scholarly journals Revisiting some physics issues related to the new mass limit for magnetized white dwarfs

2014 ◽  
Vol 29 (07) ◽  
pp. 1450035 ◽  
Author(s):  
Upasana Das ◽  
Banibrata Mukhopadhyay
Keyword(s):  
Magnetic Field ◽  
High Magnetic Field ◽  
White Dwarfs ◽  
Total Density ◽  
Mass Limit ◽  
The Magnetic Field

We clarify important physics issues related to the recently established new mass limit for magnetized white dwarfs which is significantly super-Chandrasekhar. The issues include, justification of high magnetic field and the corresponding formation of stable white dwarfs, contribution of the magnetic field to the total density and pressure, flux freezing, variation of magnetic field and related currents therein. We also attempt to address the observational connection of such highly magnetized white dwarfs.

Structure Control of Hydroxyapatite Using a Magnetic Field

2007 ◽  
Vol 561-565 ◽  
pp. 1565-1568 ◽  
Author(s):  
Kazuhiko Iwai ◽  
Jun Akiyama ◽  
Shigeo Asai
Keyword(s):  
Magnetic Field ◽  
High Magnetic Field ◽  
Slip Casting ◽  
Casting Process ◽  
Ceramic Materials ◽  
X Ray Diffraction ◽  
X Ray ◽  
Structure Control ◽  
Crystal Alignment ◽  
The Magnetic Field

A high magnetic field is a useful tool to control the crystal alignment of ceramic materials. In this study, a horizontal 10T static magnetic field was imposed on slurry containing hydroxyapatite (HAp) crystals under the horizontal mold rotation during slip casting process so as to introduce uni-axial alignment for some amount of crystals in the sample, and then it was sintered in atmosphere without the magnetic field. From X-ray diffraction, it has been found that the HAp crystals in the sample treated with the mold rotation under the magnetic field were aligned its c-axis to a particular direction.

scholarly journals Discovery of weak magnetic fields in four DZ white dwarfs in the local 20 pc volume

2019 ◽  
Vol 630 ◽  
pp. A65 ◽  
Author(s):  
S. Bagnulo ◽  
J. D. Landstreet
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
White Dwarfs ◽  
Field Measurements ◽  
Weak Magnetic Fields ◽  
Polluted Atmosphere ◽  
Highly Sensitive ◽  
Cool White Dwarfs ◽  
The Magnetic Field ◽  
Made In

We report the discovery of weak magnetic fields in three white dwarfs within the local 20 pc volume (WD 0816−310, WD 1009−184, and WD 1532+129), and we confirm the magnetic nature of a fourth star (WD 2138−332) in which we had previously detected a field at a 3σ level. The spectra of all these white dwarfs are characterised by the presence of metal lines and lack of H and He lines, that is, they belong to the spectral class DZ. The polarisation signal of the Ca II H+K lines of WD 1009−184 is particularly spectacular, with an amplitude of 20% that is due to the presence of a magnetic field with an average line-of-sight component of 40 kG. We have thus established that at least 40% of the known DZ white dwarfs with an He-rich atmosphere contained in the 20 pc volume have a magnetic field, while further observations are needed to establish whether the remaining DZ white dwarfs in the same volume are magnetic or not. Metal lines in the spectra of DZ white dwarfs are thought to have originated by accretion from rocky debris, and it might be argued that a link exists between metal accretion and higher occurrence of magnetism. However, we are not able to distinguish whether the magnetic field and the presence of a polluted atmosphere have a common origin, or if it is the presence of metal lines that allows us to detect a higher frequency of magnetic fields in cool white dwarfs, which would otherwise have featureless spectra. We argue that the new highly sensitive longitudinal field measurements that we have made in recent years are consistent with the idea that the magnetic field appears more frequently in older than in younger white dwarfs.

scholarly journals Radiation-Driven Acceleration in Photospheres of Nonaccreting Magnetic White Dwarfs

1994 ◽  
Vol 142 ◽  
pp. 783-787
Author(s):  
Vladimir V. Zheleznyakov ◽  
A. V. Serber
Keyword(s):  
Magnetic Field ◽  
Radiation Pressure ◽  
White Dwarfs ◽  
Force Balance ◽  
Pure Hydrogen ◽  
Uv Spectrum ◽  
Dipole Magnetic Field ◽  
Cyclotron Line ◽  
The Magnetic Field ◽  
Radiation Pressure Force

AbstractRadiation transfer in a pure hydrogen, fully ionized, isothermal photosphere of an isolated white dwarf with dipole magnetic field is considered, and the radiation pressure force, both in the continuum and in the cyclotron line, is determined with the line saturation effect taken into account. It is shown that the magnetic field can reduce the critical luminosity for white dwarfs. This leads to the possibility of photospheric plasma ejection driven by the radiation in the cyclotron line and the formation of radiation-driven winds from sufficiently hot isolated magnetic white dwarfs.It is shown that cyclotron radiation pressure plays a significant role in the force balance of the photospheres of the magnetic white dwarfs GD 229, GrW +70° 8247, and PG 1031+234. The strong unidentified depression in the UV spectrum of GD 229 is attributed to cyclotron scattering by the radiation-driven plasma envelope with density N ≳ 108 cm−3 .Subject headings: radiative transfer — stars: atmospheres — stars: magnetic fields — white dwarfs

Effects of High Magnetic Field Heat Treatment on the Microstructure of Fe-0.76%C Alloy

2011 ◽  
Vol 704-705 ◽  
pp. 863-869 ◽  
Author(s):  
Ming Long Gong ◽  
Xiang Zhao ◽  
Chang Shu He ◽  
J.Y. Song ◽  
Liang Zuo
Keyword(s):  
Magnetic Field ◽  
High Magnetic Field ◽  
Lamellar Spacing ◽  
Field Direction ◽  
Magnetic Field Direction ◽  
High Carbon Content ◽  
Proeutectoid Ferrite ◽  
Alloy Microstructure ◽  
And Shifts ◽  
The Magnetic Field

The present studies are to investigate the microstructure features during transformation from austenite to ferrite without and with magnetic field on Fe-0.76%C alloy. It is found that the area fraction and numbers of proeutectoid ferrite grain as well as the lamellar spacing of pearlite in Fe-0.76%C alloy increased considerably with the increase of magnetic field intensity. The reason is that, the magnetic field increases the driving force of proeutectoid ferrite nuclei and shifts the eutectoid point to the side of high carbon content and high temperature, which increases the starting-temperature of the transformation from austenite to ferrite. The proeutectoid ferrite grains are elongated along the magnetic field direction, which can be explained as follows: the proeutectoid ferrite becomes the magnetic dipolar under high magnetic field, and then the polarized austenite atoms are much easier to diffuse into ferrite grains along the magnetic field direction. Key words: high magnetic field; Fe-0.76%C alloy; microstructure

A fossil origin for the magnetic field in A stars and white dwarfs

Nature ◽  
2004 ◽  
Vol 431 (7010) ◽  
pp. 819-821 ◽  
Author(s):  
Jonathan Braithwaite ◽  
Hendrik C. Spruit
Keyword(s):  
Magnetic Field ◽  
White Dwarfs ◽  
The Magnetic Field

scholarly journals VIOLATION OF CHANDRASEKHAR MASS LIMIT: THE EXCITING POTENTIAL OF STRONGLY MAGNETIZED WHITE DWARFS

2012 ◽  
Vol 21 (11) ◽  
pp. 1242001 ◽  
Author(s):  
UPASANA DAS ◽  
BANIBRATA MUKHOPADHYAY
Keyword(s):  
Magnetic Field ◽  
Equation Of State ◽  
Density Of States ◽  
White Dwarfs ◽  
Electron Gas ◽  
Degenerate Electron ◽  
Mass Limit ◽  
Strong Magnetic Fields ◽  
Exciting Potential ◽  
Degenerate Electron Gas

We consider a relativistic, degenerate, electron gas under the influence of a strong magnetic field, which describes magnetized white dwarfs. Landau quantization changes the density of states available to the electrons, thus modifying the underlying equation of state. In the presence of very strong magnetic fields a maximum of either one, two or three Landau level(s) is/are occupied. We obtain the mass–radius relations for such white dwarfs and their detailed investigation leads us to propose the existence of white dwarfs having a mass ~2.3M⊙, which overwhelmingly exceeds the Chandrasekhar mass limit.

Effect of a High Magnetic Field on the Microstructure of Directionally Solidified NiAl-Cr(Mo)-Si Near-Eutectic Alloy at Different Withdrawal Rates

2017 ◽  
Vol 898 ◽  
pp. 407-412 ◽  
Author(s):  
Huan Liu ◽  
Wei Dong Xuan ◽  
Xing Fu Ren ◽  
Bao Jun Wang ◽  
Jian Bo Yu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
High Magnetic Field ◽  
Eutectic Alloy ◽  
Magnetic Force ◽  
Volume Fraction ◽  
Withdrawal Rate ◽  
Directionally Solidified ◽  
Combined Action ◽  
Columnar To Equiaxed Transition ◽  
The Magnetic Field

The effect of a 6T high magnetic field on the microstructure of directionally solidified NiAl-Cr (Mo)-Si near-eutectic alloy was investigated at the withdrawal rates of 2, 10 and 50 μm/s. The results showed that the microstructure evolved from planar eutectic to primary NiAl dendrites + cellular eutectic and then to dendritic eutectic with the increasing withdrawal rate. When the magnetic field was imposed, the well-aligned eutectic lamellae were disturbed and transformed into a wavy one at 2 μm/s. When the withdrawal rate increased to 10 μm/s, the application of the magnetic field destroyed the primary NiAl dendrite array and caused the occurrence of columnar-to-equiaxed transition (CET) of the NiAl dendrites. The volume fraction of primary dendrites also decreased. In addition, the width of intercellular/interdendritic regions decreased in cellular/dendritic eutectic structures when directionally solidified under the magnetic field. The above results should be attributed to the combined action of the thermoelectric magnetic force and the thermoelectric magnetic convection.

Magnetostrictive gradient in Tb0.27Dy0.73Fe1.95 induced by high magnetic field gradient applied during solidification

2016 ◽  
Vol 09 (01) ◽  
pp. 1650003 ◽  
Author(s):  
Pengfei Gao ◽  
Tie Liu ◽  
Meng Dong ◽  
Yi Yuan ◽  
Kai Wang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Gradient ◽  
High Magnetic Field ◽  
Applied Magnetic Field ◽  
Magnetic Field Gradient ◽  
Gradient Distribution ◽  
Field Gradients ◽  
Magnetic Field Gradients ◽  
The Magnetic Field

We investigated how high magnetic field gradients affected the magnetostrictive performance of Tb[Formula: see text]Dy[Formula: see text]Fe[Formula: see text] during solidification. At high applied magnetic field gradients, the magnetostriction exhibited a gradient distribution throughout the alloy. Increasing the magnetic field gradient also increased the magnetostriction gradient. We attributed the graded magnetostrictive performance to the gradient distribution of (Tb, Dy)Fe2 phase in the alloy and its orientation.

Characteristics of Recrystallization Texture Evolution in High Magnetic Field for Interstitial Free (IF) Steel Sheet

2005 ◽  
Vol 495-497 ◽  
pp. 465-470 ◽  
Author(s):  
Chang Shu He ◽  
Yu Dong Zhang ◽  
X. Zhao ◽  
Liang Zuo ◽  
Claude Esling
Keyword(s):  
Magnetic Field ◽  
High Magnetic Field ◽  
Recrystallization Texture ◽  
Steel Sheet ◽  
Texture Evolution ◽  
Interstitial Free ◽  
If Steel ◽  
Direction Parallel ◽  
The Magnetic Field ◽  
If Steel Sheet

High magnetic field is applied with the field direction parallel to the rolling direction during annealing of a cold rolled IF steel sheet. Results of X-ray ODF analysis show that, magnetic field annealing retards the normal recrystallization texture evolution for the IF steel sheet. It is worth noting that an abnormal increase of orientation intensity at {100}<110> is found after magnetic annealing for 25min at 650°C. When the magnetic field strength is increased from 10 Tesla to 14 Tesla, the a-fiber is further strengthened, especially the {100}<110> component. Combined with EBSD analysis results, it is considered that the magnetic field does not change the mechanism of recrystallization texture evolution for the IF steel sheet in the present case.

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