Search

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 $\sim 0.5\mathrm{-}3\,\mathrm{mHz}$. 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 $4\,\mathrm{yr}$ 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., Comment: 13 pages, 8 figures, plus appendices (accepted in Monthly Notices of the Royal Astronomical Society on 26 April 2023)

Future gravitational wave detectors, such as the Laser Interferometer Space Antenna (\textit{LISA}), will be able to resolve a significant number of the ultra compact stellar-mass binaries in our own Galaxy and its neighborhood. These will be mostly double white dwarf (DWD) binaries, and their underlying population characteristics can be directly correlated to the different properties of the Galaxy. In particular, with \textit{LISA} we will be able to resolve $\sim\mathcal{O}(10^4)$ binaries, while the rest will generate a confusion foreground signal. Analogously to how the total electromagnetic radiation emitted by a galaxy can be related to the underlying total stellar mass, in this work we propose a framework to infer the same quantity by investigating the spectral shape and amplitude of the confusion foreground signal. For a fixed DWD evolution model, and thus a fixed binary fraction, we retrieve percentage-level relative errors on the total stellar mass, which improves for increasing values of the mass. At the same time, we find that variations in the Milky Way shape, at a fixed mass and at scale heights smaller than 500~pc, are not distinguishable based on the shape of stochastic signal alone. We perform this analysis on simulations of the LISA data, estimating the resolvable sources based on signal-to-noise criteria. Finally, we utilize the catalogue of resolvable sources to probe the characteristics of the underlying population of DWD binaries. We show that the DWD frequency, coalescence time and chirp mass (up to $, 15 pages, 9 figures

The authors wish to thank J.M. Torrejón for the organization of the Athena-multi-messenger Workshops, held on November 27 - 29, 2018, in Alicante, Spain and on 5 May 2020 - 6 May 2020 in videoconference., In this paper we explore the scientific synergies between Athena and some of the key multi-messenger facilities that should be operative concurrently with Athena. These facilities include LIGO A+, Advanced Virgo+ and future detectors for ground-based observation of gravitational waves (GW), LISA for space-based observations of GW, IceCube and KM3NeT for neutrino observations, and CTA for very high energy observations. These science themes encompass pressing issues in astrophysics, cosmology and fundamental physics such as: the central engine and jet physics in compact binary mergers, accretion processes and jet physics in Super-Massive Binary Black Holes (SMBBHs) and in compact stellar binaries, the equation of state of neutron stars, cosmic accelerators and the origin of Cosmic Rays (CRs), the origin of intermediate and high-Z elements in the Universe, the Cosmic distance scale and tests of General Relativity and the Standard Model. Observational strategies for implementing the identified science topics are also discussed. A significant part of the sources targeted by multi-messenger facilities is of transient nature. We have thus also discussed the synergy of Athena with wide-field high-energy facilities, taking THESEUS as a case study for transient discovery. This discussion covers all the Athena science goals that rely on follow-up observations of high-energy transients identified by external observatories, and includes also topics that are not based on multi-messenger observations, such as the search for missing baryons or the observation of early star populations and metal enrichment at the cosmic dawn with Gamma-Ray Bursts (GRBs)., Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature., This research has been supported by the European Union’s Horizon 2020 programme under the AHEAD (grant agreement number 654215) and AHEAD2020 project (grant agreement n. 871158). FJC and SMN acknowledges funding under project RTI2018-096686-B-C21 funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe”, and by the Unidad de Excelencia María de Maeztu, ref. MDM-2017-0765.

The Laser Interferometer Space Antenna (LISA) will detect and characterize ∼104 Galactic Binaries, consisting predominantly of two white dwarfs (WDs). An interesting prospect within this population is a third object – another WD star, a circumbinary exoplanet (CBP), or a brown dwarf (BD) – in orbit about the inner WD pair. We present the first fully Bayesian detection and posterior analysis of substellar objects with LISA, focusing on the characterization of CBPs. We used an optimistic astrophysically motivated catalogue of these CBP third-body sources, including their orbital eccentricity around the inner binary for the first time. We examined Bayesian evidence computations for detectability, as well as the effects on the posterior distributions for both the inner binary parameters and the third-body parameters. We find that the posterior behaviour bifurcates based on whether the third-body period is above or below half the observation time. Additionally, we find that undetectable third-body sources can bias the inner binary parameters whether or not the correct template is used. We used the information retrieved from the study of the CBP population to make an initial conservative prediction for the number of detectable BD systems in the original catalogue. We end with commentary on the predicted qualitative effects on LISA global fitting and Galactic Binary population analysis. The procedure used in this work is generic and can be directly applied to other astrophysical effects expected within the Galactic Binary population. © 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society., VK acknowledges support from the Netherlands Research Council NWO (Rubicon 019.183EN.015 grant). NK acknowledges the support from the Gr-PRODEX 2019 funding program (PEA 4000132310). This research was supported in part through the computational resources and staff contributions provided for the Quest/Grail high-performance computing facility at Northwestern University. NT acknowledges support form the French space agency CNES in the framework of LISA. CD acknowledges financial support from the State Agency for Research of the Spanish MCIU through the ‘Center of Excellence Severo Ochoa’ award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709), and the Group project Ref. PID2019-110689RB-I00/AEI/10.13039/501100011033. This work was supported by the COST action CA16104 ‘Gravitational waves, black holes, and fundamental physics’ (GWverse) through a Short-Term Scientific Mission (STSM) awarded to CD (ID 48268) and VK (ID 48272). COST actions are supported by COST (European Cooperation in Science and Technology). NJC appreciates the support of the NASA LISA Foundation Science grant 80NSSC19K0320. This project has received financial support from the CNRS through the MITI interdisciplinary programs. This paper also employed the use of SCIPY (Jones et al. 2001) and MATPLOTLIB (Hunter 2007).

The Laser Interferometer Space Antenna (LISA) will unveil the non-transient gravitational wave sky full of inspiralling stellar-mass compact binaries within the Local Universe. The Large Magellanic Cloud (LMC) is expected to be prominent on the LISA sky due to its proximity and its large population of double white dwarfs (DWD). Here we present the first dedicated study of the LMC with gravitational wave sources. We assemble three LMC models based on: (1) the density distribution and star formation history from optical wavelength observations, (2) a detailed hydrodynamic simulation, and (3) combining the two. Our models yield a hundred to several hundred detectable DWDs: indeed, the LMC will be a resolved galaxy in the LISA sky. Importantly, amongst these we forecast a few tens to a hundred double degenerate supernovae type Ia progenitors, a class of binaries which have never been unambiguously observed. The range in the number of detections is primarily due to differences in the LMC total stellar mass and recent star formation in our models. Our results suggest that the total number, periods, and chirp masses of LISA sources may provide independent constraints on both LMC stellar mass and recent star formation by comparing LISA observations with the models, although such constraints will be highly model-dependent. Our publicly available model populations may be used in future studies of the LMC, including its structure and contribution to LISA confusion noise., Accepted to MNRAS. Adapted from M. A. Keim's MSc Thesis. Catalogues available at https://doi.org/10.5281/zenodo.6918083

In the paper we discuss the composition of a piece for prepared piano, Periplo del latte, that takes into account as its starting point the simulated gravitational wave data for the future LISA space mission. First, we introduce the LISA project and its output. Then, we present Einstein's Sonata, a multimedia project devoted to the artistic public display of the LISA data. Einstein's Sonata features as its main element the piece Periplo del latte. The latter is based on mapping astronomical data onto music. We thus detail a four-stage procedure for algorithmic composition, that features two data preprocessing stages, a mapping into an abstract control space and finally automatic notation generation.

White dwarf stars are a well-established tool for studying Galactic stellar populations. Two white dwarfs in a tight binary system offer us an additional messenger - gravitational waves - for exploring the Milky Way and its immediate surroundings. Gravitational waves produced by double white dwarf (DWD) binaries can be detected by the future Laser Interferometer Space Antenna (LISA). Numerous and widespread DWDs have the potential to probe shapes, masses and formation histories of the stellar populations in the Galactic neighbourhood. In this work we outline a method for estimating the total stellar mass of Milky Way satellite galaxies based on the number of DWDs detected by LISA. To constrain the mass we perform a Bayesian inference using binary population synthesis models and considering the number of detected DWDs associated with the satellite and the measured distance to the satellite as the only inputs. Using a fiducial binary population synthesis model we find that for large satellites the stellar masses can be recovered to within 1) a factor two if the star formation history is known and 2) an order of magnitude when marginalising over different star formation history models. For smaller satellites we can place upper limits on their stellar mass. Gravitational wave observations can provide mass measurements for large satellites that are comparable, and in some cases more precise, than standard electromagnetic observations., published in MNRAS Letters

So far detached compact binaries containing neutron stars have been observed either at intermediate stages of the evolution by radio telescopes or at merger by ground-based gravitational wave detectors. Sensitive to gravitational waves from binaries millions to thousands years prior to the merger, the future Laser Interferometer Space Antenna (LISA) will be crucial for bridging the gap between the currently accessible regimes. Depending on the binary type, LISA could potentially discover from a few to several hundreds in the entirely new regime throughout the Milky Way. Here we provide a concise summary of the current expectation for the detection of Galactic binaries containing neutron stars with LISA, focusing on double neutron stars and neutron star - white dwarf binaries. We outline a few examples of science investigations that LISA data will enable for these binaries.

The trajectory of the center of light of an unresolved binary is different from that of its center of mass. Binary-induced stellar centroid wobbling can therefore be detected as an excess in the goodness-of-fit of the single-star astrometric model. We use reduced $\chi^2$ of the astrometric fit in the {\it Gaia} Early Data Release 3 to detect the likely unresolved double white dwarfs (DWDs). Using parallax-based distances we convert the excess of reduced $\chi^2$ into the amplitude of the centroid wobble $\delta a$, which is proportional to the binary separation $a$. The measured $\delta a$ distribution drops towards larger wobble amplitudes and shows a break around $\delta a \approx 0.2$ where it steepens. The integral of the distribution yields DWD fraction of $6.5 \pm 3.7$ per cent in the range $0.01 < a (\text{au}) < 2$. Using synthetic models of the Galactic DWDs we demonstrate that the break in the $\delta a$ distribution corresponds to one side of a deep gap in the DWD separation distribution at around $a\approx 1$ au. Model DWDs with separations less than several au shrink dramatically due to (al least one) common envelope phase, reshaping the original separation distribution, clearing a gap and creating a pile-up of systems with $a\approx 0.01$ au and $\delta a < 0.01$. Our models reproduce the overall shape of the observed $\delta a$ distribution and its normalisation, however the predicted drop in the numbers of DWDs beyond the break is steeper than in the data., Comment: submitted to MNRAS main journal, comments are welcome

The Laser Interferometer Space Antenna (LISA) will detect and characterize $\sim10^4$ Galactic Binaries consisting predominantly of two White Dwarfs (WD). An interesting prospect within this population is a third object--another WD star, a Circumbinary Exoplanet (CBP), or a Brown Dwarf (BD)--in orbit about the inner WD pair. We present the first fully Bayesian detection and posterior analysis of sub-stellar objects with LISA, focusing on the characterization of CBPs. We used an optimistic astrophysically motivated catalogue of these CBP third-body sources, including their orbital eccentricity around the inner binary for the first time. We examined Bayesian Evidence computations for detectability, as well as the effects on the posterior distributions for both the inner binary parameters and the third-body parameters. We find that the posterior behavior bifurcates based on whether the third-body period is above or below half the observation time. Additionally, we find that undetectable third-body sources can bias the inner binary parameters whether or not the correct template is used. We used the information retrieved from the study of the CBP population to make an initial conservative prediction for the number of detectable BD systems in the original catalogue. We end with commentary on the predicted qualitative effects on LISA global fitting and Galactic Binary population analysis. The procedure used in this work is generic and can be directly applied to other astrophysical effects expected within the Galactic Binary population., 15 pages, 7 figures, 1 table

Gravitational wave science is a dynamical, fast-expanding research field founded on results, tools and methodologies drawn from different research areas and communities. Early career scientists entering this field must learn and combine knowledge and techniques from a range of disciplines. The Workshop on Gravitational-Wave Astrophysics for Early Career Scientists (GWAECS), held virtually in May 2021, planted the seeds of an interdisciplinary, well-connected and all-inclusive community of early career scientists working on gravitational waves, able to exchange relevant information and ideas, build a healthy professional and international environment, share and learn valuable skills, and ensure that ongoing research efforts are perpetuated and expanded in order to attain the main scientific goals envisioned by the whole community. GWAECS was the first event unifying early career scientists belonging to different communities, historically associated with different large-scale gravitational wave experiments. It provided a broad perspective on the future of gravitational waves, offered training on soft and transferable skills and allowed ample time for informal discussions between early career scientists and well-known research experts. The essence of those activities is summarised and collected in the present document, which presents a recap of each session of the workshop and aims to provide all early career scientists with a long-lasting, useful reference which constitutes the legacy of all the ideas that circulated at GWAECS.

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 and Badenes (2018) for the statistical analysis of the local DWD population using two complementary large, multi-epoch, spectroscopic samples: the Sloan Digital Sky Survey (SDSS), and the Supernova Ia Progenitor surveY (SPY). 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., Comment: Published in Monthly Notices of the Royal Astronomical Society, Volume 511, Issue 4, pp.5936-5947

We propose a space-based interferometer surveying the gravitational wave (GW) sky in the milli-Hz to $\mu$-Hz frequency range. By the 2040s', the $\mu$-Hz frequency band, bracketed in between the Laser Interferometer Space Antenna (LISA) and pulsar timing arrays, will constitute the largest gap in the coverage of the astrophysically relevant GW spectrum. Yet many outstanding questions related to astrophysics and cosmology are best answered by GW observations in this band. We show that a $\mu$-Hz GW detector will be a truly overarching observatory for the scientific community at large, greatly extending the potential of LISA. Conceived to detect massive black hole binaries from their early inspiral with high signal-to-noise ratio, and low-frequency stellar binaries in the Galaxy, this instrument will be a cornerstone for multimessenger astronomy from the solar neighbourhood to the high-redshift Universe., Comment: 28 pages, 8 figures; White Paper submitted to ESA's Voyage 2050 call for papers on behalf of the LISA Consortium 2050 Task Force

The population of Milky Way satellite galaxies is of great interest for cosmology, fundamental physics, and astrophysics. They represent the faint end of the galaxy luminosity function, are the most dark-matter dominated objects in the local Universe, and contain the oldest and most metal-poor stellar populations. Recent surveys have revealed around 60 satellites, but this could represent less than half of the total. Characterization of these systems remains a challenge due to their low luminosity. We consider the gravitational wave observatory LISA as a potential tool for studying these satellites through observations of their short-period double white dwarf populations. LISA will observe the entire sky without selection effects due to dust extinction, complementing optical surveys, and could potentially discover massive satellites hidden behind the disk of the galaxy., 7 pages, 2 figures

The nature of GW190425, a presumed binary neutron star (BNS) merger detected by the LIGO/Virgo Scientific Collaboration (LVC) with a total mass of $3.4^{+0.3}_{-0.1}$ M$_{\odot}$, remains a mystery. With such a large total mass, GW190425 stands at five standard deviations away from the total mass distribution of Galactic BNSs of $2.66\pm 0.12$ M$_{\odot}$. LVC suggested that this system could be a BNS formed from a fast-merging channel rendering its non-detection at radio wavelengths due to selection effects. BNSs with orbital periods less than a few hours - progenitors of LIGO/Virgo mergers - are prime target candidates for the future Laser Interferometer Space Antenna (LISA). If GW190425-like binaries exist in the Milky Way, LISA will detect them within the volume of our Galaxy and will measure their chirp masses to better than 10% for those binaries with gravitational wave frequencies larger than 2 mHz. This work explores how we can probe a population of Galactic GW190425-like BNSs with LISA and investigate their origin. We assume that the Milky Way's BNS population consists of two distinct sub-populations: a fraction $w_1$ that follows the observed Galactic BNS chirp mass distribution and $w_2$ that resembles chirp mass of GW190425. We show that LISA's accuracy on recovering the fraction of GW190425-like binaries depends on the BNS merger rate. For the merger rates reported in the literature, $21 - 212\,$Myr$^{-1}$, the error on the recovered fractions varies between $\sim 30 - 5$%., accepted by MNRAS

TianQin is a planned space-based gravitational wave (GW) observatory consisting of three earth orbiting satellites with an orbital radius of about $10^5~{\rm km}$. The satellites will form a equilateral triangle constellation the plane of which is nearly perpendicular to the ecliptic plane. TianQin aims to detect GWs between $10^{-4}~{\rm Hz}$ and $1~{\rm Hz}$ that can be generated by a wide variety of important astrophysical and cosmological sources, including the inspiral of Galactic ultra-compact binaries, the inspiral of stellar-mass black hole binaries, extreme mass ratio inspirals, the merger of massive black hole binaries, and possibly the energetic processes in the very early universe or exotic sources such as cosmic strings. In order to start science operations around 2035, a roadmap called the 0123 plan is being used to bring the key technologies of TianQin to maturity, supported by the construction of a series of research facilities on the ground. Two major projects of the 0123 plan are being carried out. In this process, the team has created a new generation $17~{\rm cm}$ single-body hollow corner-cube retro-reflector which has been launched with the QueQiao satellite on 21 May 2018; a new laser ranging station equipped with a $1.2~{\rm m}$ telescope has been constructed and the station has successfully ranged to all the five retro-reflectors on the Moon; and the TianQin-1 experimental satellite has been launched on 20 December 2019 and the first round result shows that the satellite has exceeded all of its mission requirements., 16 pages, 1 figure, invited article to a special section in PTEP

Context. Milky Way dwarf satellites are unique objects that encode the early structure formation and therefore represent a window into the high redshift Universe. So far, their study has been conducted using electromagnetic waves only. The future Laser Interferometer Space Antenna (LISA) has the potential to reveal Milky Way satellites through gravitational waves emitted by double white dwarf (DWD) binaries. Aims. We investigate gravitational wave signals that will be detectable by LISA as a possible tool for the identification and characterisation of the Milky Way satellites. Methods. We used the binary population synthesis technique to model the population of DWDs in dwarf satellites and we assessed the impact on the number of LISA detections when making changes to the total stellar mass, distance, star formation history, and metallicity of satellites. We calibrated predictions for the known Milky Way satellites on their observed properties. Results. We find that DWDs emitting at frequencies ≳3 mHz can be detected in Milky Way satellites at large galactocentric distances. The number of these high frequency DWDs per satellite primarily depends on its mass, distance, age, and star formation history, and only mildly depends on the other assumptions regarding their evolution such as metallicity. We find that dwarf galaxies with M⋆ > 106 M⊙ can host detectable LISA sources; the number of detections scales linearly with the satellite’s mass. We forecast that out of the known satellites, Sagittarius, Fornax, Sculptor, and the Magellanic Clouds can be detected with LISA. Conclusions. As an all-sky survey that does not suffer from contamination and dust extinction, LISA will provide observations of the Milky Way and dwarf satellites galaxies, which will be valuable for Galactic archaeology and near-field cosmology.

We explore the prospects of detecting of Galactic double white dwarf (DWD) binaries with the space-based gravitational wave (GW) observatory TianQin. In this work, we analyze both a sample of currently known DWDs and a realistic synthetic population of DWDs to assess the number of guaranteed detections and the full capacity of the mission. We find that TianQin can detect 12 out of $\sim100$ known DWDs; GW signals of these binaries can be modeled in detail ahead of the mission launch, and therefore they can be used as verification sources. Besides we estimate that TianQin has potential to detect as many as $10^4$ DWDs in the Milky Way. TianQin is expected to measure their orbital periods and amplitudes with accuracies of $\sim10^{-7}$ and $\sim0.2$, respectively, and to localize on the sky a large fraction (39%) of the detected population to better than 1 deg$^2$. We conclude that TianQin has the potential to significantly advance our knowledge on Galactic DWDs by increasing the sample up to 2 orders of magnitude, and will allow their multi-messenger studies in combination with electromagnetic telescopes. We also test the possibilities of different configurations of TianQin: (1) the same mission with a different orientation, (2) two perpendicular constellations combined into a network, and (3) the combination of the network with the ESA-led Laser Interferometer Space Antenna. We find that the network of detectors boosts the accuracy on the measurement of source parameters by 1-2 orders of magnitude, with the improvement on sky localization being the most significant., 21 pages, 7 figures, 6 tables, 5 appendices, to be published in Phys. Rev. D

Double white dwarf binaries with merger timescales smaller than the Hubble time and with a total mass near the Chandrasekhar limit (i.e. classical Chandrasekhar population) or with high-mass primaries (i.e. sub-Chandrasekhar population) are potential supernova type Ia (SNIa) progenitors. However, we have not yet unambiguously confirmed the existence of these objects observationally, a fact that has been often used to criticise the relevance of double white dwarfs for producing SNIa. We analyse whether this lack of detections is due to observational effects. To that end we simulate the double white dwarf binary population in the Galaxy and obtain synthetic spectra for the SNIa progenitors. We demonstrate that their identification, based on the detection of Halpha double-lined profiles arising from the two white dwarfs in the synthetic spectra, is extremely challenging due to their intrinsic faintness. This translates into an observational probability of finding double white dwarf SNIa progenitors in the Galaxy of (2.1+-1.0)x10^{-5} and (0.8+-0.4)x10^{-5} for the classical Chandrasekhar and the sub-Chandrasekhar progenitor populations, respectively. Eclipsing double white dwarf SNIa progenitors are found to suffer from the same observational effect. The next generation of large-aperture telescopes are expected to help in increasing the probability for detection by ~1 order of magnitude. However, it is only with forthcoming observations such as those provided by LISA that we expect to unambiguously confirm or disprove the existence of double white dwarf SNIa progenitors and to test their importance for producing SNIa., Comment: Re-submitted to MNRAS after applying all referee's suggestions

Binary interaction can cause stellar envelopes to be stripped, which significantly reduces the radius of the star. The orbit of a binary composed of a stripped star and a compact object can therefore be so tight that the gravitational radiation the system produces reaches frequencies accessible to the Laser Interferometer Space Antenna (LISA). Two such stripped stars in tight orbits with white dwarfs are known so far (ZTF J2130+4420 and CD-30 11223), but many more are expected to exist. These binaries provide important constraints for binary evolution models and may be used as LISA verification sources. We develop a Monte Carlo code that uses detailed evolutionary models to simulate the Galactic population of stripped stars in tight orbits with either neutron star or white dwarf companions. We predict 0-100 stripped star + white dwarf binaries and 0-4 stripped star + neutron star binaries with SNR>5 after 10 years of observations with LISA. More than 90% of these binaries are expected to show large radial velocity shifts of $\gtrsim 200$ km/s, which are spectroscopically detectable. Photometric variability due to tidal deformation of the stripped star is also expected and has been observed in ZTF J2130+4420 and CD-30 11223. In addition, the stripped star + neutron star binaries are expected to be X-ray bright with $L_X \gtrsim 10^{33} - 10^{36}$ erg/s. Our results show that stripped star binaries are promising multi-messenger sources for the upcoming electromagnetic and gravitational wave facilities., Submitted to ApJ

The Laser Interferometer Space Antenna (LISA) will enable Galactic gravitational wave (GW) astronomy by individually resolving $ > 10^4$ signals from double white dwarf (DWD) binaries throughout the Milky Way. In this work we assess for the first time the potential of LISA data to map the Galactic stellar bar and spiral arms, since GWs are unaffected by stellar crowding and dust extinction unlike optical observations of the bulge region. To achieve this goal we combine a realistic population of Galactic DWDs with a high-resolution N-Body simulation a galaxy in good agreement with the Milky Way. We then model GW signals from our synthetic DWD population and reconstruct the structure of the simulated Galaxy from mock LISA observations. Our results show that while the low signal contrast between the background disc and the spiral arms hampers our ability to characterise the spiral structure, the stellar bar will instead clearly appear in the GW map of the bulge. The bar length and bar width derived from these synthetic observations are underestimated, respectively within $1\sigma$ and at a level greater than $2\sigma$, but the resulting axis ratio agrees to well within $1\sigma$, while the viewing angle is recovered to within one degree. These are competitive constraints compared to those from electromagnetic tracers, and they are obtained with a completely independent method. We therefore foresee that the synergistic use of GWs and electromagnetic tracers will be a powerful strategy to map the bar and the bulge of the Milky Way., Comment: Accepted by MNRAS, 14 pages, 11 figures, 1 table

The upcoming LISA mission is the only experiment that offers the opportunity to map the Milky Way through gravitational wave radiation, exploiting signals from double white dwarf (DWD) binaries. I will show that the large number of DWD detections will allow us to use these systems as tracers of the Milky Way's shape and to measure scale parameters of the bulge, disc and bar. Furthermore, in the coming years, a large number of DWDs can be simultaneously detected in both electromagnetic (e.g. with Gaia and LSST) and gravitational wave radiation. This will provide a unique opportunity to perform a multi-messenger study of the Galaxy. Finally, I will talk about the prospects of using GW signals from halo DWDs for exploring the Local Group.

Accretion onto central massive black holes in galaxies is often modelled with the Bondi solution. In this paper we study a generalization of the classical Bondi accretion theory, considering the additional effects of the gravitational potential of the host galaxy, and of electron scattering in the optically thin limit. We provide a general analysis of the bias in the estimates of the Bondi radius and mass accretion rate, when adopting as fiducial values for the density and temperature at infinity the values of these quantities measured at finite distance from the central black hole. We also give general formulae to compute the correction terms of the critical accretion parameter in relevant asymptotic regimes. A full analytical discussion is presented in the case of an Hernquist galaxy, when the problem reduces to the discussion of a cubic equation, therefore allowing for more than one critical point in the accretion structure. The results are useful for observational works (especially in the case of low-luminosity systems), as well as for numerical simulations, where accretion rates are usually defined in terms of the gas properties near the, Comment: 13 pages, 5 figures, submitted to MNRAS. Comments welcome

Primordial black holes formed through the collapse of cosmological density fluctuations have been hypothesised as contributors to the dark matter content of the Universe. At the same time, their mergers could contribute to the recently observed population of gravitational-wave sources. We investigate the scenario in which primordial black holes form binaries at late times in the Universe. Specifically, we re-examine the mergers of primordial black holes in small clusters of ~30 objects in the absence of initial binaries. Binaries form dynamically through Newtonian gravitational interactions. These binaries act as heat sources for the cluster, increasing the cluster's velocity dispersion, which inhibits direct mergers through gravitational-wave two-body captures. Meanwhile, three-body encounters of tight binaries are too rare to tighten binaries sufficiently to allow them to merge through gravitational-wave emission. We conclude that in the absence of initial binaries, merger rates of primordial black holes in the Bird et al. (2016) initial cluster configuration are at least an order of magnitude lower than previously suggested, which makes gravitational-wave detections of such sources improbable., Comment: 8 pages, 4 figures

We explore the prospects for the detection of giant circumbinary exoplanets and brown dwarfs (BDs) orbiting Galactic double white dwarfs binaries (DWDs) with the Laser Interferometer Space Antenna (LISA). By assuming an occurrence rate of 50%, motivated by white dwarf pollution observations, we built a Galactic synthetic population of P-type giant exoplanets and BDs orbiting DWDs. We carried this out by injecting different sub-stellar populations, with various mass and orbital separation characteristics, into the DWD population used in the LISA mission proposal. We then performed a Fisher matrix analysis to measure how many of these three-body systems show a periodic Doppler-shifted gravitational wave perturbation detectable by LISA. We report the number of circumbinary planets (CBPs) and (BDs) that can be detected by LISA for various combinations of mass and semi-major axis distributions. We identify pessimistic and optimistic scenarios corresponding, respectively, to 3 and 83 (14 and 2218) detections of CBPs (BDs), observed during the length of the nominal LISA mission. These detections are distributed all over the Galaxy following the underlying DWD distribution, and they are biased towards DWDs with higher LISA signal-to-noise ratio and shorter orbital period. Finally, we show that if LISA were to be extended for four more years, the number of systems detected will be more than doubled in both the optimistic and pessimistic scenarios. Our results present promising prospects for the detection of post-main sequence exoplanets and BDs, showing that gravitational waves can prove the existence of these populations over the totality of the Milky Way. Detections by LISA will deepen our knowledge on the life of exoplanets subsequent to the most extreme evolution phases of their hosts, clarifying whether new phases of planetary formation take place later in the life of the stars., Comment: 16 pages, 8 figures, A&A in press

International audience; The upcoming Laser Interferometer Space Antenna (LISA) mission offers the unique opportunity to study the Milky Way through gravitational wave (GW) radiation from a large population of Galactic binaries. Among the variety of Galactic GW sources, LISA is expected to individually resolve signals from ∼10^5 ultra-compact double white dwarf (DWD) binaries. DWDs detected by LISA will be distributed across the Galaxy, including regions that are hardly accessible to electromagnetic (EM) observations such as the inner part of the Galactic disc, the bulge, and beyond. We quantitatively show that the large number of DWD detections will allow us to use these systems as tracers of the Milky Way potential. We demonstrate that density profiles of DWDs detected by LISA may provide constraints on the scale length parameters of the baryonic components that are both accurate and precise, with statistical errors of a few per cent to 10 per cent level. Furthermore, the LISA sample is found to be sufficient to disentangle between different (commonly used) disc profiles, by well covering the disc out to sufficiently large radii. Finally, up to ∼80 DWDs can be detected through both EM and GW radiation. This enables multimessenger astronomy with DWD binaries and allows one to extract their physical properties using both probes. We show that fitting the Galactic rotation curve constructed using distances inferred from GWs and proper motions from optical observations yield a unique and competitive estimate of the bulge mass. Instead robust results for the stellar disc mass are contingent upon knowledge of the dark matter content.

Detached double white dwarf (DWD) binaries are one of the main science case for the Laser Interferometer Space Antenna (LISA). As the most numerous LISA sources, they will provide important contributions towards understanding binary evolution, Supernovae Type Ia (SNIa) formation channels and the structure of the Milky Way. So far only detection prospects for the Milky Way have been computed. In this letter we show that LISA has the potential to detect DWDs in neighboring galaxies up to the border of the Local Group. In particular, we compute quantitative estimates for the number of detections in M31. We expect between a dozen to several tens of DWDs above the nominal detection threshold, for a mission duration between 4 and 10$\,$yr. We show that extra-galactic DWDs detectable by LISA are those with the shortest orbital periods and with the highest chirp masses, that are candidates SNIa progenitor, virtually undetectable at those distances in optical. This implies that LISA will be the only instrument able to provide SNIa merger rates across the Local Group., 4 pages, 3 figures

Ultracompact binaries with orbital periods less than a few hours will dominate the gravitational wave signal in the mHz regime. Until recently, 10 systems were expected have a predicted gravitational wave signal strong enough to be detectable by the Laser Interferometer Space Antenna (LISA), the so-called `verification binaries'. System parameters, including distances, are needed to provide an accurate prediction of the expected gravitational wave strength to be measured by LISA. Using parallaxes from {\sl Gaia} Data Release 2 we calculate signal-to-noise ratios (SNR) for $\approx$50 verification binary candidates. We find that 11 binaries reach a SNR$\geq$20, two further binaries reaching a SNR$\geq$5 and three more systems are expected to have a SNR$\approx$5 after four years integration with LISA. For these 16 systems we present predictions of the gravitational wave amplitude ($\mathcal{A}$) and parameter uncertainties from Fisher information matrix on the amplitude ($\mathcal{A}$) and inclination ($\iota$)., Comment: accepted for publication in MNRAS, 9 pages, 4 figures

Double white dwarf (DWD) binaries are expected to be very common in the Milky Way, but their intrinsic faintness challenges the detection of these systems. Currently, only a few tens of detached DWDs are know. Such systems offer the best chance of extracting the physical properties that would allow us to address a wealth of outstanding questions ranging from the nature of white dwarfs, over stellar and binary evolution to mapping the Galaxy. In this paper we explore the prospects for detections of ultra-compact (with binary separations of a few solar radii or less) detached DWDs in: 1) optical radiation with Gaia and the LSST and 2) gravitational wave radiation with LISA. We show that Gaia, LSST and LISA have the potential to detect respectively around a few hundreds, a thousand, and 25 thousand DWD systems. Moreover, Gaia and LSST data will extend by respectively a factor of two and seven the guaranteed sample of binaries detected in electromagnetic and gravitational wave radiation, opening the era of multi-messenger astronomy for these sources., Comment: submitted to MNRAS

AM CVn binaries are hydrogen deficient compact binaries with an orbital period in the 5-65 min range and are predicted to be strong sources of persistent gravitational wave radiation. Using Gaia Data Release 2, we present the parallaxes and proper motions of 41 out of the 56 known systems. Compared to the parallax determined using the HST Fine Guidance Sensor we find that the archetype star, AM CVn, is significantly closer than previously thought. This resolves the high luminosity and mass accretion rate which models had difficulty in explaining. Using Pan-STARRS1 data we determine the absolute magnitude of the AM CVn stars. There is some evidence that donor stars have a higher mass and radius than expected for white dwarfs or that the donors are not white dwarfs. Using the distances to the known AM CVn stars we find strong evidence that a large population of AM CVn stars have still to be discovered. As this value sets the background to the gravitational wave signal of LISA, this is of wide interest. We determine the mass transfer rate for 15 AM CVn stars and find that the majority have a rate significantly greater than expected from standard models. This is further evidence that the donor star has a greater size than expected., Accepted by A&A in main journal