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Nonlinear Stability of Rotating Hairy Black Holes
No full textInternational audienceRotating hairy black holes (RHBHs) are axisymmetric equilibrium solutions of the Einstein-Klein-Gordon equations, consisting of a spinning black hole surrounded by a toroidal distribution of complex scalar field. Despite their potential astrophysical relevance, the stability of these configurations -- naturally expected to form through superradiant growth of light bosonic fields -- remains uncertain. In this work, we investigate the stability of RHBHs by performing fully non-linear numerical evolutions of several configurations that differ in the relative mass contribution of the scalar-field torus. We find that configurations in which the scalar field mass is subdominant compared to the black hole mass remain stable throughout the evolution. In contrast, when the scalar-field mass dominates, the system develops an instability akin to the non-axisymmetric instability observed in rotating boson stars. Given the expected limits on the scalar-field mass growth achievable through superradiance, our results suggest that rotating hairy black holes formed predominantly by this process are expected to be stable
Advancing European High-Contrast Imaging R&D Towards the Habitable Worlds Observatory
No full textInternational audienceThe Habitable Worlds Observatory (HWO) will enable a transformative leap in the direct imaging and characterization of Earth-like exoplanets. For this, NASA is focusing on early investment in technology development prior to mission definition and actively seeking international partnerships earlier than for previous missions. The "R&D for Space-Based HCI in Europe" workshop, held in March 2024 at Paris Observatory, convened leading experts in high-contrast imaging (HCI) to discuss European expertise and explore potential strategies for European contributions to HWO. This paper synthesizes the discussions and outcomes of the workshop, highlighting Europe's critical contributions to past and current HCI efforts, the synergies between ground-and space-based technologies, and the importance of laboratory testbeds and collaborative funding mechanisms. Key conclusions include the need for Europe to invest in technology development for areas such as deformable mirrors and advanced detectors, and establish or enhance laboratory facilities for system-level testing. Putting emphasis on the urgency of aligning with the timeline of the HWO, the participants called on an open affirmation by the European Space Agency (ESA) that a European contribution to HWO is clearly anticipated, to signal national agencies and unlock funding opportunities at the national level. Based on the expertise demonstrated through R&D, Europe is poised to play a pivotal role in advancing global HCI capabilities, contributing to the characterization of temperate exoplanets and fostering innovation across domains.</div
Worlds Next Door: A Candidate Giant Planet Imaged in the Habitable Zone of <i>α</i> Centauri A. II. Binary Star Modeling, Planet and Exozodi Search, and Sensitivity Analysis
No full textInternational audienceThe James Webb Space Telescope (JWST) observed our closest solar twin, α Centauri A (α Cen A), with the Mid-Infrared Instrument in the F1550C (15.5 μm) coronagraphic imaging mode at three distinct epochs between 2024 August and 2025 April. For the first time with JWST, we demonstrate the application of reference star differential imaging to simultaneously subtract the coronagraphic image of a primary star (α Cen A) and the pointspread function (PSF) of its binary companion (α Cen B) to conduct a deep search for exoplanets and exozodiacal dust emission. We achieve a typical 5σ point-source contrast sensitivity between ∼10 -5 and 10 -4 at separations ≳ 1″ and an exozodiacal disk (coplanar with α Cen AB) sensitivity of ∼5-8× the solar system's zodiacal cloud around α Cen A. The latter is an extraordinary limit, representing the deepest sensitivity to exozodiacal disks achieved for any stellar system to date. Additionally, postprocessing with the principalcomponent-analysis-based Karhunen-Loéve image processing algorithm reveals a point source, called S1, in 2024 August, detected at signal-to-noise ratio of 4-6 (3.3-4.3σ), a projected separation of ≈1. 5 (2 au), and with an F1550C flux density (contrast) of ≈3.5 mJy (≈5.5 × 10 -5 ). Various tests conducted with the available data show that S1 is unlikely to be a detector artifact or PSF-subtraction artifact and confirm that it is neither a background nor a foreground object. S1 is not redetected in two follow-up observations (2025 February and April). If S1 is astrophysical in nature, the only explanation is that it has moved to a region of poor sensitivity due to orbital motion. We perform PSF injection-recovery tests and provide 2D sensitivity maps for each epoch to enable orbital completeness calculations. Additional observations, with JWST or upcoming facilities, are necessary to redetect candidate S1 and confirm its nature as a planet orbiting our nearest solar-type neighbor, α Cen A. More broadly, this program highlights the complexity of analyzing a dynamic binary astrophysical scene and the challenges associated with confirming short-period (∼few years) planet candidates identified without prior orbital constraints in direct imaging searches. This Letter is second in a series of two papers: Paper I discusses the observation strategy and presents the astrophysical case (physical and orbital properties) for S1 as a planet candidate.</div
Shaping the Milky Way: The Interplay of Mergers and Cosmic Filaments
No full textInternational audienceAbstract The large-scale morphology of Milky Way (MW)–mass dark matter halos is shaped by two key processes: filamentary accretion from the cosmic web and interactions with massive satellites. Disentangling their contributions is essential for understanding galaxy evolution and constructing accurate mass models of the MW. We analyze the time-dependent structure of MW-mass halos from zoomed cosmological-hydrodynamical simulations by decomposing their mass distribution into spherical harmonic expansions. We find that the dipole and quadrupole moments dominate the gravitational power spectrum, encoding key information about the halo’s shape and its interaction with the cosmic environment. While the dipole reflects transient perturbations from infalling satellites and damps on dynamical timescales, the quadrupole—linked to the halo’s triaxiality—is a persistent feature. We show that the quadrupole’s orientation aligns with the largest filaments, imprinting a long-lived memory on the halo’s morphology even in its inner regions (∼30 kpc). At the virial radius, the quadrupole distortion can reach 1–2 times the spherical density, highlighting the importance of environment in shaping MW-mass halos. Using multichannel singular spectrum analysis, we successfully disentangle the effects of satellite mergers and filamentary accretion on quadrupole. We find that, compared to isolated MW–LMC simulations that typically use a spherical halo, the LMC-mass satellite induces a quadrupolar response that is an order of magnitude larger in our cosmological halo. This highlights the need for models that incorporate the MW’s asymmetry and time evolution, with direct consequences for observable structures such as disk warps, the LMC-induced wake, and stellar tracers—particularly in the era of precision astrometry
Euclid Quick Data Release (Q1): The evolution of the passive-density and morphology-density relations between and
No full textInternational audienceThe extent to which the environment affects galaxy evolution has been under scrutiny by researchers for decades. With the first data from Euclid, we can begin to study a wide range of environments and their effects as a function of redshift, using 63 sq deg of space-based data. In this paper, we present results from the Euclid Q1 Release, where we measure the passive-density and morphology-density relations at -1. We determine if a galaxy is passive using the specific star-formation rate, and we classify the morphologies of galaxies using the Sérsic index n and the u-r colours. We measure the local environmental density of each galaxy using the Nth-nearest neighbour method. We find that at fixed stellar mass, the quenched fraction increases with increasing density up to . This result shows the separability of the effects from the stellar mass and the environment, at least at z<0.75. At z>0.75, we observe weak environmental effects, with most high mass galaxies being quenched independently of environment. Up to , the ETG fraction increases with density at fixed stellar mass, meaning the environment also transforms the morphology of the galaxy independently of stellar mass, at low mass. For high mass galaxies, almost all galaxies are early-types, with low impact from the environment. At z>0.75, the morphology depends mostly on stellar mass, with only low-mass galaxies being affected by the environment. Given that the morphology classifications use u-r colours, these are correlated to the star-formation rate, and as such our morphology results should be taken with caution; future morphology classifications should verify these results. To summarise, we identify the passive-density and morphology-density relations at z<0.75, but at z>0.75 the relations are less strong. At z>0.75, the uncertainties are large, and future Euclid data releases are key to confirm these trends
HESS J1831-098: Exploring a pulsar halo scenario with H.E.S.S. data
No full textInternational audiencePulsar halos are a class of extended very-high-energy (VHE) sources highlighted by the HAWC observatory towards the Geminga pulsar and PSR B065614. These VHE sources are interpreted as the inverse Compton emission from electrons and positrons diffusing in the interstellar medium at an inhibited rate, having escaped the pulsar wind nebula. Our aim is to search for new pulsar halos using H.E.S.S. data and to constrain their physical properties.Using a physically-motivated model of pulsar halos, we created template-based models of the spatial and energetic distributions of the expected gamma-ray emission using the Gammapy library. A promising candidate source to which this model can be effectively applied is HESS J1831098, an extended VHE source spatially coincident with two energetic pulsars, which also exhibits spectral continuity and morphological compatibility with the ultra-high-energy source 1LHAASO J18311007u*. It could be powered by the radio pulsar PSR J18310952 with a characteristic age of 128 kyr. We present a spectro-morphological analysis of this source with H.E.S.S. data, revealing that the emission is well described with a pulsar halo model, although we cannot reject a simple 2D Gaussian morphology. We discuss the implication of the derived physical parameters of the model
Le Service National d'Observation Gravimétrie SNOG
No full textInternational audienceLe Service National d’Observation Gravimétrie (SNOG) assure le suivi des réseaux d’observations et contribue aux services de l’Association internationale de géodésie (AIG). Il assure ainsi le suivi du réseau permanent gravimétrique (RPG) et des réseaux répétés gravimétriques (RRG). Le RPG est en particulier constitué de cinq stations multi-instrumentées, dont quatre colocalisant des mesures absolues avec des mesures de variations temporelles de la gravité à l’aide de gravimètres supraconducteurs permanents. Le SNOG contribue également au bureau central de deux services scientifiques internationaux de l’IAG: le Bureau Gravimétrique International (BGI) et le Service international de géodynamique et des marées terrestres (IGETS). Les données que le SNO récolte et distribue sont utilisées par différentes communautés pour observer les variations de masses à toutes échelles (surface, croûte, manteau...) ainsi que pour vérifier la stabilité verticale des références (marégraphes, etc.). En constante évolution pour répondre aux besoins de ses communautés scientifiques et les nouveaux déploiements technologiques, nous présentons les différentes composantes du SNOG, les missions d’observations qu’il pilote et les perspectives de développement, en particulier pour ce qui concerne la gravimétrie spatial
Stellar Models Also Limit Exoplanet Atmosphere Studies in Emission
No full textInternational audienceStellar contamination has long been recognized as a major bottleneck in transmission spectroscopy, limiting our ability to accurately characterize exoplanet atmospheres—particularly for terrestrial worlds. In response, significant observational efforts have shifted toward emission spectroscopy as a potentially more robust alternative, exemplified by initiatives such as the 500 hr JWST Rocky Worlds Director's Discretionary Time program. However, the extent to which emission spectroscopy may be affected by stellar effects remains mostly unexplored, in stark contrast with the extensive exploration and mitigation work for transmission spectroscopy. In this study, we assess the impact of imperfect knowledge of stellar spectra on exoplanet atmospheric retrievals from emission spectroscopy. At 12.8 μ m, none of the considered bare surface types—basalt, ultramafic, Fe oxidized, and granitoid—can be reliably distinguished when accounting for the 3 σ model precision between SPHINX and PHOENIX. At 15.0 μ m, only the granitoid surface is distinguishable from all others above this threshold. These results show that stellar model uncertainty alone substantially limits our ability to constrain surface composition from photometric data, even before including other sources of uncertainty, such as stellar radius. Also, we find that current 15 μ m eclipse depth estimations using different stellar models introduce a 60 ppm difference for M8 and 20 ppm for M5 stars. This model discrepancy leads to a degeneracy in retrieved planetary albedos and weakens constraints on the presence of an atmosphere. We therefore recommend that future JWST secondary eclipse observations systematically include stellar mid-IR spectroscopy to mitigate these uncertainties
A Statistical Study of Local Dust Storm Occurrences on Mars Using the 2.77 μm CO 2 Band Observed by OMEGA/Mars Express
No full textInternational audienceLocal Dust Storms (LDS) are defined as dust storm phenomena that cover an area smaller than 1.6 × 10 6 km 2 or persist for less than three sols. The study of LDS is critical for understanding dust transport processes in both horizontal and vertical directions and the evolution of large‐scale dust storms on Mars. However, the relatively small scale and short lifetime make it difficult to detect with previous studies. OMEGA onboard Mars Express (MEx) has conducted spectroscopic measurements with high spatial resolution (up to ∼400 m/pixel). Here, we present a method to retrieve dust optical depth and detect LDS using the 2.77 μm CO 2 absorption band. At this wavelength, photons are absorbed before reaching the surface, and the photons collected by OMEGA have been scattered around 20–30 km altitude by dust. We have detected 146 LDS events from the retrieved dust optical depth in MY27‐29. The LDS were generally observed in the southern summer season, while frequent occurrences of LDS were observed during the northern summer (Ls = 130°–150°) in MY27. The remarkable increase in LDS is also identified just before the global dust storm in MY28. We found a peak in the probability of LDS around noon in both seasons, Ls = 0°–180° and Ls = 180°–360°. In Ls = 0°–180°, high probability areas are found only in specific regions, such as Chryse Planitia. The probability areas expands over a wide range, except high‐latitude north of 40°N in Ls = 180°–360°. These findings highlight the spatiotemporal roles LDS play in dust transport, providing insights into the dust cycle (245/250 words)
MIRS/MMX: an imaging spectrometer to observe the Martian aerosols
No full textInternational audienceMIRS (MMX InfraRed Spectrometer) is the imaging spectrometer (0.9-3.6 µm) [1] of the JAXA MMX (Martian Moons eXploration) mission [2]. The mission will be launched in 2026 to the Martian system, with an arrival planned in 2027. The mission's main objective is to study the two Martian moons, Phobos and Deimos, to collect samples of Phobos and bring them back to Earth in 2031. Another major aim of the mission [3] and the MIRS instrument [1] is to answer key science questions regarding the transport processes of dust and water in the Martian atmosphere [3], such as: how do local and regional dust storms form, grow and evolve? What is the diurnal behaviour of water ice clouds (formation, transport, dynamics)? The MMX probe will be injected into a quasi-circular equatorial orbit around Mars at an altitude of about 6000 km. From this particular orbit, four different observation modes of MIRS are expected for Mars observations (see Figure 1): the so-called nominal mode that maximises the longitudinal overlap, global mapping mode that covers all the illuminated Martian disk up to medium-high latitudes (+/- 60°), region of interest mode that provides temporal resolution (down to 15 minutes) above a limited area, and the limb mode. Each mode will be useful to study the spatial and temporal variations of aerosols (atmospheric dust, water and CO2 ices), and their fine diurnal variations. Indeed, the particular orbit of MMX (the second probe after Hope to be in equatorial orbit) will get us access to observations at very different local times with high spatial resolution, which will certainly provide some answers to the question addressed above.Figure 1: Illustration of the four observation modes of MIRS. The red swath represents the MIRS angle of view. The blue swath corresponds to the observation footprints acquired during a sequence of each observation mode, thanks to MIRS scanning capability (scanner mirror) and spacecraft maneuvers. Credits: CNES. To prepare for future MIRS observations, we use the DISORT (DIScrete-Ordinate-method Radiative Transfer) code [4, 5] through the pyRT_DISORT Python module [6] to simulate the expected radiance of the Martian atmosphere that MIRS will measure. The idea is to produce a look-up table (simulated spectra bank) to retrieve the aerosol properties in the flight data, which allows a faster retrieval as soon as the data are downlinked. First, we will present the parameter space exploration of the radiative transfer model done to quantify the impact of each physical parameter (e.g., observation angles, surface albedo) on the generated spectra. Then, we will discuss the look-up table parameter ranges and steps, which impact the size, as well as the computation time to create the look-up table and the time to search in it. Finally, we will show MIRS images simulated with DISORT in real conditions of the MMX probe arrival, for different atmospheric conditions (dust storms, ice clouds, clear atmosphere) and considering a simulated representative instrument transfer function [7]