Space-based Gravitational Wave Observatories Research Articles

Space-based gravitational wave observatories will be able to use eccentricity to unveil stellar-mass binary black hole formation

Space-based gravitational wave observatories will be able to use eccentricity to unveil stellar-mass binary black hole formation

Design and Analysis of the Two-Impulse Transfer Orbit for a Space-Based Gravitational Wave Observatory

There are plans to set up a space-based gravitational wave observatory that will use an ultra-large-scale laser interferometer in space to detect medium- and low-frequency gravitational waves. Both heliocentric and geocentric formations adopt the method of launching three satellites with one rocket, which has high requirements in terms of the carrying capacity of the rocket. Therefore, a proper transfer design is a prerequisite for achieving space-based gravitational wave detection. In this paper, the transfer orbit for three satellites of the Taiji mission is designed based on the two-impulse transfer model. Moreover, the influence on orbit design of the position of the formation relative to Earth, the initial phase angle of the formation, and the initial time of transfer is analyzed. The Earth-leading and -trailing transfers show opposite patterns in the above three aspects. A smaller velocity increment is required if a proper initial time is selected. After taking into account the stability of the formation, C3, the required velocity increment, transfer time, and the distance to Earth, 20° is determined to be the optimal initial trailing/leading angle.

Laser-induced molecular contamination de-risking activity for the Laser Interferometer Space Antenna.

The Laser Interferometer Space Antenna (LISA) will be the first space-based gravitational wave observatory. LISA uses continuous-wave, infrared laser beams propagating among three widely separated spacecrafts to measure their distances with picometer accuracy via time-delay interferometry. These measurements put very high demands on the laser wavefront and are thus very sensitive to any deposits on laser optics that could be induced by laser-induced molecular contamination (LIMC). In this work, we describe the results of an extensive experimental test campaign assessing LIMC related risks for LISA. We find that the LIMC concern for LISA, even considering the high demands on the laser wavefront, may be greatly reduced compared to that observed at shorter wavelengths or with pulsed laser radiation. This result is very promising for LISA as well as for other space missions using continuous-wave, infrared laser radiation, e.g.,in free space laser communication or quantum key distribution.

Design and performance characterization of a new LISA-like (laser interferometer space antenna-like) gravitational reference sensor and torsion pendulum testbed.

In this paper, we present the design and performance of the upgraded University of Florida torsion pendulum facility for testing inertial sensor technology related to space-based gravitational wave observatories and geodesy missions. In particular, much work has been conducted on inertial sensor technology related to the Laser Interferometer Space Antenna (LISA) space gravitational wave observatory mission. A significant upgrade to the facility was the incorporation of a newly designed and fabricated LISA-like gravitational reference sensor (GRS) based on the LISA Pathfinder GRS. Its LISA-like geometry has allowed us to make noise measurements that are more representative of those in LISA and has allowed for the characterization of the mechanisms of noise induced on a LISA GRS and their underlying physics. Noise performance results and experiments exploring the effect of temperature gradients across the sensor will also be discussed. The LISA-like sensor also includes unique UV light injection geometries for UV LED based charge management. Pulsed and DC charge management experiments have been conducted using the University of Florida charge management group's technology readiness level 4 charge management device. These experiments have allowed for the testing of charge management system hardware and techniques as well as characterizations of the dynamics of GRS test mass charging. The work presented here demonstrates the upgraded torsion pendulum's ability to act as an effective testbed for GRS technology.

Rapid search for massive black hole binary coalescences using deep learning

The coalescences of massive black hole binaries are one of the main targets of space-based gravitational wave observatories. Such gravitational wave sources are expected to be accompanied by electromagnetic emissions. Low latency detection of the massive black hole mergers provides a start point for a global-fit analysis to explore the large parameter space of signals simultaneously being present in the data but at great computational cost. To alleviate this issue, we present a deep learning method for rapidly searching for signals of massive black hole binaries in gravitational wave data. Our model is capable of processing a year of data, simulated from the LISA data challenge, in only several seconds, while identifying all coalescences of massive black hole binaries with no false alarms. We further demonstrate that the model shows robust resistance to a wide range of generalization cases, including various waveform families and updated instrumental configurations. This method offers an effective approach that combines advances in artificial intelligence to open a new pathway for space-based gravitational wave observations.

The effects of Galactic model uncertainties on LISA observations of double neutron stars

ABSTRACT Observations of binaries containing pairs of neutron stars using the upcoming space-based gravitational wave observatory, LISA, have the potential to improve our understanding of neutron star physics and binary evolution. In this work, we assess the effect of changing the model of the Milky Way’s kinematics and star formation history on predictions of the population of double neutron stars that will be detected and resolved by LISA. We conclude that the spatial distribution of these binaries is insensitive to the choice of Galactic models, compared to the stochastic variation induced by the small sample size. In particular, the time-consuming computation of the binaries’ Galactic orbits is not necessary. The distributions of eccentricity and gravitational-wave frequency are, however, affected by the choice of star formation history. Binaries with eccentricities e > 0.1, which can be measured by LISA observations, are mostly younger than $100\, {\rm Myr}$. We caution that comparisons between different predictions for LISA observations need to use consistent star formation histories, and that the Galactic star formation history should be taken into account in the analysis of the observations themselves. The lack of strong dependence on Galactic models means that LISA detection of double neutron star binaries may provide a relatively clean probe of massive binary star evolution.

A Review of Orbital Mechanics for Space-Based Gravitational Wave Observatories

The confirmation of gravitational waves in recent years has set off a new upsurge of exploring the extreme interactions critical to the origin and evolution of stars, galaxies, and the universe. The detection of gravitational waves in space is expected to cover the largest number and the greatest variety of gravitational wave sources, which is more compelling and valuable than the initial detection on the ground. Orbital dynamics and control are the keys to realizing the detection of gravitational waves in space. This paper reviews the orbital mechanics for space-based gravitational wave observatories. The principle and typical gravitational wave observation mission concepts are first introduced and classified summarized. Then, the orbital mechanics of the space-based gravitational wave observatories in different spatial locations are reviewed. On the basis of the characteristics of different observatories, 2 groups of methods related to the observatory configuration design and optimization are summarized: the constellation configuration design and optimization method similar to the geocentric configuration and libration point configuration, the formation design and optimization method similar to heliocentric configuration. The prospects of space-based gravitational wave observatories are finally put forward, which shall provide a reference for future research on space-based gravitational wave observatories.

Structured H-infinity design for the LISA mission accelerometer mode

This article presents the application of the structured H∞ control approach to the design of the LISA mission accelerometer mode. This joint ESA/NASA mission will be the first space-based gravitational wave observatory and is characterized by very stringent scientific constraints resulting in unprecedented control challenges in terms of precision, accuracy, and complexity. The results presented in here were the first demonstration step performed within an ESA study tasked with surveying, trading-off, and applying advanced control techniques to LISA. In addition to showing the methodological gains and design capabilities of the structured H∞ approach, the effects of hardware changes as well as control switching were also analyzed for the designed controllers providing good insight on the way forward to reduce the associated transients. The results presented in this article laid the groundwork, and design process, to subsequently design and validate the full LISA accelerometer mode.

Past and Future of a Type Ia Supernovae Progenitor Candidate HD 265435

As one of the most useful cosmological distance indicators, type Ia supernovae (SNe Ia) play an important role in the study of cosmology. However, the progenitors of SNe Ia are still uncertain. It has been suggested that carbon-oxygen white dwarf (CO WD)+He subgiant systems could produce SNe Ia through the double-degenerate (DD) model, in which the He subgiant transfers He-rich matter to the primary CO WD and finally evolves to another CO WD. Recently, a CO WD+He star system (i.e., HD 265435) has been discovered to be a new SNe Ia progenitor candidate based on the DD model. The orbital period of the system is about 0.0688 days, and the masses of the CO WD and the He star are 1.01 ± 0.15 M ⊙ and M ⊙, respectively. In this work, we evolve a large number of primordial binaries to the formation of CO WD+He star systems and investigate the evolutionary history of HD 265435. We find that HD 265435 may originate from a primordial binary that has a 5.18 M ⊙ primary and a 3.66 M ⊙ secondary with an initial orbital period of 5200 days. The CO WD+He star system would be formed after the primordial binary experiences two common-envelope ejection processes. We also find that HD 265435 would evolve to a double WD system with a total mass of 1.58 M ⊙ after a stable mass-transfer process, and the double WD system would merge driven by gravitational wave radiation. We estimate that it would take about 76 Myr for HD 265435 to form an SN Ia. In addition, HD 265435 would be a potential target of space-based gravitational wave observatories (e.g., LISA, Taiji and TianQin).

Reducing phase noise coupled by wavefront errors in optical telescopes for the space measurement of gravitational waves.

Space-based gravitational-wave observatories (SGOs) promise to measure pico-meter variations in gigameter separations of a triangular constellation. Telescopes play an essential role in transmitting and receiving laser beams measuring the constellation arms with the heterodyne laser interferometry. The wavefront aberrations of the telescopes are coupled with the unavoidable misalignments caused by jitters and pointing tilts and induce additional phase changes into the heterodyne signal. As a critical aspect of achieving the measuring stability of 1p m/H z, we analytically investigate the above process and determine that by properly controlling the relevant key aberrations in the design of the telescopes, the phase noise can be reduced exponentially, which makes the heterodyne signal insensitive to jitter and reduces the demand for wavefront quality. This method is validated whether the LISA Pathfinder (LPF) signal definition or the Average Phase (AP) signal definition is adopted, underpinning the guidance for the design and manufacturing of the optical telescope in SGOs.

Configuration Stability Analysis for Geocentric Space Gravitational-Wave Observatories

Long-term configuration stability is essential for a space-based gravitational-wave observatory, which can be affected by orbit insertion errors. This paper investigated the stability of a geocentric gravitational-wave observatory from the view of the configuration uncertainty propagation. The effects of the orbit insertion errors on the configuration stability are propagated using the Unscented Transformation (UT). The best UT tuning factor is selected based on the accuracy analysis of different UT tuning factors. The effects of the position and velocity insertion errors in different directions are firstly discussed. Compared with the Monte Carlo simulations, the UT method has relative errors of no more than 2.7%, while the time cost is only 3.6%. It is found that the radial position and tangential velocity insertion errors have the largest influence on the configuration stability. Finally, based on the proposed method, the stability domain of the geocentric space gravitational-wave detection constellation is investigated by considering two kinds of insertion errors, i.e., independent and identically distributed insertion errors and insertion errors in spatial directions. The analysis results in this paper can be potentially useful for the configuration design of a geocentric gravitational-wave observatory.

Primordial black holes and gravitational waves in hybrid inflation with chaotic potentials

We study the formation of primordial black hole (PBH) dark matter and the generation of scalar induced secondary gravitational waves (SIGWs) in a non-supersymmetric model of hybrid inflation with chaotic (polynomial-like) potential, including one-loop radiative corrections. A radiatively corrected version of these models is entirely consistent with Planck's data. By adding non-canonical kinetic energy term in the lagrangian, the inflation experiences a period of ultra-slow-roll, and the amplitude of primordial power spectrum is enhanced to O(10−2). The enhanced power spectra of primordial curvature perturbations can have both sharp and broad peaks. A wide mass range of PBHs is realized in our model with the frequencies of scalar induced gravitational waves ranged from nHz to kHz. We present several benchmark points where the PBH mass generated during inflation is around (1−100)M⊙, (10−9−10−7)M⊙ and (10−16−10−11)M⊙. The PBHs can make up most of the dark matter with masses around (10−16−10−11)M⊙ and (1−100)M⊙, and their associated SIGWs can be probed by the upcoming ground and space-based gravitational wave (GW) observatories. The evidence of stochastic process recently reported by NANOGrav may be interpreted as SIGWs associated with the formation of PBHs. These SIGWs may also be tested by future interferometer-type GW observations of SKA, DECIGO, LISA, BBO, TaiJi, TianQin, CE and ET.

Detecting gravitomagnetism with space-based gravitational wave observatories

We discuss the idea of a measurement that, making use of data from space interferometers, could detect the gravito-magnetic field generated by the rotation of the Milky Way, including the possible contribution of the dark matter halo. The galactic signal would be superposed to the gravito-magnetic field of the Sun. The proposed technique is based on the asymmetric propagation of light along the closed contour of the space interferometer, in a Sagnac-like approach. We discuss the principles of detection as well as some practical aspects of the proposed experiment using, as a case study, LISA, the most mature project to date. Both gravito-magnetic signals will be modulated thanks to the annual oscillation of the plane of the interferometer with respect to the galactic plane and to the spin axis of the Sun. Although larger than the detector intrinsic noise, these signals will be superposed to a much larger kinematic modulation due to orbital motion, making them very hard to be observed. We also mention a second phenomenon, where the gravito-magnetic field rotates the polarization of the propagating electromagnetic beams: the effect will be present in LISA, although exceedingly small and out of reach of present technology.

NANOGrav signal and LIGO-Virgo primordial black holes from the Higgs field

We show that the NANOGrav signal can come from the Higgs field with a noncanonical kinetic term in terms of the scalar induced gravitational waves. The scalar induced gravitational waves generated in our model are also detectable by space-based gravitational wave observatories. Primordial black holes with stellar masses that can explain LIGO-Virgo events are also produced. Therefore, the NANOGrav signal and the BHs in LIGO-Virgo events may both originate from the Higgs field.

GRAVITATIONAL CASIMIR EFFECT IN INSPIRALLING NEUTRON STAR BINARY

Currently, the discussions and investigations for the vacuum energy are drawing great both theoretical and experimental attention. The vacuum states of variety of fields, subject to special boundary conditions, may contribute to non-trivial macroscopic vacuum energy, i.e., the Casimir effect, which become an interdisciplinary subject and plays an important role in a variety of fields of physics. We adopt Schwingers source theory and study the quantization of gravitation contributions to the Casimir effect, i.e., the gravitational Casimir effect, in inspiraling neutron star binaries with wide separation of 109 m. By considering gravitoelectromagnetism (GEM) arising from the spiral-in orbital motion and evaluating the gravitoelectromagnetic contributions to the vacuum energy of gravitons radiated during the orbital decay, we demonstrate that, when the radial separation of the system decay a distance L, the GEM results in a small Casimir correction to the gravitational vacuum energy, which contributes to an attractive gravitational Casimir force to the binary, in addition to the gravitational force. We also discuss the possible detections for such gravitational Casimir effect from both the future space-based gravitational wave observatories and cosmological observations.

GRAVITATIONAL CASIMIR EFFECT IN INSPIRALLING NEUTRON STAR BINARY

Currently, the discussions and investigations for the vacuum energy is drawing great both theoretical and experimental attention. The vacuum states of variety of fields, subject to special boundary conditions, may contribute to non-trivial macroscopic vacuum energy, i.e. the Casimir effect, which become an interdisciplinary subject and plays an important role in a variety of fields of physics. We adopt Schwinger's source theory and study the Casimir effect due to the quantization of gravitation, i.e. the gravitational Casimir effect (GCE), in inspiraling neutron star (NS) binaries with wide separation of $10^9 \rm m$. By considering gravitoelectromagnetism (GEM) arising from the spiral-in orbital motion and evaluating the contributions of GEM to the vacuum energy of gravitons radiated during the orbital decay, we demonstrate that, when the orbital separation of the binary decay a distance of $L$ in radial direction, the GEM results in a small Casimir correction to the gravitational vacuum energy, which contributes to an attractive gravitational Casimir force to the binary, in addition the gravitational force. The gravitational waves (GWs), emitted from wide inspiraling NS binaries, locate in the low-frequency band of $10^{-4}-1$ Hz. For a characteristic GW frequency of $10^{-3}$ Hz, the gravitational Casimir correction to the signals is estimated as of the order of $\sim10^{-24}$, which corresponds to a force of $10^{-20}$ N. By considering that the sensitivity of space-based gravitational wave observatory, LISA/eLISA and Taiji, can be reduced to $10^{-24}$, we would expect that LISA/eLISA and Taiji with sensitivity improvements give the powerful tool to detect GCE in the near future.

Relative-Intensity-Noise Coupling in Heterodyne Interferometers

Laser interferometers are the core measurement tool in gravitational wave observatories. An important factor that can limit the performance is the relative power instability of the laser, a problem often called relative intensity noise (RIN). But exactly how this influences the interferometer performance is not completely understood. Therefore in this paper we analyze laser RIN coupling into the phase readout in balanced and unbalanced heterodyne interferometers. We describe the coupling theoretically, then simulate and finally measure it. Our results reveal a combination of RIN contributions from the heterodyne frequency and twice the heterodyne frequency in the interferometric phase readout. We also show that when an additional, correlated reference measurement is subtracted the combined coupling factor depends on the differential phase between the two measurements and thus can be minimized. Our results have implications for noise models in future space-based gravitational wave observatories like Laser Interferometer Space Antenna, where RIN-to-phase coupling arises directly and is modulated via spacecraft jitter, testmass position and orientation.

Primordial black holes and secondary gravitational waves from string inspired general no-scale supergravity

The formation of primordial black hole (PBH) dark matter and the generation of scalar induced secondary gravitational waves (SIGWs) have been studied in the generic no-scale supergravity inflationary models. By adding an exponential term to the K\"ahler potential, the inflaton experiences a period of ultraslow-roll and the amplitude of primordial power spectrum at small scales is enhanced to $\mathcal{O}({10}^{\ensuremath{-}2})$. The enhanced power spectra of primordial curvature perturbations can have both sharp and broad peaks. A wide mass range of PBHs can be produced in our model, and the frequencies of the accompanied SIGWs are ranged form nanohertz to kilohertz. We show four benchmark points where the generated PBH masses are around $\mathcal{O}({10}^{\ensuremath{-}16}\text{ }\text{ }{M}_{\ensuremath{\bigodot}})$, $\mathcal{O}({10}^{\ensuremath{-}12}\text{ }\text{ }{M}_{\ensuremath{\bigodot}})$, $\mathcal{O}({10}^{\ensuremath{-}2}\text{ }\text{ }{M}_{\ensuremath{\bigodot}})$ and $\mathcal{O}({10}^{2}\text{ }\text{ }{M}_{\ensuremath{\bigodot}})$. The PBHs with masses around $\mathcal{O}({10}^{\ensuremath{-}16}\text{ }\text{ }{M}_{\ensuremath{\bigodot}})$ and $\mathcal{O}({10}^{\ensuremath{-}12}\text{ }\text{ }{M}_{\ensuremath{\bigodot}})$ can make up almost all the dark matter, and the accompanied SIGWs can be probed by the upcoming space-based gravitational wave observatory. Also, the SIGWs accompanied with the formation of stellar mass PBHs can be used to interpret the stochastic GW background in the nanohertz band, detected by the North American Nanohertz Observatory for Gravitational Waves, and can be tested by future interferometric gravitational wave observatory.

Sensitivity limits of space-based interferometric gravitational wave observatories from the solar wind

Space-based interferometric gravitational wave instruments such as the ESA/NASA Laser Interferometer Space Antenna (LISA) observe gravitational waves by measuring changes in the light travel time between widely-separated spacecraft. One potential noise source for these instruments is interaction with the solar wind, in particular the free electrons in the interplanetary plasma. Variations in the integrated column density of free electrons along the laser links will lead to time-of-flight delays which directly compete with signals produced by gravitational waves. In this paper we present a simplified model of the solar plasma relevant for this problem, anchor key parameters of our model using data from the NASA \emph{Wind}/SWE instrument, and derive estimates for the effect in the LISA measurement. We find that under normal solar conditions, the gravitational-wave sensitivity limit from the free-electron effect is smaller than other noise sources that are expected to limit LISA's sensitivity.

Science with the TianQin Observatory: Preliminary results on testing the no-hair theorem with extreme mass ratio inspirals

Constituted with a massive black hole and a stellar mass compact object, Extreme Mass Ratio Inspiral (EMRI) events hold unique opportunity for the study of massive black holes, such as by measuring and checking the relations among the mass, spin and quadrupole moment of a massive black hole, putting the no-hair theorem to test. TianQin is a planned space-based gravitational wave observatory and EMRI is one of its main types of sources. It is important to estimate the capacity of TianQin on testing the no-hair theorem with EMRIs. In this work, we use the analytic kludge waveform with quadrupole moment corrections and study how the quadrupole moment can be constrained with TianQin. We find that TianQin can measure the dimensionless quadrupole moment parameter with accuracy to the level of $10^{-5}$ under suitable scenarios. The choice of the waveform cutoff is found to have significant effect on the result: if the Schwarzschild cutoff is used, the accuracy depends strongly on the mass of the massive black hole, while the spin has negligible impact; if the Kerr cutoff is used, however, the dependence on the spin is more significant. We have also analyzed the cases when TianQin is observing simultaneously with other detectors such as LISA.