Effects of Silicon and Carbon Addition on Magnetic Properties of Fe2-W Type Hexagonal Ferrite

Unno, Ken; Takamura, Hitoshi; Kamegawa, Atsunori; Homma, M.; Okada, Masuo

doi:10.3379/jmsjmag.23.329

Cited by 7 publications

(8 citation statements)

References 5 publications

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“…The evolution of SMSs with various metallicities has been modeled in detail (e.g., Osaki 1966;Unno 1971;Appenzeller & Fricke 1972a,b;Fricke 1973;Fuller et al 1986). However, they do not consider the formation stage with rapid mass accretion, which could significantly change the stellar structure (e.g., Begelman 2010;Hosokawa et al 2012a;Schleicher et al 2013).…”

Section: Introductionmentioning

confidence: 99%

Formation of Primordial Supermassive Stars by Rapid Mass Accretion

Hosokawa

Yorke

Inayoshi

et al. 2013

ApJ

278

397

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Supermassive stars (SMSs) forming via very rapid mass accretion (Ṁ * 0.1 M ⊙ yr −1 ) could be precursors of supermassive black holes observed beyond redshift of about 6. Extending our previous work, we here study the evolution of primordial stars growing under such rapid mass accretion until the stellar mass reaches 10 4−5 M ⊙ . Our stellar evolution calculations show that a star becomes supermassive while passing through the "supergiant protostar" stage, whereby the star has a very bloated envelope and a contracting inner core. The stellar radius increases monotonically with the stellar mass, until ≃ 100 AU for M * 10 4 M ⊙ , after which the star begins to slowly contract. Because of the large radius the effective temperature is always less than 10 4 K during rapid accretion. The accreting material is thus almost completely transparent to the stellar radiation. Only for M * 10 5 M ⊙ can stellar UV feedback operate and disturb the mass accretion flow. We also examine the pulsation stability of accreting SMSs, showing that the pulsation-driven mass loss does not prevent stellar mass growth. Observational signatures of bloated SMSs should be detectable with future observational facilities such as the James Webb Space Telescope. Our results predict that an inner core of the accreting SMS should suffer from the general relativistic instability soon after the stellar mass exceeds 10 5 M ⊙ . An extremely massive black hole should form after the collapse of the inner core.

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Section: Introductionmentioning

confidence: 99%

Formation of Primordial Supermassive Stars by Rapid Mass Accretion

Hosokawa

Yorke

Inayoshi

et al. 2013

ApJ

278

397

View full text Add to dashboard Cite

show abstract

“…The properties and evolution of supermassive stars (SMS), with masses 10 4 M , have been studied since the early 1960s (e.g., Osaki 1966;Unno 1971;Appenzeller & Fricke 1972a,b;Fricke 1973;Shapiro & Teukolsky 1979;Fuller et al 1986). But the existence of such stars has only recently been suspected to be necessary to explain the formation of quasars by z 7, such as ULAS J1120+0641, a 2 × 10 9 M black hole at z = 7.1 (Mortlock et al 2011) and SDSS J010013.02+280225.8, a 1.2 × 10 10 M black hole at z = 6.3 (Wu et al 2015; see Smidt et al 2017).…”

Section: Introductionmentioning

confidence: 99%

The evolution of supermassive Population III stars

Haemmerlé

Woods

Klessen

et al. 2017

Monthly Notices of the Royal Astronomical Society

152

175

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Supermassive primordial stars forming in atomically-cooled halos at z ∼ 15 − 20 are currently thought to be the progenitors of the earliest quasars in the Universe. In this picture, the star evolves under accretion rates of 0.1 -1 M yr −1 until the general relativistic instability triggers its collapse to a black hole at masses of ∼ 10 5 M . However, the ability of the accretion flow to sustain such high rates depends crucially on the photospheric properties of the accreting star, because its ionising radiation could reduce or even halt accretion. Here we present new models of supermassive Population III protostars accreting at rates 0.001 -10 M yr −1 , computed with the geneva stellar evolution code including general relativistic corrections to the internal structure. We use the polytropic stability criterion to estimate the mass at which the collapse occurs, which has been shown to give a lower limit of the actual mass at collapse in recent hydrodynamic simulations. We find that at accretion rates higher than 0.001 M yr −1 the stars evolve as red, cool supergiants with surface temperatures below 10 4 K towards masses > 10 5 M , and become blue and hot, with surface temperatures above 10 5 K, only for rates 0.001 M yr −1 . Compared to previous studies, our results extend the range of masses and accretion rates at which the ionising feedback remains weak, reinforcing the case for direct collapse as the origin of the first quasars.

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“…Our calculations determine the final mass of the accreting SMSs by incorporating the realistic conditions within the context of the direct collapse scenario. Previous studies show that the GR instability causes the collapse of a non-rotating SMS with a few × 10 5 M but without considering its evolution under rapid mass accretion (e.g., Osaki 1966;Unno 1971;Fricke 1973;Fuller et al 1986). We show that gas accretion significantly alters the stellar structure.…”

Section: Introductionmentioning

confidence: 99%

The Final Fates of Accreting Supermassive Stars

Umeda

Hosokawa

Omukai

et al. 2016

ApJL

139

147

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The formation of supermassive stars (SMSs) via rapid mass accretion and their direct collapse into black holes (BHs) is a promising pathway for sowing seeds of supermassive BHs in the early universe. We calculate the evolution of rapidly accreting SMSs by solving the stellar structure equations including nuclear burning as well as general relativistic (GR) effects up to the onset of the collapse. We find that such SMSs have less concentrated structure than fully-convective counterpart, which is often postulated for non-accreting ones. This effect stabilizes the stars against GR instability even above the classical upper mass limit 10 5 M derived for the fully-convective stars. The accreting SMS begins to collapse at the higher mass with the higher accretion rate. The collapse occurs when the nuclear fuel is exhausted only for cases withṀ 0.1 M yr −1 . WithṀ 0.3 − 1 M yr −1 , the star becomes GR-unstable during the helium-burning stage at M 2 − 3.5 × 10 5 M . In an extreme case with 10 M yr −1 , the star does not collapse until the mass reaches 8.0 × 10 5 M , where it is still in the hydrogen-burning stage. We expect that BHs with roughly the same mass will be left behind after the collapse in all the cases.

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Effects of Silicon and Carbon Addition on Magnetic Properties of Fe2-W Type Hexagonal Ferrite

Cited by 7 publications

References 5 publications

Formation of Primordial Supermassive Stars by Rapid Mass Accretion

Formation of Primordial Supermassive Stars by Rapid Mass Accretion

The evolution of supermassive Population III stars

The Final Fates of Accreting Supermassive Stars

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