12,103 research outputs found
Born-Infeld magnetars: larger than classical toroidal magnetic fields and implications for gravitational-wave astronomy
Magnetars are neutron stars presenting bursts and outbursts of X- and
soft-gamma rays that can be understood with the presence of very large magnetic
fields. Thus, nonlinear electrodynamics should be taken into account for a more
accurate description of such compact systems. We study that in the context of
ideal magnetohydrodynamics and make a realization of our analysis to the case
of the well-known Born-Infeld (BI) electromagnetism in order to come up with
some of its astrophysical consequences. We focus here on toroidal magnetic
fields as motivated by already known magnetars with low dipolar magnetic fields
and their expected relevance in highly magnetized stars. We show that BI
electrodynamics leads to larger toroidal magnetic fields when compared to
Maxwell's electrodynamics. Hence, one should expect higher production of
gravitational waves (GWs) and even more energetic giant flares from nonlinear
stars. Given current constraints on BI's scale field, giant flare energetics
and magnetic fields in magnetars, we also find that the maximum magnitude of
magnetar ellipticities should be . Besides, BI electrodynamics
may lead to a maximum increase of order of the GW energy radiated
from a magnetar when compared to Maxwell's, while much larger percentages may
arise for other physically motivated scenarios. Thus, nonlinear theories of the
electromagnetism might also be probed in the near future with the improvement
of GW detectors.Comment: 8 pages, no figures, accepted for publication in The European
Physical Journal C (EPJC
Abundance patterns in early-type galaxies: is there a 'knee' in the [Fe/H] vs. [alpha/Fe] relation?
Early-type galaxies (ETGs) are known to be enhanced in alpha elements, in
accordance with their old ages and short formation timescales. In this
contribution we aim to resolve the enrichment histories of ETGs. This means we
study the abundance of Fe ([Fe/H]) and the alpha-element groups ([alpha/Fe])
separately for stars older than 9.5 Gyr ([Fe/H]o, [alpha/Fe]o) and for stars
between 1.5 and 9.5 Gyr ([Fe/H]i, [alpha/Fe]i). Through extensive simulation we
show that we can indeed recover the enrichment history per galaxy. We then
analyze a spectroscopic sample of 2286 early-type galaxies from the SDSS
selected to be ETGs. We separate out those galaxies for which the abundance of
iron in stars grows throughout the lifetime of the galaxy, i.e. in which
[Fe/H]o < [Fe/H]i. We confirm earlier work where the [Fe/H] and [alpha/Fe]
parameters are correlated with the mass and velocity dispersion of ETGs. We
emphasize that the strongest relation is between [alpha/Fe] and age. This
relation falls into two regimes, one with a steep slope for old galaxies and
one with a shallow slope for younger ETGs. The vast majority of ETGs in our
sample do not show the 'knee' in the plot of [Fe/H] vs. [alpha/Fe] commonly
observed in local group galaxies. This implies that for the vast majority of
ETGs, the stars younger than 9.5 Gyrs are likely to have been accreted or
formed from accreted gas. The properties of the intermediate-age stars in
accretion-dominated ETGs indicate that mass growth through late (minor) mergers
in ETGs is dominated by galaxies with low [Fe/H] and low [alpha/Fe]. The method
of reconstructing the stellar enrichment histories of ETGs introduced in this
paper promises to constrain the star formation and mass assembly histories of
large samples of galaxies in a unique way.Comment: 22 pages, 25 figures, accepted for publication by A&
A agricultura e o desenvolvimento do interior
A agricultura tem e terá um papel fundamental no desenvolvimento do interior. Para atrair investimento para o interior, na agricultura ou em outro sector, é necessário criar-lhe condições favoráveis, o que exige do poder político conhecimento, capacidade e coragem para discriminar positivamente o interior
Nuclear magnetic resonance measurements reveal the origin of the Debye process in monohydroxy alcohols
Monohydroxy alcohols show a structural relaxation and at longer time scales a
Debye-type dielectric peak. From spin-lattice relaxation experiments using
different nuclear probes an intermediate, slower-than-structural dynamics is
identified for n-butanol. Based on these findings and on diffusion
measurements, a model of self-restructuring, transient chains is proposed. The
model is demonstrated to explain consistently the so far puzzling observations
made for this class of hydrogen-bonded glass forming liquids.Comment: 4 pages, 4 figure
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