Laboratoire d'Étude de l'Univers et des Phénomènes Extrêmes

Abstract In recent years, the shape of the photon ring in black holes images has been argued to provide a sharp test of the Kerr hypothesis for future black hole imaging missions. In this work, we confront this proposal to beyond Kerr geometries and investigate the degeneracy in the estimations of the black hole parameters using the circlipse shape proposed by Gralla and Lupsasca. To that end, we consider a model-independent parametrization of the deviations to the Kerr black hole geometry, dubbed Kerr off shell (KOS), which preserves the fundamental symmetry structure of Kerr known as the Killing tower. Besides exhibiting a Killing tensor and thus a Carter-like constant, all the representants of this family also possess a Killing-Yano tensor and are of Petrov type D. The allowed deviations to Kerr, selected by the symmetry, are encoded in two free functions which depend respectively on the radial and polar angle coordinates. Using the symmetries, we provide an analytic study of the radial and polar motion of photon trajectories generating the critical curve, to which the subrings composing the photon ring converge. This allows us to derive a ready-to-use closed formula for the parametric critical curve in term of the free functions parametrizing the deviations to Kerr. Using this result, we confront the circlipse fitting function to four examples of Kerr-like objects and we show that it admits a high degree of degeneracy. At a given inclination, the same circlipse can fit both a Kerr black hole of a given mass and spin ( M,a ) or a modified rotating black hole with different mass and spin parameters ( M,a ) and a new parameter α . Therefore, future tests of the Kerr hypothesis could be achieved only provided one can measure independently the mass and spin of the black hole to break this degeneracy.

Context. Stars form preferentially in clusters embedded inside massive molecular clouds, many of which contain high-mass stars. Thus, a comprehensive understanding of star formation requires a robust and statistically well-constrained characterization of the formation and early evolution of these high-mass star clusters. To achieve this, we designed the ALMAGAL Large Program that observed 1017 high-mass star-forming regions distributed throughout the Galaxy, sampling different evolutionary stages and environmental conditions. Aims. In this work, we present the acquisition and processing of the ALMAGAL data. The main goal is to set up a robust pipeline that generates science-ready products, that is, continuum and spectral cubes for each ALMAGAL field, with a good and uniform quality across the whole sample. Methods. ALMAGAL observations were performed with the Atacama Large Millimeter/submillimeter Array (ALMA). Each field was observed in three different telescope arrays, being sensitive to spatial scales ranging from ≈1000 au up to ≈0.1 pc. The spectral setup allows sensitive (≈0.1 mJy beam −1 ) imaging of the continuum emission at 219 GHz (or 1.38 mm), and it covers multiple molecular spectral lines observed in four different spectral windows that span about ≈4 GHz in frequency coverage. We have designed a Python-based processing workflow to calibrate and image these observational data. This ALMAGAL pipeline includes an improved continuum determination, suited for line-rich sources; an automatic self-calibration process that reduces phase-noise fluctuations and improves the dynamical range by up to a factor ≈5 in about 15% of the fields; and the combination of data from different telescope arrays to produce science-ready, fully combined images. Results. The final products are a set of uniformly generated continuum images and spectral cubes for each ALMAGAL field, including individual-array and combined-array products. The fully combined products have spatial resolutions in the range 800–2000 au, and mass sensitivities in the range 0.02–0.07 M ⊙ . We also present a first analysis of the spectral line information included in the ALMAGAL setup, and its potential for future scientific studies. As an example, specific spectral lines (e.g., SiO and CH 3 CN) at ≈1000 au scales resolve the presence of multiple outflows in clusters and will help us to search for disk candidates around massive protostars. Moreover, the broad frequency bands provide information on the chemical richness of the different cluster members, which can be used to study the chemical evolution during the formation process of star clusters.

Context. Complex organic molecules (COMs) are found to be abundant in various astrophysical environments, particularly toward star-forming regions, where they are observed both toward protostellar envelopes as well as shocked regions. The emission spectrum, especially that of heavier COMs, might consist of up to hundreds of lines, where line blending hinders the analysis. However, identifying the molecular composition of the gas that leads to the observed millimeter spectra is the first step toward a quantitative analysis. Aims. We have developed a new method based on supervised machine learning to recognize spectroscopic features of the rotational spectrum of molecules in the 3 mm atmospheric transmission band for a list of species including COMs, with the aim of obtaining a detection probability. Methods. We used local thermodynamic equilibrium (LTE) modeling to build a large set of synthetic spectra of 20 molecular species, including COMs with a range of physical conditions typical for star-forming regions. We successfully designed and trained a convolutional neural network (CNN) that provides detection probabilities of individual species in the spectra. Results. We demonstrate that the CNN model we developed has a robust performance to detect spectroscopic signatures from these species in synthetic spectra. We evaluated its ability to detect molecules according to the noise level, frequency coverage, and line-richness, as well as to test its performance for an incomplete frequency coverage with high detection probabilities for the tested parameter space, with no false predictions. Finally, we applied the CNN model to obtain predictions on observational data from the literature toward line-rich hot core-like sources, where the detection probabilities remain reasonable, with no false detections. Conclusions. We demonstrate the use of CNNs in facilitating the analysis of complex millimeter spectra both on synthetic spectra, along with the first tests performed on observational data. Further analyses on its explainability, as well as calibration using a larger observational dataset, will help improve the performance of our method for future applications.

For decades, scaling laws have served as the cornerstone of laboratory astrophysics, enabling quantitative comparisons between astrophysical phenomena and laboratory experiments. However, the lack of observational data and some experimental limitations has limited our ability to validate certain theoretical and numerical models when studying some of the most extreme phenomena in the universe. In this work, we present a theoretical framework for a new class of laboratory astrophysics experiments that leverage existing high-power laser facilities to investigate supersonic radiation-dominated waves. By extending Lie symmetry theory, we demonstrate that the stringent constraints imposed by traditional scaling laws can be relaxed. This approach enables the study of astrophysical phenomena in the laboratory, even when the ratio of radiation energy density to thermal energy and the micro-physics of the systems differ. These equivalence symmetry concepts are illustrated through simulations under conditions relevant to Type-I X-ray bursts and through the design of a first equivalent laboratory experiment. These findings pave the way for a broader range of astrophysical systems to be explored using laboratory experiments, marking the birth of a new innovative approach in laboratory astrophysics.

Growing evidence shows that most stars in the Milky Way, including the Sun, are born in high-mass star-forming regions, but due to both observational and theoretical challenges, our understanding of their chemical evolution is much less clear than that of their low-mass counterparts. Thanks to the capabilities of new generation telescopes and computers, a growing amount of observational and theoretical results have been recently obtained, which have important implications not only for our understanding of the (still mysterious) formation process of high-mass stars, but also for the chemistry that the primordial Solar System might have inherited from its birth environment. In this review, we summarise the main observational and theoretical results achieved in the last decades in the study of chemistry evolution in high-mass star-forming regions, and in the identification of chemical evolutionary indicators. Emphasis is especially given to observational studies, for which most of the work has been carried out so far. A comparison with the chemical evolution occurring in other astrophysical environments, in particular in low-mass star-forming cores and extragalactic cores, is also briefly presented. Current open questions and future perspectives are discussed.

We present a study of shearfree gravitational collapse using cylindrically symmetric spacetimes whose interior is a non-rotating dissipative fluid bounded by a cylindrical hypersurface beyond which is an Einstein–Rosen vacuum exterior. We consider three different pressure configurations: axially, azimuthally, and radially directed, for which we find new exact interior solutions of the field equations. We show that the matching conditions cannot be satisfied by the fluid with radial pressure, while the axial and azimuthal cases with a lapse function depending only on the time coordinate do satisfy these constraints. We derive, for both cases, a sufficient condition for an emission of gravitational radiation from the interior toward the exterior, Therefore we show that, at variance with what happens for spherical symmetry, in the simplified picture of an infinite cylinder of anisotropic shearfree matter, gravitational waves can be emitted during collapsing motion.

Infrared Dark Clouds (IRDCs) are cold, dense structures representative of the initial conditions of star formation. Many studies of IRDCs employ CO to investigate cloud dynamics. However, CO can be highly depleted from the gas phase in IRDCs, impacting its fidelity as tracer. CO depletion is also of great interest in astrochemistry, since CO ice in dust grain mantles provides the raw material for forming complex organic molecules. We study CO depletion toward four IRDCs to investigate how it correlates with volume density and dust temperature, calculated from Herschel images. We use 13CO(1-0) and (2-1) maps to measure CO depletion factor, $f_D$, across IRDCs G23.46-00.53, G24.49-00.70, G24.94-00.15, and G25.16-00.28. We also consider a normalized CO depletion factor, f_D', which takes a value of unity, i.e., no depletion, in the outer, lower density, warmer regions. We then investigate the dependence of f_D and f_D' on gas density, $n_H$ and dust temperature, $T_{dust}$. We find CO depletion rises as density increases, reaching maximum values of f_D'$\sim$10 in regions with $n_H>3\times10^5\:{cm}^{-3}$, although with significant scatter at a given density. We find a tighter, less scattered relation of f_D' with temperature, rising rapidly for temperatures <18 K. We propose a functional form $f_D^\prime = \:{exp}(T_0/[T_{dust}-T_1])$ with $T_0\simeq4\:$K and $T_1\simeq12\:$K to reproduce this behaviour. We conclude that CO is heavily depleted from the gas phase in cold, dense regions of IRDCs. Thus CO depletion can lead to underestimation of total cloud masses based on CO line fluxes by factors up to 5. These results indicate a dominant role for thermal desorption in setting near equilibrium abundances of gas phase CO in IRDCs, providing important constraints for both astrochemical models and the chemodynamical history of gas during the early stages of star formation.

Context . Low-velocity shocks from supernova remnants (SNRs) may set the physical and chemical conditions of star formation in molecular clouds. Recent evidence suggests that even the Sun might have formed through this process. However, the chemical conditions of shock-induced star-forming regions remain poorly constrained. Aims . We study the chemical complexity of a shock-impacted clump, with the potential to yield star formation, named the Clump and located at the interface between the SNR W44 and the infrared dark cloud G034.77-00.55. We test whether the Clump has chemical properties consistent with those observed in star-forming regions unaffected by SNRs. Methods . We used high-sensitivity, broad spectral surveys at 3 and 7 mm obtained with the 30m antenna at the Instituto de Radioastronomia Millímetrica and the 40 m antenna at the Yebes observatory, to identify D-bearing molecules and complex organic molecules (COMs) towards the Clump. For all species, we estimated molecular abundances and compared them with those observed across starforming regions at different evolutionary stages and masses, as well as comets. Results . We detect multiple deuterated molecules (DCO + , DNC, DCN, CH 2 DOH) and COMs (CH 3 OH, CH 3 CHO, CH 3 CCH, CH 3 CN, CH 3 SH) with excitation temperatures of 5-13 K. To the best of our knowledge, this is the first detection of COMs towards a site of SNR-cloud interaction. The derived D/H ratios (~0.01-0.04) and COM abundances are consistent with those reported towards typical low-mass starless cores and comparable to cometary values. The overall level of chemical complexity is relatively low, in line with an early evolutionary stage. Conclusions . We suggest that the Clump is an early stage shock-induced low-mass star-forming region, not yet protostellar. We speculate that SNR-driven shocks may set the physical and chemical conditions to form stars. The resulting chemical budget may be preserved along the formation process of a planetary system, being finally incorporated into planetesimals and cometesimals.

Low-velocity shocks from Supernova Remnants (SNRs) may set the physical and chemical conditions of star formation in molecular clouds. Recent evidence suggests that the Sun might have formed through this process. However, the chemical conditions of shock-induced star forming region remain poorly constrained. We study the chemical complexity of a shock-impacted clump, with potential to yield star formation, named the Clump, and located at the interface between the SNR W44 and the infrared dark cloud G034.77-00.55. We test whether the Clump has chemical properties consistent with those observed in star forming regions unaffected by SNRs. We use high-sensitivity, broad spectral surveys at 3 and 7 mm obtained with the 30m antenna at IIRAM and the 40 m YEBES antenna, to identify D-bearing species and complex organic molecules (COMs) toward the Clump. For all species, we estimate molecular abundances and compare them with those observed across star forming regions at different evolutionary stages and masses, as well as comets. We detect multiple deuterated molecules (DCO+, DNC, DCN, CH2DOH) and COMs (CH3OH, CH3CHO, CH3CCH, CH3CN, CH3SH) with excitation temperatures of 5-13 K. To the best of our knowledge, this is the first detection of COMs toward a site of SNR-cloud interaction. The derived D/H ratios (0.01-0.04) and COM abundances are consistent with those reported toward typical low-mass starless cores and comparable to cometary values. The overall level of chemical complexity is relatively low, in line with an early evolutionary stage. We suggest that the Clump is a early stage shock-induced low-mass star forming region, not yet protostellar. We speculate that SNR shocks may set the physical and chemical conditions to form stars. The resulting chemical budget may be preserved along the formation process of a planetary system, being finally incorporated into planetesimals and cometesimals.

A theoretical study of Cf I spectrum has been carried out, based on the relativistic Hartree–Fock (HFR) method and parametric calculations using Cowan codes and also using the orthogonal operator method. The calculations provide energies, compositions of wavefunctions and Landé factors, on one hand, for two odd excited configurations 5 f 10 7 s 7 p and 5 f 9 6 d 7 s 2 , which give rise to resonance lines by decaying to the ground configuration, and on the other hand, for three even configurations including the ground 5 f 10 7 s 2 , and two interacting configurations 5 f 10 6 d 7 s and 5 f 9 7 s 2 7 p . Transition probabilities have been calculated with the two parametric approaches for the strongest resonance lines, which are electric dipole transitions, and for the predicted magnetic dipole forbidden transitions within the ground configuration. The bound-bound contribution of opacity of Cf I from the transitions between the studied configurations is estimated under typical conditions of kilonovae. The orthogonal operator method has been applied to hyperfine structure calculations, and the results are compared with existing theoretical or experimental ones. • First detailed parametric study for two excited odd configurations of californium. • Better description of the ground configuration taking into account two interacting even configurations. • Calculation of radiative transition probabilities for E1 lines between the studied configurations and for M1 lines within the ground configuration. Estimation of uncertainties. • Application to bound – bound opacity. • Hyperfine structure calculation applying the orthogonal operator method.

Osmium is an element of the Periodic Table with an atomic number Z equal to 76. In Tokamaks with divertors made of tungsten (Z=74), it is produced in the neutron-induced transmutation of the latter. Therefore one can expect that their sputtering may generate ionic impurities of all possible charge states in the fusion plasma. As a consequence, these could contribute to radiation losses in these controlled nuclear devices. The knowledge of radiative rates in all the spectra of osmium is thus important in this field. In this framework, a multiplatform approach has been used to determine the Os V radiative properties and estimate their accuracy. The transition probabilities have been computed for the 2677 electric dipole (E1) transitions falling in the spectral range from 400 Å to 12,000 Å. Three independent atomic structure models have been considered; one based on the fully relativistic ab initio multiconfiguration Dirac–Hartree–Fock (MCDHF) method and two based on the semi-empirical pseudo-relativistic Hartree–Fock (HFR) method.

Context . Infrared dark clouds (IRDCs) are cold, dense structures that are likely representative of the initial conditions of star formation. Many studies of IRDCs employ CO to investigate cloud dynamics, but CO can be highly depleted from the gas phase in IRDCs, which affects its fidelity as tracer. The CO depletion process is also of great interest in astrochemistry because CO ice in dust grain mantles provides the raw material for the formation of complex organic molecules. Aims . We study CO depletion towards four IRDCs to investigate its correlation with the H 2 number density and dust temperature, calculated from Herschel far-infrared images. Methods . We used 13 CO J = 1 → 0 and 2 → 1 maps to measure the CO depletion factor, f D , across IRDCs G23.46-00.53, G24.49-00.70, G24.94-00.15, and G25.16-00.28. We also considered a normalised CO depletion factor, f′ D , which takes a value of unity, that is, no depletion, in the outer lower-density and warmer regions of the clouds. We then investigated the dependence of f D and f′ D on the gas density, n H , and dust temperature, T dust . Results . The CO depletion rises as the density increases and reaches maximum values of f′ D ∼ 10 in some regions with n H ≳ 3 × 10 5 cm −3 , although with significant scatter at a given density. We find a tighter, less scattered relation of f′ D with temperature that rapidly rise for temperatures ≲18 K. We propose a functional form f′ D = exp( T 0 /[ T dust − T 1 ]) with T 0 ≃ 4 K and T 1 ≃ 12 K to reproduce this behaviour. Conclusions . We conclude that CO is strongly depleted from the gas phase in cold, dense regions of IRDCs. This means that if it is not accounted for, CO depletion can lead to an underestimation of the total cloud masses based on CO line fluxes by factors up to ∼5. These results indicate a dominant role for thermal desorption in setting near equilibrium abundances of gas-phase CO in IRDCs and provide important constraints for astrochemical models and the chemodynamical history of gas in the early stages of star formation.

This review summarizes the application of Laurent Nottale’s scale relativity (SRT) theory to hydrodynamic turbulence, a framework he has developed over four decades by rethinking physical laws under the principle of scale relativity. Initially aimed to derive quantum mechanics in fractal position space–time, SRT has more recently been extended to turbulent flows, with equations written in velocity space. This innovative approach enables SR to address long-standing issues in turbulence, such as non-Gaussian velocity distributions and intermittency, through macroscopic analogues of quantum mechanics. Specifically, SR has already provided theoretical insights into: (1) homogeneous, isotropic turbulence, where it predicts deviations consistent with empirical observations for accelerations; (2) rotating turbulence, where it accounts for rotation-induced patterns relevant to planetary and stellar flows; and (3) shear flows, such as turbulent jets, offering accurate predictions of key flow parameters, including turbulent intensity profiles and Reynolds stress distributions. Overall, SR opens new avenues for understanding turbulence across various contexts by providing a unified, non-classical framework in order to fulfill this purpose. • Extension to Turbulence: SRT, from fractal spacetime, now models turbulence in velocity space. • Contributions - Homogeneous Turbulence: SRT predicts acceleration deviations seen in experiments. • Contributions - Rotating Turbulence: SRT explains rotation-driven patterns in geophysical flows. • Contributions - Shear Flows & Jets: SRT models intensity and stress profiles in turbulent shear flows. • Novel Insights: SRT gives a unified, non-classical view on intermittency and velocity statistics. • Implications: SRT links quantum-like behavior to turbulence, offering new understanding paths.

Growing evidence shows that most stars in the Milky Way, including our Sun, are born in high-mass star-forming regions, but due to both observational and theoretical challenges, our understanding of their chemical evolution is much less clear than that of their low-mass counterparts. Thanks to the capabilities of new generation telescopes and computers, a growing amount of observational and theoretical results have been recently obtained, which have important implications not only for our understanding of the (still mysterious) formation process of high-mass stars, but also for the chemistry that the primordial Solar System might have inherited from its birth environment. In this review, we summarise the main observational and theoretical results achieved in the last decades in the study of chemistry evolution in high-mass star-forming regions, and in the identification of chemical evolutionary indicators. Emphasis is especially given to observational studies, for which most of the work has been carried out so far. A comparison with the chemical evolution occurring in other astrophysical environments, in particular in low-mass star-forming cores and extragalactic cores, is also briefly presented. Current open questions and future perspectives are also discussed.

Low-velocity, large-scale shocks impacting on the interstellar medium have been suggested as efficient mechanisms that shape molecular clouds and trigger star formation within them. These shocks, both driven by galactic bubbles and/or cloud-cloud collisions, leave specific signatures in the morphology and kinematics of the gas. Observational studies of such signatures are crucial to investigate if and how shocks affect the clouds formation process and trigger their future star formation. We have analysed the shocked and dense gas tracers SiO(2-1) and H^13CO^+(1-0) emission towards the Infrared Dark Cloud G035.39-00.33, using new, larger-scale maps obtained with the 30 m telescope at the Instituto de Radioastronomía Millimétrica. We find that the dense gas is organised into a northern filament and a southern one that have different velocities and tilted orientations with respect to each other. The two filaments, seen in H^13CO^+, are spatially separated yet connected by a faint bridge-like feature also seen in a position-velocity diagram extracted across the cloud. This bridge feature, typical of cloud-cloud collisions, also coincides with a very spectrally narrow SiO-traced gas emission. We suggest that the northern filament is interacting with the nearby supernova remnant G035.6-0.4. Towards the southern filament, we also report the presence of a parsec-scale, spectrally narrow SiO emission likely driven by the interaction between this filament and a nearby expanding shell. The shell is visible in the 1.3 GHz and 610 MHz continuum images and our preliminary analysis suggests it may be the relic of a supernova remnant. We conclude that the two filaments represent the densest part of two colliding clouds, pushed towards each other by nearby supernova remnants. We speculate that this cloud-cloud collision driven by stellar feedback may have assembled the infrared dark cloud. We also evaluate the possibility that star formation may have been triggered within G035.39-00.33 by the cloud-cloud collision.