Suppression of cooling by strong magnetic fields in white dwarf stars

Valyavin, G. G.; Shulyak, D.; Wade, G. A.; Antonyuk, K. A.; Zharikov, S. V.; Галазутдинов, Г. А.; Plachinda, S. I.; Bagnulo, S.; Fox-Machado, L.; Álvarez, M.; Clark, David M.; López, J. M.; Hiriart, D.; Han, Inwoo; Jeon, Young‐Beom; Zurita, C.; Mújica, R.; Burlakova, T. E.; Szeifert, T.; Burenkov, A. N.

doi:10.1038/nature13836

Cited by 59 publications

(52 citation statements)

References 32 publications

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“…The convective coupling occurs at T eff values lower than 6000 K in white dwarfs, hence the suppression of convection is not expected to impact cooling rates for warmer remnants. This argument contradicts the suggestion from Valyavin et al (2014;see their Figure 3(a)) that the suppression of convection changes the cooling rates and explains the observed temperature distribution of magnetic white dwarfs, for which their coolest bin is at T eff = 6000 K. To demonstrate it quantitatively, this section presents new evolution sequences that we have computed with our state-of-the-art white dwarf evolutionary code (Fontaine et al 2001;Fontaine et al 2013). To fully appreciate the results, we also review the important properties of white dwarf cooling in Section 2.3.…”

Section: Evolutionary Modelscontrasting

confidence: 54%

“…It is therefore essential, at this stage, to build precise model atmospheres and evolution sequences for these peculiar degenerate stars. It has been suggested for a long time that convection is completely inhibited in HFMWDs (Wickramasinghe & Martin 1986;Valyavin et al 2014), although this has not yet been verified with realistic simulations. Furthermore, Kepler et al (2013) suggest that small undetected magnetic fields could impact the mass distribution of cool convective white dwarfs.…”

Section: Introductionmentioning

confidence: 98%

“…Furthermore, while we have only performed simulations with a vertically oriented magnetic field, it is generally thought that the damping of convection is even stronger for horizontally oriented fields since the Lorentz force will act against vertical flows. In other words, convection is expected to be globally inhibited above a certain magnetic field strength (Valyavin et al 2014).…”

Section: Magnetohydrodynamic Simulationsmentioning

confidence: 99%

“…Furthermore, Kepler et al (2013) suggest that small undetected magnetic fields could impact the mass distribution of cool convective white dwarfs. Valyavin et al (2014) have recently proposed that the inhibition of convection in magnetic white dwarfs has a large impact on cooling rates by increasing the cooling times by a factor of two to three. However, they arrived at this conclusion with a simple analytical argument and it needs to be verified with state-of-the-art evolution models.…”

Section: Introductionmentioning

confidence: 99%

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On the Evolution of Magnetic White Dwarfs

Tremblay

Fontaine

Freytag

et al. 2015

ApJ

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We present the first radiation magnetohydrodynamic simulations of the atmosphere of white dwarf stars. We demonstrate that convective energy transfer is seriously impeded by magnetic fields when the plasma-β parameter, the thermal-to-magnetic-pressure ratio, becomes smaller than unity. The critical field strength that inhibits convection in the photosphere of white dwarfs is in the range B = 1-50 kG, which is much smaller than the typical 1-1000 MG field strengths observed in magnetic white dwarfs, implying that these objects have radiative atmospheres. We have employed evolutionary models to study the cooling process of high-field magnetic white dwarfs, where convection is entirely suppressed during the full evolution (B  10 MG). We find that the inhibition of convection has no effect on cooling rates until the effective temperature (T eff ) reaches a value of around 5500 K. In this regime, the standard convective sequences start to deviate from the ones without convection due to the convective coupling between the outer layers and the degenerate reservoir of thermal energy. Since no magnetic white dwarfs are currently known at the low temperatures where this coupling significantly changes the evolution, the effects of magnetism on cooling rates are not expected to be observed. This result contrasts with a recent suggestion that magnetic white dwarfs with T eff  10,000 K cool significantly slower than non-magnetic degenerates.

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Section: Evolutionary Modelscontrasting

confidence: 54%

Section: Introductionmentioning

confidence: 98%

Section: Magnetohydrodynamic Simulationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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On the Evolution of Magnetic White Dwarfs

Tremblay

Fontaine

Freytag

et al. 2015

ApJ

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“…Recently, Valyavin et al (2014) showed that convection is completely suppressed starting from surface magnetic fields of the order of 10 MG, and therefore strong magnetic fields slow down the white dwarf cooling process. As a consequence, the CHZ for strongly magnetic white dwarfs may extend even more in time, well beyond 8 Gyr.…”

Section: Introductionmentioning

confidence: 99%

Polarimetry as a tool to find and characterise habitable planets orbiting white dwarfs

et al. 2014

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Abstract. There are several ways planets can survive the giant phase of the host star, hence one can consider the case of Earth-like planets orbiting white dwarfs. As a white dwarf cools from 6000 K to 4000 K, a planet orbiting at 0.01 AU from the star would remain in the continuous habitable zone (CHZ) for about 8 Gyr. Polarisation due to a terrestrial planet in the CHZ of a cool white dwarf (CWD) is 10 2 (10 4 ) times larger than it would be in the habitable zone of a typical M-dwarf (Sun-like star). Polarimetry is thus a powerful tool to detect close-in planets around white dwarfs. Multi-band polarimetry would also allow one to reveal the presence of a planet atmosphere, even providing a first characterisation. With current facilities a superEarth-sized atmosphereless planet is detectable with polarimetry around the brightest known CWD. Planned future facilities render smaller planets detectable, in particular by increasing the instrumental sensitivity in the blue. Preliminary habitability study show also that photosynthetic processes can be sustained on Earth-like planets orbiting CWDs and that the DNA-weighted UV radiation dose for an Earth-like planet in the CHZ is less than the maxima encountered on Earth, hence white dwarfs are compatible with the persistence of complex life from the perspective of UV irradiation.

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