Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userProbing the Nature of Black Holes: Deep in the mHz Gravitational-Wave Sky
72
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Black holes are unique among astrophysical sources: they are the simplest macroscopic objects in the Universe, and they are extraordinary in terms of their ability to convert energy into electromagnetic and gravitational radiation. Our capacity to probe their nature is limited by the sensitivity of our detectors. The LIGO/Virgo interferometers are the gravitational-wave equivalent of Galileos telescope. The first few detections represent the beginning of a long journey of exploration. At the current pace of technological progress, it is reasonable to expect that the gravitational-wave detectors available in the 2035-2050s will be formidable tools to explore these fascinating objects in the cosmos, and space-based detectors with peak sensitivities in the mHz band represent one class of such tools. These detectors have a staggering discovery potential, and they will address fundamental open questions in physics and astronomy. Are astrophysical black holes adequately described by general relativity? Do we have empirical evidence for event horizons? Can black holes provide a glimpse into quantum gravity, or reveal a classical breakdown of Einsteins gravity? How and when did black holes form, and how do they grow? Are there new long-range interactions or fields in our universe, potentially related to dark matter and dark energy or a more fundamental description of gravitation? Precision tests of black hole spacetimes with mHz-band gravitational-wave detectors will probe general relativity and fundamental physics in previously inaccessible regimes, and allow us to address some of these fundamental issues in our current understanding of nature.
rate research
Read More
Third generation gravitational-wave (GW) detectors are expected to detect a large number of binary black holes (BBHs) to large redshifts, opening up an independent probe of the large scale structure using their clustering. This probe will be complementary to the probes using galaxy clustering -- GW events could be observed up to very large redshifts ($z sim 10$) although the source localization will be much poorer at large distances ($sim$ tens of square degrees). We explore the possibility of probing the large scale structure from the spatial distribution of the observed BBH population, using their two-point (auto)correlation function. We find that we can estimate the bias factor of population of BBH (up to $z sim 1$) with a few years of observations with these detectors. Our method relies solely on the source-location posteriors obtained the GW events and does not require any information from electromagnetic observations. This will help in identifying the type of galaxies that host the BBH population, thus shedding light on their origins.
Gravitational waves can probe the existence of planetary-mass primordial black holes. Considering a mass range of $[10^{-7}-10^{-2}]M_odot$, inspiraling primordial black holes could emit either continuous gravitational waves, quasi-monochromatic signals that last for many years, or transient continuous waves, signals whose frequency evolution follows a power law and last for $mathcal{O}$(hours-months). We show that primordial black hole binaries in our galaxy may produce detectable gravitational waves for different mass functions and formation mechanisms. In order to detect these inspirals, we adapt methods originally designed to search for gravitational waves from asymmetrically rotating neutron stars. The first method, the Frequency-Hough, exploits the continuous, quasi-monochromatic nature of inspiraling black holes that are sufficiently light and far apart such that their orbital frequencies can be approximated as linear with a small spin-up. The second method, the Generalized Frequency-Hough, drops the assumption of linearity and allows the signal frequency to follow a power-law evolution. We explore the parameter space to which each method is sensitive, derive a theoretical sensitivity estimate, determine optimal search parameters and calculate the computational cost of all-sky and directed searches. We forecast limits on the abundance of primordial black holes within our galaxy, showing that we can constrain the fraction of dark matter that primordial black holes compose, $f_{rm PBH}$, to be $f_{rm PBH}lesssim 1$ for chirp masses between $[4times 10^{-5}-10^{-3}]M_odot$ for current detectors. For the Einstein Telescope, we expect the constraints to improve to $f_{rm PBH}lesssim 10^{-2}$ for chirp masses between [$10^{-4}-10^{-3}]M_odot$.
Merging compact black-hole (BH) binaries are likely to exist in the nuclear star clusters around supermassive BHs (SMBHs), such as Sgr A$^ast$. They may also form in the accretion disks of active galactic nuclei. Such compact binaries can emit gravitational waves (GWs) in the low-frequency band (0.001-1 Hz) that are detectable by several planned space-borne GW observatories. We show that the orbital axis of the compact binary may experience significant variation due to the frame-dragging effect associated with the spin of the SMBH. The dynamical behavior of the orbital axis can be understood analytically as a resonance phenomenon. We show that rate of change of the binary orbital axis encodes the information on the spin of the SMBH. Therefore detecting GWs from compact binaries around SMBHs, particularly the modulation of the waveform associated with the variation of the binary orbital axis, can provide a new probe on the spins of SMBHs.
The recently discovered burst of gravitational waves GW150914 provides a good new chance to verify the current view on the evolution of close binary stars. Modern population synthesis codes help to study this evolution from two main sequence stars up to the formation of two final remnant degenerate dwarfs, neutron stars or black holes [Massevich 1988]. To study the evolution of the GW150914 predecessor we use the Scenario Machine code presented by [Lipunov 1996]. The scenario modelling conducted in this study allowed to describe the evolution of systems for which the final stage is a massive BH+BH merger. We find that the initial mass of the primary component can be $100div 140 M_{odot}$ and the initial separation of the components can be $50div 350 R_{odot}$. Our calculations show the plausibility of modern evolutionary scenarios for binary stars and the population synthesis modelling based on it.
We present the first numerical simulations of gravitational waves (GWs) passing through a potential well generated by a compact object in 3-D space, with a realistic source waveform derived from numerical relativity for the merger of two black holes. Unlike the previous work, our analyses focus on the time-domain, in which the propagation of GWs is a well-posed initial-value problem for the hyperbolic equations with rigorous rooting in mathematics and physics. Based on these simulations, we investigate for the first time in realistic 3-D space how the wave nature of GWs affects the speed and waveform of GWs in a potential well. We find that GWs travel faster than the prediction of the Shapiro time-delay in the geometric limit due to the effects of diffraction and wavefront geometry. As the wave speed of GWs is closely related to the locality and wavefront geometry of GWs, which are inherently difficult to be addressed in the frequency-domain, our analyses in the time-domain, therefore, provide the first robust analyses to date on this issue based on solid physics. Moreover, we also investigate, for the first time, the interference between the incident and the scattered waves (the echoes of the incident waves). We find that such interference makes the total lensed waveforms dramatically different from those of the original incident ones not only in the amplitude but also in the phase and pattern, especially for signals near the merger of the two back holes.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
