Star clusters stand at the intersection of much of modern astrophysics: the ISM, gravitational dynamics, stellar evolution, and cosmology. Here, we review observations and theoretical models for the formation, evolution, and eventual disruption of star clusters. Current literature suggests a picture of this life cycle including the following several phases: ▪ Clusters form in hierarchically structured, accreting molecular clouds that convert gas into stars at a low rate per dynamical time until feedback disperses the gas. ▪ The densest parts of the hierarchy resist gas removal long enough to reach high star-formation efficiency, becoming dynamically relaxed and well mixed. These remain bound after gas removal. ▪ In the first ∼100 Myr after gas removal, clusters disperse moderately fast, through a combination of mass loss and tidal shocks by dense molecular structures in the star-forming environment. ▪ After ∼100 Myr, clusters lose mass via two-body relaxation and shocks by giant molecular clouds, processes that preferentially affect low-mass clusters and cause a turnover in the cluster mass function to appear on ∼1–10-Gyr timescales. ▪ Even after dispersal, some clusters remain coherent and thus detectable in chemical or action space for multiple galactic orbits. In the next decade, a new generation of space– and adaptive optics–assisted ground-based telescopes will enable us to test and refine this picture.
Abstract We present infrared (IR) spectra from our monitoring of the symbiotic Mira, R Aquarii, using the Stratospheric Observatory for Infrared Astronomy. New mid-IR photometric and spectroscopic observations using the FORCAST instrument were obtained in 2022 September, when the system was well into the eclipse phase. The 10 μm silicate feature has increased in strength since the previous observations, obtained in 2019 October. Radiative transfer models of the emission show that the dust density has increased by a factor of about 2 in this period. Three epochs of far-IR photometric observations obtained with the HAWC+ instrument between 2018 July and 2020 September are also presented here. The emission at the sampled wavelength bands ranging from 53 to 214 μm does not vary significantly, in contrast to the mid-IR silicate dust emission that shows large variations. The models suggest that the far-IR emission arises much further out in the circumstellar dust shell and is not affected by the dynamics in the inner regions that impact the mid-IR emission.
We present a novel method for cosmic microwave background (CMB) foreground removal based on deep learning techniques. This method employs a Transformer model, referred to as TCMB , which is specifically designed to effectively process HEALPix-format spherical sky maps. TCMB represents an innovative application in CMB data analysis, as it is an image-based technique that has rarely been utilized in this field. Using simulated data with noise levels representative of current ground-based CMB polarization observations, the TCMB method demonstrates robust performance in removing foreground contamination. The mean absolute variance for the reconstruction of the noisy CMB Q/U map is significantly less than the CMB polarization signal. To mitigate biases caused by instrumental noise, a cross-correlation approach using two half-mission maps was employed, successfully recovering CMB EE and BB power spectra that align closely with the true values, and these results validate the effectiveness of the TCMB method. Compared to the previously employed convolutional neural network (CNN)-based approach, the TCMB method offers two significant advantages: (1) It demonstrates superior effectiveness in reconstructing CMB polarization maps, outperforming CNN-based methods. (2) It can directly process HEALPix spherical sky maps without requiring rectangular region division, a step necessary for CNN-based approaches that often introduces uncertainties such as boundary effects. This study highlights the potential of Transformer-based models as a powerful tool for CMB data analysis, offering a substantial improvement over traditional CNN-based techniques.
Luis E. Salazar Manzano, Hsing Wen Lin, Aster G. Taylor
et al.
Interstellar objects provide a direct window into the environmental conditions around stars other than the Sun. The recent discovery of 3I/ATLAS, a new interstellar comet, offers a unique opportunity to investigate the physical and chemical properties of interstellar objects and to compare them with those of comets in our own solar system. In this Letter we present the results of a 10 night spectroscopic and photometric monitoring campaign with the 2.4 m Hiltner and 1.3 m McGraw–Hill telescopes at the MDM Observatory. The campaign was conducted between August 8 and 17 while 3I/ATLAS was inbound at heliocentric distances of 3.2–2.9 au. Our observations captured the onset of optical gas activity. Nightly spectra reveal a weak CN emission feature in the coma of 3I/ATLAS, absent during the first nights but steadily strengthening thereafter. We measure a CN production rate of Q (CN) ∼ 6 × 10 ^24 s ^−1 , toward the lower end of activity observed in solar system comets. Simultaneous photometry also indicates a small but measurable increase in the coma’s radial profile and increasing r -band Afρ with values in the order of ∼300 cm. We derived a gas-to-dust production ratio of ${\mathrm{log}}\,Q({\rm{CN}})/Af\rho \sim 22.4$ . Our upper limit on the C _2 -to-CN ratio ( ${\mathrm{log}}\,Q({{\rm{C}}}_{2})/Q({\rm{CN}})\lesssim -0.8$ ) indicates that 3I/ATLAS is a strongly carbon-chain-depleted comet. Further observations of 3I/ATLAS are required to verify the apparent carbon-chain depletion and to explore whether such composition represents a recurring trait of the interstellar comet population.
The ATLAS collaboration, G. Aad, E. Aakvaag
et al.
Abstract This article presents a search for a heavy charged Higgs boson produced in association with a top quark and a bottom quark, and decaying into a W boson and a 125 GeV Higgs boson h. The search is performed in final states with one charged lepton, missing transverse momentum, and jets using proton-proton collision data at s $$ \sqrt{s} $$ = 13 TeV recorded with the ATLAS detector during Run 2 of the LHC at CERN. This data set corresponds to a total integrated luminosity of 140 fb −1. The search is conducted by examining the reconstructed invariant mass distribution of the Wh candidates for evidence of a localised excess in the charged Higgs boson mass range from 250 GeV to 3 TeV. No significant excess of data over the expected background is observed and 95% confidence-level upper limits between 2.8 pb and 1.2 fb are placed on the production cross-section times branching ratio for charged Higgs bosons decaying into Wh.
Nuclear and particle physics. Atomic energy. Radioactivity
Yinuo Han, Ryan M. T. White, Joseph R. Callingham
et al.
Carbon-rich Wolf–Rayet (W-R) stars are significant contributors of carbonaceous dust to the galactic environment; however, the mechanisms and conditions for formation and subsequent evolution of dust around these stars remain open questions. Here we present JWST observations of the W-R+W-R colliding-wind binary Apep, which reveal an intricate series of nested concentric dust shells that are abundant in detailed substructure. The striking regularity in these substructures between successive shells suggests an exactly repeating formation mechanism combined with a highly stable outflow that maintains a consistent morphology even after reaching 0.6 pc (assuming a distance of 2.4 kpc) into the interstellar medium. The concentric dust shells show subtle deviations from spherical outflow, which could reflect orbital modulation along the eccentric binary orbit or nonsphericity in the stellar wind. Tracking the evolution of dust across the multitiered structure, we measure the dust temperature evolution that can broadly be described assuming an amorphous carbon composition in radiative thermal equilibrium with the central stars. The temperature profile and orbital period place new distance constraints that support Apep being at a greater distance than previously estimated, reducing the line-of-sight and sky-plane wind speed discrepancy previously thought to characterize the system.
Adam Burrows, Tianshu Wang, David Vartanyan
et al.
Using 20 long-term 3D core-collapse supernova simulations, we find that lower compactness progenitors that explode quasi-spherically due to the short delay to explosion experience smaller neutron star recoil kicks in the ∼100−200 km s ^−1 range, while higher compactness progenitors that explode later and more aspherically leave neutron stars with kicks in the ∼300−1000 km s ^−1 range. In addition, we find that these two classes are correlated with the gravitational mass of the neutron star. This correlation suggests that the survival of binary neutron star systems may in part be due to their lower kick speeds. We also find a correlation between the kick and both the mass dipole of the ejecta and the explosion energy. Furthermore, one channel of black hole birth leaves masses of ∼10 M _⊙ , is not accompanied by a neutrino-driven explosion, and experiences small kicks. A second channel is through a vigorous explosion that leaves behind a black hole with a mass of ∼3.0 M _⊙ kicked to high speeds. We find that the induced spins of nascent neutron stars range from seconds to ∼10 ms, but do not yet see a significant spin/kick correlation for pulsars. We suggest that if an initial spin biases the explosion direction, a spin/kick correlation would be a common byproduct of the neutrino mechanism of core-collapse supernovae. Finally, the induced spin in explosive black hole formation is likely large and in the collapsar range. This new 3D model suite provides a greatly expanded perspective and appears to explain some observed pulsar properties by default.
Lingfeng Wei, Christopher A. Theissen, Quinn M. Konopacky
et al.
We present the kinematic analysis of 246 stars within $4^{\prime} $ from the center of Orion Nebula Cluster (ONC), the closest massive star cluster with active star formation across the full mass range, which provides valuable insights in the formation and evolution of star cluster on an individual-star basis. High-precision radial velocities and surface temperatures are retrieved from spectra acquired by the NIRSPEC instrument used with adaptive optics (NIRSPAO) on the Keck II 10 m telescope. A 3D kinematic map is then constructed by combining with the proper motions previously measured by the Hubble Space Telescope Advanced Camera for Surveys/WFPC2/WFC3IR and Keck II NIRC2. The measured root-mean-squared velocity dispersion is 2.26 ± 0.08 km s ^−1 , significantly higher than the virial equilibrium’s requirement of 1.73 km s ^−1 , suggesting that the ONC core is supervirial, consistent with previous findings. Energy equipartition is not detected in the cluster. Most notably, the velocity of each star relative to its neighbors is found to be negatively correlated with stellar mass. Low-mass stars moving faster than their surrounding stars in a supervirial cluster suggests that the initial masses of forming stars may be related to their initial kinematic states. Additionally, a clockwise rotation preference is detected. A weak sign of inverse mass segregation is also identified among stars excluding the Trapezium stars, although it could be a sample bias. Finally, this study reports the discovery of four new candidate spectroscopic binary systems.
Denny M. Oliveira, Robert C. Allen, Livia R. Alves
et al.
Abstract Interplanetary (IP) shocks are perturbations observed in the solar wind. IP shocks correlate well with solar activity, being more numerous during times of high sunspot numbers. Earth‐bound IP shocks cause many space weather effects that are promptly observed in geospace and on the ground. Such effects can pose considerable threats to human assets in space and on the ground, including satellites in the upper atmosphere and power infrastructure. Thus, it is of great interest to the space weather community to (a) keep an accurate catalog of shocks observed near Earth, and (b) be able to forecast shock occurrence as a function of the solar cycle (SC). In this work, we use a supervised machine learning regression model to predict the number of shocks expected in SC25 using three previously published sunspot predictions for the same cycle. We predict shock counts to be around 275 ± 10, which is ∼47% higher than the shock occurrence in SC24 (187 ± 8), but still smaller than the shock occurrence in SC23 (343 ± 12). With the perspective of having more IP shocks on the horizon for SC25, we briefly discuss many opportunities in space weather research for the remainder years of SC25. The next decade or so will bring unprecedented opportunities for research and forecasting effects in the solar wind, magnetosphere, ionosphere, and on the ground. As a result, we predict SC25 will offer excellent opportunities for shock occurrences and data availability for conducting space weather research and forecasting.
The first-forbidden transition of nuclear β decay is expected to play crucial roles in many aspects in nuclear physics, nuclear astrophysics and particle physics such as the stellar β-decay rates and the reactor anti-neutrino spectra. In this work we develop the projected shell model (PSM) for description of first-forbidden transition of nuclear β decay for the first time. Detailed theoretical framework and logics are provided, and 35 dominant first-forbidden transitions that are expected to be important for the reactor anti-neutrino spectra problems are calculated and compared systematically with the data to test the new development of the PSM. The corresponding experimental Logf0t values are described reasonably, and the quenching factors of nuclear matrix elements are found to affect the Logf0t values as well as the related shape factors, which may be helpful for better understanding of the reactor anti-neutrino spectra problems.
The origin of genetic coding is characterised as an event of cosmic significance in which quantum mechanical causation was transcended by constructive computation. Computational causation entered the physico-chemical processes of the pre-biotic world by the incidental satisfaction of a condition of reflexivity between polymer sequence information and system elements able to facilitate their own production through translation of that information. This event, which has previously been modelled in the dynamics of Gene–Replication–Translation systems, is properly described as a process of self-guided self-organisation. The spontaneous emergence of a primordial genetic code between two-letter alphabets of nucleotide triplets and amino acids is easily possible, starting with random peptide synthesis that is RNA-sequence-dependent. The evident self-organising mechanism is the simultaneous quasi-species bifurcation of the populations of information-carrying genes and enzymes with aminoacyl-tRNA synthetase-like activities. This mechanism allowed the code to evolve very rapidly to the ~20 amino acid limit apparent for the reflexive differentiation of amino acid properties using protein catalysts. The self-organisation of semantics in this domain of physical chemistry conferred on emergent molecular biology exquisite computational control over the nanoscopic events needed for its self-construction.
Learning invariant (causal) features for out-of-distribution (OOD) generalization have attracted extensive attention recently, and among the proposals, invariant risk minimization (IRM) is a notable solution. In spite of its theoretical promise for linear regression, the challenges of using IRM in linear classification problems remain. By introducing the information bottleneck (IB) principle into the learning of IRM, the IB-IRM approach has demonstrated its power to solve these challenges. In this paper, we further improve IB-IRM from two aspects. First, we show that the key assumption of support overlap of invariant features used in IB-IRM guarantees OOD generalization, and it is still possible to achieve the optimal solution without this assumption. Second, we illustrate two failure modes where IB-IRM (and IRM) could fail in learning the invariant features, and to address such failures, we propose a <i>Counterfactual Supervision-based Information Bottleneck (CSIB)</i> learning algorithm that recovers the invariant features. By requiring counterfactual inference, CSIB works even when accessing data from a single environment. Empirical experiments on several datasets verify our theoretical results.
Andres F. Ordonez, David Ayuso, Piero Decleva
et al.
Abstract Chiral molecules are instrumental for molecular recognition in living organisms. Distinguishing between two opposite enantiomers, the mirror twins of the same chiral molecule, is both vital and challenging. Geometric magnetism enables a broad class of phenomena in solids including the anomalous electron velocity, the Hall effect, and related topological observables. Here we show that ultrafast electron currents excited in chiral molecules can generate geometric fields which enable a class of anomalous enantio-sensitive observables in photoionization. Next, we introduce the first member of this class: enantio-sensitive orientation of chiral molecules via photoionization. This effect opens unexplored routes to both enantio-separation and imaging of chiral dynamics on ultrafast time scales. Our work suggests that geometric magnetism in photoionization provides the bridge between the two geometrical properties, chirality and topology.
Abstract Effects of non-linear small-x evolution of the gluon distribution given by the Balitsky–Kovchegov equation are analyzed within the collinear approximation framework. We perform a twist decomposition of the proton structure functions $$F_2$$ F 2 and $$F_{\textrm{L}}$$ F L obtained from the Balitsky–Kovchegov equation using the Mellin representation of the scattering cross-sections at high energies. In both the structure functions we find strong corrections coming from the non-linear effects in the gluon evolution at twist 2, and strongly suppressed higher twist effects. This implies that unitarization effects of high energy scattering amplitudes are mostly the leading twist effect. Furthermore we consider the double logarithmic limit of the Balitsky–Kovchegov equation for the collinear gluon distribution, and compare the result to the Gribov–Levin–Ryskin equation. We find that these two equations differ by two powers of the hard scale logarithm for the large scales.
Astrophysics, Nuclear and particle physics. Atomic energy. Radioactivity
Daniela Carollo, Norbert Christlieb, Patricia B. Tissera
et al.
We explore the chemodynamical properties of a sample of very metal-poor (VMP) stars selected from the Hamburg/ESO survey, matched with Gaia EDR3, in the phase space identified by the three integrals of motion ( L _z , E , I _3 ). Disk and halo orbits are separated by using the criteria defined in Carollo & Chiba. We found 26 stars with [Fe/H] ≤ −2.5 possessing disk kinematics, of which 13 are extremely metal-poor. At these metallicities, the number of stars with disk kinematics is three times its retrograde counterpart. In the same range of metallicity we also identified 37 halo stars most tightly bound to the gravitational potential of the progenitor halo. The origins of these stars are investigated by comparing the observational results with simulated galaxies from the Aquarius Project and the IllustrisTNG simulations. We found two mechanisms of formation of VMP stars with disk kinematics: accretion from early satellites (which is dominant), and in situ formation. These stars are very old, with ages >12.5 Gyr ( z > 5), and they are α -enriched. Accretion and in situ formation are also found for the retrograde counterparts, with accretion also being the dominant mode. Contributing accreted satellites have stellar masses in the range 10 ^6 –10 ^9 M _☉ and are very gas-rich. The most bound halo stars are the oldest detected, with a median age of ∼13.3 Gyr ( z ∼ 11), and are α -enriched. Our finding clearly shows that very old, VMP stars store important information on the first stages of assembly of our Galaxy and its halo.
Boris S. Kalita, John D. Silverman, Emanuele Daddi
et al.
A key question in galaxy evolution has been the importance of the apparent “clumpiness” of high-redshift galaxies. Until now, this property has been primarily investigated in rest-frame UV, limiting our understanding of their relevance. Are they short-lived or are they associated with more long-lived massive structures that are part of the underlying stellar disks? We use JWST/NIRCam imaging from the Cosmic Evolution and Epoch of Reionization Survey to explore the connection between the presence of these “clumps” in a galaxy and its overall stellar morphology, in a mass-complete ( $\mathrm{log}\,{M}_{* }/{M}_{\odot }\gt 10.0$ ) sample of galaxies at 1.0 < z < 2.0. Exploiting the uninterrupted access to rest-frame optical and near-IR light, we simultaneously map the clumps in galactic disks across our wavelength coverage, along with measuring the distribution of stars among their bulges and disks. First, we find that the clumps are not limited to the rest-frame UV and optical, but are also apparent in near-IR with ∼60% spatial overlap. This rest-frame near-IR detection indicates that clumps would also feature in the stellar-mass distribution of the galaxy. A secondary consequence is that these will hence be expected to increase the dynamical friction within galactic disks leading to gas inflow. We find a strong negative correlation between how clumpy a galaxy is and strength of the bulge. This firmly suggests an evolutionary connection, either through clumps driving bulge growth or the bulge stabilizing the galaxy against clump formation, or a combination of the two. Finally, we find evidence of this correlation differing from rest-frame optical to near-IR, which could suggest a combination of varying formation modes for the clumps.
Martin Lindberg, Andris Vaivads, Savvas Raptis
et al.
We use Magnetospheric Multiscale (MMS) data to study electron kinetic entropy per particle <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>S</mi><mi mathvariant="normal">e</mi></msub></semantics></math></inline-formula> across Earth’s quasi-perpendicular bow shock. We have selected 22 shock crossings covering a wide range of shock conditions. Measured distribution functions are calibrated and corrected for spacecraft potential, secondary electron contamination, lack of measurements at the lowest energies and electron density measurements based on plasma frequency measurements. All crossings display an increase in electron kinetic entropy across the shock <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>Δ</mo><msub><mi>S</mi><mi mathvariant="normal">e</mi></msub></mrow></semantics></math></inline-formula> being positive or zero within their error margin. There is a strong dependence of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>Δ</mo><msub><mi>S</mi><mi mathvariant="normal">e</mi></msub></mrow></semantics></math></inline-formula> on the change in electron temperature, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>Δ</mo><msub><mi>T</mi><mi mathvariant="normal">e</mi></msub></mrow></semantics></math></inline-formula>, and the upstream electron plasma beta, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>β</mi><mi mathvariant="normal">e</mi></msub></semantics></math></inline-formula>. Shocks with large <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>Δ</mo><msub><mi>T</mi><mi mathvariant="normal">e</mi></msub></mrow></semantics></math></inline-formula> have large <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>Δ</mo><msub><mi>S</mi><mi mathvariant="normal">e</mi></msub></mrow></semantics></math></inline-formula>. Shocks with smaller <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>β</mi><mi mathvariant="normal">e</mi></msub></semantics></math></inline-formula> are associated with larger <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>Δ</mo><msub><mi>S</mi><mi mathvariant="normal">e</mi></msub></mrow></semantics></math></inline-formula>. We use the values of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>Δ</mo><msub><mi>S</mi><mi mathvariant="normal">e</mi></msub></mrow></semantics></math></inline-formula>, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>Δ</mo><msub><mi>T</mi><mi mathvariant="normal">e</mi></msub></mrow></semantics></math></inline-formula> and density change <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>Δ</mo><msub><mi>n</mi><mi mathvariant="normal">e</mi></msub></mrow></semantics></math></inline-formula> to determine the effective adiabatic index of electrons for each shock crossing. The average effective adiabatic index is <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>⟨</mo><msub><mi>γ</mi><mi mathvariant="normal">e</mi></msub><mo>⟩</mo><mo>=</mo><mn>1.64</mn><mo>±</mo><mn>0.07</mn></mrow></semantics></math></inline-formula>.