Discovery Of Magnetic Field Research Articles

Discovery of magnetic fields along stacked cosmic filaments as revealed by radio and X-ray emission

ABSTRACT Diffuse filaments connect galaxy clusters to form the cosmic web. Detecting these filaments could yield information on the magnetic field strength, cosmic ray population, and temperature of intercluster gas; yet, the faint and large-scale nature of these bridges makes direct detections very challenging. Using multiple independent all-sky radio and X-ray maps we stack pairs of luminous red galaxies as tracers for cluster pairs. For the first time, we detect an average surface brightness between the clusters from synchrotron (radio) and thermal (X-ray) emission with ≳5σ significance, on physical scales larger than observed to date (${\ge}3$ Mpc). We obtain a synchrotron spectral index of α ≃ −1.0 and estimates of the average magnetic field strength of $30\,\mathrm{ nG} \le B \le 60 $ nG, derived from both equipartition and inverse-Compton arguments, implying a 5–15 per cent degree of field regularity when compared with Faraday rotation measure estimates. While the X-ray detection is inline with predictions, the average radio signal comes out higher than predicted by cosmological simulations and dark matter annihilation and decay models. This discovery demonstrates that there are connective structures between mass concentrations that are significantly magnetized, and the presence of sufficient cosmic rays to produce detectable synchrotron radiation.

Discovery of magnetic fields in the very young, massive stars W601 (NGC 6611) and OI 201 (NGC 2244)

Context. Recent spectropolarimetric observations of Herbig Ae/Be stars have yielded new arguments in favour of a fossil origin for the magnetic fields of intermediate mass stars.

Discovery of magnetic fields in three He variable Bp stars with He and Si spots

AbstractIt is essential for the understanding of stellar structure models of high mass stars to explain why constant stars, nonpulsating chemically peculiar hot Bp stars and pulsating stars co‐exist in the slowly pulsating B stars and β Cephei instability strips. We have conducted a search for magnetic fields in the four Bp stars HD55522, HD105382, HD131120, and HD138769 which previously have been wrongly identified as slowly pulsating B stars. A recent study of these stars using the Doppler Imaging technique revealed that the elements He and Si are inhomogeneously distributed on the stellar surface, causing the periodic variability. Using FORS 1 in spectropolarimetric mode at the VLT, we have acquired circular polarisation spectra to test the presence of a magnetic field in these stars. A variable magnetic field is clearly detected in HD55522 and HD105382, but no evidence for the existence of a magnetic field was found in HD131120. The presence of a magnetic field in HD138769 is suggested by one measurement at 3σ level. We discuss the occurrence of magnetic B stars among the confirmed pulsating B stars and find strong magnetic fields of order kG and oscillations to be mutually exclusive. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Discovery of magnetic fields in the βCephei star ξ1 CMa and in several slowly pulsating B stars

Abstract We present the results of a magnetic survey of a sample of eight β Cephei stars and 26 slowly pulsating B (SPBs) stars with the FOcal Reducer low dispersion Spectrograph at the Very Large Telescope. A weak mean longitudinal magnetic field of the order of a few hundred Gauss is detected in the β Cephei star ξ1CMa and in 13 SPB stars. The star ξ1CMa becomes the third magnetic star among the β Cephei stars. Before our study, the star ζ Cas was the only known magnetic SPB star. All magnetic SPB stars for which we gathered several magnetic field measurements show a field that varies in time. We do not find a relation between the evolution of the magnetic field with stellar age in our small sample. Our observations imply that β Cephei and SPB stars can no longer be considered as classes of non-magnetic pulsators, but the effect of the fields on the oscillation properties remains to be studied.

Discovery of magnetic fields in hot subdwarfs

We present polarisation measurements of sdB and sdO stars using FORS1 on the VLT . The observations were made as part of a project to determine whether magnetic fields in two super-metal-rich stars can explain their extreme abundance peculiarities. Field strengths of up to ~1.5 kG range have been measured at varying levels of significance in each of our six targets, however no clear evidence was found between apparently normal subdwarfs and the metal-rich objects. The origin of the magnetic fields is unknown. We also discuss the implications of our measurements for magnetic flux conservation in late stages of stellar evolution.

Discovery of magnetic fields in central stars of planetary nebulae

For the first time we have directly detected magnetic fields in central stars of planetary nebulae by means of spectro-polarimetry with FORS1 at the VLT. In all four objects of our sample we found kilogauss magnetic fields, in NGC 1360 and LSS 1362 with very high significance, while in EGB 5 and Abell 36 the existence of a magnetic field is probable but with less certainty. This discovery supports the hypothesis that the non-spherical symmetry of most planetary nebulae is caused by magnetic fields in AGB stars. Our high discovery rate demands mechanisms to prevent full conservation of magnetic flux during the transition to white dwarfs.

Discovery of magnetic fields in three short-period AP stars.

Magnetic fields of the order of several hundred gauss have been detected in the short-period Ap stars theta Aur (P=1/sup d/.37), CU Vir (P=0/sup d/.52), and phi Dra (P=1/sup d/.72) using an H..beta.. magnetograph technique. In each case the fields are variable with the periods previously determined from photometry or spectroscopy. The observed magnetic curves are compatible with dipole field geometries on the oblique rotator model. The inferred polodial fields are of the right order of magnitude to suppress thermal circulation currents. In CU Vir, the region of helium deficiency and silicon excess seems to lie near the magnetic equator, a geometry which Strittmatter and Norris predicted would arise during the magnetic braking of an Ap star by a centrifugal wind.

Peculiarity Parameters

Ap stars are peculiar in many aspects. During this century astronomers have been trying to collect data about these and have found a confusing variety of peculiar behaviour even from star to star that Struve stated in 1942 that at least we know that these phenomena are not supernatural. A real push to start deeper theoretical work on Ap stars was given by an additional observational evidence, namely the discovery of magnetic fields on these stars by Babcock (1947). This originated the concept that magnetic fields are the cause for spectroscopic and photometric peculiarities. Great leaps for the astronomical mankind were the Oblique Rotator model by Stibbs (1950) and Deutsch (1954), which by the way provided mathematical tools for the later handling pulsar geometries, anti the discovery of phase coincidence of the extrema of magnetic field, spectrum and photometric variations (e.g. Jarzebowski, 1960).

Magnetism of the moon and meteorites

One of the exciting results of the Apollo program is the observation that all returned lunar samples contain a remanent magnetization. This finding, together with the direct measurement of lunar surface magnetic anomalies [Dyal et al., 1970; Coleman et al., 1972] and the discovery of magnetic fields on Mars [Dolginov et al., 1973] and Mercury [Ness et al., 1974], has provided specific incentive for the study of planetary magnetic fields. The magnetic properties of meteorites attained special importance as the second source of extraterrestrial samples. The study of the remanent magnetization in these samples can provide important information about the role of magnetic fields in the evolution of planetary bodies and the solar system.

Ferromagnetism in White Dwarfs

THE discovery of magnetic fields of up to ≃107 G in two white dwarfs1,2 has stimulated interest in the magnetic properties of high density matter. Discussion largely centres around the theory of Landau Orbital Ferromagnetism3–6 (LOFER), proposed by Canuto et al.3,7, which states that a gas of free electrons can, through its magnetic moment, self consistently maintain a magnetic field B, of order 107−108 G at typical white dwarf densities, even after dissipation has extinguished any external sources (charge drifts) of the magnetic field. Similarly the 1012 G fields expected for pulsars on theoretical grounds8 are comparable with the 1012−1013 G values predicted by LOFER theory for objects at neutron star densities.