develop from their natal gas distribution. Observational evidence indicates that many star clusters follow a Plummer-like density profile. However, most studies have focused on the phase after gas ejection, neglecting the influence of gas on early dynamical evolution. We investigate the development of star clusters forming within gas clouds, particularly those with a centrally concentrated gas profile. Simulations were conducted using the Torch framework, integrating the FLASH magnetohydrodynamics code into AMUSE. This permitted detailed modeling of star formation, stellar evolution, stellar dynamics, radiative transfer, and gas magnetohydrodynamics. We study the collapse of centrally concentrated, turbulent spheres with a total mass of 2.5 × 10³ M_⊙, investigating the effects of varying numerical resolution and star formation scenarios. The free-fall time is shorter at the center than at the edges of the cloud, with a minimum value of 0.55 Myr. The key conclusions from this study are: (1) the final stellar density profile is more centrally concentrated than was analytically predicted, reflecting the role of global gas collapse and feedback; (2) subclusters can initially form even in centrally concentrated gas clouds; (3) gas collapses globally toward the center on the central free-fall timescale, contradicting the assumption in analytical models of local fragmentation and star formation; and (4) the mass of the most massive star formed is directly correlated with the cluster effective radius and inversely correlated with the velocity dispersion, while the duration of star formation correlates with the star formation efficiency.