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Supermassive stars (SMSs) with masses of 𝑀∗ ≃ 104–105 M⊙ are invoked as possible seeds of high-redshift supermassive black holes, but it remains under debate whether their protostar indeed acquires sufficient mass via gas accretion overcoming radiative feedback. We investigate protostellar growth in dynamically heated atomic-cooling haloes (ACHs) found in recent cosmological simulations, performing three-dimensional radiation hydrodynamical (RHD) simulations that consider stellar evolution under variable mass accretion. We find that one of the ACHs feeds the central protostar at rates exceeding a critical value, above which the star evolves in a cool bloating phase and hardly produces ionizing photons. Consequently, the stellar mass reaches 𝑀∗ 104 M⊙ unimpeded by radiative feedback. In the other ACH, where the mass supply rate is lower, the star spends most of its life as a hot main-sequence star, emitting intense ionizing radiation. Then, the stellar mass growth is terminated around 500 M⊙ by photoevaporation of the circumstellar disk. A series of our RHD simulations provide a formula of the final stellar mass determined either by stellar feedback or their lifetime as a function of the mass supply rate from the parent cloud in the absence of stellar radiation. Combining the results with the statistical properties of SMS-forming clouds in high-redshift quasar progenitor haloes, we construct a top-heavy mass distribution of primordial stars over 𝑀∗ ≃ 100–105 M⊙, approximately following a power-law spectrum of ∝ 𝑀−1.3 with a steeper decline at 𝑀 2 × 104 M . Their massive BH remnants would be ∗∗⊙ further fed via the dense debris disk, powering “milli-quasars" with a bolometric luminosity of 𝐿bol 1043 erg s−1.
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Radiative feedback for supermassive star formation in a massive cloud with H2 molecules in an atomic-cooling halo
ABSTRACT Recent three-dimensional cosmological simulations of protogalaxy formation have suggested that supermassive stars (SMSs) can form in gas clouds in which H2 cooling is suppressed by dynamical heating prior to the activation of atomic cooling, but they stopped short of the following growth of a central protostar. Here, we examine whether accretion on the protostellar core in this cloud is sufficiently rapid, in the face of the radiation feedback, to produce an SMS. We perform one-dimensional radiation-hydrodynamical simulations of the hot collapsing cloud with non-equilibrium chemical reactions directly adopting the cloud properties from Wise et al. as an initial condition. We find that the stellar Lyman–Werner (LW) radiation from the SMS dissociates H2 in the inner regions of the gas flow, increasing gas temperature and thermal pressure, and temporarily stopping the accretion. However, this negative feedback ceases when the self-gravity and inward ram pressure force on larger scales push the gas inwards. The central protostar is unable to expand an H ii region due to the high density, and grows to a mass of $${\gtrsim}10^5\, {\rm M}_{\odot }$$. Our results suggests the successful formation of SMSs, and resulting massive ($${\sim}10^5\, {\rm M}_{\odot }$$) remnant black holes in the clouds, but need to be confirmed in two- or three-dimensional simulations.
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- Award ID(s):
- 2006176
- PAR ID:
- 10225706
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 499
- Issue:
- 4
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- 5960 to 5971
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1093/mnras/staa3227
