The linear polarization produced by scattering processes in the spectral lines of the IR triplet of Ca II can be observed near the edge of the solar disk. The cause of this polarization was considered a true enigma until the year 2003, in which IAC researchers could carry out sophisticated calculations based on the quantum theory of the spectral line polarization. In this way, they could demonstrate that the physical origin of the enigmatic polarization is the presence of "atomic polarization" in the lower levels of such spectral lines, which produces dichroism (i.e., selective absorption of the polarization components of the radiation beam that propagates towards the observer) without the need of a magnetic field. This result is important because it provides a way to detect extremely weak magnetic fields in Astrophysics, both in the solar atmosphere and in other astrophysical plasmas (e.g., in the atmospheres of supernovae).
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The development of the latest generation of Imaging Atmospheric Cherenkov Telescopes (IACTs) over recent decades has led to the discovery of new extreme astrophysical phenomena in the very-high-energy (VHE, E > 100 GeV) gamma-ray regime. Time-domain and multi-messenger astronomy are inevitably connected to the physics of transient VHE emitters, which show unexpected (and mostly unpredictable) flaring or exploding episodes at different timescales. These transients often share the physical processes responsible for the production of the gamma-ray emission, through cosmic-ray accelerationAdvertised on
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The cosmic evolution of the barred galaxy population provides key information about the secular evolution of galaxies and the settling of rotationally dominated discs. We study the bar fraction in the SMACSJ0723.37323 (SMACS0723) cluster of galaxies at z = 0.39 using the Early Release Observations obtained with the NIRCam instrument mounted on the JWST telescope. We visually inspected all cluster member galaxies using the images from the NIRCam F200W filter. We classified the galaxies into ellipticals and discs and determine the presence of a bar. The cluster member selection was based on aAdvertised on
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Accretion disks around compact objects are expected to enter an unstable phase at high luminosity. One instability may occur when the radiation pressure generated by accretion modifies the disk viscosity, resulting in the cyclic depletion and refilling of the inner disk on short timescales. Such a scenario, however, has only been quantitatively verified for a single stellar-mass black hole. Although there are hints of these cycles in a few isolated cases, their apparent absence in the variable emission of most bright accreting neutron stars and black holes has been a continuing puzzle. HereAdvertised on