arXiv subjects

Sukanya Chakrabarti

Publications and source records attributed to Sukanya Chakrabarti.

At least 19 recordsLinked to original sources

arXiv2026

A Galactic-scale extreme-precision radial velocity survey

We describe the first Galactic-scale extreme-precision radial velocity (EPRV) survey and outline our goals of measuring Galactic accelerations and deriving constraints on the dark matter distribution in our Galaxy. We are targeting quiet subgiant stars within a kiloparsec in radius of the Sun and about 2 kiloparsec in vertical height relative to the Galactic mid-plane. The observations described here were carried out using the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO) at the Very Large Telescope (VLT), between 2021-2025. We began by operating at a typical RV precision of $\sim$ 70 cm/s to select quiet stars from stellar activity indicators, and are now operating at $\sim$ 50 cm/s. We selected stars with low stellar jitter (determined from their RV scatter as a function of epoch) with the goal that they yield a measurement of the Galactic acceleration on approximately a decade timescale. We refer to this as our ``gold" sample. We also identify stars with possible companions (either brown dwarfs or planetary companions) or hitherto unknown stellar binaries that we have culled from our survey. For a few cases, we present initial constraints on the companion mass and orbital period. We also present the photospheric and fundamental stellar parameters for our ``gold" sample of sub-giant stars. This first Galactic-scale EPRV survey provides a pathfinder for next-generation surveys with extremely large telescopes, opening the possibility of directly mapping the gravitational acceleration field across the Milky Way and potentially beyond.

astro-ph.GA↗

arXiv2026

Radial Velocity Orbital Solutions for Candidate Black Hole and Neutron Star Binary Systems in the Gaia Data Release 3 Catalog

We present spectroscopic followup observations of binary systems from the Gaia Data Release 3 (DR3) binary catalog that were selected to have large enough mass functions for their companions to be black holes or neutron stars. The selection includes 20 stars that are astrometric and/or spectroscopic binaries, as well as 11 stars with large accelerations both in the plane of the sky and along the line of sight but no DR3 orbital solution. We provide classifications for this entire sample, including radial velocity orbital solutions for 12 binaries. Apart from the previously published binaries Gaia BH1, Gaia BH2, and Gaia NS1, we show that the Gaia orbits are incorrect for all of the stars with candidate dark companions above 2 Msun. We suggest more conservative cuts on the significance and goodness of fit parameters that may be useful for identifying reliable orbital solutions in the tail of the binary star distribution. Although we find no new confirmed black hole or neutron star companions, one accelerating system has a minimum companion mass of 1.16 +/- 0.01 Msun that is likely to be a neutron star or an ultramassive white dwarf. The acceleration catalogs may therefore provide a largely unexplored source of additional wide binaries containing compact objects.

astro-ph.SR↗

arXiv2026

An Acceleration is Worth a Hundred Thousand Phase Space Measurements

It is now possible to directly measure the accelerations that arise from the distribution of (dark) matter in the Milky Way. These acceleration-based measurements of the local dark matter density are now becoming competitive with estimates obtained through traditional kinematic techniques such as Jeans modeling. While classical methods can now draw on the positions and velocities of many millions of stars, recent acceleration-based studies have used fewer than 100 sources, yet achieve comparable precision. A key limitation of kinematic approaches is their reliance on assumptions of dynamical equilibrium and symmetry; direct acceleration measurements do not inherently suffer from this constraint. We find that, for the specific problem of estimating the local dark matter density, a single direct acceleration measurement can provide information comparable to $\sim$10$^5$ stars. We test the theoretical performance of direct acceleration techniques and Jeans modeling in estimating the local dark matter density using hydrodynamical N-body simulations of a MW-like galaxy, both in isolation and including a Sagittarius-like dwarf to generate disequilibrium. In the equilibrium scenario, Jeans modeling requires one thousand times more sources to achieve the same precision as the direct acceleration approach. This confirms that the per-source information advantage is intrinsic, and does not require disequilibrium to manifest. However, in the perturbed disk, the acceleration-based approach outperforms the Jeans analysis regardless of how many stars are available, due to significant bias in the result inferred from kinematics alone. Our results support earlier findings that non-equilibrium dynamics in the Galactic disk cause Jeans-based methods to systematically overestimate the local dark matter density; we show that this issue may also be present in other types of kinematic studies.

astro-ph.GA↗

arXiv2026

Las Cumbres Observatory Gravitational-Wave Follow-up in the Third and Fourth Observing Runs: Strengths and Weaknesses of a Rapid Response Galaxy Targeted Strategy

We present a summary of gravitational-wave (GW) follow-up using the Las Cumbres Observatory global network of telescopes during the third (O3) and fourth (O4) observing runs of the GW detectors. As in O2, we implemented the Gehrels et al. 2016 galaxy-targeted strategy. Here we test its efficacy in O3 and O4 and analyze the Las Cumbres Observatory response time and depth for nine GW alerts that showed a possibility of having an electromagnetic counterpart (GW190425, GW190426_152155, S190510g, GW190728_064510, GW190814, S190822c, GW191216_213338, S240422ed and S250206dm). We find that Las Cumbres Observatory is able to begin observations in response to GW alerts within minutes of the alert, with the observations being deep enough to detect possible GW170817-like kilonovae out to a median distance of 250 Mpc. In this sense a global rapid-response network of telescopes like Las Cumbres is an excellent GW follow-up facility. However, the galaxy-targeted follow-up strategy was much less efficient in O3 and O4 than originally predicted, given the larger than assumed GW localizations. We conclude that coordination between various facilities to include both wide-field and rapid-response capabilities is required to achieve efficient and comprehensive follow-up of GW events.

astro-ph.HE↗

arXiv2026

Weighing the Milky Way's Satellite Galaxies Using Pulsar Accelerations

The properties of dwarf galaxies orbiting the Milky Way (MW) are useful for testing models of the formation of our Galaxy, and by extension various theories of cosmology. Recent efforts to measure the masses of the MW's satellite dwarf galaxies have relied on the motions and positions of stars in the MW's disk and halo, which are perturbed by the passage of satellite galaxies. As there are many known processes in our Galaxy that lead to observed disequilibrium in stars, these kinematic methods have been limited by the inherent difficulty in identifying only the perturbations due to particular satellite galaxies. We present a novel method for determining the masses of two MW satellite galaxies -- the Large Magellanic Cloud (LMC) and the Sagittarius Dwarf Spheroidal Galaxy (Sgr dSph) -- using only direct, instantaneous acceleration data derived from extremely precise timing of millisecond pulsars near the Sun. As the LMC and Sgr dSph orbit the MW, they cause wave-like distortions in the structure of the disk plus a large-scale offset in the centers of mass of the dark matter halo and the baryonic disk. These two effects lead to asymmetric accelerations above and below the disk midplane near the Sun, which is observed in the pulsar acceleration data. Notably, the amplitude of this asymmetry is shown to depend on the masses of the orbiting satellites. We analyze a grid of simulations with varying masses of each satellite. We find the total (dark + baryon) mass enclosed within the tidal radius at the present day for the LMC to be 4.1 $\pm$ 1.0 $\times$ 10$^{10}$ M$_\odot$ within a radius of 16.6 kpc, and for Sgr to be 3.5 $\pm$ 2.4 $\times$ 10$^8$ M$_\odot$ within a radius of 5 kpc. These results are generally consistent and competitive with previous determinations of the masses of these objects, but entirely independent of any stellar kinematic data for the first time.

astro-ph.GA↗

arXiv2026

Winding, Unwinding, Rewinding the Gaia Phase Spiral

The Gaia Space Satellite has transformed the field of Galactic Dynamics by collecting 6D phase space information for hundreds of millions of stars. In 2018, it enabled the discovery of the Gaia Phase Spiral (Antoja et al., 2018), a clear signal in the vertical motion of the stars that reveals how far from equilibrium the Galactic disk is. Seven years after the discovery of this structure, a workshop dedicated to the Phase Spiral took place at the Lorentz Center. Workshop participants summarized the current state of knowledge about the Phase Spiral and identified open questions and key areas to continue progressing in understanding the origin of the Phase Spiral and the physics governing the response of the disk to perturbations. Here, we aim to summarize the content and discussions of this workshop, share the resources that have been produced at this workshop with the broader community, and invite interested individuals to join on the projects that started.

astro-ph.GA↗

arXiv2026

Mean Mass Density near the Sun from the Divergence Theorem and Pulsar Accelerations

We introduce a new, non-parametric method for estimating the mass enclosed within a sphere of arbitrary radius centered on the Sun. The method is based on the divergence theorem as applied to measurements of the line-of-sight accelerations of millisecond pulsars. We describe a procedure for inferring the mean mass density within a sphere of a given radius centered on the Sun and find results that are consistent with previous analyses. When combined with a model for the distribution of baryons, this provides the mean mass density of dark matter as a function of distance from the Sun, rather than a single value as is typically reported by kinematic studies. However, with the present pulsar data, the method cannot unambiguously measure a signal from the local distribution of dark matter at this time; such a measurement is expected to soon become possible as the amount of pulsar acceleration data grows and its precision improves. We derive an extension of the well-known shell theorem to a spherical-harmonics expansion of the density and potential, and use the result to obtain estimates for density asymmetries with respect to the Galactic midplane from the observed acceleration data. The predicted asymmetries do not follow the observed distribution of MW disk stars or gas; this can potentially be explained by a non-uniform distribution of dark matter in the Solar neighborhood.

astro-ph.GA↗

arXiv2025

Chemical enrichment of metal-poor stars orbiting massive black hole companions

There are millions of undetected black holes wandering through our galaxy. Observatories like {\it Chandra}, LIGO, and more recently, {\it Gaia}, have provided valuable insights into the configurations of these elusive objects when residing in binary systems. Motivated by these advances, we study, for the first time, the enhanced accretion of metals from the interstellar medium (ISM) onto low-mass companions in binary systems with highly unequal mass ratios, utilizing a series of hydrodynamical simulations. Our study demonstrates that a stellar companion's metal accretion history from the ISM alone, from its formation to the present, can significantly influence its surface abundances, especially when enhanced by a massive black hole companion. However, this effect is likely only measurable in stars that are still in the main sequence. Once a stellar companion evolves off the main sequence, similar to what has been observed with the {\it Gaia} BH3 companion, the initial dredge-up process are likely to erase any excess surface abundance resulting from the metals that were accreted. As we discover more unequal mass ratio binary systems, it is crucial to understand how the observed metallicity of sun-like companions may differ from their birth metallicity, especially if they are not yet evolved.

astro-ph.SR↗

arXiv2025

Constraints on a dark matter sub-halo near the Sun from pulsar timing

Using pulsar accelerations, we identify and constrain the properties of a dark matter sub-halo in the Galaxy for the first time from analyzing the acceleration field of binary and solitary pulsars. Our MCMC calculations show that this sub-halo has a mass of $2.45^{+1.07}_{-0.96} \times 10^{7}~M_{\odot}$ and is located at Galactocentric coordinates $X = 7.43^{+0.2}_{-0.12}~\rm$ kpc, $Y = 0.38^{+0.11}_{-0.16} ~\rm kpc$, $Z = 0.21^{+0.06}_{-0.11} ~\rm kpc$, 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 $\sim$ 20-40, which indicates tentative evidence (though not yet decisive) for the sub-halo. Modeling the sub-halo with a NFW profile gives a sub-halo mass within the scale radius (0.1 kpc) of $0.48^{0.15}_{-0.16} \times 10^{7} M_{\odot}$, located at $X = 7.47^{+0.21}_{-0.14}$, $Y=0.38^{+0.11}_{-0.16}$, $Z=0.21^{+0.06}_{-0.11}$. We examine \textit{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. By analyzing the full sample of binary pulsars with available acceleration measurements, we find that massive (with mass $>10^{8}~M_{\odot}~$) sub-halos are disfavored for the Milky Way within several kiloparsec of the Sun. Smaller sub-halos are beyond the reach of current direct acceleration measurements. The presence of a $\sim 10^{7}~M_{\odot}$ sub-halo within a few kpc of the Sun is potentially consistent with the expected number counts of sub-halos in the prevailing $Λ$CDM paradigm, for a substantial sub-halo mass fraction. This work now provides a proof of principle for probing nearby, low-mass sub-halos, and has implications across many fields of astrophysics - from understanding the nature of dark matter to galaxy formation.

astro-ph.GA↗

arXiv2025

Laser Interferometer Lunar Antenna (LILA): Advancing the U.S. Priorities in Gravitational-wave and Lunar Science

The Laser Interferometer Lunar Antenna (LILA) is a next-generation gravitational-wave (GW) facility on the Moon. By harnessing the Moon's unique environment, LILA fills a critical observational gap in the mid-band GW spectrum ($0.1 - 10$ Hz) between terrestrial detectors (LIGO, Virgo, KAGRA) and the future space mission LISA. Observations enabled by LILA will fundamentally transform multi-messenger astrophysics and GW probes of fundamental physics. LILA will measure the lunar deep interior better than any existing planetary seismic instruments. The LILA mission is designed for phased development aligned with capabilities of the U.S.'s Commercial Lunar Payload Services and Artemis programs. LILA is a unique collaboration between universities, space industries, U.S. government laboratories, and international partners.

gr-qc↗

arXiv2025

A map of the outer gas disk of the Galaxy with direct distances from young stars

For more than fifty years, astronomers have mapped the neutral hydrogen gas in the Galaxy assuming kinematically derived distances. We employ the distances of nearby young stars, which trace the gas from which they formed, in longitude-latitude-velocity space to map this gas without using kinematic distances. We denote this new method "pattern matching". Analysis of simulated spiral galaxies indicates that our pattern matching distances are 24% more accurate than kinematic distances for gas within 15 kpc of the Sun. The two methods provide similar agreement with parallaxes towards these masers, although the kinematic method shows a small systematic offset in the distance that is not present in the pattern matching distance. Using parallaxes and velocities for masers, we show that this novel method, when matched with nearby Cepheids, performs well compared to kinematics. This analysis is restricted to sources that have a reasonably good match with a member of our Cepheid sample. The distances derived here, and the associated map, have broad utility - from improving our understanding of star formation and the dynamical structure of the Galaxy, to informing 3-D dust maps.

astro-ph.GA↗

arXiv2025

Empirical Modeling of Magnetic Braking in Millisecond Pulsars to Measure the Local Dark Matter Density and Effects of Orbiting Satellite Galaxies

We present a novel method that enables us to estimate the acceleration of individual millisecond pulsars (MSPs) using only their spin period and its time derivative. For our binary MSP sample, we show that one can obtain an empirical calibration of the magnetic braking term that relies only on observed quantities. We find that such a model for magnetic braking is only valid for MSPs with small surface magnetic field strengths ($<3\times10^8$ G) and large characteristic ages ($>$ 5 Gyr). With this method we are able to effectively double the number of pulsars with line-of-sight acceleration measurements, from 27 to 53 sources. This expanded dataset leads to an updated measurement of the total density in the midplane, which we find to be $ρ_0$ = 0.108 $\pm$ 0.008 \textit{stat}. $\pm$ 0.011 \textit{sys} M$_\odot$/pc$^3$, and the first $>3σ$ measurement of the local dark matter density from direct acceleration measurements, which we calculate to be $ρ_{0,\mathrm{DM}}$ = 0.0098 $\pm$ 0.0025 \textit{stat.} $\pm$ 0.0003 \textit{sys}. M$_\odot$/pc$^3$ (0.37 $\pm$ 0.10 GeV/cm$^3$). This updated value for $ρ_{0,\mathrm{DM}}$ is in good agreement with literature values derived from kinematic estimates. The pulsar accelerations are very asymmetric above and below the disk; we show that the shape and size of this asymmetry can be largely explained by the north-south asymmetry of disk star counts and the offset in the Milky Way disk and halo centers of mass due to the Large Magellanic Cloud.

astro-ph.HE↗

arXiv2025

The Anomalous Acceleration of PSR J2043+1711: Long-Period Orbital Companion or Stellar Flyby?

Based on the rate of change of its orbital period, PSR J2043+1711 has a substantial peculiar acceleration of 3.5 $\pm$ 0.8 mm/s/yr, which deviates from the acceleration predicted by equilibrium Milky Way models at a $4σ$ level. The magnitude of the peculiar acceleration is too large to be explained by disequilibrium effects of the Milky Way interacting with orbiting dwarf galaxies ($\sim$1 mm/s/yr), and too small to be caused by period variations due to the pulsar being a redback. We identify and examine two plausible causes for the anomalous acceleration: a stellar flyby, and a long-period orbital companion. We identify a main-sequence star in \textit{Gaia} DR3 and Pan-STARRS DR2 with the correct mass, distance, and on-sky position to potentially explain the observed peculiar acceleration. However, the star and the pulsar system have substantially different proper motions, indicating that they are not gravitationally bound. However, it is possible that this is an unrelated star that just happens to be located near J2043+1711 along our line of sight (chance probability of 1.6\%). Therefore, we also constrain possible orbital parameters for a circumbinary companion in a hierarchical triple system with J2043+1711; the changes in the spindown rate of the pulsar are consistent with an outer object that has an orbital period of 80 kyr, a companion mass of 0.3 $M_\odot$ (indicative of a white dwarf or low-mass star), and a semi-major axis of 2000 AU. Continued timing and/or future faint optical observations of J2043+1711 may eventually allow us to differentiate between these scenarios.

astro-ph.SR↗

arXiv2025

LensWatch. II. Improved Photometry and Time-delay Constraints on the Strongly Lensed Type Ia Supernova 2022qmx ("SN Zwicky") with HST Template Observations

Strongly lensed supernovae (SNe) are a rare class of transient that can offer tight cosmological constraints that are complementary to methods from other astronomical events. We present a follow-up study of one recently-discovered strongly lensed SN, the quadruply-imaged Type Ia SN 2022qmx (aka, "SN Zwicky") at z = 0.3544. We measure updated, template-subtracted photometry for SN Zwicky and derive improved time delays and magnifications. This is possible because SNe are transient, fading away after reaching their peak brightness. Specifically, we measure point spread function (PSF) photometry for all four images of SN Zwicky in three Hubble Space Telescope WFC3/UVIS passbands (F475W, F625W, F814W) and one WFC3/IR passband (F160W), with template images taken $\sim 11$ months after the epoch in which the SN images appear. We find consistency to within $2σ$ between lens model predicted time delays ($\lesssim1$ day), and measured time delays with HST colors ($\lesssim2$ days), including the uncertainty from chromatic microlensing that may arise from stars in the lensing galaxy. The standardizable nature of SNe Ia allows us to estimate absolute magnifications for the four images, with images A and C being elevated in magnification compared to lens model predictions by about $6σ$ and $3σ$ respectively, confirming previous work. We show that millilensing or differential dust extinction is unable to explain these discrepancies and find evidence for the existence of microlensing in images A, C, and potentially D, that may contribute to the anomalous magnification.

astro-ph.HE↗

arXiv2024

The imprint of dark matter on the Galactic acceleration field

Measurements of the accelerations of stars enabled by time-series extreme-precision spectroscopic observations, from pulsar timing, and from eclipsing binary stars in the Solar Neighborhood offer insights into the mass distribution of the Milky Way that do not rely on traditional equilibrium modeling. Given the measured accelerations, we can determine a total mass density, and from this, by accounting for the mass in stars, gas, and dust, we can infer the amount of dark matter. Leveraging the FIRE-2 simulations of Milky Way-mass galaxies, we compare vertical acceleration profiles between cold dark matter (CDM) and self-interacting dark matter (SIDM) with constant cross-section of 1 cm$^2$ g$^{-1}$ across three halos with diverse assembly histories. Notably, significant asymmetries in vertical acceleration profiles near the midplane at fixed radii are observed in both CDM and SIDM, particularly in halos recently affected by mergers with satellites of Sagittarius/SMC-like masses or greater. These asymmetries offer a unique window into exploring the merger history of a galaxy. We show that SIDM halos consistently exhibit higher local stellar and dark matter densities and steeper vertical acceleration gradients, up to 30% steeper near the Solar Neighborhood. SIDM halos also manifest a more oblate halo shape in the Solar Neighborhood. Furthermore, enhanced precision in acceleration measurements and larger datasets promise to provide better constraints on the local dark matter density, complementing our understanding from kinematic analysis of their distribution within galaxies.

astro-ph.GA↗

arXiv2024

A targeted search for strongly lensed supernovae with the Las Cumbres Observatory

Gravitationally lensed supernovae (glSNe) are of interest for time delay cosmology and SN physics. However, glSNe detections are rare, owing to the intrinsic rarity of SN explosions, the necessity of alignment with a foreground lens, and the relatively short window of detectability. We present the Las Cumbres Observatory Lensed Supernova Search, LCOLSS, a targeted survey designed for detecting glSNe in known strong lensing systems. Using cadenced r'-band imaging, LCOLSS targeted 114 galaxy-galaxy lensing systems with high expected SN rates, based on estimated star formation rates. No plausible glSN was detected by LCOLSS during our two year observing program. We carry out an analysis here to measure a detection efficiency for these observations. We then perform Monte Carlo simulations using the predicted supernova rates to determine the expected number of glSN detections. The results of the simulation suggest an expected number of detections and $68\%$ Poisson confidence intervals, $N_{SN} = 0.20, [0,2.1] $, $N_{Ia} = 0.08, [0,2.0]$, $N_{CC} = 0.12, [0,2.0]$, for all SNe, Type Ia SNe, and core-collapse (CC) SNe respectively. These results are broadly consistent with the absence of a detection in our survey. Analysis of the survey strategy can provide insights for future efforts to develop targeted glSN discovery programs, especially considering the large anticipated yields of upcoming surveys.

astro-ph.CO↗

arXiv2024

Galactic Structure From Binary Pulsar Accelerations: Beyond Smooth Models

We measure the line-of-sight accelerations of 26 binary pulsars due to the Milky Way's gravitational potential, and produce a 3-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 ($ρ_0=0.062\pm0.017$ \msun/pc$^3$) and the dark matter density in the midplane ($ρ_{0,\textrm{DM}}=-0.010\pm0.018$ \msun/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 $A=15.4\pm2.6$ km/s/kpc and $B=-13.1\pm2.6$ km/s/kpc (consistent with results from \textit{Gaia}), and the slope of the rotation curve near the Sun is $-2\pm5$ km/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 $2.3 \times 10^{11}$ M$_\odot$, 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.

astro-ph.GA↗

arXiv2024

A $1.9\,M_{\odot}$ neutron star candidate in a 2-year orbit

We report discovery and characterization of a main-sequence G star orbiting a dark object with mass $1.90\pm 0.04 M_{\odot}$. The system was discovered via Gaia astrometry and has an orbital period of 731 days. We obtained multi-epoch RV follow-up over a period of 639 days, allowing us to refine the Gaia orbital solution and precisely constrain the masses of both components. The luminous star is a $\gtrsim 12$ Gyr-old, low-metallicity halo star near the main-sequence turnoff ($T_{\rm eff}\approx 6000$ K; $\log(g/\left[{\rm cm\,s^{-2}}\right])\approx 4.0$; $\rm [Fe/H]\approx-1.25$; $M\approx0.79 M_{\odot}$) with a highly enhanced lithium abundance. The RV mass function sets a minimum companion mass for an edge-on orbit of $M_2 > 1.67 M_{\odot}$, well above the Chandrasekhar limit. The Gaia inclination constraint, $i=68.7\pm 1.4$ deg, then implies a companion mass of $M_2=1.90\pm0.04 M_{\odot}$. The companion is most likely a massive neutron star: the only viable alternative is two massive white dwarfs in a close binary, but this scenario is disfavored on evolutionary grounds. The system's low eccentricity ($e=0.122\pm 0.002$) disfavors dynamical formation channels and implies that the neutron star likely formed with little mass loss ($\lesssim1\,M_{\odot}$) and with a weak natal kick ($v_{\rm kick}\lesssim 20\,\rm km\,s^{-1}$). The current orbit is too small to have accommodated the neutron star progenitor as a red supergiant or super-AGB star. The simplest formation scenario -- isolated binary evolution -- requires the system to have survived unstable mass transfer and common envelope evolution with a donor-to-accretor mass ratio $>10$. The system, which we call Gaia NS1, is likely a progenitor of symbiotic X-ray binaries and long-period millisecond pulsars. Its discovery challenges binary evolution models and bodes well for Gaia's census of compact objects in wide binaries.

astro-ph.SR↗