2022MNRAS.509.4758H

G0.253+0.016, commonly referred to as 'the Brick' and located within the Central Molecular Zone, is one of the densest (≃10^3–4 cm^–3) molecular clouds in the Galaxy to lack signatures of widespread star formation. We set out to constrain the origins of an arc-shaped molecular line emission feature located within the cloud. We determine that the arc, centred on {l₀,b₀} = {0_.^○248, 0_.^○018}, has a radius of 1.3 pc and kinematics indicative of the presence of a shell expanding at 5.2^+2.7_–1.9 km s^–1. Extended radio continuum emission fills the arc cavity and recombination line emission peaks at a similar velocity to the arc, implying that the molecular gas and ionized gas are physically related. The inferred Lyman continuum photon rate is N_LyC = 10^46.0-10^47.9 photons s^–1, consistent with a star of spectral type B1-O8.5, corresponding to a mass of ≃12-20 M_☉. We explore two scenarios for the origin of the arc: (i) a partial shell swept up by the wind of an interloper high-mass star and (ii) a partial shell swept up by stellar feedback resulting from in situ star formation. We favour the latter scenario, finding reasonable (factor of a few) agreement between its morphology, dynamics, and energetics and those predicted for an expanding bubble driven by the wind from a high-mass star. The immediate implication is that G0.253+0.016 may not be as quiescent as is commonly accepted. We speculate that the cloud may have produced a <=10³ M_☉ star cluster >=0.4 Myr ago, and demonstrate that the high-extinction and stellar crowding observed towards G0.253+0.016 may help to obscure such a star cluster from detection.