Laser Interferometer Space Antenna Mission Research Articles

Tidal heating as a discriminator for horizons in equatorial eccentric extreme mass ratio inspirals

Tidal heating in a binary black hole system is driven by the absorption of energy and angular momentum by the black hole’s horizon. Previous works have shown that this phenomenon becomes particularly significant during the late stages of an extreme mass ratio inspiral (EMRI) into a rapidly spinning massive black hole, a key focus for future low-frequency gravitational-wave observations by (for instance) the Laser Interferometer Space Antenna mission. Past analyses have largely focused on quasicircular inspiral geometry, with some of the most detailed studies looking at equatorial cases. Though useful for illustrating the physical principles, this limit is not very realistic astrophysically, since the population of EMRI events is expected to arise from compact objects scattered onto relativistic orbits in galactic centers through many-body events. In this work, we extend those results by studying the importance of tidal heating in equatorial EMRIs with generic eccentricities. Our results suggest that accurate modeling of tidal heating is crucial to prevent significant dephasing and systematic errors in EMRI parameter estimation. We examine a phenomenological model for EMRIs around exotic compact objects by parametrizing deviations from the black hole (BH) picture in terms of the fraction of radiation absorbed compared to the BH case. Based on a mismatch calculation, we find that reflectivities as small as |R|2∼O(10−5) are distinguishable from the BH case, irrespective of the value of the eccentricity. We stress, however, that this finding should be corroborated by future parameter estimation studies. Published by the American Physical Society 2024

Introducing the BRAHMA simulation suite: signatures of low-mass black hole seeding models in cosmological simulations

ABSTRACT While the first “seeds” of supermassive black holes (BH) can range from $\sim 10^2-10^6 \rm ~{\rm M}_{\odot }$, the lowest mass seeds ($\lesssim 10^3~\rm {\rm M}_{\odot }$) are inaccessible to most cosmological simulations due to resolution limitations. We present our new BRAHMA simulations that use a novel flexible seeding approach to predict the $z\ge 7$ BH populations for low-mass seeds. We ran two types of boxes that model $\sim 10^3~\rm {\rm M}_{\odot }$ seeds using two distinct but mutually consistent seeding prescriptions at different simulation resolutions. First, we have the highest resolution $[9~\mathrm{Mpc}]^3$ (BRAHMA-9-D3) boxes that directly resolve $\sim 10^3~\rm {\rm M}_{\odot }$ seeds and place them within haloes with dense, metal-poor gas. Second, we have lower resolution, larger volume $[18~\mathrm{Mpc}]^3$ (BRAHMA-18-E4), and $\sim [36~\mathrm{Mpc}]^3$ (BRAHMA-36-E5) boxes that seed their smallest resolvable $\sim 10^4~\&~10^5~\mathrm{{\rm M}_{\odot }}$ BH descendants using new stochastic seeding prescriptions calibrated using BRAHMA-9-D3. The three boxes together probe key BH observables between $\sim 10^3\,\mathrm{ and}\,10^7~\rm {\rm M}_{\odot }$. The active galactic nuclei (AGN) luminosity function variations are small (factors of $\sim 2-3$) at the anticipated detection limits of potential future X-ray facilities ($\sim 10^{43}~ \mathrm{ergs~s^{-1}}$ at $z\sim 7$). Our simulations predict BHs $\sim 10-100$ times heavier than the local $M_*$ versus $M_{\mathrm{ bh}}$ relations, consistent with several JWST-detected AGN. For different seed models, our simulations merge binaries at $\sim 1-15~\mathrm{kpc}$, with rates of $\sim 200-2000$ yr−1 for $\gtrsim 10^3~\rm {\rm M}_{\odot }$ BHs, $\sim 6-60$ yr−1 for $\gtrsim 10^4~\rm {\rm M}_{\odot }$ BHs, and up to $\sim 10$ yr−1 amongst $\gtrsim 10^5~\rm {\rm M}_{\odot }$ BHs. These results suggest that Laser Interferometer Space Antenna mission has promising prospects for constraining seed models.

Bridging machine learning and diagnostics of the ESA LISA space mission with equation discovery via explainable artificial intelligence

The Laser Interferometer Space Antenna (LISA) of the European Space Agency will be the first interferometer for low-frequency (10-4–10-1 Hz) gravitational wave detection in space. LISA will detect spurious accelerations of the test masses, the end mirrors of the interferometer, of the order of femto-g. Amongst spurious signals, Coulomb forces due to stray electric fields coupling with charge deposited on the test masses by galactic and solar particles and the noise associated to the charging process must be monitored during the mission lifetime. Precious clues on spurious forces acting on the test masses have been studied with the LISA Pathfinder mission, meant for the testing of the instrumentation that will be placed on board LISA, in 2016–2017. In this work we present the design and implementation of a workflow leading to equation discovery for the relationship between solar wind speed, galactic cosmic-ray variations and interplanetary magnetic field intensity observations for the diagnostics of LISA. The workflow exploits explainable artificial intelligence tools to build a bridge between the opaque predictions obtained with machine learning (ML) models and data analysis performed by humans with space mission observations. The core step of the workflow is the implementation, tuning and optimisation of an opaque ML regressor explicitly designed for the future LISA mission, based on input observations of the galactic cosmic-ray flux and of the interplanetary magnetic field intensity. The regressor is aimed at reconstructing the solar wind speed, a parameter of fundamental importance, but not available, for the mission environment monitoring. The workflow ends with the application of explainable clustering techniques to the opaque model in order to (i) obtain human-interpretable outputs instead of opaque ones without any noticeable loss in the predictive performance and (ii) discover an equation describing the quantitative relationship between the involved variables, currently missing in the literature. The correlation amongst the transit of interplanetary structures, galactic cosmic-ray variations and LISA test-mass charging is illustrated here.

LISA and LISA-like mission test-mass charging for gamma-ray burst detection

Cubic gold-platinum test-masses (TMs) play the role of free-falling geodesic reference and interferometer end mirrors of the future Laser Interferometer Space Antenna (LISA) observatory for low-frequency gravitational wave detection in space. A similar arrangement has been proposed for the Chinese missions Taiji and TianQin and for the LISA follow-on missions such as ALIA and BBO. The TMs are charged by high-energy particles and photons. The deposited charge couples with stray electric fields surrounding the TMs thus inducing spurious forces that limit the sensitivity of the mission mainly at low frequencies. The TM charging was measured in space in 2016-2017 with LISA Pathfinder (LPF), meant for the testing of the LISA instrumentation. Unfortunately, during the time LPF remained in orbit, no solar energetic particle events or major astrophysical phenomena were observed. We aim at estimating the LISA TM charging attributable to long, short gamma-ray bursts (GRBs) and magnetar flares in comparison to that of charged particles of galactic and solar origin. The contribution of these major astrophysical phenomena to the LISA TM charging is discussed here for the first time. The results found here can be extended to LISA-like missions. The response of the radiation monitors hosted on the three LISA S/C is also evaluated. We show that long, intense extragalactic GRBs and galactic magnetar flares at kpc distances can be detected and monitored through a sudden change from positive to negative charging of the TMs and an increase of the TM charging noise. This is a unique signature since both galactic and solar particles charge positively the LISA TMs. This peculiar behavior of the TM charging would allow monitoring the whole dynamics of GRBs. The suggestion reported in the literature, about the detection of long GRBs and gravitational waves from the same sources, in principle, may apply to LISA and other LISA-like missions since the increase of the TM charging noise during these extreme transient phenomena is estimated to remain below the mission sensitivity while particle detectors are expected to saturate.

Impacts of gravitational-wave background from supermassive black hole binaries on the detection of compact binaries by LISA* *Supported by the NSFC (12250010, 11991052) and Key Research Program of Frontier Sciences, CAS, (ZDBS-LY-7009)

In the frequency band of the Laser Interferometer Space Antenna (LISA), extensive research has been conducted on the impact of foreground confusion noise generated by galactic binaries within the Milky Way Galaxy. Additionally, recent evidence of a stochastic signal, announced by the NANOGrav, EPTA, PPTA, CPTA, and InPTA, indicates that the stochastic gravitational-wave background (SGWB) generated by supermassive black hole binaries (SMBHBs) can contribute strong background noise within the LISA band. Given the presence of such strong noise, it is expected to have significant impacts on LISA's scientific missions. In this study, we investigate the impacts of the SGWB generated by SMBHBs on the detection of individual massive black hole binaries, verified galactic binaries, and extreme mass ratio inspirals in the context of LISA. We find it essential to resolve and eliminate the excess noise from the SGWB to guarantee the success of LISA's missions.

Bilby in space: Bayesian inference for transient gravitational-wave signals observed with LISA

ABSTRACT The Laser Interferometer Space Antenna (LISA) is scheduled to launch in the mid-2030s, and is expected to observe gravitational-wave candidates from massive black hole binary mergers, extreme mass ratio inspirals, and more. Accurately inferring the source properties from the observed gravitational-wave signals is crucial to maximize the scientific return of the LISA mission. bilby, the user-friendly Bayesian inference library, is regularly used for performing gravitational-wave inference on data from existing ground-based gravitational-wave detectors. Given that Bayesian inference with LISA includes additional subtitles and complexities beyond its ground-based counterpart, in this work we introduce bilby_lisa , a python package that extends bilby to perform parameter estimation with LISA. We show that full nested sampling can be performed to accurately infer the properties of LISA sources from transient gravitational-wave signals in (a) zero noise and (b) idealized instrumental noise. By focusing on massive black hole binary mergers, we demonstrate that higher order multipole waveform models can be used to analyse a year’s worth of simulated LISA data, and discuss the computational cost and performance of full nested sampling compared with techniques for optimizing likelihood calculations, such as the heterodyned likelihood.

An ultra-stable laser based on molecular iodine with a short-term instability of 3.3 × 10−15 for space based gravity missions

Many space based gravity missions require frequency stabilized lasers with stringent requirements. Toward those requirements, we develop a compact frequency-stabilized laser which is referenced to the R(56)32−0: a1 transition of molecular iodine based on the modulation transfer spectroscopy technique. The stability of the laser is limited by the beam pointing noise, the electronic servo noise, and the residual amplitude modulation (RAM) noise. To improve the beam pointing stability, the system is constructed by gluing most components of the optical system on an ultra-low expansion glass base. We use a pre-amplifier to suppress the electronic servo noise, and use a wedged electro-optic phase modulator to suppress the RAM noise. The fractional frequency instability of the system is evaluated to be 3.3 × 10−15 at 2 s and 4 s averaging time, and is lower than 6 × 10−15 at averaging times from 1 s to 10 000 s. To our knowledge, this is the best short-term (1–4 s) instability reported so far for an iodine stabilized laser. The stability fully meets the requirements of next generation gravity mission and laser interferometer space antenna mission.

Recovery strategies to cope with micrometeoroid impacts in the LISA mission

We propose an analysis of the recovery strategies for the science mode of the Laser Interfer-ometer Space Antenna (LISA) mission after a meteoroid impacts the spacecraft. The mission consists of a three-spacecraft constellation traveling in a heliocentric orbit, detecting gravitational waves through laser interferometry. To this end, each spacecraft must travel in a free-fall condition in order to reject any possible disturbance and noise affecting the control loop. Nevertheless, if one of the three satellites crosses a meteoroids stream, the collisions can produce attitude perturbations that must be compensated by the control loop. Indeed, in this latter case, the interferometer laser links can be lost. Unfortunately, the link recovery is accomplished through a quite time-consuming re-acquisition maneuver, implying a significant reduction of the science mode time. For this reason, we propose different strategies for a fast recovery of the nominal attitude. The strategies are supported and traded-off by means of extensive simulations, including a Monte Carlo campaign and a worst-case analysis.

Identifying LISA verification binaries among the Galactic population of double white dwarfs

ABSTRACT Double white dwarfs (DWDs) will be the most numerous gravitational-wave (GW) sources for the Laser Interferometer Space Antenna (LISA). Most of the Galactic DWDs will be unresolved and will superpose to form a confusion noise foreground, the dominant LISA noise source around ${\sim} 0.5\!-\!3\, \mathrm{mHz}$ . A small fraction of these sources will stand out from the background and be individually detectable. Uniquely among GW sources, a handful of these binaries will be known in advance from electromagnetic (EM) observations and will be guaranteed sources of detectable GWs in the LISA band; these are known as verification binaries (VBs). High-cadence photometric surveys are continuously discovering new VB systems, and their number will continue to grow ahead of the launch of LISA. We analyse, in a fully Bayesian framework, all the currently known VB candidates with the latest design requirements for the LISA mission and find that 25 of the considered sources can be detected within a 4 yr observation time. We explore what can be expected from GW observations, both alone and in combination with EM observations, and estimate the VB’s time to detection in the early months of LISA operations. We also show how VBs can be analysed in the case where their GW signals compete with many other unknown binary signals (both resolved and unresolved) from a realistic Galactic population of DWDs.

Gravitational Wave Sources in Our Galactic Backyard: Predictions for BHBH, BHNS, and NSNS Binaries Detectable with LISA

Future searches for gravitational waves from space will be sensitive to double compact objects in our Milky Way. We present new simulations of the populations of double black holes (BHBHs), BH neutron stars (BHNSs), and double neutron stars (NSNSs) that will be detectable by the planned space-based gravitational-wave detector called Laser Interferometer Space Antenna (LISA). For our estimates, we use an empirically informed model of the metallicity-dependent star formation history of the Milky Way. We populate it using an extensive suite of binary population-synthesis predictions for varying assumptions relating to mass transfer, common-envelope, supernova kicks, remnant masses, and wind mass-loss physics. For a 4(10) yr LISA mission, we predict between 30–370(50–550) detections over these variations, out of which 6–154 (9–238) are BHBHs, 2–198 (3–289) are BHNSs, and 3–35 (4–57) are NSNSs. We expect that about 50% (60%) can be distinguished from double white dwarf sources based on their mass or eccentricity and localization. Specifically, for about 10% (15%), we expect to be able to determine chirp masses better than 10%. For 13% (13%), we expect sky-localizations better than 1°. We discuss how the variations in the physics assumptions alter the distribution of properties of the detectable systems, even when the detection rates are unchanged. We further discuss the possibility of multimessenger observations of pulsar populations with the Square Kilometre Array and assess the benefits of extending the LISA mission.

New self-force method via elliptic partial differential equations for Kerr inspiral models

We present a new method designed to avoid numerical challenges that have impeded calculation of the Lorenz gauge self-force acting on a compact object inspiraling into a Kerr black hole. This type of calculation is valuable in creating waveform templates for extreme mass-ratio inspirals, which are an important source of gravitational waves for the upcoming Laser Interferometer Space Antenna mission. Prior hyperbolic partial differential equation (PDE) formulations encountered numerical instabilities involving unchecked growth in time; our new method is based on elliptic PDEs, which do not exhibit instabilities of that kind. For proof of concept, we calculate the self-force acting on a scalar charge in a circular orbit around a Kerr black hole. We anticipate this method will subsequently facilitate calculation of first-order Lorenz gauge Kerr metric perturbations and self-force, which could serve as a foundation for second-order Kerr self-force investigations.

Postprocessing subtraction of tilt-to-length noise in LISA

The coupling of an angular jitter into the interferometric phase readout is summarized under the term tilt-to-length (TTL) coupling. This noise is expected to be a major noise source in the intersatellite interferometry for the Laser Interferometer Space Antenna (LISA) space mission. Despite efforts to reduce it by satellite construction, some remaining TTL noise will need to be removed in postprocessing on Earth. Therefore, such a procedure needs to be developed and validated to ensure the success of the LISA mission. This paper shows a method to calibrate and subtract TTL noise that has no impact on LISA science operations. This solution relies on noise minimization and uses the differential wavefront sensing (DWS) measurements to estimate the TTL contribution. Our technique is applied after the laser frequency noise is suppressed via the time-delay interferometry (TDI) postprocessing algorithm. We use a simulation to show as a proof-of-principle that we can estimate the TTL coefficients to the required accuracy level based on the current design configuration of LISA. We then use these estimates to subtract the TTL noise, ensuring that any remaining TTL noise is below the current estimate of the other noise sources. We validate the procedure on simulated data for different operating scenarios. Our work shows that it is indeed possible to estimate the effect of TTL coupling and subtract it a posteriori from the TDI data streams.

Arm locking performance with the new LISA design

The laser interferometer space antenna (LISA) is a future space-based gravitational wave detector designed to be sensitive to sources radiating in the low frequency regime (0.1 mHz to 1 Hz). LISA’s interferometer signals will be dominated by laser frequency noise which has to be suppressed by about seven orders of magnitude using an algorithm called time delay interferometry (TDI). Arm locking has been proposed to reduce the laser frequency noise by a few orders of magnitude to reduce the potential risks associated with TDI. In this paper, we present an updated performance model for arm locking for the new LISA mission using 2.5 Gm arm lengths, the currently assumed clock noise, spacecraft motion based on LISA Pathfinder data and shot noise. We also update the Doppler frequency pulling estimates during lock acquisition.

Enhanced frequency noise suppression for LISA by combining cavity and arm locking control systems

This paper presents a novel method for laser frequency stabilization in the Laser Interferometer Space Antenna (LISA) mission by locking a laser to two stable length references-the arms of the interferometer and an on-board optical cavity. The two references are digitally fused using carefully designed control systems, attempting minimal or no changes to the baseline LISA mission hardware. The interferometer arm(s) provides the most stable reference available in the LISA science band (0.1 mHz--1 Hz), while the cavity sensor's wideband and linear readout enables additional control system gain below and above the LISA band. The main technical issue with this dual sensor approach is the undesirable slow laser frequency pulling which couples into the control system with the imperfect knowledge of the Doppler shift of the light due to relative spacecraft motion along the LISA arm. This paper outlines requirements on the Doppler shift knowledge to maintain the cavity well within the resonance when activating the fused control system. Two Doppler shift estimation methods are presented that use the already on-board measurements, the inter-spacecraft interferometer link (the main science measurement), and the absolute inter-spacecraft laser ranging system. Both methods reach the required precision after a few thousand seconds of measurement integration. The paper demonstrates an approach to initialize and engage the proposed laser stabilization system, starting from free-running laser and ending with the dual sensor frequency control system. The results show that the technique lowers the residual laser frequency noise in the LISA science band by over 3 orders of magnitude: from $30\text{ }\text{ }\mathrm{Hz}/\sqrt{\mathrm{Hz}}$ to as low as $7\text{ }\text{ }\mathrm{mHz}/\sqrt{\mathrm{Hz}}$, potentially allowing the requirements on Time Delay Interferometry (TDI) to be relaxed---possibly to the point where first-generation TDI may be sufficient.

Observationally driven Galactic double white dwarf population for LISA

ABSTRACT Realistic models of the Galactic double white dwarf (DWD) population are crucial for testing and quantitatively defining the science objectives of the Laser Interferometer Space Antenna (LISA), a future European Space Agency’s gravitational-wave observatory. In addition to numerous individually detectable DWDs, LISA will also detect an unresolved confusion foreground produced by the underlying Galactic population, which will affect the detectability of all LISA sources at frequencies below a few mHz. So far, the modelling of the DWD population for LISA has been based on binary population synthesis (BPS) techniques. The aim of this study is to construct an observationally driven population. To achieve this, we employ a model developed by Maoz, Hallakoun & Badenes for the statistical analysis of the local DWD population using two complementary large, multi-epoch, spectroscopic samples: the Sloan Digital Sky Survey, and the Supernova Ia Progenitor surveY. We calculate the number of LISA-detectable DWDs and the Galactic confusion foreground, based on their assumptions and results. We find that the observationally driven estimates yield (1) 2–5 times more individually detectable DWDs than various BPS forecasts, and (2) a significantly different shape of the DWD confusion foreground. Both results have important implications for the LISA mission. A comparison between several variations to our underlying assumptions shows that our observationally driven model is robust, and that the uncertainty on the total number of LISA-detectable DWDs is in the order of 20 per cent.

A higher probability of detecting lensed supermassive black hole binaries by LISA

ABSTRACT Gravitational lensing of gravitational waves (GWs) is a powerful probe of the matter distribution in the universe. Here we revisit the wave-optics effects induced by dark matter (DM) haloes on the GW signals of merging massive black hole binaries (MBHBs), and we study the possibility of discerning these effects using the Laser Interferometer Space Antenna (LISA). In particular, we include the haloes in the low-mass range of $10^5\!-\!10^8\, \mathrm{M}_\odot$ since they are the most numerous according to the cold DM model. We simulate the lensed signals corresponding to a wide range of impact parameters, and we find distinguishable deviation from the standard best-fitting GW templates even when the impact parameter is as large y ≃ 50. Consequently, we estimate that over $(0.1\!-\!1.6){{\ \rm per\ cent}}$ of the MBHBs in the mass range of $10^{5.0}\!-\!10^{6.5}\, \mathrm{M}_\odot$ and the redshift range of 4 − 10 should show detectable wave-optics effects. This probability is one order of magnitude higher than that derived in previous works. The uncertainty comes mainly from the mass function of the DM haloes. Not detecting any signal during the LISA mission would imply that DM haloes with $10^5\!-\!10^8\, \mathrm{M}_\odot$ are less numerous than what the cold DM model predicts.

Dual fields of massive/massless gravitons in IR/UV completions

In the holographic picture, the Brout-Englert-Higgs (BEH) mechanism in [Formula: see text]-dimensional Yang–Mills theories is conjectured to provide a Higgs-like mechanism for gravity in [Formula: see text] dimensions, resulting in massive (or massless) gravitons in IR (or UV) completions. Accordingly, one could imagine dual (magnetic-type) fields of massive gravitons in the IR (low-energy) limit that are coupled to the curl of their own energy–momentum, as well as to the rotation of matter fields on large scales. This hypothesis, which might solve cosmological issues currently ascribed to dark matter and dark energy, needs to be examined by the future Laser Interferometer Space Antenna mission using observations of gravitational waves emitted from extragalactic sources.

Trajectory Design for the ESA LISA Mission

The three Laser Interferometer Space Antenna (LISA) spacecraft are going to be placed in a triangular formation in an Earth-trailing or Earth-leading orbit. They will be launched together on a single rocket and transferred to that science orbit using Solar Electric Propulsion. Since the transfer Δv depends on the chosen science orbit, both transfer and science orbit have been optimised together. For a thrust level of 90 mN, an allocation of 1092 m/s per spacecraft is sufficient for an all-year launch in 2034. For every launch month a dedicated science orbit is designed with a corner angle variation of 60° ± 1.0° and an arm length rate of maximum 10 m/s. Moreover, a detailed navigation analysis of the science orbit insertion and the impact on insertion errors on the constellation stability has been conducted. The analysis shows that Range/Doppler measurements together with a series of correction manoeuvres at the beginning of the science orbit phase can reduce insertion dispersions to a level where corner angle variations remain at about 60° ± 1.1° at 99% C.L. However, the situation can become significantly worse if the self-gravity accelerations acting during the science orbit phase are not sufficiently characterised prior to science orbit insertion.

Identifying and addressing nonstationary LISA noise

We anticipate noise from the Laser Interferometer Space Antenna (LISA) will exhibit nonstationarities throughout the duration of its mission due to factors such as antenna repointing, cyclostationarities from spacecraft motion, and glitches as highlighted by LISA Pathfinder. In this paper, we use a surrogate data approach to test the stationarity of a time series which does not rely on the Gaussianity assumption. The main goal is to identify noise nonstationarities in the future LISA mission. This will be necessary for determining how often the LISA noise power spectral density (PSD) will need to be updated for parameter estimation routines. We conduct a thorough simulation study illustrating the power/size of various versions of the hypothesis tests and then apply these approaches to differential acceleration measurements from LISA Pathfinder. We also develop a data analysis strategy for addressing nonstationarities in the LISA PSD, where we update the noise PSD over time, while simultaneously conducting parameter estimation, with a focus on planned data gaps.

LISA: Heliocentric formation design for the laser interferometer space antenna mission

The LISA (Laser Interferometer Space Antenna) mission has been selected by the European Space Agency’s Science Programme Committee as the third large-class mission of the Cosmic Vision Programme, addressing the science theme of the Gravitational Universe. With a planned launch date in 2034, LISA will be the first ever space-borne Gravitational Wave observatory, relying on laser interferometry between three spacecraft orbiting the Sun in a triangular formation. Airbus is currently leading an industrial Phase A system study on behalf of the European Space Agency. The paper will address the astrodynamics challenges associated with the LISA constellation design, driven by tight requirements on the geometric quality metrics of the near equilateral formation.