2006.01161
The CMB Rayleigh-Jeans tail as a detector of high-frequency gravitational waves
Domcke, Garcia-Cely
In the presence of magnetic fields, gravitational waves are converted into photons and vice versa. We demonstrate that this conversion leads to a distortion of the cosmic microwave background (CMB), which can serve as a detector for MHz to GHz gravitational wave sources active before reionization. The measurements of the radio telescope EDGES can be cast as a bound on the gravitational wave amplitude, $h_c < 10^{-21} (10^{-12})$ at 78 MHz, for the strongest (weakest) cosmic magnetic fields allowed by current astrophysical and cosmological constraints. Similarly, the results of ARCADE 2 imply $h_c < 10^{-24} (10^{-14})$ at $3 - 30$ GHz. For the strongest magnetic fields, these constraints exceed current laboratory constraints by about seven orders of magnitude. Future advances in 21cm astronomy may conceivably push these bounds below the sensitivity of cosmological constraints on the total energy density of gravitational waves.
The CMB Rayleigh-Jeans tail as a detector of high-frequency gravitational waves
Domcke, Garcia-Cely
In the presence of magnetic fields, gravitational waves are converted into photons and vice versa. We demonstrate that this conversion leads to a distortion of the cosmic microwave background (CMB), which can serve as a detector for MHz to GHz gravitational wave sources active before reionization. The measurements of the radio telescope EDGES can be cast as a bound on the gravitational wave amplitude, $h_c < 10^{-21} (10^{-12})$ at 78 MHz, for the strongest (weakest) cosmic magnetic fields allowed by current astrophysical and cosmological constraints. Similarly, the results of ARCADE 2 imply $h_c < 10^{-24} (10^{-14})$ at $3 - 30$ GHz. For the strongest magnetic fields, these constraints exceed current laboratory constraints by about seven orders of magnitude. Future advances in 21cm astronomy may conceivably push these bounds below the sensitivity of cosmological constraints on the total energy density of gravitational waves.
2006.01269
Accretion disk luminosity for black holes surrounded by dark matter
Boshkayev, et al
We consider the observational properties of a static black hole space-time immersed in a dark matter envelope. We thus investigate how the modifications to geometry, induced by the presence of dark matter affect the luminosity of the black hole's accretion disk. We show that the same disk's luminosity produced by a black hole in vacuum may be produced by a smaller black hole if surrounded by dark matter under certain conditions. In particular, we demonstrate that the luminosity of the disk is markedly altered by dark matter's presence, suggesting that mass estimation of distant super-massive black holes may be changed if they are immersed in dark matter. We argue that a similar effect holds in more realistic scenarios and we discuss about the refractive index related to dark matter lensing. Hence we show how this may help explain the observed luminosity of super-massive black holes in the early universe.
2006.01814
Influence of the Galactic gravitational field on the positional accuracy of extragalactic sources. II Observational appearances and detectability
Larchenkova, et al
We consider a possibility of detecting the jitter effect of apparent celestial positions of distant sources due to local fluctuations of the Galaxy gravitational field. It is proposed to observe two samples of extragalactic sources (target and control) in different sky directions using the high-precision radio interferometry. It is shown that on a scale of ~2 years, it is possible to detect a systematic increase in the standard deviation of measured arc lengths of pairs of target sources compared to the control ones at the $3\sigma$-level if the accuracy of differential astrometric observations is around 10 $\mu$as. For the current state-of-the-art accuracy of 30 $\mu$as achieved at the KVN or VERA interferometers, which have shorter baselines in comparison with VLBI, the target and control samples will differ only at the 2$\sigma$-level on the scale of 10 years. To achieve the $3\sigma$-level on this time interval, it is necessary to improve the accuracy up to ~20 $\mu$as. Other possible effects that can also affect the arc length measurements between two sources are discussed, and an observational strategy to minimize them is suggested.
2006.01826
Observational support for massive black hole formation driven by runaway stellar collisions in galactic nuclei
Escala
We explore here an scenario for massive black hole formation driven by stellar collisions in galactic nuclei, proposing a new formation regime of global instability in nuclear stellar clusters triggered by runaway stellar collisions. Using order of magnitude estimations, we show that observed nuclear stellar clusters avoid the regime where stellar collision are dynamically relevant over the whole system, while resolved detections of massive black holes are well into such collision-dominated regime. We interpret this result in terms of massive black holes and nuclear stellar clusters being different evolutionary paths of a common formation mechanism, unified under the standard terminology of being both central massive objects. We propose a formation scenario where central massive objects more massive than $\rm \sim 10^8 \, M_O$ will be too dense (in virial equilibrium) to be globally stable against stellar collisions and most of its mass will collapse towards the formation of a massive black hole. Contrarily, this will only be the case at the core of less dense central massive objects leading to the formation of black holes with much lower black hole efficiencies $\rm \epsilon_{BH} = \frac{M_{BH}}{M_{CMO}}$, with these efficiencies $\rm \epsilon_{BH}$ drastically growing for central massive objects more massive than $\rm \sim 10^7 \,M_O$, approaching unity around $\rm M_{CMO} \sim 10^8 \, M_O$. We show that the proposed scenario successfully explain the relative trends observed in the masses, efficiencies and scaling relations between massive black holes and nuclear stellar cluster
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