分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Intermediate/Extreme mass ratio inspiral (I/EMRI) system provides a good tool to test the nature of gravity in strong field. Based on the method of osculating orbits, we compute the orbital evolutions of I/EMRIs on quasi-elliptic orbits in both Einstein's general relativity and Brans-Dicke theory. The extra monopolar and dipolar channels in Brans-Dicke theory accelerate the orbital decay, so it is important to consider the effects of monopolar and dipolar emissions on the waveform. With the help of accurate orbital motion, we generate waveform templates which include both monopolar and dipolar contributions for I/EMRIs on eccentric orbits in Brans-Dicke theory. With a two-year observation of gravitational waves emitted from I/EMRIs by LISA, we get the most stringent constraint on the Brans-Dicke coupling parameter $\omega_0>10^6$.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Using the analytic, static and spherically symmetric metric for a Schwarzschild black hole immersed in dark matter (DM) halos with Hernquist type density distribution, we derive analytic formulae for the orbital period and orbital precession, the evolutions of the semi-latus rectum and the eccentricity for eccentric EMRIs with the environment of DM halos. We show how orbital precessions are decreased and even reverse the direction if the density of DM halo is large enough. The presence of local DM halos slows down the decrease of the semi-latus rectum and the eccentricity. Comparing the number of orbital cycles with and without DM halos over one-year evolution before the merger, we find that DM halos with the compactness as small as $10^{-4}$ can be detected. By calculating the mismatch between GW waveforms with and without DM halos, we show that we can use GWs from EMRIs in the environments of galaxies to test the existence of DM halos and detect the compactness as small as $10^{-5}$.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Using the analytic, static and spherically symmetric metric for a Schwarzschild black hole immersed in dark matter (DM) halos with Hernquist type density distribution, we derive analytic formulae for the orbital period and orbital precession, the evolutions of the semi-latus rectum and the eccentricity for eccentric EMRIs with the environment of DM halos. We show how orbital precessions are decreased and even reverse the direction if the density of DM halo is large enough. The presence of local DM halos slows down the decrease of the semi-latus rectum and the eccentricity. Comparing the number of orbital cycles with and without DM halos over one-year evolution before the merger, we find that DM halos with the compactness as small as $10^{-4}$ can be detected. By calculating the mismatch between GW waveforms with and without DM halos, we show that we can use GWs from EMRIs in the environments of galaxies to test the existence of DM halos and detect the compactness as small as $10^{-5}$.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The accurate sky localization of gravitational wave (GW) sources is an important scientific goal for space-based GW detectors. Due to the effects of gravity on three spacecrafts, it is hard to maintain the equality of the arm length, so the time-delay interferometry (TDI) method is needed to cancel out the laser frequency noise for space-based GW detectors. By considering the first-generation TDI combination, we employ the Fisher information matrix to study the accuracy of sky localizations for future space-based GW detectors and their combined network. The main difference between future space-based GW detectors includes the time-changing orientation of the detector plane, the arm length, the orbital period of spacecrafts and the noise curve. We study the effects of these factors on the accuracy of source localization at different frequencies. We find that the amplitude modulation caused by the rotation of the detector plane can help LISA and Taiji not only to improve the accuracy of source localization but also to enlarge the sky coverage at frequencies below 1 mHz. As the frequency of monochromatic GWs increases, the Doppler modulation becomes dominate and the equatorial pattern appears in the sky map. The effect of arm length on the angular resolution mainly comes from the noise curve and it is almost the same for both heliocentric and geocentric constellations. The orbital period of the spacecrafts has little effect on the angular resolutions. The improvement on the angular resolutions by the network of combined detectors is small compared with a single detector and the angular resolutions are almost the same with and without the TDI combination.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Intermediate/Extreme mass ratio inspiral (I/EMRI) system provides a good tool to test the nature of gravity in strong field. Based on the method of osculating orbits, we compute the orbital evolutions of I/EMRIs on quasi-elliptic orbits in both Einstein's general relativity and Brans-Dicke theory. The extra monopolar and dipolar channels in Brans-Dicke theory accelerate the orbital decay, so it is important to consider the effects of monopolar and dipolar emissions on the waveform. With the help of accurate orbital motion, we generate waveform templates which include both monopolar and dipolar contributions for I/EMRIs on eccentric orbits in Brans-Dicke theory. With a two-year observation of gravitational waves emitted from I/EMRIs by LISA, we get the most stringent constraint on the Brans-Dicke coupling parameter $\omega_0>10^6$.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The accurate sky localization of gravitational wave (GW) sources is an important scientific goal for space-based GW detectors. Due to the effects of gravity on three spacecrafts, it is hard to maintain the equality of the arm length, so the time-delay interferometry (TDI) method is needed to cancel out the laser frequency noise for space-based GW detectors. By considering the first-generation TDI combination, we employ the Fisher information matrix to study the accuracy of sky localizations for future space-based GW detectors and their combined network. The main difference between future space-based GW detectors includes the time-changing orientation of the detector plane, the arm length, the orbital period of spacecrafts and the noise curve. We study the effects of these factors on the accuracy of source localization at different frequencies. We find that the amplitude modulation caused by the rotation of the detector plane can help LISA and Taiji not only to improve the accuracy of source localization but also to enlarge the sky coverage at frequencies below 1 mHz. As the frequency of monochromatic GWs increases, the Doppler modulation becomes dominate and the equatorial pattern appears in the sky map. The effect of arm length on the angular resolution mainly comes from the noise curve and it is almost the same for both heliocentric and geocentric constellations. The orbital period of the spacecrafts has little effect on the angular resolutions. The improvement on the angular resolutions by the network of combined detectors is small compared with a single detector and the angular resolutions are almost the same with and without the TDI combination.
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