457 research outputs found
Stochastic gravitational-wave background from spin loss of black holes
Although spinning black holes are shown to be stable in vacuum in general
relativity, there exists exotic mechanisms that can convert the spin energy of
black holes into gravitational waves. Such waves may be very weak in amplitude,
since the spin-down could take a long time, and a direct search may not be
feasible. We propose to search for the stochastic background associated with
the spin-down, and we relate the level of this background to the formation rate
of spinning black holes from the merger of binary black holes, as well as the
energy spectrum of waves emitted by the spin-down process. We argue that
current LIGO-Virgo observations are not inconsistent with the existence of a
spin-down process, as long as it is slow enough. On the other hand, the
background may still exist as long as a moderate fraction of spin energy is
emitted within Hubble time. This stochastic background could be one interesting
target of next generation GW detector network, such as LIGO Voyager, and could
be extracted from total stochastic background
Determining the nature of white dwarfs from low-frequency gravitational waves
An extreme-mass-ratio system composed of a white dwarf (WD) and a massive
black hole can be observed by the low-frequency gravitational wave detectors,
such as the Laser Interferometer Space Antenna (LISA). When the mass of the
black hole is around , the WD will be disrupted by the
tidal interaction at the final inspiraling stage. The event position and time
of the tidal disruption of the WD can be accurately determined by the
gravitational wave signals. Such position and time depend upon the mass of the
black hole and especially on the density of the WD. We present the theory by
using LISA-like gravitational wave detectors, the mass-radius relation and then
the equations of state of WDs could be strictly constrained (accuracy up to
). We also point out that LISA can accurately predict the disruption
time of a WD, and forecast the electromagnetic follow-up of this tidal
disruption event.Comment: 7 pages, 2 figure
The wave nature of continuous gravitational waves from microlensing
Gravitational wave predicted by General Relativity is the transverse wave of
spatial strain. Several gravitational waveform signals from binary black holes
and from a binary neutron star system accompanied by electromagnetic
counterparts have been recorded by advanced LIGO and advanced Virgo. In analogy
to light, the spatial fringes of diffraction and interference should also exist
as the important features of gravitational waves. We propose that observational
detection of such fringes could be achieved through gravitational lensing of
continuous gravitational waves. The lenses would play the role of the
diffraction barriers. Considering peculiar motions of the observer, the lens
and the source, the spatial amplitude variation of diffraction or interference
fringes should be detectable as an amplitude modulation of monochromatic
gravitational signal.Comment: Accepted for publication in The Astrophysical Journa
Galaxy evolution by chemical and SED model
2010/2011In this thesis, we have studied the ISM, QSO, LGRB hosts and LBGs by galactic
chemical evolution and spectro-photometric models. We also tested the so-called mono-
lithic scenario of elliptical galaxies formation. Here we present the main results of this work:
1. The star formation history is the main driver of galaxy evolution. The predictions
of elliptical chemical evolution models with the so-called monolithic scenario of
elliptical galaxies formation are consistent with the data of high redshift LBGs and
QSOs. Both the infall and the star formation timescale are suggested to decrease
with galactic mass. This scenario is confirmed by the spectro-photometric models
by reproducing the average SED of MIPS-LBGs. This so-called â downsizingâ of
SFH is consistent with many observations.
2. Our M = 1012Mâ elliptical model can reproduce super-massive BH mass, stellar
mass, gas mass and dust mass of one of the most distant QSO ever observed
J1148+5251 (z â 6.4). The same model can also reproduce [N/C] versus [C/H]
and [Si/C] versus [C/H] of the NLRs in QSO hosts. The very high C abundance
observed in these QSOs can be explained only by assuming yields with mass loss
from massive stars with a strong dependence on metallicity, as those of Maeder
(1992)
3. Our elliptical models suggested the LBGs at hight redshift are likely to be young
(age < 0.6 Gyr) ellipticals. This picture is consist with the results of spectro-
photometric models. By chemical evolution models, we found that, LBGs in A-
MAZE and LSD samples, CB 58, Clone and Cosmic Horseshoe are of intermediate
mass(1010
â 3 · 1010Mâ). Our elliptical model for 3 · 1010Mâ well reproduces the
[O/H] abundance as a function of redshift for these LBGs. By spectro-photometric
models, we found that theMIPS-LBGs are more massive (⌠1011Mâ). Our spectro-
photometric models for 1011Mâ well reproduce the average SED of MIPS-LBGs.
4. Our elliptical models suggested that if the observed high-redshift LGRB-DLAs and
local LGRB host galaxies belonged to an evolutionary sequence, they should be
irregulars with a common galaxy-formation redshift as high as zf = 10, observed
at different phases of their evolution. We cannot exclude, however, that they
correspond to the outermost regions of spiral disks, since their properties are similar
to those of irregulars. Elliptical galaxies cannot be LGRB host galaxies at low
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redshift and that they are very unlikely hosts of LGRB-DLAs even at high redshift,
because of their rapid chemical enrichment at high redshift following the occurrence
of a galactic wind several Gyrs ago and subsequent passive evolution.
5. Our elliptical models suggested that a dust mass-stellar mass relation exists, with
more massive galaxies attaining a higher dust content at earlier time. The dust
evolution in ISM make the main contribution for the large amount of dust in high
redshift QSOs. QSO itself produced dust but this production appears negligible
compared to that from stellar sources, unless one focuses on the very central regions
at times very close to the galactic wind onset.
6. The dust mass estimation in the average MIPS-LBGs based on the combination
of our elliptical models and spectro-photometric models is not consistent with
the one based on simple temperature grey-body fitting. The Milky Way dust
parameters can not reproduce the average SED of MIPS-LBGs with the SFHs
from chemical evolution models. The more dense dusty environments and flatter
dust size distributions are needed to reproduce the average SED of MIPS-LBGs
with these SFHs.
7. IGIMF of starburst galaxies can improve the [α/Fe] ratios, however it still can-
not solve the discrepancy between predictions and data. Dust effect is the most
plausible solution.XXIV Ciclo198
Precision cosmology from future lensed gravitational wave and electromagnetic signals
The standard siren approach of gravitational wave cosmology appeals to the
direct luminosity distance estimation through the waveform signals from
inspiralling double compact binaries, especially those with electromagnetic
counterparts providing redshifts. It is limited by the calibration
uncertainties in strain amplitude and relies on the fine details of the
waveform. The Einstein Telescope is expected to produce
gravitational wave detections per year, of which will be lensed. Here
we report a waveform-independent strategy to achieve precise cosmography by
combining the accurately measured time delays from strongly lensed
gravitational wave signals with the images and redshifts observed in the
electromagnetic domain. We demonstrate that just 10 such systems can provide a
Hubble constant uncertainty of for a flat Lambda Cold Dark Matter
universe in the era of third generation ground-based detectors
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