Gas infall via accretion disk feeding Cepheus A HW2

¹ INAF, Osservatorio Astronomico di Cagliari, via della Scienza 5, 09047 Selargius, Italy
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
³ Département d’Astronomie, Université de Genève, Chemin Pegasi 51, 1290 Versoix, Switzerland
⁴ Space Research Center (CINESPA), School of Physics, University of Costa Rica, 11501 San José, Costa Rica
⁵ INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁶ Instituto de Radioastronomía y Astrofísica UNAM, Apartado Postal 3-72 (Xangari), 58089 Morelia, Michoacán, Mexico
⁷ INAF – Istituto di Radioastronomia & Italian ALMA Regional Centre, Via P. Gobetti 101, 40129 Bologna, Italy
⁸ NRAO, 520 Edgemont Road, Charlottesville, VA 22903, USA
⁹ Institut de Ciéncies de l’Espai (ICE-CSIC), Can Magrans s/n, 08193, Bellaterra, Barcelona, Spain
¹⁰ Institut d’Estudis Espacials de Catalunya (IEEC), Barcelona, Spain
¹¹ Instituto de Astronomía Téorica y Experimental (IATE, CONICET-UNC), Córdoba, Argentina
¹² INAF – Osservatorio Astronomico di Capodimonte, salita Moiariello 16, 80131 Napoli, Italy
¹³ Faculty of Physics, University of Duisburg-Essen, Lotharstra β e 1, 47057 Duisburg, Germany

^★ Corresponding author: alberto.sanna@inaf.it

Received: 11 April 2024
Accepted: 19 February 2025

Abstract

The star-forming region Cepheus A hosts a very young star, called HW2, that is the second closest to us growing a dozen times more massive than our Sun. The circumstellar environment surrounding HW2 has been the subject of extensive debate on the possible presence of an accretion disk, whose existence is at the foundation of our current paradigm of star formation. Here, we look to answer this long-standing question by resolving the gaseous disk component and its kinematics through sensitive observations at centrimetre (cm) wavelengths of hot ammonia (NH₃) with the Jansky Very Large Array. We mapped the accretion disk surrounding HW2 at radii between 200 and 700 au, showing how fast circumstellar gas collapses and slowly orbits to pile up near the young star at very high rates of 2 × 10⁻³ M_⊙ yr⁻¹. These results, corroborated by state-of-the-art simulations, show that an accretion disk is still efficient in terms of focusing huge mass-infall rates near the young star, even after this star had already achieved a large mass of 16 M_⊙.