6,657 research outputs found
Merging massive black holes: the right place and the right time
The LIGO/Virgo detections of gravitational waves from merging black holes of
30 solar mass suggest progenitor stars of low metallicity
(Z/Z). In this talk I will provide constrains on where
the progenitors of GW150914 and GW170104 may have formed, based on advanced
models of galaxy formation and evolution combined with binary population
synthesis models. First I will combine estimates of galaxy properties
(star-forming gas metallicity, star formation rate and merger rate) across
cosmic time to predict the low redshift BBH merger rate as a function of
present day host galaxy mass, formation redshift of the progenitor system and
different progenitor metallicities. I will show that the signal is dominated by
binaries formed at the peak of star formation in massive galaxies with and
binaries formed recently in dwarf galaxies. Then, I will present what very high
resolution hydrodynamic simulations of different galaxy types can learn us
about their black hole populations.Comment: Proceeding of IAU Symposium 338 : "Gravitational Waves Astrophysics :
Early results from GW searches and EM counterparts
Colliding wind binaries and gamma-ray binaries : relativistic version of the RAMSES code
Gamma-ray binaries are colliding wind binaries (CWB) composed of a massive
star a non-accreting pulsar with a highly relativistic wind. Particle
acceleration at the shocks results in emission going from extended radio
emission to the gamma-ray band. The interaction region is expected to show
common features with stellar CWB. Performing numerical simulations with the
hydrodynamical code RAMSES, we focus on their structure and stability and find
that the Kelvin-Helmholtz instability (KHI) can lead to important mixing
between the winds and destroy the large scale spiral structure. To investigate
the impact of the relativistic nature of the pulsar wind, we extend RAMSES to
relativistic hydrodynamics (RHD). Preliminary simulations of the interaction
between a pulsar wind and a stellar wind show important similarities with
stellar colliding winds with small relativistic corrections.Comment: Proceeding of the 5th International Symposium on High-Energy
Gamma-Ray Astronomy (Gamma2012). arXiv admin note: text overlap with
arXiv:1212.404
Short article: When are moving images remembered better? Study–test congruence and the dynamic superiority effect
It has previously been shown that moving images are remembered better than static ones. In two experiments, we investigated the basis for this dynamic superiority effect. Participants studied scenes presented as a single static image, a sequence of still images, or a moving video clip, and 3 days later completed a recognition test in which familiar and novel scenes were presented in all three formats. We found a marked congruency effect: For a given study format, accuracy was highest when test items were shown in the same format. Neither the dynamic superiority effect nor the study–test congruency effect was affected by encoding (Experiment 1) or retrieval (Experiment 2) manipulations, suggesting that these effects are relatively impervious to strategic control. The results demonstrate that the spatio-temporal properties of complex, realistic scenes are preserved in long-term memory. </jats:p
Thermal H/D exchange in polar ice - deuteron scrambling in space
We have investigated the thermally induced proton/deuteron exchange in mixed
amorphous HO:DO ices by monitoring the change in intensity of
characteristic vibrational bending modes of HO, HDO, and DO with time
and as function of temperature. The experiments have been performed using an
ultra-high vacuum setup equipped with an infrared spectrometer that is used to
investigate the spectral evolution of homogeneously mixed ice upon
co-deposition in thin films, for temperatures in the 90 to 140 K domain. With
this non-energetic detection method we find a significantly lower activation
energy for H/D exchange -- K -- than previously reported. Very
likely this is due to the amorphous nature of the interstellar ice analogues
involved. This provides reactive timescales ( K)
fast enough for the process to be important in interstellar environments.
Consequently, an astronomical detection of DO will be even more challenging
because of its potential to react with HO to form HDO. Furthermore,
additional experiments, along with previous studies, show that proton/deuteron
swapping also occurs in ice mixtures of water with other hydrogen bonded
molecules, in particular on the OH and NH moieties. We conclude that H/D
exchange in ices is a more general process that should be incorporated into ice
models that are applied to protoplanetary disks or to simulate the warming up
of cometary ices in their passage of the perihelion, to examine the extent of
its influence on the final deuteron over hydrogen ratio.Comment: 10 pages, 8 figures, accepted for publication in MNRA
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