Disc fragmentation and intermittent accretion on to supermassive stars

Matsukoba, Ryoki; Vorobyov, Eduard I.; Sugimura, Kazuyuki; Chon, Sunmyon; Hosokawa, Takashi; Omukai, Kazuyuki

doi:10.1093/mnras/staa3462

Cited by 12 publications

(6 citation statements)

References 68 publications

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“…Although the barotropic EOS is obtained for the evolution during the early collapse stage, it has been applied to study the disc fragmentation in the literature. Clark et al (2011) show that, at least for the primordial cases, applying the barotropic EOS tends to result in the lower disc temperature and thus more fragmentation than solving the thermal and chemical processes in a time-dependent hydrodynamic code (see also Matsukoba et al 2021). Nonetheless, Susa (2019) has found that the previous simulations with both approaches show similar evolution of the clump number as described by equation (1).…”

Section: Equation Of State At Different Metallicitiesmentioning

confidence: 96%

Gravitational Fragmentation of Extremely Metal-poor Circumstellar Discs

Shima,

Hosokawa

2021

Preprint

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We study the gravitational fragmentation of circumstellar discs accreting extremely metal-poor (𝑍 ≤ 10 −3 Z ) gas, performing a suite of three-dimensional hydrodynamic simulations using the adaptive mesh refinement code Enzo. We systematically follow the long-term evolution for 2 × 10 3 years after the first protostar's birth, for the cases of 𝑍 = 0, 10 −5 , 10 −4 , and 10 −3 Z . We show that evolution of number of self-gravitating clumps qualitatively changes with 𝑍. Vigorous fragmentation induced by dust cooling occurs in the metal-poor cases, temporarily providing ∼ 10 self-gravitating clumps at 𝑍 = 10 −5 and 10 −4 Z . However, we also show that the fragmentation is a very sporadic process; after an early episode of the fragmentation, the number of clumps continuously decreases as they merge away in these cases. The vigorous fragmentation tends to occur later with the higher 𝑍, reflecting that the dust-induced fragmentation is most efficient at the lower density. At 𝑍 = 10 −3 Z , as a result, the clump number stays smallest until the disc fragmentation starts in a late stage. We also show that the clump mass distribution also depends on the metallicity. A single or binary clump substantially more massive than the others appear only at 𝑍 = 10 −3 Z , whereas they are more evenly distributed in mass at the lower metallicities. We suggest that the disc fragmentation should provide the stellar multiple systems, but their properties drastically change with a tiny amount of metals.

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Section: Equation Of State At Different Metallicitiesmentioning

confidence: 96%

Gravitational Fragmentation of Extremely Metal-poor Circumstellar Discs

Shima,

Hosokawa

2021

Preprint

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“…Finally, we remark the different spatial distributions of stars in the Salpeter-like and massive log-flat components. Massive stars tend to be found around the cloud center and constitute a binary or higher-order multiple system, as it is frequently found in simulations for primordial star-forming clouds (Stacy et al 2016;Chon et al 2018;Chon & Hosokawa 2019;Susa 2019;Sugimura et al 2020;Matsukoba et al 2021). Around the binary/multiple system, there is a massive gas disk, which feeds the massive member stars with gas (e.g.…”

Section: Mass Spectrummentioning

confidence: 88%

Impact of the cosmic background radiation on the initial mass function of metal-poor stars

Chon,

Ono,

Omukai

et al. 2022

Preprint

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We study star cluster formation at low metallicities of Z/Z = 10 −4 -10 −1 using three-dimensional hydrodynamics simulations. Particular emphasis is put on how the stellar mass distribution is affected by the cosmic microwave background radiation (CMB), which sets the temperature floor to the gas. Starting from the collapse of a turbulent cloud, we follow the formation of a protostellar system resolving ∼au scale. In relatively metal-enriched cases of Z/Z 10 −2 , where the mass function resembles the present-day one in the absence of the CMB, high temperature CMB suppresses cloud fragmentation and reduces the number of low-mass stars, making the mass function more top-heavy than in the cases without CMB heating at z 10. In lower-metallicity cases with Z/Z 10 −3 , where the gas temperature is higher than the CMB value due to inefficient cooling, the CMB has only a minor impact on the mass distribution, which is top-heavy regardless of the redshift. In cases either with a low metallicity of Z/Z 10 −2 or at a high redshift z 10, the mass spectrum consists of a low-mass Salpeter-like component, peaking at 0.1 M , and a top-heavy component with 10-50 M , with the fraction in the latter increasing with increasing redshift. In galaxies forming at z 10, the major targets of the future instruments including JWST, CMB heating makes the stellar mass function significantly top-heavy, enhancing the number of supernova explosions by a factor of 1.4 (2.8) at z = 10 (20, respectively) compared to the prediction by Chabrier initial mass function when Z/Z = 0.1.

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“…If such very rapid accretion continues for ∼ 1 Myr, supermassive stars with 10 5 -10 6 M form and they may provide massive seeds of supermassive black holes after they die (see Volonteri 2010;Inayoshi et al 2020, for reviews). However, previous simulations also show that the circumstellar disks form (e.g., Latif et al 2013) and fragment also for this case (Becerra et al 2015;Sakurai et al 2016;Chon et al 2018;Latif et al 2020;Matsukoba et al 2020). If too many fragments appear, they might evolve into a cluster of lower-mass stars instead of a single supermassive star (e.g., Regan & Downes 2018).…”

Section: Introductionmentioning

confidence: 84%

Growth of Massive Disk and Early Disk Fragmentation in the Primordial Star Formation

Kimura,

Hosokawa,

Sugimura

2020

Preprint

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Recent high-resolution simulations demonstrate that disks around primordial protostars easily fragment in the accretion phase before the protostars accrete less than a solar mass. To understand why the gravitational instability generally causes the fragmentation so early, we develop a one-dimensional (1D) non-steady model of the circumstellar disk that takes the mass supply from an accretion envelope into account. We also compare the model results to a three-dimensional (3D) numerical simulation performed with a code employing the adaptive mesh refinement. Our model shows that the self-gravitating disk, through which the Toomre Q parameter is nearly constant at Q ∼ 1, gradually spreads as the disk is fed by the gas infalling from the envelope. We further find that the accretion rate onto the star is an order of magnitude smaller than the mass supply rate onto the disk. This discrepancy makes the disk more massive than the protostar in an early evolutionary stage. Most of the infalling gas is used to extend the outer part of the self-gravitating disk rather than transferred inward toward the star through the disk. We find that similar evolution also occurs in the 3D simulation, where the disk becomes three times more massive than the star before the first fragmentation occurs. Our 1D disk model well explains the evolution of the disk-to-star mass ratio observed in the simulation. We argue that the formation of such a massive disk leads to the early disk fragmentation.

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Disc fragmentation and intermittent accretion on to supermassive stars

Cited by 12 publications

References 68 publications

Gravitational Fragmentation of Extremely Metal-poor Circumstellar Discs

Gravitational Fragmentation of Extremely Metal-poor Circumstellar Discs

Impact of the cosmic background radiation on the initial mass function of metal-poor stars

Growth of Massive Disk and Early Disk Fragmentation in the Primordial Star Formation

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