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Abraham Loeb

Publications and source records attributed to Abraham Loeb.

At least 19 recordsLinked to original sources
arXiv2026

Dark Matter-Baryon Separability Predicts the Dynamics of an Almost-Dark Galaxy

We extend the Dark Matter-Baryon Separability Condition to show that the same framework developed for dark matter deficient galaxies naturally admits a conjugate branch describing preferential baryonic depletion. Using the recently discovered almost-dark galaxy TTT J1237327+143535 as a worked example, we derive a family of dynamical consistency relations parameterized by the unknown progenitor ratio $\mu_i$, including thresholds for $\sigma_{\rm los}$, $M_{\rm dyn}$, the enclosed baryonic fraction and the dynamical mass to light ratio. We further connect the separability framework to the expected globular cluster population, providing an independent consistency test of the inferred halo mass. We also provide some bounds on the baryon ratio using the tidal properties of Virgo Cluster. Future measurements of stellar kinematics, gas content and globular clusters can therefore determine whether this galaxy occupies the positive separability branch and also test whether dark matter deficient and baryon depleted systems can be described within a common framework.

astro-ph.CO↗
arXiv2026

Optical Flashes from Beam-Driven Light Sails with the Roman, Rubin and Euclid Observatories

The primary challenge of rocket propulsion is the burden of accelerating the spacecraft's own fuel. Light sails leave the propellant at home, with the achievable speed set by the sail area, the thermal tolerance of its material, and the power of the driving array. In GL15 we showed that leakage from a microwave array driving such a sail between habitable worlds produces Jansky-level radio transients lasting tens of seconds at $100$~pc. We take that leak to optical and near-infrared, where Fresnel matching would shrink the aperture to $\sim\!20$--$100$~m at $1\,\mu{\rm m}$, but the intensity on that aperture is $2\times10^{8}\,{\rm W\,m^{-2}}$, five orders above published directed-energy loadings. Spreading $1.5$~TW at $\sim20\,{\rm kW\,m^{-2}}$ is a $\sim10$~km phased array, pushing the emitters; Lubin's $10^{3}\,{\rm W\,m^{-2}}$ loading is a $40$~km array, comfortable but more expensive. A tenth-wave delay on $40$~m tiles sized so one tile still covers the sail leaks $0.054$ of the power ($80$~GW) into a halo. The typical Galactic detection is a single $\sim30$~s peak at $m_{\rm AB}\simeq19.4$ in F146 at $8$~kpc; a pair $87$~s apart, about one in five, is the confirmation test. \emph{Roman}'s Galactic Bulge Time Domain Survey reaches $109$~kpc at $8\sigma$ on a faint host, so a pointed flash of that halo is visible from anywhere in the Galaxy if the beam points at us. For $10$--$40$~km optical beamers held to $\sim\lambda/10$ at $v_{\rm max}\gtrsim250\,{\rm km\,s^{-1}}$, $N_{\rm det}=1$ wants $\Gamma_{6{\rm h}}\simeq16$ and a null search limits $\Gamma_{6{\rm h}}\lesssim49$, a factor-of-three window in launch rate. The real threshold is set by PSF-coincident stellar and instrumental transients. If intensity-limited optical beamers are commonly employed in our galaxy, this activity could be revealed by Roman, Rubin and Euclid at no additional observing cost.

astro-ph.IM↗
arXiv2026

Calibration of CNEOS Fireball Velocities and the Robustness of Nominally Hyperbolic Events

The NASA/JPL CNEOS Fireball Data catalogue provides a near-global record of bright atmospheric entries but does not report per-event velocity covariance. We calibrate its kinematic accuracy using 19 events with independent reference trajectories and use optical, satellite, radar, and infrasound catalogues as source-specific controls. For nine modern high-quality comparisons, the CNEOS-minus-reference speed residual has mean -1.00 km s$^{-1}$ and standard deviation 0.86 km s$^{-1}$; variance decomposition assigns 0.77 km s$^{-1}$ to the CNEOS component. The radiant residuals have a 0.74 degree per-axis core plus one 16.3 degree outlier, so the extreme tail remains poorly determined. Seven of 354 complete CNEOS states are nominally hyperbolic without correction. A +0.9935 km s$^{-1}$ atmospheric-stage shift produces five additional crossings, but these are treated only as sensitivity cases. Polar-IM (2026 April 1) is the strongest post-2018 CNEOS anomaly, whereas independent GLM-LI stereo solutions yield 57.3 +/- 2.0 and 56.7 +/- 3.0 km s$^{-1}$, close to their direction-specific parabolic thresholds. We conclude that CNEOS can identify priority candidates, but secure interstellar classification requires an independent, uncertainty-bearing three-dimensional trajectory for the same event.

astro-ph.EP↗
arXiv2026

Radiative Signatures from Warp Drives Traveling Through the Earth's Atmosphere

We investigate the observable signatures of zero ADM mass warp drive spacetimes traversing Earth's atmosphere. Numerical simulations indicate that an aircraft-scale spacetime bubble moving at relativistic velocities would have a pronounced observational signature, where interaction with the atmosphere can produce luminosities exceeding one terawatt. The signature of a spacetime bubble at rest or moving at low velocity relative to the Earth would not generate such extreme luminosities. These results establish observational constraints on spacetime-based propulsion operating within the terrestrial environment and provide a framework for identifying potential high-velocity signatures. In particular, a warp drive traveling through the atmosphere at speeds exceeding approximately 10% of the speed of light would produce a unique brilliant glow.

gr-qc↗
arXiv2026

Dark Matter Deficient Galaxies as Probes of Dark Matter

Dark matter deficient galaxies provide a direct way to test whether baryons and dark matter can become sufficiently separated during galaxy evolution. We formulate a Dark Matter-Baryon Separability condition based on the relative incorporation efficiencies of the two components, requiring the final dark matter to baryon ratio to fall below an observationally defined threshold. Applied to high speed collisions, this condition constrains dark matter baryon momentum transfer cross section, interacting dark matter fraction and the efficiency of gravitational recapture. The same framework gives us bounds on the abundance and cooling time of dissipative dark matter, and on the integrated escape rate of ultralight fuzzy dark matter from shallow or tidally disturbed potentials. These results show how dark matter deficient galaxies can complement cosmological and laboratory probes by constraining late time dark matter interactions, dissipation and halo stability.

gr-qc↗
arXiv2026

Prospects for Panspermia via Interstellar Objects like 3I/ATLAS

We study the feasibility of natural and directed panspermia via interstellar objects (ISOs) like 3I/ATLAS. The paper is organized around two questions. First, could natural panspermia occur if microbes or biomolecules survived inside shielded ice and were later exposed during perihelion and outbound activity? Second, could directed panspermia occur if a technological civilization planted life-bearing material inside or onto an icy ISO so that it later transported life through the Milky Way? We combine data on 3I/ATLAS with order-of-magnitude thermal, biological, and mission constraints. SPHEREx provides the volatile and organic context through CO$_2$, H$_2$O, CO, dust, and a broad C--H feature, while JWST/MIRI provides the first direct CH$_4$ detection in an interstellar object and confirms an unusual volatile inventory, including enhanced CO$_2$:H$_2$O and CH$_4$:H$_2$O ratios. We distinguish dormant interstellar cruise from active perihelion. Natural panspermia is plausible as microbes can survive or repair damage in ice films, veins, or frozen matrices at very low metabolic rates. Methane production is more nuanced. Frozen survival metabolism would require $\sim10^{14}$--$10^{15}$ kg of biomass to match the JWST CH$_4$ rates, but active methanogenic archaea in warm, liquid, substrate-rich settings can produce methane many orders of magnitude faster, reducing the required biomass in optimistic laboratory-rate comparisons. Directed panspermia faces a different challenge: a direct 60 km s$^{-1}$ impact releases $1.8\times10^9$ J kg$^{-1}$, hundreds of times the specific energy of TNT, and would destroy a biological capsule. 3I/ATLAS-like objects are therefore best treated as test cases for panspermia diagnostics rather than as evidence for life. Natural panspermia requires preservation plus a credible liquid-water or near-surface activation pathway.

astro-ph.EP↗
arXiv2026

A High-Likelihood Polar Interstellar Meteor Candidate

We report a newly identified polar interstellar meteor candidate, labeled polarIM, detected on 2026-04-01 02:13:14 UTC at latitude $-41.9^\circ$, longitude $-54.7^\circ$, and altitude 90.5 km over the South Atlantic Ocean, east of Argentina. We transform the reported Earth-fixed velocity vector $(+3.6,\,-34.6,\,+59.8)~\mathrm{km\,s^{-1}}$ to an inertial geocentric state, remove Earth's gravitational acceleration with a two-body hyperbolic model, add the JPL Horizons heliocentric velocity of Earth, and test the resulting heliocentric orbit against solar escape speed. The final velocity component in the polar ($z$) direction of $+47.09~\mathrm{km\,s^{-1}}$ exceeds by itself the local solar escape speed $v_{\rm esc,\odot}=42.14~\mathrm{km\,s^{-1}}$. The full heliocentric speed is $v_{\rm hel}=51.73~\mathrm{km\,s^{-1}}$, corresponding to positive heliocentric specific energy $\varepsilon_\odot=+450.1~\mathrm{km^2\,s^{-2}}$, heliocentric excess speed $v_{\infty,\odot}=30.00~\mathrm{km\,s^{-1}}$, and a two-body inclination $i=89.4^\circ$. We propagate measurement uncertainty through 1,000,000 Monte Carlo realizations using the empirical post-2018 low-discrepancy CNEOS error model of Pena-Asensio et al. (2025), with $\sigma_v=0.55~\mathrm{km\,s^{-1}}$, $\sigma_{\rm RA}=1.35^\circ$, and $\sigma_{\rm Dec}=0.84^\circ$. No realization yields a bound heliocentric orbit, giving a statistical confidence on the interstellar fraction of $>99.9997\%$. The Monte Carlo margin above escape is $\langle\Delta\rangle=9.60\pm0.75~\mathrm{km\,s^{-1}}$, corresponding to a $12.82\sigma$ margin-to-scatter ratio under the adopted perturbation model. The result identifies polarIM as the highest-margin post-2018 candidate in the CNEOS catalog.

astro-ph.EP↗
arXiv2026

Is the Dark Comet 1998 KY$_{26}$ the Spacecraft Phobos 1?

Since the discovery of new kinds of celestial bodies known as $dark~comets$, scientists have speculated about their ontology. A curious hybrid of comet and asteroid, these objects show significant non-gravitational accelerations (NGAs) yet exhibit absolutely no signs of cometary outgassing in the form of a coma or tail. The planned rendezvous of the Hayabusa2 spacecraft with 1998 KY$_{26}$ in July 2031 elevates the question of this so-called dark comet's nature beyond a purely research exercise, as the true nature of the object may have practical implications for the scientific return of the mission. This study examines the hypothesis that 1998 KY$_{26}$ may be of technogenic origin, in fact a relic of a historical Russian mission to Mars, the Phobos 1 probe, which suffered a failure 2 months after the launch in July 1988, due to upload of a faulty command. We find that two propulsive DeltaVs combined at 1.9 km/s, the first just after loss of mission and the second in May 1996, allow the orbits and phases of the two bodies to align, with an arbitrarily low $Mahalanobis~distance$ using the covariance of the dark comet in 6D phase space. There is also evidence that 1.9 km/s was within the performance envelope of Phobos 1, which had a powerful nitric acid and amine-based autonomous thruster for Mars Orbital Insertion (MOI).

astro-ph.EP↗
arXiv2026

A Framework for Applying the Loeb-Turner $\alpha$-Slope Test to Archival Photometry of Trans-Neptunian Objects

Reflected sunlight from a solar-system body produces a flux at Earth that scales as the heliocentric distance to the negative fourth power, whereas self-luminous emission scales as the negative second power. This difference defines the Loeb--Turner $\alpha$-slope test, a photometric technosignature diagnostic applicable to any solar-system body observed at multiple heliocentric distances. Of 22 (observatory $\times$ band) analysis bins for Pluto in the Minor Planet Center (MPC) archive, none recovers the reflected-sunlight flux--distance slope predicted when photometry is restricted to a single instrument and band. The archive cannot cleanly execute the $\alpha$-slope test on the brightest, most-observed trans-Neptunian object. We formalize a six-criterion eligibility pipeline (Q1--Q6) for the Loeb \& Turner technosignature test and apply it to every numbered TNO. Of 8,606 candidate bins (KBO $\times$ observatory $\times$ band), 1,089 pass Q1--Q3 and 186 additionally pass Q4--Q6, splitting into 53 consistent with reflected sunlight ($\alpha = -4$), 24 with self-luminous emission ($\alpha = -2$), and 109 anomalous. The anomalous bins exhibit slopes steeper than $\alpha = -4$ or shallower than $-2$, consistent with uncorrected per-instrument calibration offsets rather than any single physical mechanism. All 24 self-luminous-like bins originate from Pan-STARRS PS1/PS2; no other observatory contributes any. This indicates a per-instrument calibration systematic. The Rubin Observatory's ten-year survey will deliver uniform single-instrument calibration on a roughly threefold larger sample and either resolve the test at $>10\sigma$ on hundreds of TNOs or, by reproducing the same clustering, falsify the calibration-systematic interpretation.

astro-ph.EP↗
arXiv2026

Unique Gravitational-Wave Signals from Negative-Mass Binaries

Negative masses have long been explored, but their observational viability remains unclear. In this work, we develop a unified, observationally testable framework to constrain negative masses using both coupling level and dynamical probes. We establish that while dipole radiation bounds require universality of gravitational charge, the intrinsic dynamics of negative mass binaries generically lead to anomalous behaviors such as anti-chirps, dispersal and runaway motion. These signatures are absent in current gravitational wave observations, providing a robust exclusion channel independent of modified gravity assumptions.

gr-qc↗
arXiv2026

Pulsational mass loss from supermassive stars creates the compact shells of Little Red Dots

Little Red Dots (LRDs) have emerged as one of the central puzzles of the JWST era. Their spectra increasingly require dense gas close to the source, yet the physical origin of that cocoon-like structure remains unclear. We examine whether late pulsational mass loss from supermassive stars (SMS)leads to dense gas cocoons. We analyze five accreting GENEC models at different metallicities with characteristic masses of order $10^5\,M_\odot$, following them through post-accretion evolution with radial pulsation calculations and general relativistic (GR) stability diagnostics. Mass loss during the final stages of evolution occurs not as a steady wind, but through discrete strange-mode ejection episodes. In the $Z=10^{-2}\,Z_\odot$ model, which provides the clearest LRD analogue, four late episodes last $41$--$282$ yr and eject $10$--$348\,M_\odot$ each, for a total loss of $(4.8-10)\times10^2\,M_\odot$; the final episode alone contributes $\simeq 73\%$ of that budget. Since the last episode dominates the mass-loss, it is the only event sufficiently massive enough to leave behind a compact, optically thick shell extending out to 0.4 pc that reproduces the LRD dense gas cocoon. The final ejecta are H/He dominated but chemically distinctive, with a robust nitrogen-rich composition, $\log(\mathrm{N/O})\simeq0.13$ and $\log(\mathrm{C/O})\simeq-0.23$. The SMS reaches GR instability at an age of $\sim 1$ Myr and collapses in $\sim10^4$ s, retaining $\sim 99\%$ all of its mass. Across the full metallicity range from Pop III to $10^{-2}\,Z_\odot$, this shell-ejection channel persists. Pulsational mass-loss from SMSs therefore provides a physically motivated origin for the compact cocoon-like structure implied by LRDs, while remaining the natural progenitors of the massive black hole seeds invoked in direct collapse scenario.

astro-ph.HE↗
arXiv2026

From Anomaly to Candidate Technosignature: The Threshold Problem of the Loeb Scale

Recent work on the Loeb Scale has provided astronomy a structured framework for assessing anomalous interstellar objects, including a quantitative mapping of a classification ranking, its evolution with the addition of data, and a broader observational strategy for firming its verdict. What remains unclear is the epistemic and methodological meaning of the threshold built into that framework. Here we argue that the central philosophical issue is no longer whether astronomy can define such a threshold, but how a threshold already in place should regulate scientific inquiry under uncertainty. We suggest that candidate technosignature status, such as Level 4 on the Loeb Scale, should be understood as an intermediate epistemic status: stronger than permissive openness, weaker than confirmation, yet sufficient to justify methodological escalation. The argument proceeds in three steps. First, it reconstructs the recent philosophical debate through the work of Lomas, Lane, and Cowie. Second, it turns to historical cases discussed by Kaplan (2026) to show that important discoveries are often delayed not only by weak evidence, but also by paradigms, prestige, and institutional filtering. Third, it interprets candidate status as a form of structured scientific commitment under uncertainty, one that justifies intensified observation, broader hypothesis management, and more deliberate allocation of attention and resources without licensing belief in artificial origin. The paper concludes by arguing that AI should not be the arbitrator in deducing an extraterrestrial origin, but can support the detection, comparison, and prioritization of anomalies once a candidate status has been formally recognized.

physics.pop-ph↗
arXiv2026

Linking System of Jets to the Non-Gravitational Acceleration of 3I/ATLAS

Building on the jet morphology and periodic wobble analysis of 3I/ATLAS in Scarmato & Loeb (2026), we link observed jet position angles (PAs) and the non-gravitational acceleration components (A1,A2,A3) in the 3D RTN (radial, transverse, normal) frame relative to the Sun. We: (i) compute RTN directions from heliocentric state vectors and project them on the sky at the measured astromet ric pointings; (ii) compare projected RTN PAs to three persistent jets (Jet1-Jet2-Jet3) and quantify angular offsets; and (iii) estimate order-of-magnitude thrust and accelerations from HST/WFC3-UVIS F350LP net counts via transformations from photometry to cross-section, dust mass, mass-loss rate, and thrust. We explicitly document the uncertainties through background handling, phase-function systematics, and geometric degeneracies along the line of sight. For U.T. 2025-11-30.80903, Jet2 is aligned with the projected transverse direction to within 0.5 degs, while Jet3 is the closest to the pro jected normal direction with a moderate offset (about 25 degs). For UT 2025-12-27, Jet2 exhibits a monotonic PA drift over 24 minutes with a larger oscillation amplitude.

astro-ph.EP↗
arXiv2026

Dark energy, spatial curvature, and star formation efficiency from JWST photometric and spectroscopic high-redshift galaxies

Early observations from the James Webb Space Telescope (JWST) have revealed an overabundance of massive high-redshift galaxies, raising the question of whether this points to new physics beyond $\Lambda$CDM, or an enhanced formation efficiency of massive stars. We revisit this issue going beyond earlier analyses based on direct comparisons to theoretical bounds at a fixed cosmology, by performing a full Bayesian analysis of the most extreme galaxies in the CEERS imaging and FRESCO spectroscopic samples, jointly constraining cosmological parameters and the baryon-to-star conversion efficiency $\epsilon$. We do so not only within the spatially flat $\Lambda$CDM model, but also in models where the dark energy equation of state $w$ and/or the spatial curvature parameter $\Omega_K$ are allowed to vary, carefully discussing the impact of both $w$ and $\Omega_K$ on the cumulative comoving stellar mass density. Within the flat $\Lambda$CDM model, once cosmological parameters are marginalized over, the CEERS sample provides a weak $2\sigma$ lower limit of $\epsilon \gtrsim 0.07$, compatible with astrophysical expectations. In contrast, the FRESCO sample requires $\epsilon \gtrsim 0.5$ at $2\sigma$, with values $\epsilon \lesssim 0.2$ disfavored at $>5\sigma$. These results do not qualitatively change when we allow $w$ and/or $\Omega_K$ to vary, with no evidence for deviations from $w=-1$ or $\Omega_K=0$. Our results therefore suggest that the origin of the ``JWST tension'' is unlikely to be cosmological, but lies in the astrophysics of galaxy formation.

astro-ph.CO↗
arXiv2026

Inferring the mass and size of 3I/ATLAS from its non-gravitational acceleration

Observations of the interstellar object 3I/ATLAS have revealed a strong production of gas and dust near perihelion, together with rapid brightening. The outgassing from the nucleus has led to a detectable non-gravitational acceleration. In this work, we combine models of the mass loss rate of water and carbon dioxide to derive the non-gravitational parameters and estimate the mass and size of 3I/ATLAS. In addition, we take into account a conservative constraint on the nucleus size from the active surface area required for sublimation. If the mass loss is dominated by the sublimation of CO$_2$, then the nucleus radius and mass are $R_{\rm 3I}=0.42\,\rm{km}$ and $M_{\rm 3I}=1.6\times10^{11}\,\rm{kg}$, assuming a density of $\rho=0.5\,\rm{g\,cm}^{-3}$ and an asymmetry factor of $\zeta=0.5$. This estimate is consistent with the lower bound from the active surface and independently supported by the slight preference of the orbital fit for a $a_{\rm ng}(r)\sim 1/r^2$ scaling of the non-gravitational acceleration. Models that cover the range of reported water production near perihelion give $R_{3I}=0.74-1.15\,\rm{km}$ and $M_{\rm 3I}=8.5-32\times10^{11}\,\rm{kg}$ but require a cometary surface that is in tension with the estimate from the rocket effect. Therefore, our results indicate that a large fraction of water sublimation is occurring in the coma and that CO$_2$ dominates sublimation on the surface. The nucleus radius that we obtain is much smaller than a recent photometric estimate of $R_{\rm 3I}\sim 1.3\,\rm{km}$, which could be resolved if CO$_2$ production is larger than observed or if the density of 3I/ATLAS is significantly lower than assumed. An overall lighter nucleus of 3I/ATLAS might be favored based on its recently claimed origin from a metal-poor environment and the corresponding mass budget of interstellar objects.

astro-ph.EP↗
arXiv2026

Electromagnetic Radiation from Cosmic-Ray Scatterings on Relic Neutrinos

Cosmic-ray scatterings on the cosmic neutrino background induce a flux of gamma-rays and X-rays from boosted meson decays and charged lepton processes. Here we present the first estimate of this flux and its cumulative cosmological contribution. Confronting expectations with Fermi-LAT diffuse gamma-ray data, we find a limit on the cosmic neutrino background overdensity at the level of $\eta \lesssim 2 \times 10^{4}$ for a lightest neutrino mass of $m_{\nu}\gtrsim0.1$ eV, orders of magnitude stronger than current direct laboratory probes, and comparable to constraints on the cosmic neutrino background obtained with IceCube. We further show that X-ray synchrotron emission from cascade electron-positron pairs in intergalactic magnetic fields provides a complementary, albeit weaker, constraint. We discuss how anisotropic signatures and future gamma-ray data from CTA could further improve bounds on the relic neutrino overdensity, approaching in sensitivity the $\Lambda$CDM expected density.

hep-ph↗
arXiv2026

Periodic Wobble of the Post-Perihelion Jet Structure Around 3I/ATLAS

We analyse data on the post-perihelion morphology, including jet position angles (PAs) and coma dominated photometry of the interstellar object 3I/ATLAS. From Hubble Space Telescope (HST) images processed with a Larson Sekanina rotational gradient filter, we measure the PAs of three main persistent jet like features between November 30 and December 27, 2025 and fit a weighted Fourier model in a period scan. The dominant jet PA wobble yields Pjet = 7.20 +/- 0.05 h. An independent Gr (R band) time-series photometry data set, using two different apertures from MPC station L92, analyzed with nightly offsets and 30 minute binning, gives Pphot = 7.136 +/- 0.001 h (formal 1sigma), with a semiamplitude A about 0.311 mag and scatter sigmajit about 0.089 mag. The close agreement beetwen the periods supports a characteristic post-perihelion period of about 7.1 h. We interpret this period as an attitude precession/nutation (non principal axis rotation) traced by jet orientation and coma flux redistribution. The jet structure precesses about the rotation axis with a characteristic angular excursion of order about 20 degs, and the rotation axis is aligned with the sunward direction to within about 20 degs.

astro-ph.EP↗
arXiv2026

Habitable Zones Around Massive Stars: From the Main Sequence to Supergiants

Massive stars dominate the feedback of young stellar populations, yet their ultraviolet fields and winds are often presumed to preclude Earth like habitability. We test this by mapping time dependent habitable zones (HZs) for solar metallicity stars of $0.8$--$120\,M_\odot$. Using rotating and non rotating \textsc{GENEC} tracks, we compute bolometric climate HZ boundaries and impose XUV energy limited escape and wind ram pressure constraints for a dipole-magnetized Earth analogue. The retention limited inner edge is the most restrictive limit. We measure annulus lifetime, longest fixed orbit residence, and maximum dynamically packed terrestrial multiplicity, finding a sharp main-sequence ceiling. A rotating $9\,M_\odot$ star sustains a retention limited HZ for $\sim 30$ Myr at $\sim 70$--$130$ AU, but becomes brief and narrow by $12\,M_\odot$ and disappears by $15\,M_\odot$. Post main-sequence evolution can reopen HZs up to $\sim 25$--$30\,M_\odot$, but only for $\sim 0.03$--$1.5$ Myr at hundreds to $\sim 10^3$ AU, disappearing by $\sim 40\,M_\odot$. Stellar rotation modestly increases habitable lifetimes near the upper main sequence without altering the high mass ceiling. IMF weighting shows that massive stars contribute only $\sim 10^{-4}$ of the habitable planet time budget. Even so, for the fiducial occurrence normalization and if rocky planets form or survive at the required wide separations, they add a few $10^5$ Earth analogues satisfying the adopted criteria to the Milky Way at any instant. Massive star systems do not dominate the Galaxy-wide habitability budget, but may provide short-lived, distinct targets for biosignature searches.

astro-ph.SR↗