Program

Opening words from the SOC to kick off the meeting

Observations of the spatial distribution of galaxies and their peculiar velocities (deviations from the pure Hubble expansion) are expected  to probe unprecedented scales and redshifts. A central challenge is to extract as much cosmological information as possible from these data while accounting for observational biases. 

On sufficiently large scales, where linear theory applies, existing analyses have already yielded robust conclusions. 

We will review these results and discuss their implications for the gravitational instability paradigm of cosmic structure formation. 

We will then present a new analysis that extends this approach to smaller, quasi-nonlinear scales beyond the outskirts of galaxy clusters. Particular attention will be given to identifying and mitigating observational biases in peculiar-velocity studies, enabling these measurements to provide more reliable tests of structure formation.

Galaxy recession velocities are commonly used to measure the Hubble constant, H_0, with peculiar velocities treated as random noise. Around massive clusters, however, these motions can be predicted by the gravitational potential of the central halo, allowing them to be modeled rather than averaged over. Past analyses relied on analytic approximations for the distance-infall-velocity relation,  whose accuracy has not been tested using realistic cosmological simulations. We use halos from the IllustrisTNG simulation to quantify the bias and precision of several commonly used Hubble-flow models. We find that widely used fitting functions systematically underestimate H_0, whereas the full analytical solution reduces but does not eliminate these biases. We develop a simulation-based method to infer H_0 and apply it to TRGB distance samples around the Virgo Cluster. We find H_0=74.4+- 2.9 and 73.4+- 3.9, km s^{-1} Mpc^{-1} for the minor and the major infall models, respectively.

We show that statistical errors are dominated by the residual velocity scatter around the infall model, while systematic errors are dominated by the transformation to the structure's comoving frame and halo population variance. These results establish a framework for interpreting cluster infall measurements and explain trends in previous H_0 inferences.

Small-scale gas dynamics within cosmic filaments contribute to the baryon cycle by pre-processing the gas funneled towards galaxy clusters and influencing galaxy evolution inside filaments. However, it remains poorly constrained since it is hardly observable yet, and has rarely been targeted by specific zoom simulations. I will present the results from the first simulation of the WEFT project (Web Evolution in Filament Targeted zoom simulations), a new suite of high-resolution zoom-in hydrodynamical simulations targeted on cosmic filaments. Using the AREPO code, I simulate a filament from z=63 to z=0 with a resolution down to a few kiloparsecs, allowing a detailed investigation of the formation and drivers of turbulence, using tracers such as enstrophy, helicity or baroclinicity. I also use higher-order velocity structure functions to probe intermittency beyond the idealised Kolmogorov turbulence.

Higher-order statistics of line-intensity maps capture information on the highly-clustered, non-Gaussian distribution of line-emitting sources, that is inaccessible to the power spectrum, but the natural statistic to extract it, the bispectrum, is a function of the full triangle configuration space, making its estimation and its covariance costly for realistic survey pipelines. skew spectra, originally introduced for galaxy clustering, compress the bispectrum information on amplitude-like parameters into power-spectrum-like observables by cross-correlating the field with quadratic combinations built from the operators of its bias expansion. We present the first application of skew spectra to line-intensity mapping. As a proof of concept, we show that in a SPHEREx-like H$\alpha$ survey at~$z \simeq 0.2 - 4.6$ the skew spectra recover the full-bispectrum constraints on the luminosity-weighted bias parameters~$b_1$, $b_2$, and~$b_{\mathcal{G}_2}$, and on deviations from Poissonian shot noise, to within no more than~$3\%$, at a fraction of the computational cost. A joint analysis of the skew spectra and the power spectrum breaks the degeneracy between mean intensity and linear bias, which plagues each individual statistics in real space, and measures the relation of the higher-order biases with the linear bias, which offers insights into the properties of the emitters and the physics governing structure formation.

Abstract

Multi-tracer line-intensity mapping (LIM) is a potential framework for probing the poorly understood epoch of reionization (EoR) at large scales. The multi-tracer LIM framework provides ample opportunities to obtain a synergistic view of the EoR via HI 21cm, CII, H-alpha, and Ly-alpha line emissions. Therefore, developing adequate frameworks to forward-model and forecast LIM observations is crucial. We present a large-scale multi-tracer LIM approach from the POLAR framework, which combines a cosmological N-body dark matter simulation of box size 300 Mpc/h and contains 6144^3 dark matter particles, resolving collapsed halos down to 2x10^8 M_sun/h, and self-consistently models galaxy formation and cosmic reionization with the semi-analytic galaxy formation model L-GALAXIES and the 1-D radiative transfer simulation of reionization, GRIZZLY. Our predictions for the HI 21cm, CII, H-alpha, and Ly-alpha LIM power spectra are broadly consistent with the predictions from other LIM frameworks such as THESAN and LIMFAST at z~7. We also introduce a monte-carlo approach to simulate instrument noise with multiple realizations for forecasts of LIM observations. Preliminary forecasts from our framework suggest that at z~7, the HI 21cm signal from EoR can be detected at ~30 sigma significance at k_perp ~ 0.5 h Mpc^-1 & k_par ~ 0.5 h Mpc^-1 with 1000 hrs of SKA-Low AA*. Our forecasts also suggest that the CII x 21cm cross-power spectrum could be detected at ~80 sigma significance at k_perp ~ 0.3 h Mpc^-1 & k_par ~ 0.2 h Mpc^-1, considering cross-correlation of overlapping surveys from a FYST-like instrument and 1000 hrs of observation with SKA-Low AA*. This framework can be extended to forecast H-alpha and Ly-alpha intensity mapping probes of the EoR, considering the SPHEREx & CDIM surveys and their synergies with surveys like the FYST and SKA-Low.

The redshifted 21-cm signal from neutral hydrogen provides a powerful way to study reionisation, but its detection is challenging because it is much fainter than the foreground emission and instrumental systematics present in radio observations. Recently, Ceccotti et al. (2025) showed that a single night (~6 hours) of LOFAR observations of the 3C 196 field at (z=9.16) produced an upper limit on the 21-cm power more than twice as low as that from a single night (~13 hours) of NCP observations by Patil et al. (2017). This improvement was attributed to lower systematics in the 3C 196 data, suggesting the potential to achieve deeper upper limits than in the NCP field. However, these upper limits are still limited by excess power, which does not average down with increasing integration time in the same way as thermal noise and whose origin is still under investigation.

A largely overlooked aspect of this excess power is the need to investigate the statistics of the underlying visibilities before performing any averaging. Visibilities are the fundamental measurements made by a radio interferometer and contain information about the radio emission from the observed sky. Averaging these measurements over frequency, time, or baselines is commonly used to reduce noise and reduce data. However, in the presence of coherent or non-Gaussian systematics, such as residual RFI, foregrounds, or calibration errors, averaging can amplify the final power and introduce irreversible biases into the data, potentially contributing to the excess.

In this work, we focus on calibrated visibilities from LOFAR observations of the 3C 196 field at z~9-10 and investigate their statistics in delay space (the Fourier domain of frequency). In particular, we collect baselines that have very close transverse spatial wavenumbers at a reference frequency and study how their values are distributed at each delay mode. For purely Gaussian noise, we expect these measurements to follow a Gaussian distribution at every delay. Instead, we observe significant outliers at specific delays, that coincide with those expected from bright off-axis sources, suggesting that the observed outliers may be associated with such sources which were not completely subtracted after calibration. We use an iterative method to flag the baselines that produce extreme outliers at specific delays. We end up flagging only an additional few % of the data, but observe an improvement of up to a factor of 2 in the power on certain nights. This leads to tighter upper limits on the 21-cm power spectrum.

Fast radio bursts (FRBs) have rapidly evolved from a rare class of enigmatic millisecond transients into a powerful probe of both extreme compact-object physics and the distribution of matter across the Universe. With thousands of bursts now detected and an expanding sample of precisely localized sources, FRBs provide a unique opportunity to connect phenomena on scales ranging from neutron-star magnetospheres to the cosmic web.

In this talk, I will review the current observational picture of FRBs, focusing on what their energetics, repetition properties, host galaxies, and local environments reveal about their progenitors. I will discuss recent progress in identifying FRB host galaxies and the emerging evidence for a diverse population of environments, including the importance of persistent radio sources and dense local plasma. I will also highlight how selection effects can shape the observed FRB population and influence inferences about their formation channels and cosmic evolution.

I will then turn to the cosmological potential of FRBs. The dispersion measure of an FRB encodes the integrated free-electron column along its line of sight, making FRBs sensitive probes of the Milky Way halo, circumgalactic gas, the intergalactic medium, and the distribution of the otherwise elusive cosmic baryons. I will discuss recent measurements of the cosmic baryon content and, increasingly, its spatial distribution through correlations between FRB dispersion measures and large-scale structure. I will also examine the prospects and challenges for using localized FRBs to constrain the expansion history of the Universe, emphasizing the astrophysical systematics associated with the Milky Way and host-galaxy contributions.

Finally, I will discuss the prospects for the next generation of wide-field radio surveys and precision localizations, and how substantially larger FRB samples could transform studies of compact-object populations, galaxy evolution, baryonic feedback, and cosmology. I will conclude with a perspective on emerging wide-field GHz facilities, including the GARUDA pathfinder, and the opportunities they offer for exploring the dynamic radio sky.

Understanding the progenitors of fast radio bursts (FRBs) is one of the key open questions in astrophysics. Host-galaxy properties and the positions of transients within their hosts provide valuable clues about their progenitors. In my talk, I will explore what the host galaxies of FRBs can tell us about their origin. With the rapidly growing number of FRBs detected by ongoing surveys with CHIME, ASKAP, and DSA-110, we compare a sample of 100 FRBs with localised hosts to the hosts of short and long gamma-ray bursts (sGRBs and lGRBs) and core-collapse supernovae. I will show that FRB hosts are more massive and older than GRB hosts, placing them in a distinct region in the plane of specific star formation rate versus stellar mass, and that the physical offsets of FRBs lie between those of lGRBs and sGRBs. I will also discuss how the metallicities of FRB hosts compare with those of GRB hosts, and how this comparison changes at z < 1. Finally, I will touch upon why FRB offsets differ across early-type, late-type, and green-valley hosts, and what this reveals about whether the offsets are set mainly by the distribution of the progenitor stars or by neutron-star natal kicks.

In the first part of talk, I will discuss some of my works, while at ARCO, using Fast radio bursts (FRBs) as cosmological probes. FRBs are radio transients with very precise measurements of their dispersion measure (DM). The extragalactic component of DM captures information regarding the expansion history of the universe. With a sample of FRBs with host galaxy identification at z<1, we infer the Hubble constant of the universe assuming LambdaCDM universe. We also constrain the redshift dependence of host DM by assuming it to vary as a simple power law as a function of redshift.  Current data can constrain the power law exponent <=2 at a 68 percent confidence interval which will strengthen with more data. Such constraints have implications for our understanding of galaxy formation and can be used to inform galaxy and large scale simulations. In the second part of the talk, I will talk about some of my recent work with Line Intensity Mapping (LIM). LIM maps will measure cumulative luminosity of photons from galaxies across the universe. These measurements are made at the characteristic frequency of a given line transition such as 21cm, CO, CII lines etc. These maps can be highly non-gaussian due to the spatial as well as luminosity distribution of these galaxies. We capture the non-gaussian information in these maps using Minkowski functionals. I will show some results regarding future prospects of LIM maps in constraining modification to inflationary power spectrum. 

We propose different estimators to probe the intergalactic medium (IGM) during epoch of reionization (EoR) using the dispersion measure (DM) of the fast radio bursts. We consider three different reionization histories, which we can distinguish with a total of <1000 DM measurements during EoR if their redshifts are known. We note that the redshift derivatives of DM are also directly sensitive to the reionization history. The major point of this work is to explore the variance in the DM measurements and the information encoded in them. We find that the all-sky average DM(z) gets biased from the line-of-sight (LoS) fluctuations in the DM measurements introduced by the ionization of IGM during EoR. We find that the ratio σDM/DM depends directly on the ionization bubble sizes as well as the reionization history. On the other hand, we also find that angular variance (coined as structure function) of DM encodes the information about the duration of reionization and the typical bubble sizes as well. We establish the usefulness of variances in DM using toy models of reionization and later verify it with the realistic reionization simulations.

Open questions in gravity (including its quantization), are often approached by a geometrically guided extension of general relativity. This leads to a landscape of candidate theories, including torsionful and metric-affine ones, that are empirically almost indistinguishable from GR and from one another. This talk asks how dispensable geometry is as a guide. Can extensions be reached by extrapolating an empirically guided, non-geometrical route to GR itself, and does such a route constrain the options more tightly?

In a recent paper [1] we showed that GR can be reached from special relativity in this way. The evidence for special relativity is local: it supports inertial frames within bounded regions, not a single global one. If the preferred inertial representation may vary from place to place, the terms that appear in the laws when written in arbitrary coordinates can be promoted to a dynamical field with the familiar index structure, range of local values and transformation properties. This “methodological equivalence principle”, a generalization of the gauge argument, together with universality of gravitational coupling, yields the metric and its Levi-Civita connection. Geometry is then an interpretation added afterwards, not a presupposition.

However, this reconstruction concerns the simplest case of the coupling of classical matter (or bosonic fields) to the metric. Once one moves to more advanced cases, geometry seems to take the lead again. This situation already appears with spinors, which describe most matter. In the familiar account, coupling spinors to gravity requires a tetrad that relates local Lorentz frames to the metric, and a spin connection, both introduced as geometrical structure. This requires additional geometrical assumptions (the “tetrad postulate”) and results in connection that can be independent of the metric, manifesting together a generalized geometrical structure that accommodates non-Riemannian properties such as torsion and non-metricity. 

To extend the non-geometrical route, we apply the same principle to the Dirac equation, whose empirical support is likewise local. It yields the tetrad as the field that determines the locally preferred representation, together with its coupling to spinors. Neither the tetrad–metric relation nor the tetrad postulate is imposed on geometrical grounds. Both follow from the principle together with universality of coupling, and they are exactly the conditions under which the standard geometrical reading is available. The result is torsion-free GR, a restricted subclass of the metric-affine family that the geometrical route permits.

As a demonstration beyond familiar territory, we apply the procedure to local supersymmetry. Invariance of the Wess–Zumino model under spacetime-dependent supersymmetry transformations introduces the gravitino and the metric. In this sense, minimal super-gravitational coupling is in line with the presented procedure (in contrast to supersymmetry, which itself rests on additional and different symmetry\geometry assumptions).

Geometry remains an excellent language to describe gravitational phenomena. But where candidate theories are empirically indistinguishable, following the evidence narrows the range of possibilities more than following geometry.

[1] G. Hetzroni and J. Read, “How to Teach General Relativity”, British Journal for the Philosophy of Science (forthcoming), doi:10.1086/729059.

Recent advances in cosmological measurements such as DESI and ACT may indicate an increase in the preferred value of the spectral tilt 

ns such that it disfavors rather popular models such as the Higgs or Starobinski inflation models. We argue that it actually means that the data is now sensitive enough to quantum corrections beyond simple tree-level models. Resurrecting the old theme of Coleman-Weinberg effective potential, we analyze the predictions of such models, as well as likelihood analysis, leading to a more established and interesting predictive framework. 

Several arguments suggest that the Hilbert space of a closed universe must be trivial, leading proposed resolutions to typically modify quantum mechanics or alter gravitational path integrals.

By extending the $AS^2$ model to include two heavy CFT operators in an entangled state, this work demonstrates that a non-trivial Hilbert space for closed universes can be generated in the bulk. 

Material in the vicinity of black holes is significantly affected by strong gravitational field excited by them. This regime provides unique possibilities how to study Einstein's general relativity, given exceptionally strong gravitational effects. One of the most suitable ways for this study is to analyze the lensed photons which orbit around a black hole and are influenced mainly by its gravity. Using simulated data, we discuss how the lensing effects might be revealed in the future measurements provided  by the Event Horizon Telescope (EHT) Collaboration. We calculate (auto-)correlation functions of the intensity fluctuations and demonstrate that this signal can be used to test the Kerr nature of a black hole without applying complex modelling techniques which enter additional priors. We provide a methodology how this can be achieved and discuss main difficulties for its detection in the measurements of the two main EHT sources - M87 and Sgr A*.

A growing number of gamma-ray bursts (GRBs) show that the central engine does not switch off with the main burst, and the soft X-ray window of Einstein Probe (EP) now allows this long-lived activity to be observed directly. In EP250704a, a ~560 s soft X-ray flash immediately follows the 0.4 s short GRB 250704B, revealing a distinct phase of prompt emission that would have gone undetected without EP; in EP250404a, a soft–hard–flat spectral evolution traces a ~300 s soft X-ray prompt phase, over three times the gamma-ray T90, before the afterglow emerges. Together with the extended emission of long-duration Type I GRBs such as GRB 211211A and GRB 230307A, these observations indicate that minutes-long engine activity is a common feature of merger-driven bursts and challenge the standard picture of a short-lived, hyperaccreting black-hole engine. A long-lived, highly magnetized neutron star is a natural alternative, and I will discuss the accumulating evidence. I will close with the implications of these results for post-merger gravitational-wave searches in the EP era.

In recent years, China has launched and operated several space astronomy missions including Insight-HXMT, China’s first X-ray astronomy satellite, embarking on a journey to explore the extreme universe. Nevertheless, numerous key scientific questions about the extreme universe remain to be solved. These include problems related to extreme gravity, extreme density, and extreme magnetic fields which will be addressed by the enhanced X-ray Timing and Polarimetry (eXTP) space observatory to be launched in 2030. The eXTP mission will carry an array of powerful X-ray telescopes with unprecedented capabilities in simultaneous X-ray spectro-timing-polarimetry capabilities to observe black holes, neutron stars and extreme explosions in the universe, in order to explore the astrophysics and fundamental physics under extreme physical conditions, which are not available in the normal astrophysical environments or accessible on the earth. Also equiped with a wide-band and wide-field carema and designed with autonomous onboard trigger, fast re-pointing capability, eXTP will be a powerful X-ray observatory in the era of time-domain and multi-messenger astronomy

Gamma-ray burst (GRB) 030329 displays one clear and, possibly, multiple less intense fast-rising jumps in its optical afterglow light curve. The decay rate of the optical light curve remains the same before and after each flux jump, indicating that these may be a series of energy injection events into the material at the head of the jet -- i.e., a series of refreshed shocks. We modeled the GRB outflow as  a 1-D series of shells, keeping track of all dynamical interactions of the ejecta with itself (i.e., internal shocks) and with the surrounding circum-burst medium (i.e., the external reverse and forward shocks), and calculated the synchrotron emission from each shock interaction. We were able to confirm that the jumps in the optical afterglow light curve of GRB 030329 could have been produced by a series of energy injection events. The refreshed shocks in our model were caused by the collision between earlier ejected material with an average Lorentz of ~100 and later ejected material with an average Lorentz factor ~10 once the early material was decelerated due to sweeping up the material of the circum-burst medium. We found that even if the late ejecta material is launched with a spread of Lorentz factors, internal shocks naturally produced a narrow distribution of Lorentz factors (∆Γ/Γ ≲ 0.1) by the time the refreshed shocks occurred, which is a necessary condition to produce the observed quick rise times of the flux jumps. If a phase of internal shocks is indeed required at some point in the dynamical evolution of the outflow, this would imply a low magnetization within the outflow. 

The long-duration gamma-ray burst GRB 221009A, the B.O.A.T. (“Brightest of All Time”), was the brightest prompt-phase GRB ever recorded. Among its most intriguing properties is a narrow spectral feature whose centroid energy decays from ~12 MeV to ~6 MeV toward the end of the prompt emission. This feature has been interpreted as electron–positron annihilation produced within the relativistic jet. In this talk, I will show that the commonly considered high-latitude emission scenario from a single-zone emitting region is incompatible with the feature's observed properties. Instead, within an internal-shock dissipation framework, we find that a structured jet with the prompt emission originating predominantly from the jet core and the annihilation feature produced in an off-axis region, provides a natural explanation for several key observations: (i) the delayed onset of the annihilation feature relative to the prompt emission, (ii) the temporal decrease of its centroid energy, and (iii) the observed correlation between the line energy and the peak luminosity. We further show that the line shape can evolve dynamically during this phase, providing an additional diagnostic of the jet structure and emission geometry. Our results suggest that annihilation features in GRB prompt emission can serve as a novel probe of relativistic jet structure and motivate searches for similar signatures in other GRBs.

In this talk, I will present recent works of the astrophysics group in

Warsaw, CTP PAS, focused on central engines of GRBs.

The observations of GW170817 compact binary merger revealed the presence of relativistic jet and the kilonova powered by heavy-element nucleosynthesis.

Our GR MHD simulations involve detailed microphysics treatment, neutrino cooling, nuclear reactions and radiative transfer calculations, addressing multi-component picture of the post-merger system. I will highlight the role of accretion disk winds in this GRB scenario, and I'll also address the open question of how the lifetime of a hypermassive neutron star, possibly formed after the merger and ultimately undergoing collapse to a black hole, shapes the ejecta. 

In the second part of the talk, I'll present some results on the hidden evolution of GRB jets that may be revealed by their GW signals. It can be shown that detection or non-detection of GWs from nearby GRBs and Type Ic SNe could help constrain the mechanisms operating in the central engine.

Finally, I will highlight the recent developments of numerical methods by our group, related to self-gravitating collapsar models.

Gamma-ray bursts (GRBs) release a star's lifetime energy in seconds through an ultra relativistic jet, but the exact process behind the jet prompt emission remains unknown. In the internal shocks model, variations in the jet velocity causes the material to collide at a large distance from the source. These collisions accelerates electrons which emits this energy as gamma-rays through efficient synchrotron cooling. However, observations have shown more photons at low energies than usual synchrotron models can predict, pushing towards alternate explanations.

In this work, we evolve electron distributions across the entirety of a shell's hydrodynamical evolution after an internal shock. Controling the relative importance of synchrotron and adiabatic cooling through a global cooling parameter, we compute the observed emission across a wide range of cooling regimes. We find that effects from an extended emission region become relevant even in radiatively efficient regimes. Moreover, material that keeps on radiating after shock crossing and subsequent rarefaction wave significantly contribute to the low-energy spectra of internal shocks. Finally, we set the basis for a GRB spectral model controlled by physical parameters.

Very-high-energy (VHE; E>100 GeV) observations of gamma-ray burst (GRB) afterglows provide a powerful probe of the energetics of ultrarelativistic blast waves and the nature of the circumburst environment. The VHE component is commonly interpreted as synchrotron self-Compton (SSC) emission. Accurate modeling of this component generally requires computationally expensive numerical calculations, making it challenging to fit observations using Markov Chain Monte Carlo (MCMC) methods.

In this talk, we present a new efficient framework for modeling SSC emission that incorporates Klein--Nishina effects, adiabatic cooling, photon escape, and equal-arrival-time-surface integration. We further develop a neural-network (NN) emulator of this SSC model to accelerate its evaluation and enable efficient broadband X-ray-to-TeV modeling and Bayesian inference.

As a representative application, we apply the numerical SSC model to the TeV-bright GRB 190114C. Using the full numerical calculation, we infer an energetic blast wave with $E_{k,iso}\sim10^{55}$ erg expanding into a radially stratified external medium, $n(r)\propto r^{-k}$, with $k\simeq1.67$. We use this result to benchmark the NN emulator and will present its performance in recovering the numerical SSC predictions and physical parameters. This framework enables efficient inference of ultrarelativistic blast-wave properties from VHE GRB afterglows and can be extended to the growing population of VHE-detected GRBs.

Gamma-ray bursts are observed across the electromagnetic spectrum and on timescales from milliseconds to months, by a fleet spanning prompt keV–MeV detectors, GeV and TeV telescopes, and X-ray, optical and radio facilities.

Turning those observations into measurements requires standardized computation wrapped around repeated expert judgement. This talk reviews what GRB observations provide and where the human effort actually falls. We then present how multiple agents can be built to carry that workflow, and the challenges we expect to face along the way. In the approach we are developing, a supervising agent deploys subagents equipped with stage-specific skills and deterministic domain tools, and orchestrates the analysis, product verification, literature comparison and failure diagnosis. Analysis state, provenance and approvals are retained, and verified failures become versioned lessons. Our experience so far is that the agents carry out the computation reliably, while human approval remains essential, because the agents struggle to recall the skills transferred to them and to apply them at the right time and place, a problem that remains an active area of research in AI engineering. We set out a roadmap for developing such a system and applying it to single-pulse GRBs observed by the Fermi Gamma-ray Space Telescope, and outline the path toward multi-pulse prompt emission analysis, afterglow analysis, multimessenger data, and rapid-response follow-up of newly detected bursts.

Tidal disruption events (TDEs) occur when stars are torn apart by supermassive black holes. They offer a unique opportunity to watch a dormant black hole switch on, assemble an accretion flow, launch outflows or jets, and inject energy into its galactic nucleus. Yet the basic engine of these events remains poorly understood. How TDE engines operate is the major open question in this field. Resolving it is essential for extracting physical parameters, such as black hole masses, from observations.

The traditional picture assumes that the returning debris stream forms a small compact (a few dozen rg) disk that powers the events. However, most observed TDEs emit primarily in the optical/UV and not as expected at X-rays, from locations farther out than such a compact accretion disk, and they radiate promptly only a fraction of the available energy. Based on these basic observations, we have proposed a new paradigm in which TDEs are powered by stream self-intersection shocks occurring at about 1000 rg. Remarkably, this picture is supported by several different large-scale numerical simulations.

In this talk, I describe the new paradigm and its implications for interpretations of TDE observations. 

Tidal Disruption Events (TDEs) occur when a star approaches a black hole closely enough to be torn apart by tidal forces, after which the stellar debris begins to orbit the black hole. Over the past decade, dozens of TDEs have been identified, with many more expected from upcoming surveys. A small subset of these events launches transient, highly luminous relativistic jets (10^47-10^48 erg/s isotropic-equivalent), implying the presence of dynamically important magnetic flux near the black hole horizon. The question arises: what is the origin of this flux? 

A non-negligible fraction of TDEs are expected to occur in Active Galactic Nuclei (AGNs), where a pre-existing accretion flow and magnetic fields are already present. This raises key questions: how does the stellar debris interact with the ambient AGN accretion flow? Can this interaction enhance magnetic flux accumulation near the horizon? And what observational signatures distinguish TDEs occurring in AGN environments? We investigate these questions using relativistic magnetohydrodynamic (RMHD) simulations with the astrophysical code Athena++.

Magnetic fields are of crucial importance in all accreting systems, providing angular momentum transfer and feeding relativistic jets. In the particular case of a tidal disruption of a star by a supermassive black hole (TDE), the stellar magnetic fields are insufficient to provide any measurable impact on the dynamics of the accretion flows. I will present the results of our MHD simulations and discuss the possibilities of how can the newly-formed disc in a TDE still be magnetized and power relativistic jets in the few known jetted TDEs. 

Gamma-ray bursts (GRBs) are the strongest explosions in the Universe, and are powered by initially ultra-relativistic jets. The angular profile of GRB jets encodes important information about their launching and propagation near the central source, and can be probed through their afterglow emission. Detailed analysis of the multiwavelength afterglow light curves of recent GRBs shows evidence of an extended angular structure beyond the jet’s narrow core. The afterglow emission is determined by the jet angular structure, our viewing angle, and the magnetic field structure behind the shock, often leading to degeneracies when considering the light curves and broadband spectrum alone. Such degeneracies can be lifted with joint modeling of the afterglow light curves and polarization, which is expected for synchrotron radiation. In this talk I will explain the origin of polarized emission in GRB afterglows, and expand our basic intuition to the regime of structured jets. Finally, I will show the potential and implications such models have for energetic GRBs and orphan afterglow candidates.

With the most distant gamma-ray burst (GRB) detected at a redshift greater than 9, 

the intrinsically high luminosity of GRBs allows them to be used as probes of the early 

cosmos. New instruments are being developed to detect high redshift GRBs. These 

are expected to be powered by the core-collapse of massive first generation (aka 

Population III) stars that ended the dark ages when the Universe was young. Simpler 

calculations have offered optimistic detection rates, but there are several uncertainties 

that need to be considered. In this talk, I will present an improved calculation of how 

efficient massive Pop III stars can be in producing GRBs. This requires an understanding 

of the role of stellar rotation, mass loss, accretion physics and jet launching. I will present 

results from new stellar evolution (MESA) simulations and discuss how they can be used 

to infer the rate of the most distant GRBs.

Over the past decade, major advances in both observations and numerical simulations have transformed our understanding of relativistic jets in astrophysical systems. In this talk, I will review recent progress in jet physics, focusing on jet launching, propagation, and energy dissipation. I will discuss the role of magnetic fields in the jet evolution, from field amplification and rearrangement near the central engine to energy dissipation at large distances. I will focus on two main dissipation processes: fast dissipation via the current-driven kink instability, followed by slower dissipation through a turbulent cascade, and dissipation in large-scale current sheets that can form in striped jets. I will discuss the implications of these processes for the production of the observed high-energy emission, particularly in BL Lac objects.

Shocks in low density plasmas (so-called "collisionless shocks") are ubiquitous throughout the Universe and are thought to produce nonthermal particles spanning decades of energy (such as cosmic rays). The process of shock acceleration is an intrinsically multiscale problem, connecting plasma microphysics at the shock to self-generated instabilities driven by accelerated particles far from the shock. I will describe the progress in modeling collisionless shock structure and particle acceleration using ab-initio kinetic simulations, focusing on the current understanding of magnetic field amplification mechanisms and the conditions necessary for particle injection into the acceleration process. Our large scale simulations are beginning to show the effects of nonlinear cosmic ray feedback on shock structure and on the resulting cosmic ray spectrum in high-Mach-number shocks. These results help to interpret the emission spectra from young supernova remnants and transient sources.

The secondary component of GW190814, with a mass of $2.50$--$2.67 M_{\odot}$, lies in the mass range between the heaviest observed neutron stars and the lightest black holes, raising the possibility of an unusually massive neutron star. If the secondary is a neutron star, the appearance of hyperons in its core can significantly soften the equation of state and reduce its maximum mass. Rapid rotation can provide additional centrifugal support, but may also trigger the Chandrasekhar--Friedman--Schutz ($r$)-mode instability. In hyperon-rich matter, bulk viscosity arising from nonleptonic weak interactions can efficiently damp these oscillations and enhance the stability of rapidly rotating stars. In this work, we investigate the interplay between rotation, thermal evolution, and hyperon-induced bulk viscosity in massive neutron stars. We study the resulting $r$-mode instability windows and identify the conditions under which hyperonic stars can remain stable against gravitational-wave-driven oscillations. Our results demonstrate that bulk-viscous damping can play a crucial role in stabilizing rapidly rotating, massive hyperon-rich neutron stars, providing a possible interpretation of the GW190814 secondary as a neutron star rather than a low-mass black hole.

Gravitational waves from core-collapse supernovae provide a

unique probe of the processes occurring deep inside dying massive

stars. Unlike electromagnetic radiation, they offer a direct view of

the stellar interior. In this talk, I will briefly review the physical

processes that generate these signals and discuss how their detection

can help reveal the nature of the supernova engine and the properties of matter at extreme densities. 

Enhanced mass loss from core-collapse supernova (SN) progenitors shortly before explosion appears to be common, creating a compact, optically thick circumstellar medium (CSM) at ∼10¹⁴–10¹⁵ cm. In this seminar, I will present an analytic description of the light curves and spectra of high-energy neutrinos emitted by nonrelativistic SN shock breakouts through such CSM, as a function of shock velocity and CSM parameters, accounting for the evolution of the hydrodynamic structure and the electromagnetic (EM) spectrum as the shock transitions from being radiation-mediated to collisionless. This evolution determines the time-dependent neutrino production efficiency, the maximum proton/neutrino energy, and the pair-production optical depth. A significant fraction of the neutrino energy is typically emitted within a few days of explosion, during breakout and before the EM light curve peak, with 1–100 TeV neutrinos carrying ≈10% of the energy of shock-accelerated protons. The escape of high-energy photons (>1 GeV) is suppressed by pair-production for compact CSM configurations. If enhanced mass losses are common, and assuming that shock-accelerated protons carry ≈10% of the collisionless shock energy, CSM SN breakouts may significantly contribute to the observed high-energy neutrino background, without overproducing a corresponding high-energy gamma-ray background. SNe producing >1 neutrino events in a 1(10) km² detector are expected at a rate of ∼0.05(1) yr⁻¹.

Type Iax Supernovae (SNe) are a subclass of Type Ia SNe that are less energetic and remarkably diverse, raising questions about their progenitor systems. While no progenitor system of a normal SN Ia has ever been detected, a luminous blue star was identified in pre-explosion images of the site of the bright Iax SN 2012Z, and is suggested to be a helium giant companion star acting as a mass donor to a WD SN progenitor. This is in line with models of weak mass accretion of a WD from a binary companion, producing an explosion that does not fully disrupt the star. However, these models fail to explain the properties of the faintest Type Iax explosions, suggesting either that they originate from other WD binary systems or even from massive progenitor stars. Here, we present panchromatic observations of the extremely faint Type Iax SN 2024vjm and its immediate environment in the very nearby galaxy NGC 6744. At a peak B-band maximum of -12.68, SN 2024vjm is one of the faintest supernovae observed to date. We investigate the immediate environment of the explosion site in a deep archival image from the new Euclid space mission. No direct progenitor or companion star candidate is detected in the pre-explosion images; however, we place limits on the possible progenitor system and find that it must be fainter than previous Iax SNe progenitor system candidates, such as that of SN 2012Z.

We further find that the ejecta of SN 2024vjm are unusually optically thick, with a slow optical decline rate. Compared to other faint Iax SNe, SN 2024vjm sets a trend whereby the fainter the SN, the slower it declines in reverse of the famous Phillips relation. The SN lightcurve also exhibits an unusually long 56Ni Gamma-ray escape time (t0~80 days), confirming an optically thick ejecta and explaining the slow early decline rate. These results provide new constraints on the progenitor channel and explosion mechanism of faint SNe Iax.

The center of the Milky Way is home to a rich array of exotic sources, including the highest concentration of accreting compact objects identified in our Galaxy.  Among those are low-mass X-ray binaries (LMXBs) and cataclysmic variables (CVs), as well as tens of thousands of faint X-ray sources whose composition remains unidentified.  Classifying these faint populations of X-ray point sources is key to constraining dynamical evolution and binary formation channels in and near the Galactic center, and predicting the rate of gravitational wave events. Utilizing data from two new groundbreaking surveys that were carried out with the XMM-Newton and Chandra X-ray observatories, in conjunction with near-infrared surveys, we are conducting a comprehensive population study into the characteristics and distributions of the X-ray sources in the Galactic center and the surrounding areas.  We have identified a distinct population of extremely hard X-ray sources within a region coincident with the Nuclear Stellar Disk (NSD).  Simulations indicate that this population is likely dominated by intermediate polars with massive white dwarfs, which may have been enhanced through dynamical formation mechanisms.  Upcoming multi-wavelength studies utilizing the Roman Galactic Bulge Time Domain Survey will shed further light on the X-ray point source populations prevalent in different regions of the Galaxy.

Over the last two decades, high-cadence rolling surveys (e.g., PS1, ZTF, ATLAS) have given us large statistical samples of supernovae (SNe) and other transients in the low-z range up to redshifts of 1. With the James Webb Space Telescope (JWST), going deeper and redder than any telescope before, we can now expand transient astronomy into the early, high-redshift universe, which offers us a direct approach for probing both the first stars and the epoch of reionization, insights into rare high energy physics and explosion mechanisms (e.g., Pair-Instability SNe and Superluminous SNe), as well as SN Ia cosmology. I will discuss recent discoveries with JADES and COSMOS-Web, yielding hundreds of SNe, many with redshifts between 2-5, a previously unreachable range. These growing high-z samples will soon be augmented by even larger data sets from Rubin, Euclid, and Roman, ushering in a new era of high-z transients.

The Euclid mission, though primarily designed for cosmology, offers wide-field, high-resolution, deep, multi-wavelength imaging that makes it a powerful asset for time-domain astronomy. While its observing strategy is not optimized for transient searches, several fields are revisited multiple times over the mission lifetime. In these regions, difference imaging enables the discovery of thousands of transients, creating valuable opportunities for studying time-variable phenomena and fostering strong synergies with upcoming surveys such as the Vera Rubin Observatory with LSST, and the Nancy Grace Roman Space Telescope. In this talk, we will present results from a pilot key project in the Self-Calibration field, using both optical and NIR data obtained during the first three years of observations, carried out by the Supernova and Transient working group of the Euclid collaboration. This project highlights Euclid’s capability to detect and characterize transients and serves as a stepping stone toward the transient program planned for the Euclid Deep Fields, in coordination with Rubin LSST and Roman 

Dust extinction is the perennial obstacle of transient astronomy: for most explosive sources there is no extinction-free reference for the intrinsic emission. The Na I D doublet traces the intervening gas and dust, but its quantitative use has been crippled by two facts — the lines saturate, and diagnosing that saturation was thought to require resolving the velocity structure of individual interstellar clouds ($\lambda/\Delta\lambda \sim 3\times10^{4}$–$3\times10^{5}$). We show that it does not. Because D$2$ and D$1$ share the same ground state and differ only in oscillator strength, their equivalent-width ratio alone encodes the saturation correction: the classical curve-of-growth inversion collapses to a one-dimensional problem the moment the two doublet members are separated — requiring only $\lambda/\Delta\lambda \gtrsim 10^{3}$, two orders of magnitude below velocity-resolved methods and within reach of workhorse medium-resolution spectrographs. The framework delivers three estimators from just two equivalent widths: the exact Gaussian inversion $N{\tilde\kappa}$, a closed-form second-order approximation $N{\rm 2nd}$, and $N_{\min}$ — a strict, optimal lower bound valid for any unresolved velocity structure — plus a built-in, per-object diagnostic that flags when saturation defeats any equivalent-width method. We validate the estimators against high-resolution profile-fitting column densities toward Type Ia supernovae, then turn SNe Ia into a testbed for extinction: their photometric reddening enables the first direct $A_V$–$A_V$ confrontation along the same host-galaxy sight lines, and a reassessment of the puzzling SNe Ia with blueshifted, anomalously strong Na I D absorption. 

Upcoming surveys such as LSST and Roman will observe large numbers of Type Ia supernovae (SNe Ia) in the rest-frame ultraviolet (UV), where current light-curve models remain poorly constrained and possible redshift evolution could bias cosmological measurements. I will present SALT3-UV, a new optical–UV SN Ia model trained with high-quality HST UV spectroscopy, which improves model uncertainties by more than a factor of three down to ~2000 Å. I will also discuss tentative differences between the UV properties of low- and high-redshift SNe Ia and show that, if such evolution is real, including rest-frame UV data could bias measurements of the dark-energy equation-of-state parameter w at the few-percent level. These results highlight the challenges of using rest-frame UV observations for next-generation SN Ia cosmology.

Neutron stars provide extreme environments in which axion-like particles can be produced, propagate  and convert into observable photons in strong magnetic fields. In this talk, I will discuss recent developments connecting microscopic production mechanisms in neutron-star interiors with resonant axion-photon conversion in their magnetospheres. I will emphasize how dense-matter composition, plasma properties, magnetic-field geometry, and binary dynamics shape the emerging electromagnetic signal. Particular attention will be given to time-dependent signatures in neutron-star binaries and to the prospects for multimessenger searches combining gravitational-wave information with radio, X-ray, or gamma-ray observations.

Recent IXPE observations of Her X-1 reveal correlations between flux, polarization degree, and polarization angle with its 35 day superorbital cycle. These measurements have been interpreted as strong evidence that the 35 day period is driven by nearly free precession of the neutron star. We show that this interpretation carries far-reaching implications for the dynamics of the crustal superfluid. In particular, maintaining precession over the ~50 yr observational baseline of Her X-1 would require that superfluid vortices remain unpinned for centuries and experience extremely weak mutual friction while traversing the heavy-ion lattice of the inner crust---conditions that challenge conventional wisdom and standard models of glitch dynamics.

Shocks are ubiquitous in astrophysical sources, many of which involve relativistic bulk motions, leading to the formation of relativistic shocks. Such relativistic shocks have so far been studied mainly in one dimension, for simplicity, but the complex nature of the relevant astrophysical flows often requires higher-dimensional studies. Here, we study the two-dimensional problem of the reflection of a planer shock off of a wall for a general incidence angle and a cold unshocked medium. We use primarily relativistic hydrodynamic numerical simulations and elaborately compare the results to an analytic treatment. The simulations are performed both in the rest frame S of the unshocked fluid, where the dimensionless proper speed of the singly shocked fluid is  and the shock incidence angle is α1, and in the rest frame S  of the point P of intersection of the incident shock and the wall for regular reflection (RR). Good agreement is obtained between the simulations in these two frames and with the analytic solution. The establishment of a steady flow in frame S  is explored, along with the transition between the strong and weak shock RR solutions. The transition line between RR and Mach reflection is studied numerically in the u1 − α1 plane and found to coincide with the analytic detachment/sonic line. The flow properties along the sonic line are investigated in detail focusing on how they vary between the Newtonian and relativistic limits.

The most distant planets in the solar system, Uranus and Neptune, are known as 'ice giants'. This term has been deemed appropriate because according to the prevailing belief of the last several decades, they contain roughly twice as much water as rock. We recently challenged this view and questioned the dominance of water. Modern observations of outer solar system bodies rather show them to be refractory-, and not ice-rich. Therefore, how can one form ice giants from ice-poor building blocks? As a first step to solve this composition tension problem, we develop a new technique to generate hundreds of thousands of random computer-generated models for the internal structure and composition of Uranus and Neptune. Mapping the space of possible compositions, we show that these planets cannot be rock giants instead of ice giants, thereby eliminating this as a potential solution. Alternatively, we propose an entirely new solution to form ice giants from ice-poor planetesimals. Contemporary observations show that the refractory materials inside outer solar system planetesimals contain a large fraction of refractory organics. We use several different codes in order to show that these organics are chemically transformed by reacting with the hydrogen in the growing atmospheres of Uranus and Neptune, during and after their accretion, thereby generating copious amounts of methane. This would make Uranus and Neptune methane-giants, and since methane is an ice, the term 'ice giants' turns out to be strictly appropriate. We show that there is an excellent agreement between random models of Uranus and Neptune with methane and chemistry-derived models. We offer a prediction to check our result in an upcoming mission to Uranus, in the next decade.

Over the past decade, NASA’s Juno spacecraft has provided an unprecedented view of Jupiter’s atmosphere and deep interior. Through precise radio tracking of the spacecraft, Juno has measured Jupiter’s gravity field with remarkable accuracy, allowing us to probe the planet’s internal structure and the dynamics of its deep atmosphere. In this talk, I will review how these measurements have revealed that Jupiter’s powerful atmospheric jets extend thousands of kilometers below the visible clouds, provided new constraints on the planet’s internal density distribution and the nature of its dilute core, and uncovered the interaction between atmospheric circulation and the deeper planetary interior. Comparisons with Saturn, drawing on measurements from the Cassini mission, will highlight both the similarities and differences in the atmospheric dynamics and internal structures of the two gas giants. I will also discuss how recent advances in interior modeling, combining gravity measurements with machine learning approaches, are providing new constraints on Jupiter’s internal structure and composition.

Context:

Strong stellar irradiation produces large day–night thermal contrasts in tidally locked hot Jupiters. Atmospheric circulation can transport chemical species faster than finite-rate chemistry restores local equilibrium, leading to longitudinal chemical homogenization and quenching. Three-dimensional circulation–chemistry calculations, pseudo-two-dimensional models, and chemical-timescale analyses have established this coupling, particularly for CO–CH₄ chemistry. Studies of atmospheric dynamics and condensation further highlight the role of transport in shaping observable thermal structures and chemical abundances.

Aims:

We develop an analytical framework linking atmospheric thermal structure to horizontal transport and chemical quenching, deriving a physically interpretable wind scaling to determine when transport dominates chemical relaxation.

Methods:

Starting from the ideal-gas law and hydrostatic equilibrium, we derive the day–night displacement of constant-pressure surfaces by integrating T(P)/μₘ(P) over logarithmic pressure. This forcing is incorporated into a steady, one-dimensional, drag-balanced shallow-water-type model, yielding an analytical longitudinal velocity structure and pressure-dependent terminator velocity. Chemical disequilibrium is characterized by χ ≡ τ_{chem}/τ_{trans}, where τ_{trans} is the effective substellar–antistellar transport timescale and τ_{chem} is calculated from a modified Arrhenius expression for a rate-limiting reaction. The quench boundary is defined by χ = 1. We apply the framework to WASP-43b using the temperature–pressure profiles from literature, with μₘ=2.3, and a fiducial drag timescale of τ_{drag} = 10⁴ s.

Results:

The pressure-integrated model yields a maximum terminator velocity of approximately 1.8 km s⁻¹, comparable in magnitude to the characteristic-velocity estimate of approximately 2.2 km s⁻¹ obtained for WASP-43b using the evolutionary-model scaling. The calculated pressure dependence reflects the integrated day–night thermal forcing rather than assuming a constant local temperature contrast throughout the atmospheric column. Coupling this transport scaling to chemical kinetics provides an analytical means of locating the quench boundary and estimating its day–night displacement.

Conclusions:

This framework connects thermal forcing, atmospheric circulation, and chemical disequilibrium within a common analytical model. It provides a basis for investigating horizontal chemical homogenization in hot Jupiters and can be extended to ultra-hot Jupiters, where thermal dissociation and pressure-dependent composition may produce different day- and night-side mean molecular weights.

We further find that the ejecta of SN 2024vjm are unusually optically thick, with a slow optical decline rate. Compared to other faint Iax SNe, SN 2024vjm sets a trend whereby the fainter the SN, the slower it declines in reverse of the famous Phillips relation. The SN lightcurve also exhibits an unusually long 56Ni Gamma-ray escape time (t0~80 days), confirming an optically thick ejecta and explaining the slow early decline rate. These results provide new constraints on the progenitor channel and explosion mechanism of faint SNe Iax.

We consider a low-viscosity gas-and-dust disk around the early-stage 

Sun using a self-consistent system of Navier-Stokes and Poisson equations. Formation of 

the Solar System about 4.6 Gyr ago through an internal instability of small gravity perturbations in the thin, differentially rotating, and 

self-gravitating disk is suggested. This type of macroscopic instability is driven by a strong non-resonant interaction of the spontaneous 

gravitational fluctuations with the bulk of the particle population, and, therefore, the fluid-dynamics description is used to describe the 

phenomenon. It is shown that the instability process itself is quite fast and could form all the planets in their original places in 

about 1 Myr without any special trigger process. A collective process, forming the basis of the disk gravitational instability 

hypothesis, with surprising simplicity, solves one of the main problems of the dynamical characteristics of the system, 

which is associated with its observed roughly geometric spacing of planet orbital distances. The analysis is also found 

to imply a possibility of the existence of new planets or other Kuiper-type belts of icy bodies and debris, still not 

discovered, orbiting the Sun at mean distances of about 90 au, 150 au, 260 au, 450 au, 780 au, $\dots$ 

(Mercury, Venus, $\dots$, asteroid belt, $\dots$, Neptune, Kuiper Belt, new planets or other 

Kuiper-type belts).

M-dwarf stars are the most abundant stars in the Galaxy and frequently host close-in Super-Earths and Mini-Neptunes. Massive planets at larger separations (Cold Jupiters, or CJs) are much less common, but their presence can provide important insights into the formation and dynamical evolution of planetary systems. However, we still do not know whether M dwarfs with outer CJs are more or less likely to host smaller inner planets than otherwise similar M dwarfs. Measuring this relation, together with the multiplicity, orbital-period distribution, and eccentricity of the inner planets, can distinguish between scenarios in which inner and outer planets form together and scenarios in which the massive outer planets disrupt inner planetary systems. Until now, the rarity and long orbital periods of CJs around M dwarfs have made such a population study impractical. Gaia DR4 provides a new way to perform this experiment. Instead of monitoring large samples of M dwarfs to detect a few outer massive planets, we can start with M-dwarf CJs identified by DR4 astrometry and systematically search for their inner planetary systems. Current Gaia yield simulations predict more than 2,000 CJs orbiting M dwarfs. Our preliminary analysis predicts approximately 200 M0–M7V candidates with J < 10 mag that are suitable for precision radial-velocity (RV) observations. In this talk, I will review how RV follow-up observations of Gaia-detected CJ hosts will soon determine whether and how the occurrence and architecture of inner planetary systems around M dwarfs depend on the presence of outer massive planets. Importantly, these studies will test whether massive outer planets suppress, preserve, or accompany compact inner planetary systems, thereby providing new observational constraints on planet formation and dynamical evolution in low-mass protoplanetary disks.

Gaia has transformed our understanding of the Milky Way and opened a new window onto binary stars and their formation. Its next frontier is exoplanets. If everything goes according to plan, Gaia DR4 will arrive just one day before this talk. I will highlight what Gaia has already taught us about stellar companions and explore how DR4 could extend this revolution into the planetary regime. From the brown-dwarf desert to giant planets around metal-poor stars, DR4 offers an opportunity to investigate a fundamental question: where do planet formation and star formation overlap?

Internal gravity wave (IGW) dissipation is believed to be one of the most significant processes affecting the evolution of planets following the dispersal of the protoplanetary disk. The IGW-driven orbital decay timescales of sufficiently short-period planets, especially hot Jupiters, are expected to be orders of magnitude shorter than the main-sequence lifetimes of solar-type stars. Therefore, implementing IGW dissipation in planetary migration models is essential for the accurate determination of the evolutionary outcomes for a given star-planet system. In this talk, I present a comprehensive study of tidally driven orbital migration of hot Jupiters. By implementing the tidal prescriptions developed by Barker (2020) within the orbital evolution code, I explore regions of the parameter space in which IGW dissipation becomes important.

Planetary orbital migration can lead to the engulfment of planets with the smallest separations, leaving imprints on the orbital period distribution of the surviving systems. Applying the tidal prescription to the observed sample of hot Jupiters with known ages, I identify systems whose host stars are sufficiently evolved to have entered the regime of efficient IGW dissipation. These systems exhibit an orbital-period distribution qualitatively different from that of the remaining sample: whereas young, slowly migrating planets tend to have a nearly uniform orbital period distribution, systems with active IGW dissipation are characterized by a steep decline at short orbital periods. Building upon these findings, I apply a population synthesis approach to demonstrate that the observed patterns in age-orbital period distribution of hot Jupiters can be naturally explained by our model of IGW-driven orbital migration. This result provides compelling evidence that IGW dissipation is responsible for sculpting the population of hot Jupiter systems. To guide future observations,  I identify the most promising candidates for the detection of tidally driven orbital decay.

The well-known correlation between stellar metallicity and planet occurrence is strongest for giant planets, but weaker for smaller planets, suggesting that detailed elemental patterns beyond [Fe/H] may be relevant. Using stellar abundances from the GALAH spectroscopic survey, we analyzed a set of planet-host stars with planets whose radii are known (transiting planets). We find that large-planet host stars are enriched in iron and in highly volatile elements (C, N, O), whereas small-planet hosts exhibit an enhanced contribution of the classical rock-forming elements (Mg, Si, Ca, Ti), relative to iron. We use a matched control sample of non-planet-host stars to confirm that the stronger chemical signatures are indeed linked to the planetary characteristics. These results refine the planet-metallicity relation, highlighting the role of the relative balance between iron, volatiles, and rock-forming elements in planet formation.

 Water-rich exoplanets with several percent water by mass may develop a high-pressure ice layer separating their rocky interiors from the outer hydrosphere, potentially regulating the transport of trace chemical species to the surface. Here we investigate the incorporation of the sulfur-bearing species H$_2$S and SO$_2$ into ice VII, filled ice, and the chiral hydrate structure S$\chi$. We find that H$_2$S can be incorporated as substitutional defects in ice VII up to a mole fraction of approximately 0.002. For water worlds with habitable surface temperatures, we further find that an H$_2$S filled ice with an H$_2$S:H$_2$O ratio of approximately 1:2 is thermodynamically favored in the interior. In contrast, SO$_2$ mixing is unfavorable over the concentrations investigated. Combining cometary sulfur abundances with our calculated solubility constraints yields $\mathrm{H_2S/SO_2}>20$ for sulfur transported through the high-pressure ice, compared with $\sim0.1$ for terrestrial volcanic emissions. Sulfur supplied to the outer hydrosphere of such water worlds may therefore be predominantly reduced, in contrast to terrestrial volcanic sulfur. Finally, we estimate an H$_2$S flux into the outer hydrosphere of $\sim1.4\times10^{10}$ molecules cm$^{-2}$ s$^{-1}$, comparable to or potentially exceeding Earth's global volcanic sulfur flux.

Over the past three decades, astrophysics has undergone a remarkable transformation with the discovery of nearly 6,000 exoplanets. This rapid progress has shifted the focus from detection to the detailed characterization of exoplanetary atmospheres. Spectroscopy across a broad spectral range (currently 0.2–24 μm) is the primary tool for probing atmospheric composition, chemical processes, and physical conditions, thereby addressing fundamental questions related to planetary formation, evolution, and potential habitability. As the field enters a golden era of atmospheric studies of exoplanets and the first light of the Extremely Large Telescope draws closer, it is crucial that spectroscopic and chemical modelling techniques reach a level of maturity and reliability that can be confidently adopted by the wider scientific community. Accurate interpretation of exoplanetary spectra requires extensive time and temperature-dependent photodissociation cross-section data, including photodissociation cross sections and two-body and three-body reaction rate coefficients. However, for the high-temperature conditions typical of many exoplanetary atmospheres, such data remain largely unavailable from laboratory measurements. This work aims to fill this critical gap by providing a comprehensive and self-consistent set of chemical data for molecules relevant to exoplanet atmospheres. These datasets will also be directly applicable to studies of cool stars, brown dwarfs, and circumstellar environments.

As our Galaxy ages, the mix of chemical elements in newborn stars slowly changes. I show how this changing "recipe" alters the interiors of rocky planets: worlds that form early tend to have smaller iron cores, while those around younger stars have larger cores and are denser. This helps us predict which kinds of stars are more likely to host Earth-like, potentially habitable rocky planets.

Topic

Closing remarks