arXiv subjects

W. Vlemmings

Publications and source records attributed to W. Vlemmings.

At least 19 recordsLinked to original sources

arXiv2026

A giant magnetic eruption from the asymptotic giant branch star Mira A

Mass loss during the advanced evolutionary stages of low- and intermediate-mass stars is traditionally attributed to dust-driven winds, whereas the influence of magnetic fields remains poorly constrained. However, recent observations show massive directional mass ejections from the nearby asymptotic giant branch (AGB) star Mira~A that appear not to be driven by radiation pressure on the dust. We observationally investigate whether magnetic fields are responsible for the mass loss ejections from Mira A. We obtained full-polarisation ALMA observations of the SiO $v=1$, $J=5\rightarrow4$ maser transition at 215 GHz with angular resolutions of 1.5-2.6 au. The observations reveal a highly magnetized loop-like mass ejection traced by strongly polarised SiO masers extending to approximately eight stellar radii. The morphology, polarisation pattern, energetics, and kinematics indicate a magnetically driven eruption analogous to a stellar coronal mass ejection. The observations demonstrate that magnetic eruptions can dominate mass loss from evolved stars and imply that magnetic fields must become an integral component of future models of AGB, and potentially other cool giant, winds.

astro-ph.SR↗

arXiv2026

Periodic activity on the (sub)mm surface of the AGB star Mira A

Evolved stars on the asymptotic giant branch (AGB) lose mass through stellar winds launched from their dynamic extended atmospheres. Recent high-angular-resolution observations of the archetypal AGB star Mira A (o Ceti) have revealed compact hotspots on its submillimetre (submm) surface, whose origin remains unclear. We aim to characterise the submm photosphere of Mira A and investigate the properties and temporal behaviour of the compact hotspots detected on its surface. We analysed 19 epochs of high-angular-resolution observations obtained with the Atacama Large Millimetre/submillimetre Array in Bands 4, 6, 7, and 9, ranging from 134.34 to 669.25 GHz. The complex visibilities were fitted with parametric models to derive the flux density, size, morphology, and brightness temperature of the stellar disc and an additional more compact component across multiple pulsation phases and observing frequencies.Our results show that the flux density of the stellar disc increases with frequency while its apparent size decreases, in agreement with the expected stratified radio photosphere. In Band 6, both the flux density and the size of the stellar disc vary with pulsation phase, reaching maximum values close to optical maximum light and decreasing toward minimum light. Compact hotspots are detected in Bands~6 and 7 near maximum light, with their brightness temperatures exceeding those of the stellar disc by several thousand kelvins, reaching T>8600 K in Band 6. They are highly energetic and persist on timescales of weeks but evolve over longer timescales, showing changes in both position and intensity. Hotspot activity appears to occur repeatedly across multiple pulsation cycles and may be linked to strong shocks, magnetic activity, and/or episodic mass ejections, and could therefore play an important role in the mass-loss process in AGB stars.

astro-ph.SR↗

arXiv2026

Silicate cosmic dust grain collisions in the interstellar medium: A molecular dynamics study

(abridged) We aim to predict the most important parameters for grain-grain collision outcomes for models of interstellar grain population evolution on astrophysical scales: the threshold velocity above which colliding grains shatter, the threshold for vaporization, and resulting distributions of grain sizes. We use molecular dynamics simulations which evolve the dynamics of each atom in a dust grain to explore the outcomes of collisions between silicate grains of radii $a \in [5,50]~Å$ at velocities $0.1-20$ km/s. We run simulations of grains with two materials: amorphous SiO$_2$ and an amorphous silicate of composition suggested by Draine \& Hensley (2021). With these simulations, we quantify the collision velocity dependence of shattered and vaporized mass fractions, and the resulting size distributions of shattering products. We find grain shattering thresholds are $\sim$6 km/s for both amorphous SiO$_2$ and astrodust material, which is a factor of $\sim$2 higher than the canonical value for silicates of 2.7 km/s from Jones et al. (1996). This discrepancy is mostly alleviated by correcting an error in the expression for these velocity thresholds derived in Tielens et al. (1994). We find that the size distributions of shattered products are generally not consistent with the power law distributions predicted by this previous model. We also find that their expression fails to predict the fraction of shattered or vaporized material observed in our numerical simulations. The model of Hirashita \& Kobayashi (2013) for the same quantities similarly fails to match the simulations. We provide updated shattering velocity thresholds for candidate grain materials. Broadly, our updated threshold velocity prescription suggests that astrophysical dust grains, particularly those composed of silicate materials, may be more robust to shattering in the interstellar medium than previously assumed.

astro-ph.GA↗

arXiv2025

X TrA through the eyes of MATISSE: More evidence of clumpy molecular layers around C-type asymptotic giant branch stars

Aims. The goal of this study is to further the understanding of the wind formation mechanism in asymptotic giant branch (AGB) stars through the analysis of the close environment (within a few stellar radii) of the carbon star X TrA. Methods. X TrA was observed for the first time with the Mid-Infrared SpectroScopic Experiment instrument (MATISSE) in the L and N bands in low spectral resolution mode (R=30), and its close surroundings were mapped in specific wavelength ranges corresponding to specific molecules ($C_2H_2$ and HCN, at 3.1 and 3.8 $μ$m) and dust (amorphous carbon and, for example, Sic at 11.3 $μ$m), via image reconstruction techniques. Results. The angular diameter of the star ranges from 10 mas in the L band pseudo-continuum (3.5 $μ$m) to 20 mas at 3.1 and 11.3 $μ$m. The reconstructed images show some mild elongated features (along the east-west direction) and asymmetric protrusions, which are most evident around 3.1 $μ$m. Imaging results highlight the clumpy nature of the circumstellar environment, starting from the photospheric region up to more distant layers. Conclusions. The angular diameters found for X TrA in the image data are in agreement with previous photospheric diameter estimates (following VLTI/MIDI 8-13 $μ$m observations), and their wavelength dependence is similar to values found for other carbon stars observed with MATISSE (R Scl and V Hya). The 3.1 $μ$m images presented here show highly asymmetric features, another case of a C-rich star with irregular morphologies close to the stellar disk; this supports the notion that the $C_2H_2+HCN$ abundance distribution usually originates from a clumpy layer around carbon stars.

astro-ph.SR↗

arXiv2024

One month convection timescale on the surface of a giant evolved star

The transport of energy through convection is important during many stages of stellar evolution, and is best studied in our Sun or giant evolved stars. Features that are attributed to convection are found on the surface of massive red supergiant stars. Also for lower mass evolved stars, indications of convection are found, but convective timescales and sizes remain poorly constrained. Models indicate that convective motions are crucial for the production of strong winds that return the products of stellar nucleosynthesis into the interstellar medium. Here we report a series of reconstructed interferometric images of the surface of the evolved giant star R Doradus. The images reveal a stellar disc with prominent small scale features that provide the structure and motions of convection on the stellar surface. We find that the dominant structure size of the features on the stellar disc is $0.72\pm0.05$ astronomical units (au). We measure the velocity of the surface motions to vary between $-18$ and $+20$ km s$^{-1}$, which means the convective timescale is approximately one month. This indicates a possible difference between the convection properties of low-mass and high-mass evolved stars.

astro-ph.SR↗

arXiv2023

Exploring the environment, magnetic fields, and feedback effects of massive high-redshift galaxies with [CII]

Massive galaxies are expected to grow through different transformative evolutionary phases where high-redshift starburst galaxies and quasars are examples of such phases. The physical mechanisms driving these phases include companion galaxy interactions, active galactic nuclei feedback, and magnetic fields. Our aim is to characterize the physical properties and the environment of the submillimeter galaxy AzTEC-3 at z = 5.3 and the lensed quasar BRI 0952-0115 at z = 4.4, to set a limit on the polarization properties, as well as placing both in the broader context of galaxy evolution. We used full polarization, sub-arcsecond-resolution, ALMA band-7 observations of both BRI 0952-0115 and AzTEC-3 and detect [CII] line emission towards both galaxies, along with companions in each field. We present an updated gravitational lensing model for BRI 0952-0115. We present infrared luminosities, star-formation rates, and [CII] line to infrared luminosity ratios for each source. The [CII] emission line profile for both BRI 0952-0115 and AzTEC-3 exhibit a broad, complex morphology, indicating the possible presence of outflows. We present evidence of a 'gas bridge' between AzTEC-3 and a companion source. Using a simple dynamical mass estimate for the sources, we suggest that both systems are undergoing minor or major mergers. No polarization is detected for the [CII], placing an upper limit below that of theoretical predictions. Our results show that high-velocity wings are detected, indicating possible signs of massive outflows; however, the presence of companion galaxies can affect the final interpretation. Furthermore, the results provide additional evidence in support of the hypothesis that massive galaxies form in overdense regions, growing through interactions. Finally, strong, ordered magnetic fields are unlikely to exist at the kiloparsec scale in the two studied sources.

astro-ph.GA↗

arXiv2021

Milliarcsecond localisation of the repeating FRB 20201124A

Very long baseline interferometric (VLBI) localisations of repeating fast radio bursts (FRBs) have demonstrated a diversity of local environments: from nearby star-forming regions to globular clusters. Here we report the VLBI localisation of FRB 20201124A using an ad-hoc array of dishes that also participate in the European VLBI Network (EVN). In our campaign, we detected 18 total bursts from FRB 20201124A at two separate epochs. By combining the visibilities from both observing epochs, we were able to localise FRB 20201124A with a 1-$σ$ error of 4.5 milliarcseconds (mas). We use the relatively large burst sample to investigate astrometric accuracy, and find that for $\gtrsim20$ baselines ($\gtrsim7$ dishes) that we can robustly reach milliarcsecond precision even using single-burst data sets. Sub-arcsecond precision is still possible for single bursts, even when only $\sim$ six baselines (four dishes) are available. We explore two methods for determining the individual burst positions: the peaks of the dirty maps and a Gaussian fit to the cross fringe pattern on the dirty maps. We found the latter to be more reliable due to the lower mean and standard deviation in the offsets from the FRB position. Our VLBI work places FRB 20201124A 705$\pm$26 mas (1-$σ$ errors) from the optical centre of the host galaxy, and consistent with originating from within the recently-discovered extended radio structure associated with star-formation in the host galaxy. Future high-resolution optical observations, e.g. with Hubble Space Telescope, can determine the proximity of our FRB 20201124A VLBI position to nearby knots of star formation.

astro-ph.HE↗

arXiv2021

Burst timescales and luminosities link young pulsars and fast radio bursts

Fast radio bursts (FRBs) are extragalactic radio flashes of unknown physical origin. Their high luminosities and short durations require extreme energy densities, like those found in the vicinity of neutron stars and black holes. Studying the burst intensities and polarimetric properties on a wide range of timescales, from milliseconds down to nanoseconds, is key to understanding the emission mechanism. However, high-time-resolution studies of FRBs are limited by their unpredictable activity levels, available instrumentation and temporal broadening in the intervening ionised medium. Here we show that the repeating FRB 20200120E can produce isolated shots of emission as short as about 60 nanoseconds in duration, with brightness temperatures as high as $3\times 10^{41}$ K (excluding relativistic effects), comparable to `nano-shots' from the Crab pulsar. Comparing both the range of timescales and luminosities, we find that FRB 20200120E observationally bridges the gap between known Galactic young pulsars and magnetars, and the much more distant extragalactic FRBs. This suggests a common magnetically powered emission mechanism spanning many orders of magnitude in timescale and luminosity. In this work, we probe a relatively unexplored region of the short-duration transient phase space; we highlight that there likely exists a population of ultra-fast radio transients at nanosecond to microsecond timescales, which current FRB searches are insensitive to.

astro-ph.HE↗

arXiv2021

A repeating fast radio burst source in a globular cluster

Fast radio bursts (FRBs) are exceptionally luminous flashes of unknown physical origin, reaching us from other galaxies (Petroff et al. 2019). Most FRBs have only ever been seen once, while others flash repeatedly, though sporadically (Spitler et al. 2016, CHIME/FRB Collaboration et al. 2021). Many models invoke magnetically powered neutron stars (magnetars) as the engines producing FRB emission (Margalit & Metzger 2018, CHIME/FRB Collaboration et al. 2020). Recently, CHIME/FRB announced the discovery (Bhardwaj et al. 2021) of the repeating FRB 20200120E, coming from the direction of the nearby grand design spiral galaxy M81. Four potential counterparts at other observing wavelengths were identified (Bhardwaj et al. 2021) but no definitive association with these sources, or M81, could be made. Here we report an extremely precise localisation of FRB 20200120E, which allows us to associate it with a globular cluster (GC) in the M81 galactic system and to place it ~2pc offset from the optical center of light of the GC. This confirms (Bhardwaj et al. 2021) that FRB 20200120E is 40 times closer than any other known extragalactic FRB. Because such GCs host old stellar populations, this association strongly challenges FRB models that invoke young magnetars formed in a core-collapse supernova as powering FRB emission. We propose, instead, that FRB 20200120E is a highly magnetised neutron star formed via either accretion-induced collapse of a white dwarf or via merger of compact stars in a binary system (Margalit et al. 2019). Alternative scenarios involving compact binary systems, efficiently formed inside globular clusters, could also be responsible for the observed bursts.

astro-ph.HE↗

arXiv2021

SiO masers and 7 mm Continuum in Mira and R Aqr

Interactions between AGB stars and a secondary in a close orbit are one possible explanation of why some AGB stars develop into aspherical planetary nebulae. This study uses millimeter observations of the continuum and SiO maser emission in several symbiotic Miras looking for evidence of an interaction between the two stars. New JVLA observations at ~45 mas resolution are analyzed, imaging continuum and SiO masers. Two of the three targets were detected and accurately registered continuum and line images were derived. No clear evidence of an interaction was found between components B and A in Mira. R Aqr has a well known jet arising from the secondary star. The jet may be disturbing the circumstellar envelop of the AGB star or possibly just nearly aligned with it.

astro-ph.SR↗

arXiv2020

Gravity and rotation drag the magnetic field in high-mass star formation

The formation of hot stars out of the cold interstellar medium lies at the heart of astrophysical research. Understanding the importance of magnetic fields during star formation remains a major challenge. With the advent of the Atacama Large Millimeter Array, the potential to study magnetic fields by polarization observations has tremendously progressed. However, the major question remains how much magnetic fields shape the star formation process or whether gravity is largely dominating. Here, we show that for the high-mass star-forming region G327.3 the magnetic field morphology appears to be dominantly shaped by the gravitational contraction of the central massive gas core where the star formation proceeds. We find that in the outer parts of the region, the magnetic field is directed toward the gravitational center of the region. Filamentary structures feeding the central core exhibit U-shaped magnetic field morphologies directed toward the gravitational center as well, again showing the gravitational drag toward the center. The inner part then shows rotational signatures, potentially associated with an embedded disk, and there the magnetic field morphology appears to be rotationally dominated. Hence, our results demonstrate that for this region gravity and rotation are dominating the dynamics and shaping the magnetic field morphology.

astro-ph.SR↗

arXiv2020

ALMA resolves the remarkable molecular jet and rotating wind in the extremely radio-quiet galaxy NGC 1377

Submillimetre and millimetre observations are important in probing the properties of the molecular gas and dust around obscured active galactic nuclei (AGNs) and their feedback. With very high-resolution (0."02x0."03 (2x3 pc)) ALMA 345 GHz observations of CO 3-2, HCO$^+$ 4-3, HCN 4-3 $ν_2$=1$f$, and continuum we have studied the molecular outflow and nucleus of the extremely radio-quiet lenticular galaxy NGC1377. The outflow is resolved, revealing a 150 pc long, clumpy, high-velocity, collimated molecular jet. The molecular emission is emerging from the spine of the jet with an average diameter of 3-7 pc. A narrow-angle, rotating molecular wind surrounds the jet and is enveloped by a larger-scale, slower CO-emitting structure. The jet and narrow wind are turbulent ($σ>$40 kms$^{-1}$) and have steep radial gas excitation gradients. The jet shows velocity reversals that we propose are caused by precession, or episodic directional changes. We suggest that an important process powering the outflow is magneto-centrifugal driving. In contrast, the large-scale CO-envelope may be a slow wind, or cocoon that stems from jet-wind interactions. An asymmetric, nuclear r$\sim$2 pc and hot (>180 K) dust structure with a high molecular column density, N(H$_2$)$\sim1.8 \times 10^{24}$ cm$^{-2}$, is detected in continuum and vibrationally excited HCN. Its luminosity is likely powered by a buried AGN. The mass of the supermassive black hole (SMBH) is estimated to $\sim9\times10^6$ M$_\odot$ and the SMBH of NGC1377 appears to be at the end of an intense phase of accretion. The nuclear growth may be fuelled by low-angular momentum gas inflowing from gas ejected in the molecular jet and wind. Such a feedback-loop of cyclic accretion and outflows would be an effective process in growing the nuclear SMBH. This result invites new questions as to SMBH growth processes in obscured, dusty galaxies.

astro-ph.GA↗

arXiv2019

VLA cm-wave survey of young stellar objects in the Oph A cluster: constraining extreme UV- and X-ray-driven disk photo-evaporation -- A pathfinder for Square Kilometre Array studies

Observations of young stellar objects (YSOs) in centimeter bands can probe the continuum emission from growing dust grains, ionized winds, and magnetospheric activity, which are intimately connected to the evolution of protoplanetary disks and the formation of planets. We have carried out sensitive continuum observations toward the Ophiuchus A star-forming region using the Karl G. Jansky Very Large Array (VLA) at 10 GHz over a field-of-view of 6$'$ with a spatial resolution of $θ_{maj}$ $\times$ $θ_{min}$ $\sim$ 0.4$''$ $\times$ 0.2$''$. We achieved a 5 $μ$Jy beam$^{-1}$ root-mean-square noise level at the center of our mosaic field of view. Among the eighteen sources we detected, sixteen are YSOs (three Class 0, five Class I, six Class II, and two Class III) and two are extragalactic candidates. We find that thermal dust emission generally contributes less that 30% of the emission at 10 GHz. The radio emission is dominated by other types of emission such as gyro-synchrotron radiation from active magnetospheres, free-free emission from thermal jets, free-free emission from the outflowing photo-evaporated disk material, and/or synchrotron emission from accelerated cosmic-rays in jet or protostellar surface shocks. These different types of emission could not be clearly disentangled. Our non-detections towards Class II/III disks suggest that extreme UV-driven photoevaporation is insufficient to explain the disk dispersal, assuming that the contribution of UV photoevaporating stellar winds to radio flux does not evolve with time. The sensitivity of our data cannot exclude photoevaporation due to X-ray photons as an efficient mechanism for disk dispersal. Deeper surveys with the Square Kilometre Array will be able to provide strong constraints on disk photoevaporation.

astro-ph.SR↗

arXiv2019

Astro2020 Science White Paper: The fundamentals of outflows from evolved stars

Models of the chemical evolution of the interstellar medium, galaxies, and the Universe rely on our understanding of the amounts and chemical composition of the material returned by stars and supernovae. Stellar yields are obtained from stellar-evolution models, which currently lack predictive prescriptions of stellar mass loss, although it significantly affects stellar lifetimes, nucleosynthesis, and chemical ejecta. Galaxy properties are derived from observations of the integrated light of bright member stars. Stars in the late stages of their evolution are among the infrared-brightest objects in galaxies. An unrealistic treatment of the mass-loss process introduces significant uncertainties in galaxy properties derived from their integrated light. We describe current efforts and future needs and opportunities to characterize AGB outflows: driving mechanisms, outflow rates, underlying fundamental physical and chemical processes such as dust grain formation, and dependency of these on metallicity.

astro-ph.SR↗

arXiv2018

Magnetic fields at the onset of high-mass star formation

Context: The importance of magnetic fields at the onset of star formation related to the early fragmentation and collapse processes is largely unexplored today. Aims: We want to understand the magnetic field properties at the earliest evolutionary stages of high-mass star formation. Methods: The Atacama Large Millimeter Array is used at 1.3mm wavelength in full polarization mode to study the polarized emission and by that the magnetic field morphologies and strengths of the high-mass starless region IRDC18310-4. Results: The polarized emission is clearly detected in four sub-cores of the region. In general it shows a smooth distribution, also along elongated cores. Estimating the magnetic field strength via the Davis-Chandrasekhar-Fermi method and following a structure function analysis, we find comparably large magnetic field strengths between ~0.6 and 3.7mG. Comparing the data to spectral line observations, the turbulent-to-magnetic energy ratio is low, indicating that turbulence does not significantly contribute to the stability of the gas clump. A mass-to-flux ratio around the critical value 1.0 - depending on column density - indicates that the region starts to collapse which is consistent with the previous spectral line analysis of the region. Conclusions: While this high-mass region is collapsing and thus at the verge of star formation, the high magnetic field values and the smooth spatial structure indicate that the magnetic field is important for the fragmentation and collapse process. This single case study can only be the starting point for larger sample studies of magnetic fields at the onset of star formation.

astro-ph.GA↗

arXiv2017

Deep into the Water Fountains: The case of IRAS 18043-2116

(Abridged) The formation of large-scale (hundreds to few thousands of AU) bipolar structures in the circumstellar envelopes (CSEs) of post-Asymptotic Giant Branch (post-AGB) stars is poorly understood. The shape of these structures, traced by emission from fast molecular outflows, suggests that the dynamics at the innermost regions of these CSEs does not depend only on the energy of the radiation field of the central star. Deep into the Water Fountains is an observational project based on the results of programs carried out with three telescope facilities: The Karl G. Jansky Very Large Array (JVLA), The Australia Telescope Compact Array (ATCA), and the Very Large Telescope (SINFONI-VLT). Here we report the results of the observations towards the WF nebula IRAS 18043$-$2116: Detection of radio continuum emission in the frequency range 1.5GHz - 8.0GHz; H$_{2}$O maser spectral features and radio continuum emission detected at 22GHz, and H$_{2}$ ro-vibrational emission lines detected at the near infrared. The high-velocity H$_{2}$O maser spectral features, and the shock-excited H$_{2}$ emission detected could be produced in molecular layers which are swept up as a consequence of the propagation of a jet-driven wind. Using the derived H$_{2}$ column density, we estimated a molecular mass-loss rate of the order of $10^{-9}$M$_{\odot}$yr$^{-1}$. On the other hand, if the radio continuum flux detected is generated as a consequence of the propagation of a thermal radio jet, the mass-loss rate associated to the outflowing ionized material is of the order of 10$^{-5}$M$_{\odot}$yr$^{-1}$. The presence of a rotating disk could be a plausible explanation for the mass-loss rates estimated.

astro-ph.SR↗

arXiv2016

ALMA Compact Array observations of the Fried Egg nebula: Evidence for large-scale asymmetric mass-loss from the yellow hypergiant IRAS 17163-3907

Yellow hypergiants are rare and represent a fast evolutionary stage of massive evolved stars. That evolutionary phase is characterised by a very intense mass loss, the understanding of which is still very limited. Here we report ALMA Compact Array observations of a 50$"$-mosaic toward the Fried Egg nebula, around one of the few Galactic yellow hypergiants IRAS 17163-3907. The emission from the $^{12}$CO J=2-1 line, H30$α$ recombination line, and continuum is imaged at a resolution of $\sim$8$"$, revealing the morphology of the molecular environment around the star. The continuum emission is unresolved and peaks at the position of the star. The radio recombination line H30$α$ shows unresolved emission at the star, with an approximately gaussian spectrum centered on a velocity of 21$\pm$3~km/s with a width of 57$\pm$6~km/s. In contrast, the CO 2-1 emission is complex and decomposes into several components beyond the contamination from interstellar gas in the line of sight. The CO spectrum toward the star is a broad plateau, centered at the systemic velocity of +18 km/s and with an expansion velocity of 100$\pm$10 km/s. Assuming isotropic and constant mass-loss, we estimate a mass-loss rate of 8$\pm$1.5 $\times10^{-5}$~M$_\odot$ yr$^{-1}$. At a radius of 25$"$ from the star, we detect CO emission associated with the dust ring previously imaged by {\it Herschel}. The kinematics of this ring, however, is not consistent with an expanding shell, but show a velocity gradient of $v_{sys} \pm$20 km/s. In addition, we find a puzzling bright feature radially connecting the star to the CO ring, at a velocity of +40 km/s relative to the star. This spur feature may trace a unidirectional ejection event from the star. Our ACA observations reveal the complex morphology around IRAS 17163 and illustrate the breakthroughs that ALMA will bring to the field of massive stellar evolution.

astro-ph.SR↗

arXiv2016

The first low-mass black hole X-ray binary identified in quiescence outside of a globular cluster

The observed relation between the X-ray and radio properties of low-luminosity accreting black holes has enabled the identification of multiple candidate black hole X-ray binaries (BHXBs) in globular clusters. Here we report an identification of the radio source VLA J213002.08+120904 (aka M15 S2), recently reported in Kirsten et al. 2014, as a BHXB candidate. They showed that the parallax of this flat-spectrum variable radio source indicates a 2.2$^{+0.5}_{-0.3}$ kpc distance, which identifies it as lying in the foreground of the globular cluster M15. We determine the radio characteristics of this source, and place a deep limit on the X-ray luminosity of $\sim4\times10^{29}$ erg s$^{-1}$. Furthermore, we astrometrically identify a faint red stellar counterpart in archival Hubble images, with colors consistent with a foreground star; at 2.2 kpc its inferred mass is 0.1-0.2 $M_{\odot}$. We rule out that this object is a pulsar, neutron star X-ray binary, cataclysmic variable, or planetary nebula, concluding that VLA J213002.08+120904 is the first accreting black hole X-ray binary candidate discovered in quiescence outside a globular cluster. Given the relatively small area over which parallax studies of radio sources have been performed, this discovery suggests a much larger population of quiescent BHXBs in our Galaxy, $2.6\times10^4-1.7\times10^8$ BHXBs at $3σ$ confidence, than has been previously estimated ($\sim10^2-10^4$) through population synthesis.

astro-ph.HE↗