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 $10^4 \sim 10^5 M_\odot$, 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 $0.1\%$). 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 “ downsizing” of SFH is consistent with many observations. 2. Our M = 1012M⊙ 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 ≃ 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 − 3 · 1010M⊙). Our elliptical model for 3 · 1010M⊙ 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 (∼ 1011M⊙). Our spectro- photometric models for 1011M⊙ 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 111 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 $10^4-10^5$ gravitational wave detections per year, $50-100$ 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 $0.68\%$ for a flat Lambda Cold Dark Matter universe in the era of third generation ground-based detectors