Gravitational waves emitted from compact binary coalescence can be subject to wave diffraction if they are gravitationally lensed by an intervening mass clump whose Schwarzschild time scale matches ...the wave period. Waves in the ground-based frequency band f∼10–103 Hz are sensitive to clumps with masses ME∼102–103 M⊙ enclosed within the impact parameter. These can be the central parts of low mass ML∼103–106 M⊙ dark matter halos, which are predicted in cold dark matter scenarios but are challenging to observe. Neglecting finely-tuned impact parameters, we focus on lenses aligned generally on the Einstein scale for which multiple lensed images may not form in the case of an extended lens. In this case, diffraction induces amplitude and phase modulations whose sizes ∼10%–20% are small enough so that standard matched filtering with unlensed waveforms do not degrade, but are still detectable for events with high signal-to-noise ratio. We develop and test an agnostic detection method based on dynamic programming, which does not require a detailed model of the lensed waveforms. For pseudo-Jaffe lenses aligned up to the Einstein radius, we demonstrate that a pair of fully upgraded aLIGO/Virgo detectors can extract diffraction imprints from binary black hole mergers out to zs∼0.2–0.3. The prospect will improve dramatically for a third-generation detector for which binary black hole mergers out to zs∼2–4 will all become valuable sources.
We examine the possibility for the existence of gravitomagnetic monopole (
n
∗
) in M87* by using the results obtained from its first Event Horizon Telescope image. By numerically deducing the shadow ...sizes in Kerr-Taub-NUT (KTN) spacetime, we show that the shadow size increases with increasing
|
n
∗
|
for a fixed Kerr parameter
|
a
∗
|
in case of the KTN black hole, whereas for a KTN naked singularity it increases with increasing
n
∗
for a fixed
a
∗
>
0
if
n
∗
>
-
cot
17
∘
. In general, the asymmetry of shadow shape increases if the central dark object in M87 is a KTN/Kerr naked singularity instead of a KTN/Kerr black hole. We find that a non-zero gravitomagnetic monopole is still compatible with the current EHT observations, in which case the upper limit of
n
∗
cannot be greater than 1.1, i.e.,
n
∗
≲
1.1
for the prograde rotation (
a
∗
>
0
), and the lower limit of
n
∗
cannot be less than
-
1.1
, i.e.,
n
∗
≳
-
1.1
for the retrograde rotation (
a
∗
<
0
). Moreover, if the circularity of the shadow can be measured on a precision of
≲
1
%
, the Kerr and KTN naked singularities can be falsified for M87*.
Semiconductor crystals with well-defined morphology, porous nanostructure, and spatially separated active sites are attractive for use in photocatalysis. This paper describes a controlled synthesis ...of cake-like porous TiO2 photocatalyst with surface-localized doping of copper and cobalt by using a well-defined MIL-125(Ti) metal organic framework as template precursor. The series of the modified TiO2 photocatalysts present the improved activity for photocatalytic CO2 reduction with water vapor. It is found that 1%Cu-doped TiO2 shows an enhanced behavior for breaking CO bonds. In this case, the outcomes are primarily CO and CH4, yielding up to 135.94 and 127.05 μmol, respectively, under the irradiation of simulated sunlight for 3 h. The performance can be further improved by incorporating trace cobalt. Besides the improved property for CO and CH4 production, the selectivity also shifts to high-value hydrocarbons (C2+). The yields for C2H6 and C3H8 can be up to 267.60 and 10.07 μmol, respectively, by using 0.02%Co-1%Cu/TiO2. Our in situ Fourier transform infrared spectra together with theoretical calculations indicate that efficient charge separation on copper and cobalt ions is achieved. This altered charge behavior leads to the generation and enrichment of methyl radicals on the surface of cobalt ions, giving rise to the production of C2+ hydrocarbons. This work demonstrates a vibrant catalyst platform for solar fuel generation by photocatalytic CO2 conversion in water.
Abstract
More than 100 tidal disruption events (TDEs) have been detected at multiple bands, which can be viewed as extreme laboratories to investigate the accretion physics and gravity in the ...immediate vicinity of massive black holes. Future transient surveys are expected to detect several tens of thousands of TDEs, among which a small fraction may be strongly gravitationally lensed by intervening galaxies. In this paper, we statistically estimate the detection rate of lensed TDEs, with dependence on the limiting magnitude of the transient all-sky surveys searching for them. We find that the requisite limiting magnitude for an all-sky transient survey to observe at least 1 yr
−1
is ≳21.3, 21.2, and 21.5 mag in the
u
,
g
, and
z
bands, respectively. If the limiting magnitude of the all-sky survey can reach ∼25–26 mag in the
u
,
g
, and
z
bands, the detection rate can be up to about several tens to hundreds per year. The discovery and identification of the first image of the lensed TDE can be taken as an early warning of the second and other subsequent images, which may enable detailed monitoring of the pre-peak photometry and spectroscopy evolution of the TDE. The additional early-stage information may help to constrain the dynamical and radiation processes involved in the TDEs.
Abstract
Stars can be either disrupted as tidal disruption events (TDEs) or swallowed whole by massive black holes (MBHs) at galactic centers when they approach sufficiently close to these MBHs. In ...this work, we investigate the correlations of such stellar consumption rates with both the MBH mass
M
BH
and the inner slope of the host-galaxy mass density distribution
α
. We introduce a simplified analytical power-law model with a power-law stellar-mass density distribution surrounding MBHs and separate the contributions of two-body relaxation and stellar orbital precession for the stellar orbital angular momentum evolution in nonspherical galaxy potentials. The stellar consumption rates derived from this simplified model can be well consistent with the numerical results obtained with a more realistic treatment of stellar distributions and dynamics around MBHs, providing an efficient way to estimate TDE rates. The origin of the correlations of stellar consumption rates with
M
BH
and
α
is explained by the dependence of this analytical model on those MBH/host-galaxy properties and by the separation of the stellar angular momentum evolution mechanisms. We propose that the strong positive correlation between the rates of stellar consumption due to two-body relaxation and
α
provides one interpretation for the overrepresentation of TDEs found in some rare E+A/poststarburst galaxies. We find high TDE rates for giant stars, up to those for solar-type stars. Understanding the origin of the correlations of the stellar consumption rates will be necessary for obtaining the demographics of MBHs and their host galaxies via TDEs.
Abstract
Pulsar timing arrays (PTAs) are anticipated to detect the stochastic gravitational-wave background (GWB) from supermassive binary black holes (BBHs) as well as the gravitational waves from ...individual BBHs. Recently, a common process signal was reported by several PTAs. In this paper, we investigate the constraints on the BBH population model(s) by current PTA observations and further study the detections of both the GWB and individual BBHs by current and future PTAs. We find that the massive black hole–host galaxy scaling relation, an important ingredient of the BBH population model, is required to either evolve significantly with redshift or have a normalization ∼0.86–1.1 dex higher than the empirical ones if the GWB is the same as the common process signal. For both cases, the estimated detection probability for individual BBHs is too small for a positive detection by current PTAs. By involving either the constrained scaling relations or those empirical ones into the BBH population models, we estimate that the GWB may be detected with a signal-to-noise ratio ≳3 by the China Five-hundred-meter Aperture Spherical radio Telescope PTA (CPTA) and the Square Kilometre Array PTA (SKAPTA) after ∼2–3 (or ∼6–11) yr observation if it is the same as (or 1 order of magnitude lower than) the common process signal. The detection time of individual BBHs by CPTA and SKAPTA is close to that of the GWB detection. We show that the BBH population model can be strongly constrained by the number and property distributions of BBHs to be detected by future PTAs.
ABSTRACT
We investigate the effects of mass transfer and gravitational wave (GW) radiation on the orbital evolution of contact neutron-star–white-dwarf (NS–WD) binaries, and the detectability of ...these binaries by space GW detectors (e.g. Laser Interferometer Space Antenna, LISA; Taiji; Tianqin). A NS–WD binary becomes contact when the WD component fills its Roche lobe, at which the GW frequency ranges from ∼0.0023 to 0.72 Hz for WD with masses ∼0.05–1.4 M⊙. We find that some high-mass NS–WD binaries may undergo direct coalescence after unstable mass transfer. However, the majority of NS–WD binaries can avoid direct coalescence because mass transfer after contact can lead to a reversal of the orbital evolution. Our model can well interpret the orbital evolution of the ultra-compact X-ray source 4U 1820–30. For a 4-yr observation of 4U 1820–30, the expected signal-to-noise-ratio (SNR) in GW characteristic strain is ∼11.0/10.4/2.2 (LISA/Taiji/Tianqin). The evolution of GW frequencies of NS–WD binaries depends on the WD masses. NS–WD binaries with masses larger than 4U 1820–30 are expected to be detected with significantly larger SNRs. For a $(1.4+0.5) \, {\rm M}_{\odot }$ NS–WD binary close to contact, the expected SNR for a one week observation is ∼27/40/28 (LISA/Taiji/Tianqin). For NS–WD binaries with masses of $(1.4+\gtrsim 1.1) \, {\rm M}_{\odot }$, the significant change of GW frequencies and amplitudes can be measured, and thus it is possible to determine the binary evolution stage. At distances up to the edge of the Galaxy (∼100 kpc), high-mass NS–WD binaries will be still detectable with SNR ≳ 1.
ABSTRACT In this paper, we investigate the quality of constraining the spin of the massive black hole (MBH) at the Galactic center (GC) by using full general relativistic simulations of the motion of ...a surrounding star. We obtain the dependence mapping of the spin-induced signals on any spin direction of the MBH for given example stars, which indicates the feasibility to test whether the spin direction is the same as the normal of the young stellar disk located at the GC, and, further, to provide insights into the assembly history of the MBH. We demonstrate the quality of constraining the MBH spin that may be achieved, given any set of the astrometric and the redshift precisions of observational facilities. We find that in the ranges of the astrometric and the velocity precisions with 1-30 as and 0.1-10 , an improvement in astrometric precision would be more effective at improving the quality of constraining the spin than an improvement in velocity precision. We obtain the parameter space of the semimajor axis and the eccentricity for the orbit of the target star that a high-precision constraint on the GC MBH spin can be obtained via the motion of the star. Our results show that the spin of the GC MBH can be constrained with a 1 error 0.1 or even 0.02 by monitoring the orbital motion of a star, if existing as expected, with a semimajor axis 300 au and eccentricity 0.95 over a period shorter than a decade through future facilities.
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