Electromagnetic Observations Research Articles

Heaven and Earth: Nuclear Astrophysics after GW170817

The historical detection of gravitational waves from the binary neutron star merger GW170817 is providing fundamental new insights into the astrophysical site for the creation of the heaviest elements in the cosmos and the equation of state of neutron-rich matter. Shortly after this historical detection, electromagnetic observations of neutron stars together with measurements of the properties of neutron-rich nuclei at terrestrial facilities have placed additional constraints on the dynamics of neutron-rich matter. It is this unique synergy between heaven and earth that is the focus of this article.

An updated nuclear-physics and multi-messenger astrophysics framework for binary neutron star mergers

The multi-messenger detection of the gravitational-wave signal GW170817, the corresponding kilonova AT2017gfo and the short gamma-ray burst GRB170817A, as well as the observed afterglow has delivered a scientific breakthrough. For an accurate interpretation of all these different messengers, one requires robust theoretical models that describe the emitted gravitational-wave, the electromagnetic emission, and dense matter reliably. In addition, one needs efficient and accurate computational tools to ensure a correct cross-correlation between the models and the observational data. For this purpose, we have developed the Nuclear-physics and Multi-Messenger Astrophysics framework NMMA. The code allows incorporation of nuclear-physics constraints at low densities as well as X-ray and radio observations of isolated neutron stars. In previous works, the NMMA code has allowed us to constrain the equation of state of supranuclear dense matter, to measure the Hubble constant, and to compare dense-matter physics probed in neutron-star mergers and in heavy-ion collisions, and to classify electromagnetic observations and perform model selection. Here, we show an extension of the NMMA code as a first attempt of analyzing the gravitational-wave signal, the kilonova, and the gamma-ray burst afterglow simultaneously. Incorporating all available information, we estimate the radius of a 1.4M⊙ neutron star to be R=11.98−0.40+0.35\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$R=11.9{8}_{-0.40}^{+0.35}$$\\end{document} km.

Fractal Features in kHz Electromagnetic Observations Preceding Near-Field Earthquakes in Ilia, Greece

This paper reports kHz EM observations recorded by the Kardamas station in Ilia, Greece a few days before four near-field earthquakes occurred within a 24 km radius, with epicentral depths below 29 km. This work investigated the fractal features hidden in the EM observations via power-law analysis. All EM signals exhibited characteristic fractal epochs with organisation in space and time. A significant number of accurate fractal segments were delineated in the majority of the EM observations. A significant number of fractal areas corresponded to predictable Class I fBm category with 1 ≤ b ≤ 3 (0 ≤ H ≤ 1). Numerous persistent key-periods are reported with 2 < b ≤ 3 (0.5 ≤ H ≤ 1) which are deemed as signs of impeding earthquakes according to the literature. Numerous segments were found with strong persistent b-values in the range (2.3 ≤ b ≤ 3) (0.65 ≤ H ≤ 1) and b-values corresponding to switching between antipersistency and persistency with (1.7 ≤ b < 2.3) (0.35 ≤ H < 0.65). These are deemed as the most significant precursory signs. Interpretations are given via the asperity model.

Rapid Premerger Localization of Binary Neutron Stars in Third-generation Gravitational-wave Detectors

Premerger localization of binary neutron stars (BNSs) is one of the most important scientific goals for the third-generation (3G) gravitational-wave detectors. It will enable the electromagnetic observation of the whole process of BNS coalescence, especially for the premerger and merger phases, which have not been observed yet, opening a window for deeper understandings of compact objects. To reach this goal, we describe a novel combination of multiband matched filtering and semianalytical localization algorithms to achieve early-warning localization of long BNS signals in 3G detectors. Using our method we are able to efficiently simulate one month of observations with a three-detector 3G network, and show that it is possible to provide accurate sky localizations more than 30 minutes before the merger. Our simulation shows that there could be ∼10 (∼100) BNS events localized within 100 deg2, 20 (6) minutes before merger, per month of observation.

Shear‐Enhanced Electrical Conductivity of Synthetic Quartz‐Graphite Gouges: Implications for Electromagnetic Observations in Carbonaceous Shear Zones

AbstractGraphite is considered as a material that promotes fault weakening and electrical conductivity (σ) enhancement at fault zones. We studied how shear deformation may affect the evolution of friction and electrical conductivity of synthetic quartz (Qz)‐graphite (Gr) mixtures and, more importantly, whether the σ of the mixtures present visible changes at the beginning of the simulated fault slip. Long‐displacement friction experiments were performed on 1.2–2.3 mm‐thick gouge specimens of varied Gr volume fraction (XGr = 0–100 vol.%) under identical normal stress (2 or 5 MPa), slip rate (∼1.0 mm/s), and N2‐flushing conditions. The experimental results suggested that the σ of the specimens with ≥4.6 vol.% XGr abruptly increased under limited shear displacement. With continued shear, the steady‐state electrical conductivity (σss) increased by more than seven orders of magnitude when XGr > 3.4 vol.%, while the steady‐state frictional coefficient remained high (0.54–0.80) except for the specimens with XGr > 13.6 vol.%. The post‐mortem microstructures revealed that the high σss observed in the intermediate Gr content specimens (3.4–13.6 vol.%) is associated with an ad‐hoc fabric (graphite–cortex clasts) present in the principal slip zone. For high Gr content, excess Gr flakes fill the pores and help develop mechanically lubricated surfaces. We propose that low Gr content (i.e., as low as 3.4 vol.%) can cause high conductivity anomalies in natural shear zones. Overall, the findings suggest that the initiation of slips within carbonaceous shear zones can be detected by identifying unusual temporal signals using electromagnetic stations.

Acoustical Power of Lightning Flashes

AbstractLightning is a ubiquitous source of infrasound. To study lightning flashes, thunder measurement efficiently complements electromagnetic observation. Using acoustical arrays, time delays between sensors inform on the direction of sound arrival, while the difference between emission time and sound arrival provides the source distance. Combining the two allows a geometrical reconstruction of individual lightning flashes, each viewed as a set of sound point sources. The measured sound amplitude can also be back‐propagated, compensating for absorption and density stratification. This allows to evaluate the acoustical power of each detected source, and the total power of an individual flash. This methodology is carried out to analyze data from two campaigns in Southern continental France (HyMeX‐SOP1, 2012) and in Corsica (EXAEDRE, 2018). Acoustic reconstruction is compared with ground and altitude localizations provided respectively by electromagnetic low frequency range Lightning Location Systems (LLS), and very high frequency range Lightning Mapping Array (LMA). In Corsica, power from reconstructed sources is also forward‐propagated toward several isolated microphones, and compared to measured signal, giving an additional validation of the power evaluation. Seventy eight events from the two campaigns are analyzed, including negative and positive cloud‐to‐ground discharges and intracloud ones. The analysis outlines the method efficiency and the strong variability of lightning as sound sources in terms of both power spatial distribution and overall value. Lastly, the correlation of this later with electrical parameters is investigated, either peak current (provided by LLS) or Charge Moment Change, resulting from broadband Extremely Low Frequency (ELF) measurements.

GRMHD study of accreting massive black hole binaries in astrophysical environment: A review

We present an overview of recent numerical advances in the theoretical characterization of massive binary black hole (MBBH) mergers in astrophysical environments. These systems are among the loudest sources of gravitational waves (GWs) in the universe and particularly promising candidates for multimessenger astronomy. Coincident detection of GWs and electromagnetic (EM) signals from merging MBBHs is at the frontier of contemporary astrophysics. One major challenge in observational efforts searching for these systems is the scarcity of strong predictions for EM signals arising before, during, and after merger. Therefore, a great effort in theoretical work to-date has been to characterize EM counterparts emerging from MBBHs concurrently to the GW signal, aiming to determine distinctive observational features that will guide and assist EM observations. To produce sharp EM predictions of MBBH mergers it is key to model the binary inspiral down to coalescence in a full general relativistic fashion by solving Einstein’s field equations coupled with the magnetohydrodynamics equations that govern the evolution of the accreting plasma in strong-gravity. We review the general relativistic numerical investigations that have explored the astrophysical manifestations of MBBH mergers in different environments and focused on predicting potentially observable smoking-gun EM signatures that accompany the gravitational signal.

Detector induced anisotropies on the angular distribution of gravitational wave sources and opportunities of constraining horizon scale anisotropies

ABSTRACT The cosmological principle has been verified using electromagnetic observations. However its verification with high accuracy is challenging due to various foregrounds and selection effects, and possible violation of the cosmological principle has been reported in the literature. In contrast, gravitational wave (GW) observations are free of these foregrounds and related selection biases. This may enable future GW experiments to test the cosmological principle robustly with full sky distribution of millions of standard bright/dark sirens. However, the sensitivities of GW detectors are highly anisotropic, resulting in significant instrument induced anisotropies in the observed GW catalogue. We investigate these instrumental effects for 3rd generation detector networks in term of multipoles aℓm of the observed GW source distribution, using Monte Carlo simulations. (1) We find that the instrument induced anisotropy primarily exists at the m = 0 modes on large scales (ℓ ≲ 10), with amplitude 〈|aℓ0|2〉 ∼ 10−3 for two detectors (ET-CE) and ∼10−4 for three detectors (ET-2CE). This anisotropy is correlated with the sky distribution of signal-to-noise ratio and localization accuracy. Such anisotropy sets a lower limit on the detectable cosmological aℓ0. (2) However, we find that the instrument induced anisotropy is efficiently cancelled by rotation of the Earth in m ≠ 0 components of aℓm. Therefore aℓm (m ≠ 0) are clean windows to detect cosmological anisotropies. (3) We investigate the capability of 3rd generation GW experiments to measure the cosmic dipole. Through Monte Carlo simulations, we find that cosmic dipole with an amplitude of ∼10−2 reported in the literature can be detected/ruled out by ET-CE and ET-2CE robustly, through the measurement of a11.

Unpacking Merger Jets: A Bayesian Analysis of GW170817, GW190425 and Electromagnetic Observations of Short Gamma-Ray Bursts

We present a novel fully Bayesian analysis to constrain short gamma-ray burst (sGRB) jet structures associated with cocoon, wide-angle, and simple top-hat jet models, as well as the binary neutron star (BNS) merger rate. These constraints are made given the distance and inclination information from GW170817, observed flux of GRB 170817A, observed rate of sGRBs detected by Swift, and the neutron star merger rate inferred from LIGO’s first and second observing runs. A separate analysis is conducted where a fitted sGRB luminosity function is included to provide further constraints. The jet structure models are further constrained using the observation of GW190425, and we find that the assumption that it produced a GRB 170817–like sGRB which went undetected due to the jet geometry is consistent with previous observations. We find and quantify evidence for low-luminosity and wide-angle jet structuring in the sGRB population, independently from afterglow observations, with log Bayes factors of 0.45–0.55 for such models when compared to a classical top-hat jet. Slight evidence is found for a Gaussian jet structure model over all others when the fitted luminosity function is provided, producing log Bayes factors of 0.25–0.9 ± 0.05 when compared to the other models. However, without considering GW190425 or the fitted luminosity function, the evidence favors a cocoon-like model with log Bayes factors of 0.14 ± 0.05 over the Gaussian jet structure. We provide new constraints to the BNS merger rates of 1–1300 Gpc−3 yr−1 or 2–680 Gpc−3 yr−1 when a fitted luminosity function is assumed.

Universal relations to measure neutron star properties from targeted r-mode searches

ABSTRACT R-mode oscillations of rotating neutron stars (NS) are promising candidates for continuous gravitational wave (GW) observations. In our recent work, we derived universal relations between the NS parameters compactness and dimensionless tidal deformability with the r-mode frequency. In this work, we investigate how these universal relations can be used to infer various NS intrinsic parameters following a successful detection of the r-modes. In particular, we show that for targeted r-mode searches, these universal relations along with the ‘I–Love–Q’ relation can be used to estimate both the moment of inertia and the distance of the NS, thus breaking the degeneracy of distance measurement for continuous gravitational wave (CGW) observations. We also discuss that, with a prior knowledge of the distance of the NS from electromagnetic observations, these universal relations can also be used to constrain the dense matter equation of state (EOS) inside the NS. We quantify the accuracy to which such measurements can be done using the Fisher information matrix for a broad range of possible, unknown parameters for both the a-LIGO and Einstein Telescope (ET) sensitivities.

Measuring mass transfer of AM CVn binaries with a space-based gravitational wave detector

ABSTRACT The formation mechanism of AM CVn binary has not been well understood yet. Accurate measurements of the mass transfer rate can help us to determine the formation mechanism. But unfortunately such observation by electromagnetic means is quite challenging. One possible formation channel of AM CVn binary is a semidetached white dwarf binary. Such system emits strong gravitational wave radiation which could be measured by the future space-based detectors. We can simultaneously extract the mass transfer rate and the orbital period from the gravitational wave signal. We employ a post-Keplerian waveform model of gravitational wave and carry out a Fisher analysis to estimate the measurement accuracy of mass transfer rate through gravitational wave detection. Special attention is paid to the observed sources in Gaia Data Release 2. We found that we can accurately measure the mass transfer rate for those systems. Comparing to electromagnetic observations, gravitational wave detection improves the accuracy more than two orders of magnitude. Our results imply that the gravitational wave detection will help much in understanding the formation mechanism of AM CVn binaries.

Cocoon cooling emission in neutron star mergers

ABSTRACT In the gravitational wave event GW170817, there was a ∼10 h gap before electromagnetic (EM) observations, without detection of the cocoon. The cocoon is heated by a short gamma-ray burst (sGRB) jet propagating through the ejecta of a neutron star (NS) merger, and a part of the cocoon escapes the ejecta with an opening angle of 20°–30°. Here, we model the cocoon and calculate its EM emission. Our 2D hydrodynamic simulations suggest that the density and energy distributions, after entering homologous expansion, are well-fitted with power-law functions, in each of the relativistic and non-relativistic parts of the escaped cocoon. Modelling these features, we calculate the cooling emission analytically. We find that the cocoon outshines the r-process kilonova/macronova at early times (10–103 s), peaking at UV bands. The relativistic velocity of the cocoon’s photosphere is measurable with instruments such as Swift, ULTRASAT, and LSST. We also imply that energetic cocoons, including failed jets, might be detected as X-ray flashes. Our model clarifies the physics and parameter dependence, covering a wide variety of central engines and ejecta of NS mergers and sGRBs in the multimessenger era.

Probing Accretion Physics with Gravitational Waves

Gravitational-wave observations of extreme mass ratio inspirals (EMRIs) offer the opportunity to probe the environments of active galactic nuclei (AGN) through the torques that accretion disks induce on the binary. Within a Bayesian framework, we study how well such environmental effects can be measured using gravitational wave observations from the Laser Interferometer Space Antenna (LISA). We focus on the torque induced by planetary-type migration on quasicircular inspirals, and use different prescriptions for geometrically thin and radiatively efficient disks. We find that LISA could detect migration for a wide range of disk viscosities and accretion rates, for both $\alpha$ and $\beta$ disk prescriptions. For a typical EMRI with masses $50M_\odot+10^6M_\odot$, we find that LISA could distinguish between migration in $\alpha$ and $\beta$ disks and measure the torque amplitude with $\sim 20\%$ relative precision. Provided an accurate torque model, we also show how to turn gravitational-wave measurements of the torque into constraints on the disk properties. Furthermore, we show that, if an electromagnetic counterpart is identified, the multimessenger observations of the AGN EMRI system will yield direct measurements of the disk viscosity. Finally, we investigate the impact of neglecting environmental effects in the analysis of the gravitational-wave signal, finding 3$\sigma$ biases in the primary mass and spin, and showing that ignoring such effects can lead to false detection of a deviation from general relativity. This work demonstrates the scientific potential of gravitational observations as probes of accretion-disk physics, accessible so far through electromagnetic observations only.

Compact Stars in the vBag Model and Its f-Mode Oscillations

Electromagnetic (EM) observations and gravitational wave (GW) measurements enable us to determine the mass and radius of neutron stars (NSs) and their tidal deformability, respectively. These parameters offer valuable insights into the properties of dense matter in NSs. In this study, the vector-interaction-enhanced bag model (vBag model) is employed to investigate strange and hybrid stars’ properties. The parameters of the vBag model are constrained using multi-messenger observations, revealing that strange stars are incompatible with current observations. In contrast, hybrid stars can exhibit a substantial mixed phase region and a thin hadronic shell. Furthermore, we present the frequencies and damping time of fundamental mode (f-mode) oscillations of hybrid stars and test their universal relations with compactness and tidal deformability. The findings indicate that the presence of mixed phase components leads to larger frequencies and shorter damping time of the f-mode oscillation of hybrid stars, and the softer equation of state (EoS) affects this behavior more significantly. The universal relations of hybrid stars in the vBag model can be described by fourth-order/seventh-order polynomials, which do not break the previous results.

Interaction of Interplanetary Shocks With the Moon: Hybrid Simulations and ARTEMIS Observations

AbstractWhen in the solar wind, the Moon is exposed to its embedded discontinuities such as interplanetary (IP) shocks. In this study we utilize 3‐D electromagnetic hybrid (kinetic ions, fluid electrons) simulations and observations of two events, by THEMIS/ARTEMIS spacecraft to understand the interaction of IP shocks with the Moon. Simulation parameters are based on one of the ARTEMIS events and include the presence of supra‐thermal ions in the solar wind. The results show that the absorption of the cold solar wind protons on the Moon's dayside leads to a density hole in the shock front behind the Moon. This density hole refills and recovers as the IP shock moves down the lunar tail. Penetration of the interplanetary magnetic field through Moon's body leads to the survival of a steepened magnetic structure associated with the shock surface. However, due to the lower pressures in the lunar tail the structure broadens in space and is expected to steepen when the IP shock is beyond the tail. The IP shock is also found to interact with the energetic ions in the lunar tail resulting in their acceleration to higher energies. Comparing the densities measured by ARTEMIS in the solar wind and lunar tail shows the absence of a shock front in density in the tail consistent with the formation of a density hole at the shock front. Similarly, comparing the magnetic field profiles in the solar wind and lunar tail shows the expected broadening of the magnetic field shock front.

Unmasking strange dwarfs with gravitational-wave observations

The advent of space-based gravitational-wave detectors like the Laser Interferometer Space Antenna will allow us to observe signals, most of which are expected to be emitted by white-dwarf binaries. Among these systems another kind of compact objects could be hidden, postulated by Glendenning, Kettner, and Weber in 1995, containing a small core made of strange quark matter surrounded by layers of hadronic matter reaching densities much higher than in white dwarfs. These so-called strange dwarfs cannot be easily distinguished from white dwarfs through electromagnetic observations alone; their outermost envelopes are expected to have the same composition and their radii are quite similar (except for low masses). However, future measurements of the tidal deformability through gravitational-wave observations could provide a new way to reveal their existence. In this paper, we revisit the structure and the tidal deformability of strange dwarfs in full general relativity taking into account the possible crystallization of their envelope. Unlike most previous studies, we do not describe the hadronic layers using the equation of state of Baym, Pethick, and Sutherland, which was originally designed for the outer crust of a neutron star. The conditions leading to such heavy elements in gravitational-core collapse supernova explosions are not expected to be met during the stellar evolution leading to the formation of strange dwarfs. Instead, we consider the same light elements as found in white dwarfs but we take into account electron captures by nuclei and possibly pycnonuclear fusions that may be triggered by compression. We find that the radius of strange dwarfs is systematically smaller than that of their white dwarf relatives. These deviations can be large for very low-mass stars but mostly lie within the current observational uncertainties for typical white dwarf masses. On the other hand, the observable tidal deformability coefficient ${\mathrm{\ensuremath{\Lambda}}}_{2}$ is strongly reduced in comparison to white dwarfs and the deviation will be potentially measurable by future space-based gravitational-wave detectors.

Prospects for constraining interacting dark energy models from gravitational wave and gamma ray burst joint observation

With the measurement of the electromagnetic (EM) counterpart, a gravitational wave (GW) event could be treated as a standard siren. As a novel cosmological probe, GW standard sirens will bring significant implications for cosmology. In this paper, by considering the coincident detections of GW and associated γ ray burst (GRB), we find that only about 400 GW bright standard sirens from binary neutron star mergers could be detected in a 10-year observation of the Einstein Telescope and the THESEUS satellite mission. Based on this mock sample, we investigate the implications of GW standard sirens on the interaction between dark energy and dark matter. In our analysis, four viable interacting dark energy (IDE) models, with interaction forms Q = 3βHρ de and Q = Q = 3βHρ c, are considered. Compared with the traditional EM observational data such as CMB, BAO, and SN Ia, the combination of both GW and EM observations could effectively break the degeneracies between different cosmological parameters and provide more stringent cosmological fits. We find that the GW data could play a more important role for determining the interaction in the models with Q = 3βHρ c, compared with the models with Q = 3βHρ de. We also show that constraining IDE models with mock GW data based on different fiducial H 0 values yield different results, indicating that accurate determination of H 0 is significant for exploring the interaction between dark energy and dark matter.

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.

The Gravitational Wave Universe Toolbox

Context. In the current multi-messenger astronomy era, it is important that information about joint gravitational wave (GW) and electromagnetic (EM) observations through short gamma-ray bursts (sGRBs) remains easily accessible to each member of the GW-EM community. The possibility for non-experts to execute quick computations of joint GW-sGRB detections should be facilitated. Aims. For this study, we constructed a model for sGRBs and added this to the framework of the previously built Gravitational Wave Universe Toolbox (GWToolbox or Toolbox). We provide expected joint GW-sGRB detection rates for different combinations of GW detectors and high-energy (HE) instruments. Methods. We employed and adapted a generic GRB model to create a computationally low-cost top-hat jet model suitable for the GWToolbox. With the Toolbox, we simulated a population of binary neutron stars (BNSs) observed by a user-specified GW detector such as LIGO, Virgo, the Einstein Telescope (ET), or the Cosmic Explorer (CE). Based on the characteristics of each binary, our model predicts the properties of a resulting sGRB, as well as its detectability for HE detectors such as Fermi/GBM, Swift/BAT, or GECAM. Results. We report predicted joint detection rates for combinations of GW detectors (LIGO and ET) with HE instruments (Fermi/GBM, Swift/BAT, and GECAM). Our findings stress the significance of the impact that ET will have on multi-messenger astronomy. While the LIGO sensitivity is currently the limiting factor regarding the number of joint detections, ET will observe BNSs at such a rate that the vast majority of detected sGRBs will have a GW counterpart observed by ET. These conclusions hold for CE as well. Additionally, since LIGO can only detect BNSs up to a redshift of ~0.1 where few sGRBs exist, a search for sub-threshold GW signals at higher redshifts using sGRB information from HE detectors has the potential to be very successful and significantly increase the number of joint detections. Equivalently, during the ET era, GW data can assist in finding sub-threshold sGRBs, potentially increasing, for example, the number of joint ET-Fermi/GBM observations by ~270%. Lastly, we find that our top-hat jet model underestimates the number of joint detections that include an off-axis sGRB. We corrected for this by introducing a second, wider and weaker jet component. We predict that the majority of joint detections during the LIGO/Virgo era will include an off-axis sGRB, making GRB170817A not as unlikely as one would think based on the simplest top-hat jet model. In the ET era, most joint detections will contain an on-axis sGRB.

Study of the agreement between binary neutron star ejecta models derived from numerical relativity simulations

Neutron star mergers have recently become a tool to study extreme gravity, nucleosynthesis, and the chemical composition of the Universe. To date, there has been one joint gravitational and electromagnetic observation of a binary neutron star merger, GW170817, as well as a solely gravitational observation, GW190425. In order to accurately identify and interpret electromagnetic signals of neutron star mergers, better models of the matter outflows generated by these mergers are required. We compare a series of ejecta models to see where they provide strong constraints on the amount of ejected mass expected from a system, and where systematic uncertainties in current models prevent us from reliably extracting information from observed events. We also examine 2396 neutron star equations of state compatible with GW170817 to see whether a given ejecta mass could be reasonably produced with a neutron star of said equation of state, and whether different ejecta models provide consistent predictions. We find that the difference between models is often comparable to or larger than the error generally assumed for these models, implying better constraints on the models are needed. We also note that the extrapolation of outflow models outside of their calibration window, while commonly needed to analyze gravitational wave events, is extremely unreliable and occasionally leads to completely unphysical results.