Using pulsar accelerations, we identify and constrain the properties of a dark matter subhalo in the Galaxy for the first time from analyzing the acceleration field of binary and solitary pulsars. The subhalo is characterized by analyzing a local deviation from a smooth potential. Our MCMC calculations show that this subhalo has a mass of 2.45_{-0.96}^{+1.07}×10^{7}M_{⊙} and is located at Galactocentric coordinates X=7.43_{-0.12}^{+0.2}  kpc, Y=0.38_{-0.16}^{+0.11}  kpc, Z=0.21_{-0.11}^{+0.06}  kpc, using flat, uninformative priors, where we have modeled the sub halo as a compact object. The Bayes factors for the models are in the range of ∼20-40, which indicates tentative evidence (though not yet decisive) for the subhalo. Modeling the subhalo with a NFW profile gives a subhalo mass of 6.19_{-2.03}^{+1.92}×10^{7}M_{⊙}, located at X=7.47_{-0.14}^{+0.21}, Y=0.38_{-0.16}^{+0.11}, Z=0.21_{-0.11}^{+0.06}; the mass within the scale radius (0.1 kpc) for the NFW profile is 0.48_{-0.16}^{0.15}×10^{7}M_{⊙}. We examine Gaia data and the atomic and molecular hydrogen data of our Galaxy and show that the measured deviation from a smooth potential cannot arise from the gas or the stars in our Galaxy. Additionally, by analyzing the full sample of binary pulsars with available acceleration measurements that span 3.4 kpc in Galactocentric radius from the Sun and 3.6 kpc in vertical height, we find that massive (with mass >10^{8}M_{⊙}) subhalos are disfavored for the Milky Way within several kiloparsec of the Sun. While smaller sub-halos may be present, they are beyond the reach of current direct acceleration measurements. The presence of a ∼10^{7}M_{⊙} subhalo within a few kpc of the Sun is potentially consistent with the expected number counts of sub-halos in the prevailing ΛCDM paradigm, for a substantial subhalo mass fraction. As the number and precision of direct acceleration measurements continues to grow, we will obtain tighter constraints on dark matter sub-structure in our Galaxy. This Letter now provides a proof of principle for probing nearby, low-mass subhalos, and has implications across many fields of astrophysics-from understanding the nature of dark matter to galaxy formation.

Common-envelope evolution (CEE) is one of the biggest open questions in binary stellar evolution, despite being the main channel for the formation of close binaries. One of the main reasons CEE is difficult to model is the lack of direct observations that could constrain numerical simulations. One exception is luminous red novae, which are thought to represent CEEs that end in mergers. Unfortunately, there are no confirmed direct detections of ongoing events that result in the survival of a close binary, and we must rely on observations of post-CEE systems. Among these, planetary nebulae (PNe) are particularly important because their morphologies can probe how the envelope is ejected. However, post-CEE PNe do not reflect the ejected envelope in its pristine form, as winds from the central core also affect their morphology. In this context, Water Fountains (WFs), a class of objects proposed to form during CEE, provide an ideal comparison. They are identified by their collimated water masers, and most are still in the post-AGB phase. As such, WFs provide some of the best observational constraints for simulations, since they likely capture a snapshot of the envelope ejection while it is still happening. In this paper, we show that the formation of a circumbinary disk with collimated outflows surrounding the central binary arises naturally from hydrodynamical simulations of CEE, and that their morphology and kinematics are consistent with observations of WFs. We also present insights into how the properties of WFs may provide clues to understanding how CEE proceeds and help guide future simulations.

Although well studied, our understanding of the mass ejection mechanisms of cataclysmic variables remains incomplete. Recent work suggests that binary interaction plays an important role in driving and shaping this mass ejection and may affect the long-term evolution of the system. In this paper, we perform a three-dimensional moving-mesh hydrodynamic simulation of a cataclysmic variable system to study the effect of binary interaction on mass ejection. We find that once the flow crosses the L_1 Lagrange point, the material is ejected roughly isotropically. This can be seen in a roughly spherical distribution of the ejecta at large radii. We also show that the L_2 Lagrange point is not important in the ejection of mass, contrary to the assumption in some previous work in this area. Finally, we find that the specific angular momentum of the ejected material is larger than its initial specific angular momentum. This enhanced angular momentum ejection likely affects the long-term evolution of the binary system.

Thorne–Żytkow objects (TŻOs) are hypothetical hybrid stars with a neutron star at the core of a large, diffuse envelope. TŻOs may be formed when a newly formed neutron star that is kicked by its supernova collides with its main-sequence companion. Using a moving-mesh hydrodynamics solver integrated into the parallel-code Charm N -body GrAvity solver, we demonstrate that these “impact scenario” formation processes robustly form TŻOs for periastron distances less than one stellar radius. These TŻOs are dynamically stable, and they can serve as initial models for further evolutionary studies.

We measure the line-of-sight accelerations of 26 binary pulsars due to the Milky Way's gravitational potential, and produce a three-dimensional map of the acceleration field of the Galaxy. Acceleration measurements directly give us the change in the line-of-sight velocity at present day, without requiring any assumptions inherent to kinematic modeling. We measure the Oort limit (rho 0 0 = 0.062 + 0.017M circle dot/pc3) M circle dot / pc 3 ) and the dark matter density in the midplane (rho 0;DM = -0.010 + 0.018M circle dot/pc3); M circle dot / pc 3 ); these values are similar to, but have smaller uncertainties than, previous pulsar timing measurements of these quantities. Here, we provide for the first time, values for the Oort constants and the slope of the rotation curve from direct acceleration measurements. We find that A = 15.4 + 2.6 km/s/kpc / s / kpc and B = -13.1 + 2.6 km/s/kpc / s / kpc (consistent with results from Gaia), ), and the slope of the rotation curve near the Sun is -2 + 5 km/s/kpc. / s / kpc. We show that the Galactic acceleration field is clearly asymmetric, but due to data limitations it is not yet clear which physical processes drive this asymmetry. We provide updated models of the Galactic potential that account for various sources of disequilibrium; these models are incompatible with commonly used kinematic potentials. This indicates that use of kinematically derived Galactic potentials in precision tests (e.g., in tests of general relativity with pulsar timing) may be subject to larger uncertainties than reported. The acceleration data indicates that the mass of the Galaxy within the Solar circle is 2.3 x 1011M circle dot, 11 M circle dot , roughly twice as large as currently accepted models. Additionally, the residuals of the acceleration data compared to existing Galactic models have a dependence on radial position; this trend can be explained if the Sun has an additional acceleration away from the Galactic Center.

ABSTRACT We conduct a long-time-scale ($5000\,$ d) 3D simulation of a common-envelope event with a $2\, {\rm M}_{\odot }$ red giant and a $1\, {\rm M}_{\odot }$ main-sequence companion, using the moving-mesh hydrodynamic solver manga. Starting with an orbital radius of $52\, \mathrm{ R}_{\odot }$, our binary shrinks to an orbital radius of $5\, \mathrm{ R}_{\odot }$ in $200\,$ d. We show that over a time-scale of about $1500\,$ d, the envelope is completely ejected, while 80 per cent is ejected in about $400\,$ d. The complete ejection of the envelope is solely powered by the orbital energy of the binary, without the need for late-time reheating from recombination or jets. Motivated by recent theoretical and observational results, we also find that the envelope enters a phase of homologous expansion about $550\, \rm d$ after the start of our simulation. We also run a simplified 1D model to show that heating from the central binary in the envelope at late times does not influence the ejection. This homologous expansion of the envelope would likely simplify calculations of the observational implications such as light curves.

We describe the discovery of a solar neighborhood ( d = 468 pc) binary system with a main-sequence sunlike star and a massive noninteracting black hole candidate. The spectral energy distribution of the visible star is described by a single stellar model. We derive stellar parameters from a high signal-to-noise Magellan/MIKE spectrum, classifying the star as a main-sequence star with T eff = 5972 K, log g = 4.54 , and M = 0.91 M ⊙ . The spectrum shows no indication of a second luminous component. To determine the spectroscopic orbit of the binary, we measured the radial velocities of this system with the Automated Planet Finder, Magellan, and Keck over four months. We show that the velocity data are consistent with the Gaia astrometric orbit and provide independent evidence for a massive dark companion. From a combined fit of our spectroscopic data and the astrometry, we derive a companion mass of 11.39 − 1.31 + 1.51 M ⊙ . We conclude that this binary system harbors a massive black hole on an eccentric ( e = 0.46 ± 0.02), 185.4 ± 0.1 day orbit. These conclusions are independent of El-Badry et al., who recently reported the discovery of the same system. A joint fit to all available data yields a comparable period solution but a lower companion mass of 9.32 − 0.21 + 0.22 M ⊙ . Radial velocity fits to all available data produce a unimodal solution for the period that is not possible with either data set alone. The combination of both data sets yields the most accurate orbit currently available.

ABSTRACT Several tidal disruption events such as ASASSN-14li and XMMSL1 J0740-85 have recently been observed in the radio. While the radio emission of some tidal disruption events are attributed to a relativistic jet, a few others are associated with a non-relativistic outflow. This outflow can either be due to a spherical wind or unbound tidal debris. We explore this latter hypothesis in this paper. We show that the maximum velocity of the unbound debris is a function of the impact parameter, such that smaller impact parameters (closer approaches) produce larger maximum velocities. We then model this outflow which expands and shocks the local interstellar medium and compute the peak radio flux and frequency as functions of the impact parameter. Moreover, multiple epochs of observations can put additional constraints on the profile of the local interstellar medium. We apply this analysis to four tidal disruption events whose radio emission is attributed to a non-relativistic outflow and show that the velocities of the unbound material are consistent with our simulated events. We also place constraints on the density profile of three of the four tidal disruption events with multiple epochs of observations.

We present an overview of future observational facilities that will significantly enhance our understanding of the fundamental nature of dark matter. These facilities span a range of observational techniques including optical/near-infrared imaging and spectroscopy, measurements of the cosmic microwave background, pulsar timing, 21-cm observations of neutral hydrogen at high redshift, and the measurement of gravitational waves. Such facilities are a critical component of a multi-pronged experimental program to uncover the nature of dark matter, while often providing complementary measurements of dark energy, neutrino physics, and inflation.

The intergalactic medium (IGM) acts like a calorimeter recording energy injection by cosmic structure formation, shocks and photoheating from stars and active galactic nuclei. It was recently proposed that spatially inhomogeneous TeV-blazars could significantly heat up the underdense IGM, resulting in patches of both cold and warm IGM around z ≃ 2 − 3. The goal of this study is to compare predictions of different blazar heating models with recent observations of the IGM. We perform a set of cosmological simulations and carefully compute mock observables of the Lyman-α (Lyα) forest. We perform a detailed assessment of different systematic uncertainties which typically impact this type of observables and find that they are smaller than the differences between our models. We find that our inhomogeneous blazar heating model is in good agreement with the Lyα line properties and the rescaled flux probability distribution function at high redshift (2.5 < z < 3) but that our blazar heating models are challenged by lower redshift data (2 < z < 2.5). Our results could be explained by HeII reionisation although state-of-the-art models fall short on providing enough heating to the low-density IGM, thus motivating further radiative transfer studies of inhomogeneous HeII reionisation. If blazars are indeed hosted by group-mass haloes of $2\times 10^{13}\, \rm {M}_\odot$, a later onset of blazar heating in comparison to previous models would be favoured, which could bring our findings here in agreement with the evidence of blazar heating from local gamma-ray observations.

We show that a small, but \textit{measurable} shift in the eclipse mid-point time of eclipsing binary (EBs) stars of $\sim$ 0.1 seconds over a decade baseline can be used to directly measure the Galactic acceleration of stars in the Milky Way at $\sim$ kpc distances from the Sun. We consider contributions to the period drift rate from dynamical mechanisms other than the Galaxy's gravitational field, and show that the Galactic acceleration can be reliably measured using a sample of $\textit{Kepler}$ EBs with orbital and stellar parameters from the literature. Given the uncertainties on the formulation of tidal decay, our approach here is necessarily approximate, and the contribution from tidal decay is an upper limit assuming the stars are not tidally synchronized. We also use simple analytic relations to search for well-timed sources in the \textit{Kepler} field, and find $\sim$ 70 additional detached EBs with low eccentricities that have estimated timing precision better than 1 second. We illustrate the method with a prototypical, precisely timed EB using an archival \textit{Kepler} light curve and a modern synthetic \textit{HST} light curve (which provides a decade baseline). This novel method establishes a realistic possibility for obtaining fundamental Galactic parameters using eclipse timing to measure Galactic accelerations, along with other emerging new methods, including pulsar timing and extreme precision radial velocity observations. This acceleration signal grows quadratically with time. Therefore, given baselines established in the near-future for distant EBs, we can expect to measure the period drift in the future with space missions like \textit{JWST} and the \textit{Roman Space Telescope}.

ABSTRACT Stars that pass too close to a supermassive black hole are disrupted by the black hole’s tidal gravity. Some debris is ejected while the remainder accretes into the black hole. To better study the physics of these debris, we use the moving mesh code manga to follow the evolution of the star from its initial encounter to its complete destruction. By varying the impact parameter (β) of the star, we study the energy distribution of the remaining material and the fallback rate of the material into the black hole as a function of time. We show that the spread of energy in the debris and peak luminosity time (tpeak) are both directly related to the impact parameter. In particular, we find a β1/2 scaling for the energy spread for β = 2 − 10 that levels off at β ≳ 10. We discuss implication of this scaling for the rise time of the light curve and broadness of the luminosity peak for these lower β’s. These relationships provide a possible means of inferring the impact parameters for observed tidal disruption events.

A compact object moving relative to surrounding gas accretes material and perturbs the density of gas in its vicinity. In the classical picture of Bondi-Hoyle-Lyttleton accretion, the perturbation takes the form of an overdense wake behind the object, which exerts a dynamical friction drag. We use hydrodynamic simulations to investigate how the accretion rate and strength of dynamical friction are modified by the presence of outflow from the compact object. We show that the destruction of the wake by an outflow reduces dynamical friction, and reverses its sign when the outflow is strong enough, in good quantitative agreement with analytic calculations. For a strong isotropic outflow, the outcome on scales that we have simulated is a negative dynamical friction, i.e., net acceleration. For jet-like outflows driven by reprocessed accretion, both the rate of accretion and the magnitude of dynamical friction drop for more powerful jets. The accretion rate is strongly intermittent when the jet points to the same direction as the motion of the compact object. The dynamical effects of outflows may be important for the evolution of compact objects during the common envelope phase of binary systems, and for accreting compact objects and massive stars encountering AGN discs.

We use compiled high-precision pulsar timing measurements to directly measure the Galactic acceleration of binary pulsars relative to the solar system barycenter. Given the vertical accelerations, we use the Poisson equation to derive the Oort limit, i.e., the total volume mass density in the Galactic mid-plane. Our best-fitting model gives an Oort limit of 0.08 − 0.02 0.05 M ⊙ pc − 3 , which is close to estimates from recent Jeans analyses. Given the accounting of the baryon budget from McKee et al., we obtain a local dark matter density of − 0.004 − 0.02 0.05 M ⊙ pc − 3 , which is slightly below other modern estimates but consistent within the current uncertainties of our method. The error bars are currently about five times larger than kinematical estimates, but should improve in the future for this novel dynamical method. We also constrain the oblateness of the potential, finding it consistent with that expected from the disk and inconsistent with a potential dominated by a spherical halo, as is appropriate for our sample that is within a ∼kpc of the Sun. We find that current measurements of binary pulsar accelerations lead to large uncertainties in the slope of the rotation curve. We give a fitting function for the vertical acceleration a z : a z = − α 1 z ; log 10 ( α 1 / Gyr − 2 ) = 3.69 − 0.12 0.19 . By analyzing interacting simulations of the Milky Way, we find that large asymmetric variations in da z / dz as a function of vertical height may be a signature of sub-structure. We end by discussing the power of combining constraints from pulsar timing and high-precision radial velocity measurements toward lines-of-sight near pulsars, to test theories of gravity and constrain dark matter sub-structure.

Valuable information about the neutron star interior can be obtained by comparing observations of thermal radiation from a cooling neutron star crust with theoretical models. Nuclear burning of lighter elements that diffuse to deeper layers of the envelope can alter the relation between surface and interior temperatures and can change the chemical composition over time. We calculate new temperature relations and consider two effects of diffusive nuclear burning (DNB) for H-C envelopes. First, we consider the effect of a changing envelope composition and find that hydrogen is consumed on short timescales and our temperature evolution simulations correspond to those of a hydrogen-poor envelope within ~100 days. The transition from a hydrogen-rich to a hydrogen-poor envelope is potentially observable in accreting NS systems as an additional initial decline in surface temperature at early times after the outburst. Second, we find that DNB can produce a non-negligible heat flux, such that the total luminosity can be dominated by DNB in the envelope rather than heat from the deep interior. However, without continual accretion, heating by DNB in H-C envelopes is only relevant for <1-80 days after the end of an accretion outburst, as the amount of light elements is rapidly depleted. Comparison to crust cooling data shows that DNB does not remove the need for an additional shallow heating source. We conclude that solving the time-dependent equations of the burning region in the envelope self-consistently in thermal evolution models instead of using static temperature relations would be valuable in future cooling studies.

We describe the structure and implementation of a radiation hydrodynamic solver for MANGA, the moving-mesh hydrodynamics module of the large-scale parallel code, Charm N-body GrAvity solver (CHANGA). We solve the equations of time-dependent radiative transfer (RT) using a reduced speed of light approximation following the algorithm of Jiang et al. By writing the RT equations as a generalized conservation equation, we solve the transport part of these equations on an unstructured Voronoi mesh. We then solve the source part of the RT equations following Jiang et al. using an implicit solver, and couple this to the hydrodynamic equations. The use of an implicit solver ensures reliable convergence and preserves the conservation properties of these equations even in situations where the source terms are stiff due to the small coupling time-scales between radiation and matter. We present the results of a limited number of test cases (energy conservation, momentum conservation, dynamic diffusion, linear waves, crossing beams, and multiple shadows) to show convergence with analytic results and numerical stability. We also show that it produces qualitatively the correct results in the presence of multiple sources in the optically thin case.

We present the first-ever moving-mesh general relativistic hydrodynamics solver for static spacetimes as implemented in the code, MANGA. Our implementation builds on the architectures of MANGA and the numerical relativity Python package NRPy+. We review the general algorithm to solve these equations and, in particular, detail the time stepping; Riemann solution across moving faces; conversion between primitive and conservative variables; validation and correction of hydrodynamic variables; and mapping of the metric to a Voronoi moving-mesh grid. We present test results for the numerical integration of an unmagnetized Tolman-Oppenheimer-Volkoff star for 24 dynamical times. We demonstrate that at a resolution of $10^6$ mesh generating points, the star is stable and its central density drifts downward by 2% over this timescale. At a lower resolution the central density drift increases in a manner consistent with the adopted second order spatial reconstruction scheme. These results agree well with the exact solutions, and we find the error behavior to be similar to Eulerian codes with second-order spatial reconstruction. We also demonstrate that the new code recovers the fundamental mode frequency for the same TOV star but with its initial pressure depleted by 10%

High-precision spectrographs can enable not only the discovery of exoplanets, but can also provide a fundamental measurement in Galactic dynamics. Over about 10 year baselines, the expected change in the line-of-sight velocity due to the Galaxy’s gravitational field for stars at ∼kiloparsec scale distances above the Galactic midplane is ∼few tens of cm s−1, and may be detectable by the current generation of high-precision spectrographs. Here, we provide theoretical expectations for this measurement based on both static models of the Milky Way and isolated Milky Way simulations, as well from controlled dynamical simulations of the Milky Way interacting with dwarf galaxies. We simulate a population synthesis model to analyze the contribution of planets and binaries to the Galactic acceleration signal. We find that while low-mass, long-period planetary companions are a contaminant to the Galactic acceleration signal, their contribution is very small. Our analysis of ∼10 years of data from the Lick–Carnegie Exoplanet Survey HIRES/Keck precision radial-velocity (RV) survey shows that slopes of the RV curves of standard RV stars agree with expectations of the local Galactic acceleration near the Sun within the errors, and that the error in the slope scales inversely as the square root of the number of observations. Thus, we demonstrate that a survey of stars with low intrinsic stellar jitter at kiloparsec distances above the Galactic midplane for realistic sample sizes can enable a direct determination of the dark matter density.

Pair creation on the cosmic infrared background and subsequent inverse-Compton scattering on the cosmic microwave background potentially reprocesses the TeV emission of blazars into faint GeV halos with structures sensitive to intergalactic magnetic fields (IGMF). Previous work has shown that these halos are then highly anisotropic and extended. If the coherence length of the IGMF is greater than the inverse-Compton cooling length of the pairs, then the orientation of the gamma-ray halo will be correlated with the direction of the magnetic field which is unknown and expected to change for each source. In order to constructively add each source we then use angular power spectra which are insensitive to the jet orientation. By looking at known GeV blazars detected by Fermi, we exclude the existence of an IGMF with coherence lengths >100 Mpc at greater than 3.9 sigma with current-day strengths in the range 10(-16) to 10(-15) G, and at 2 sigma from 10(-17) to 10(-14) G. This provides a direct measurement of the nonexistence of gamma-ray halos, providing an important check on previous results.