Main Colloquium
Prof. Dr. Kai Schmitz	ORATED

University of Muenster

Pulsar Timing Array (PTA) collaborations around the globe recently announced compelling evidence for a gravitational-wave background (GWB) at nanohertz frequencies. This breakthrough achievement has important implications for astrophysics, as the GWB signal, if genuine, is likely to originate from a cosmic population of supermassive black holes orbiting each other at the centers of galaxies. As I will illustrate in this talk, the new PTA data is, however, also of great interest to the high-energy physics community, as it allows to probe a broad range of particle physics models of the early Universe that predict the generation of a cosmological GWB in the Big Bang. In this sense, the PTA data opens a new window onto the very early Universe and enables particle physicists to constrain scenarios of new physics beyond the Standard Model at extremely high energies. In my talk, I will give an overview of these searches for new physics at the PTA frontier and highlight several cosmological scenarios that underline the relevance of PTA observations for fundamental problems such as dark matter, neutrino masses, and the matter-antimatter asymmetry of the Universe. Finally, I will conclude with a brief outlook on future measurements that may help in discriminating between a GWB signal of astrophysical origin and a GWB signal from the Big Bang.

	Special Colloquium
Aristomenis Yfantis	ORATED

U. Radboud

Since the turn of the millennia, there has been a substantial growth in the field of black hole physics, both in observational methods and theoretical predictions. This has created a great need for methods of inference, in order to extract the most of our data and inform our models as best possible. In this talk I’ll be presenting my work on that topic exploring two different datasets and model types from SgrA*.

	Main Colloquium
Dr. Dick Manchester	ORATED

ATNF, CSIRO, Sydney, Australia

Pulsars are among the most fascinating and important objects in the Universe. Not only is their formation process and how they function of great interest, but they also serve as sensitive probes of, for example, gravitational theories and the Galactic and extragalactic interstellar medium. This talk is in two parts. In the first part I will describe how pulsars were discovered and, in particular, Jocelyn Bell-Burnell’s role in the 1968 discovery. With her thesis supervisor, Antony Hewish, she first helped construct and test the “4-acre” array near Cambridge, England. She then searched several km of chart recordings looking for compact radio sources that scintillated in the inter-planetary medium, serendipitously discovering pulsars in the process. In the second part of the talk, I will describe the Parkes Pulsar Timing Array (PPTA) and its role in the international search for nanoHertz gravitational waves using PTAs. Since mid-2018, the PPTA has made use of the “Ultra-Wideband Low” (UWL) receiver. I will describe this receiver and some recent results obtained using it.

	Promotionskolloquium
Tim Sprenger	ORATED

MPIfR

The study of scintillation arcs is a quickly growing field aiming at understanding the small-scale structure of the interstellar medium (ISM). Scintillation is caused by interference of scattered paths through the ISM. The resulting intensity variations contain information on the scattering structures, which manifests in scintillation arcs. I worked on a novel technique to extract this information with high resolution. The main object of study in my thesis is PSR B1508+55, which showed peculiar scintillation phenomena in the past. I will present observations made at the Effelsberg 100-m telescope spanning from 2020 to 2023, during which the pulsar goes through various phases of scintillation arcs with rich substructure. Many observables could be monitored over four years, one of which was newly discovered in this study. The result is one of the most constraining data sets of pulsar scintillation, which clearly points to two scattering screens instead of one. I will show how such an extended model can explain the scintillation properties of PSR B1508+55.

	Master Colloquium
Eleonore Dann	ORATED

MPIfR

Recent results of the Outer Galaxy High Resolution Survey (OGHReS, PI's: C. König, J. Urquhart) by Colombo et al. (2021) have shown that a significant number of large-scale filaments exist in the outer Milky Way as well. As the physical and chemical conditions in the outer Milky Way differ significantly compared to the inner Galaxy, these highly resolved large-scale filaments serve as a unique laboratory on how star formation changes with environment and Galactocentric distance. To study the star formation activity of these outer Galaxy large-scale filaments, we used APEX 12CO(2-1) data from the OGHReS Survey, their dendrograms (Colombo et al. 2021, Rosolowsky et al. 2008) and dust emission of the Herschel Infrared GALactic Plane Survey (Hi-GAL, Molinari et al. 2010). We investigated the 13CO(2-1) emission and determined the 13CO(2-1) to 12CO(2-1) line ratios in the filaments. Many Galactic parameters, such as the gas-to-dust ratio (Giannetti et al. 2017), are expected to change with Galactocentric distance in line with the physical and chemical conditions. The gas-to-dust ratio in the star-forming regions of the filaments has been derived and compared with the expected gas-to-dust ratio from Giannetti et al. (2017). Furthermore, we have searched for warm and cold HI gas towards the filaments using the HI4PI (Bailin et al. 2016) and SGPS survey (Griffiths et al. 2005, Haverkorn et al. 2006). While almost all filaments appear to be quiescent based on the absence of protostellar clumps, we found that the longest filament (~140 pc) in the sample stands out as a prominent candidate to host ongoing high-mass star formation. The filament is located in an inter-arm region at a Galactocentric distance of 9.6 kpc (Colombo et al. 2021) and appears to be associated with HI shells. The gas-to-dust ratios in the filaments differ significantly from each other, whereby our average logarithmic gas-to-dust ratio is in agreement with the expected value of log(ɣ)=2.36 at the average Galactocentric Distance of the filaments of 10.6 kpc by Giannetti et al. (2017). Furthermore, we observed that most of the outer Galaxy large-scale filaments are associated with warm and dense HI gas.

	Main Colloquium
Dr. Christian Fromm	ORATED

Uni. Wuerzburg

Relativistic jets are among the most powerful objects in the universe. They are launched from rotating supermassive black holes and accelerate particles to highest energies. However, the detailed mechanism behind their formation and acceleration is still unknown. In order to study relativistic jets we perform numerical simulation of jet launching as well as propagation simulation on horizon scales and beyond. In order to compare our simulations with observations we perform radiative transfer calculations and generate realistic synthetic data. In the talk we will present recent results from our numerical simulations including the exploration of particle heating mechanisms on horizon scales and jet asymmetries on parsec scales. In addition, we present possible radiative signatures which could be detected with future Very-Long-Baseline Interferometric (VLBI) observations.

	Informal Colloquium
Mr. Ezequiel Albentosa-Ruiz	ORATED

Universitat de València, Spain

The VLBI Global Observing System (VGOS) is a next-generation VLBI system developed by the International VLBI Service for Geodesy and Astrometry (IVS) to provide geodetic observations with ultra-wideband receivers observing from 3 GHz to 11 GHz. These receivers observe in linear polarisation to achieve optimal polarisation purity. In this talk we will explore the intricacies of calibrating VGOS data, including the conversion from linear to circular polarisation using PolConvert and the implementation of the Wideband Global Fringe Fitting (GFF) algorithm. Departing from the conventional geodetic approach of performing fringe-fitting separately for each baseline, we present the first results obtained by performing global fringe-fitting over a global IVS array of eight antennas with intercontinental baselines operating over the full VGOS bandwidth. This approach yields promising results and allows us to preserve critical closure information, crucial for reconstructing the full polarisation brightness distribution structure of the observed sources, which we present as preliminary images for a selection of the observed sources.

	Main Colloquium
Prof. Dr. Fatemeh Tabatabaei	ORATED

MPIA

Investigating the physics and pressure balance of the medium where galactic structures, on various scales, are formed is the most fundamental step to understanding the formation and evolution of galaxies. Galaxy evolution models suggest gas accretion from the intergalactic medium (IGM) or from cosmic filaments as a mechanism to maintain star formation and an active galactic nucleus (AGN). These models also propose supernova/ AGN feedback as mechanisms to quench massive star formation. Observational studies, however, show that feedback can, in some cases, trigger star formation, leaving the issue as an open challenge. It seems that our understanding of the formation and evolution of structures in the interstellar medium (ISM) and IGM still needs to be fundamentally improved: What are the physical parameters/factors governing structure formation on various scales? How does the ISM/IGM energy balance change over cosmic time? There is increasing evidence showing the important role of the non-thermal pressures inserted by cosmic rays, magnetic fields, and turbulence. We study the impact of the thermal and non-thermal processes in the evolution of the ISM/IGM structures over cosmic time using both observations and simulations from the radio to optical domains. I will review our findings in nearby galaxies as well as those at high redshifts.

	Informal Colloquium
Prof. Dr. Iván Martí-Vidal	ORATED

Dep. Astronomia & Observatori Astronòmic, Universitat de València, Spain

The design of broadband and/or multiband receivers for VLBI may involve the use of linear polarisation feeds to minimise the effects of instrumental polarisation. I will discuss the software-based conversion of VLBI observations taken with linear polarisation feeds. In particular, I will present new results of PolConvert successfully applied to a global IVS VGOS experiment (8 linear stations; 74 sources; 24 hours). I will discuss the reliability of the PolConvert conversion and its residual instrumental polarisation as estimated from a complete and consistent analysis of the entire dataset. The talk could be followed by a discussion of the strategy and applicability of PolConvert to future multi-band receivers to be implemented at Effelsberg.

	Special Colloquium
Dr. Yik Ki Ma	ORATED

The Australian National University, Canberra, ACT, Australia

The magnetic field is a crucial constituent of the interstellar medium, and accurately understanding its strength and structure in galaxies has significant implications for various areas of galactic astrophysics. Recent advancements in sensitivity and frequency coverage of radio telescopes have provided clearer insights into the magnetic fields of our Milky Way Galaxy and its neighbouring Small Magellanic Cloud (SMC). In this talk, I will share the new magnetic knowledge gained from these advanced radio instruments, using both linear polarisation and high-resolution HI measurements. In the case of the Milky Way, I utilised the Faraday rotation experienced by linearly polarised emission from extragalactic radio sources to find that (1) contrary to theoretical expectations, the galactic-scale magnetic field in the Galactic disk can reverse its direction across the mid-plane towards the Sagittarius spiral arm, and (2) the Galactic magnetic structures can undergo significant changes at <~ 10" scales, most likely due to the anisotropic turbulent magnetic fields shaped by compression and shearing. Meanwhile in the SMC, I find that the filamentary HI structures near its centre are preferentially aligned with the magnetic fields traced by starlight polarisation, suggesting that these HI structures can have the potential of being a new 3D tracer of the SMC's plane-of-sky magnetic field. I will conclude by highlighting the exciting prospects in magnetism studies offered by on-going southern sky radio survey, such as the POSSUM survey in polarisation and the GASKAP survey in HI.

	Promotionskolloquium
Hendrik Mueller	ORATED

MPIfR

Very Long Baseline Interferometry (VLBI) is an observational technique developed in astronomy for combining multiple radio telescopes into a single virtual instrument with an effective aperture reaching up to many thousand kilometers and enabling measurements at highest angular resolutions. Despite the proven successes of VLBI, analysis and imaging of VLBI data still remain difficult, owing in part to the fact that VLBI imaging inherently constitutes an ill-posed inverse problem. Historically, this problem has been addressed in radio interferometry by the CLEAN algorithm, a matchingpursuit inverse modeling method developed in the early 1970-s and since then established as a de-facto standard approach for imaging VLBI data. In recent years, the constantly increasing demand for improving quality and fidelity of interferometric image reconstruction has resulted in several attempts to employ new approaches, such as forward modeling and Bayesian estimation, for application to VLBI imaging. While the current state-of-the-art forward modeling and Bayesian techniques may outperform CLEAN in terms of accuracy, resolution, robustness, and adaptability, they also tend to require more complex structure and longer computation times, and rely on extensive finetuning of a larger number of non-trivial hyperparameters. This leaves an ample room for further searches for potentially more effective imaging approaches and provides the main motivation for this dissertation and its particular focusing on the need to unify algorithmic frameworks and to study VLBI imaging from the perspective of inverse problems in general. In pursuit of this goal, and based on an extensive qualitative comparison of the existing methods, this dissertation comprises the development, testing, and first implementations of two novel concepts for improved interferometric image reconstruction. The concepts combine the known benefits of current forward modeling techniques, develop more automatic and less supervised algorithms for image reconstruction, and realize them within two different frameworks.

	Special Colloquium
Dr. Yannis Liodakis	ORATED

University of Turku (Gruber Fellow)

X-ray polarization is a crucial probe of the magnetic field structure and emission processes in astrophysical systems. This is particularly true for active galactic nuclei (AGN). In radio-loud AGN, X-ray polarimetry allows us to investigate particle acceleration and composition in jets. Until now, polarization observations have been limited to the radio-to-optical range, thereby leaving a gap in our knowledge of the processes and physical conditions in the most energetic objects. The recently launched Imaging X-ray Polarimetry Explorer -- IXPE, the first X-ray polarization mission to target AGN, offers a radically new way of studying high-energy processes in relativistic jets. I will discuss the multiwavelength polarization observations and results from the first two years of IXPE observations of radio galaxies and blazars that clearly demonstrate the importance of X-ray polarization in our understanding of the Universe.

	Promotionskolloquium
Rohit Dokara	ORATED

MPIfR

A supernova event marks the death of either a high-mass (>8 Msol) star, or a white dwarf in a binary system. Such an event expels most of the stellar interiors into the surrounding interstellar medium and forms a supernova remnant (SNR). The global effects of SNRs on their native galaxies (e.g., creating/destroying dust, suppressing/accelerating star-formation activity) are poorly understood, and a complete sample of the SNRs in our own Galaxy is necessary to obtain key observational constraints in this regard. However, only about 300 SNRs are catalogued in the Milky Way so far, while the expected number is of the order of 1000 or more. In this talk, I will describe our attempts to rectify this apparent deficiency by finding new SNRs. We identified 157 SNR candidates in the images of the 4-8 GHz GLObal view on STAR formation (GLOSTAR) survey, which utilizes the Jansky Very Large Array and the 100-meter Effelsberg radio telescopes. By measuring polarization and spectral indices, we established the nonthermal nature of the radio emission from at least seven SNR candidates, providing evidence that they are indeed SNRs. In addition, we also found spurious entries in the catalog of Milky Way's SNRs. We performed a Monte-Carlo simulation of supernova events and the subsequent evolution of their remnants, which suggested that the biggest gains in the quests to find new SNRs can be made by searching for small angular-size SNRs that are only a few arcminutes wide.

	Special Colloquium
Dr. Riccardo Arcodia	ORATED

MIT

Quasi-Periodic Eruptions (QPEs) are high-amplitude bursts of X-ray radiation recurring every few hours and originating near the central black holes in galactic nuclei of low-mass galaxies. So far, only a handful of such events have been found. I will give an overview of their multi-wavelength observational properties and of some of the models proposed to explain them. The latest models suggest that these systems are extreme mass ratio inspirals (EMRI), which would make QPEs their electromagnetic counterparts.

	Master Colloquium
Niklas Czubkowski	ORATED

MPIfR

With its short distance and nearly face-on inclination, the LMC is an ideal object to study star formation in molecular clouds and its feedback onto the environment on a variety of spatial scales. Our goal is to trace and analyse kinematic signatures of stellar feedback mechanisms and colliding gas flows in the molecular gas phase of the LMC. This work is based on sensitive, high-spectral resolution observations of the 12CO(3-2) transition line with the APEX telescope at 5 pc spatial resolution in the course of the APEX LMC Legacy Survey. Thereby we will focus on identifying kinematically disturbed regions that may trace protostellar molecular outflows or other signatures of feedback over large parts of the molecular disk of the LMC in the currently covered $17.0$~deg$^2$ of the survey.\\ In order to find potentially interesting regions we searched for line-splitting in the spectra as a first step and performed a line fitting with multiple Gaussians on a selected sub-sample afterwards. In total we identified 2762 regions with disturbed kinematics, taking up 6.6 % of molecular complexes identified in the LMC. Through statistical comparisons using a multi-wavelength approach we found line-splitting regions to be mainly associated with signatures of on-going star formation, to have on average higher energy input, higher column densities and to be less virialized than single-peak regions. On the selected sub-sample we found $\sim300$ areas with multiple velocity components, including several candidates of protostellar outflows or colliding flows. For outflow candidates we also calculated molecular gas mass, momentum and energy of the individual components. Our study suggests that feedback from star formation (e.g. in form of protostellar outflows) might impact the environment of molecular gas on larger scales than typically observed in the Milky Way.

	Main Colloquium
Prof. Tomasz Kamiński	CANCELED

Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences

TBD

	Main Colloquium
Dr. Viktor Toth	ORATED

Eötvös University, Budapest

Drawing the history of Hungarian radio astronomy, one may in principal start with the successful Moon radar measurements in 1946, but at least with the HI 21cm measurements of the 1960s. Hungarian astronomers, lately even our MSc students, became users of world class facilities, carried out single-dish and interferometric measurements with ground based and space born observatories. I will sample those results in the prelude of my talk with special focus on a few topics where also the Effelsberg-100m radio telescope was used. Last decades saw a few attempts to build Hungarian radio astronomical facilities again after the mid 20s century. We conducted site tests, considered possible scientific goals and appropriate specifications to work out a concept in the last 5 years. I will give a short review of our recent activities towards establishing the first Hungarian radio astronomical observatory.

	Special Colloquium
Dr. Matthew Liska	CANCELED

Center for Astrophysics - CfA Harvard

The gravitational pull of a black hole attracts gas and forms a physical laboratory whose extreme conditions cannot be replicated on Earth. The infalling gas forms an accretion disk where the interplay between hydromagnetic processes and the warping of space-time releases gravitational energy in the form of radiation, relativistic jets, and winds. It is likely that most gas falls into supermassive black holes when the accretion rate approaches the Eddington limit (L=Ledd), at which point radiation pressure overcomes gravity. To date, our knowledge of such 'luminous’ black hole accretion disks mostly relies on semi-analytical models, supplemented by a very limited set of numerical simulations. In my talk I will discuss new insights gained from the first radiative general relativistic magnetohydrodynamics (GRMHD) simulations of luminous accretion disks. I will demonstrate that magnetic fields lead to the formation of a hot corona and that misalignment between the disk and black hole spin axis can explain quasi-periodic oscillations, which have remained a mystery for over 30 years. I will finish my talk by discussing the opportunities the next-generation of GRMHD simulations bring in addressing physical processes driving spectral variability in accreting black holes.

	Special Colloquium
Prof. Tom Megeath	ORATED

University of Toledo, Ohio

The assembly of stellar masses via accretion primarily occurs in the early, deeply embedded phase of protostellar evolution, and is shaped by powerful outflows. Infrared studies of this early phase requires sensitive observations at wavelengths > 3 microns from space-based platforms. I will first overview a program to measure the role of outbursts in protostellar accretion using space telescope data spanning 25 years, from ISO, to Spitzer and Herschel, to NEOWISE. These observations indicate low mass, Class 0 protostars undergo multi-decade, accretion driven outbursts every ~400 years. I will then present results from a Cycle I JWST, medium sized program targeting five protostars with luminosities of 0.2 to 10,000 solar luminosities and central, keplerian masses of 0.12 to 10 solar masses. I will show NIRSpec and MIRI 2.9-28 micron IFU data which map the accretion driven outflows and their interactions with the inner envelopes with spatial resolutions down to 30 au. While the shapes of the outflow cavities are traced in scattered light, the interiors of the cavities show structures in molecular hydrogen. Collimated jets are primarily visible in ionic, atomic and occasionally molecular lines. Yet even in predominately ionic jets, we find knots of molecular emission. I discuss our ongoing efforts to measure the properties of the outflows and their dependence on the masses and accretion luminosities of the protostars. Finally, I will discuss the use of mid-IR OH lines to measure UV from accretion onto the very low mass IRAS 16253-2429 protostar.

	Main Colloquium
Dr. Stanislav Babak	ORATED

APC, Paris

The sky is bright in gravitational waves in the milli-Hz band. We expect emission from millions of inspiralling white dwarf binaries in our Galaxy, merging massive black holes, stellar-mass black holes plunging into massive holes, stochastic gravitational wave signal and more. LISA is L3 ESA-led mission aiming at detecting all these sources. These observations will allow us to infer the channel of formation and evolution of massive (and not very massive) black holes, estimate the Universe's expansion rate and constrain (or observe) the deviations from General Relativity. I will review the rich science achievable with LISA.

	Main Colloquium
Dr. Maria Rioja	CANCELED

ICRAR-UWA/CSIRO, OAN, Australia

TBD

	Main Colloquium
Prof. Zakaria Meliani	ORATED

Observatoire de Paris

Relativistic jets in radio-loud active galactic nuclei (AGN) are fascinating astrophysical phenomena that emit non-thermal radiation across the electromagnetic spectrum and display diverse characteristics at different scales. With their frequent high flux variability, they are ideal objects to study high-energy physical processes. In this presentation, we conduct a comprehensive investigation of the intrinsic properties of relativistic jets and their impact on dynamics, interaction with the external medium, and resulting observed light curve.To explore the properties of relativistic jets, we employ a combination of relativistic magneto-hydrodynamic (MHD) simulations using the MPI-AMRVAC code and radiative transfer simulations with the post-processing code REPTIDE. We focus on the impact of various intrinsic properties of the jet, such as magnetization, rotation profile, and transverse structure and variability, on the formation, evolution, and behavior of standing knots and their interaction with moving knots. We also examine the observables associated with these features and their connection to observed variabilities at different wavelengths.

	Special Colloquium
Prof. Laurent Loinard	ORATED

National University of Mexico

Gaia and phase-referenced VLBI observations deliver similar levels of astrometric accuracy - of order 20 micro-arcseconds on trigonometric parallax measurements. The two types of measurements, however, are affected by different sources of error and have different limitations. Gaia, of course, provides results for more than a billion objects while VLBI astrometric observations exist only for a few hundred sources. On the other hand, VLBI observations are largely immune to dust extinction, enabling observations deep into the Galactic disk. Also, the angular resolution of VLBI observations is more than a hundred times better than Gaia's, enabling the resolution of tight binary systems that cannot be resolved with Gaia. In this talk, I will present a comparison between Gaia and VLBI emphasizing the complementarity between the two techniques. I will also briefly touch on expected VLBI astrometry improvements in the coming few decades.

	Main Colloquium
Dr. Rainer Schödel	ORATED

Instituto de Astrofísica de Andalucía - CSIC, Granada, Spain

The Galactic Centre region is dominated by the nuclear stellar disc (NSD), a rotating structure with a radius of ~200 pc that is kinematically and chemically different from the surrounding bulge. The NSD overlaps with the central molecular zone (CMZ), where ~10% of the Galaxy’s molecular gas is concentrated. The extreme conditions in the NSD and CMZ closely match those in high-redshift star forming regions. I will summarise our current knowledge about the NSD, obtained mostly through high angular resolution near-infrared studies, and how the NSD relates to the larger structure of the Milky Way. I will describe how my group are currently working on obtaining proper motions for millions of stars in the NSD, a region inaccessible to Gaia, and how we use the new data to better understand structure, formation history and recent star formation in the NSD.

	Special Colloquium
Prof. Pawan Kumar	ORATED

University of Texas

The detection of a Fast radio burst (FRB) in 2007 was a major unexpected discovery in astronomy in decades. Hunting for FRBs and measuring their physical properties have become major scientific goals in astronomy. It is well established that most FRBs are located at cosmological distances, and therefore they are the brightest known transients in the universe in the radio band. An FRB was discovered in our galaxy in April 2020, and it confirmed that at least some FRBs are associated with neutron stars with very strong magnetic fields (magnetars). I will describe recent works regarding how the FRB radiation is produced and provide a unified picture for the weak Galactic FRB as well as the bright bursts seen at cosmological distances. I will discuss how FRBs can be used as a probe of the baryon distribution in the universe and for investigating the epoch of reionization.

	Special Colloquium
Dr. Arman Tursunov	ORATED

MPIfR (Humboldt Fellow)

One of the most fascinating aspects of Einstein’s general theory of relativity is the uncanny correspondence of the black hole mechanics and thermodynamics. It implies that up to 29% of the total energy of a black hole is rotational extractable energy. It is therefore most pertinent to tap these enormous sources most effectively and ultra efficiently. In this talk, I will present two new energy extraction mechanisms, which are the ultra-efficient regime of the magnetic Penrose process (MPP) of acceleration of charged particles to ultra-high-energies and the radiative Penrose process (RPP) of energy gain by radiating charged particles inside the black hole’s ergosphere. The former one predicts supermassive black holes as the source of the highest-energy cosmic rays, while the later one -- a powerful non-thermal (synchrotron) emission peak at the edge of the ergosphere, potentially observable by future event horizon telescope observations. I will also discuss possible observational implications of given predictions in the case of the Galactic centre supermassive black hole Sgr A*.

	Main Colloquium
Dr. Daniela Korcakova	ORATED

Charles University

Our new N-body simulations show that more than half of merger products are of B-type stars. Unfortunately, the focus of the community is either to massive binaries, that later explode as supernovae, or Ap stars. This largest channel of mergers is overlooked. Recently, we identified a post-merger in a peculiar B-type group called FS CMa stars; the first post-merger found in the phase where the envelope started to be transparent. FS CMa stars are a subgroup of the B[e] stars, i.e., the forbidden emission lines and infrared excess are present in their spectra. This are signs of very extended circumstellar gaseous and dusty region. The properties of several other FS CMa stars indicate that there may be other post-mergers hidden in this group. These intermediate-mass mergers contribute to the enrichment of the interstellar, even intergalactic, material by heavier elements. Nowadays, more effective "dust factories" are AGB stars, supernovae, and red giants, however, B-type mergers may play an important role in the early universe.

	Special Colloquium
Dr. Frederic Jaron	ORATED

TU Vienna

The stellar binary system LS I +61°303 is composed of a Be type star and a compact object in an eccentric orbit. Detected across the electromagnetic spectrum, from the radio until the very high-energy gamma-rays, its emission is not only variable but also periodic on different time-scales. Focus of my talk is a super-orbital modulation with a period of 4.6 years. Decades-spanning radio monitoring reveals that this long-term modulation has remained stable for eight cycles. Ongoing monitoring shows that this behavior continues. I will present how the long-term modulation pattern shows a systematic trend as a function of energy at all observed wavelengths. This systematic trend finds a straightforward explanation in a scenario including a precessing jet. But I will also mention alternative scenarios.

	Special Colloquium
Dr. Arshia Maria Jacob	ORATED

Johns Hopkins University (Baltimore, Maryland)

Formed at an early stage of gas-phase ion-molecule chemistry, hydrides– molecules containing a heavy element covalently bonded to one or more hydrogen atoms – play an important role in interstellar chemistry as they are the progenitors of larger and more complex species in the interstellar medium. In recent years, the careful analysis of the spectral signatures of hydrides have led to their use as tracers of different constituents, and phases of the interstellar medium and in particular the more diffuse environments. Diffuse clouds form an essential link in the stellar gas life-cycle as they connect both the late and early stages of stellar evolution. As a result, diffuse clouds are continuously replenished by material which makes them reservoirs for heavy elements and hence ideal laboratories for the study of astrochemistry. In this talk we will journey through a renaissance of hydride observations detailing the past, present and future of hydride studies and in particular the legacy of the SOFIA HyGAL program.

	Special Colloquium
Dr. Luis Alberto Zapata	ORATED

National University of Mexico

The phenomenon of molecular outflow was first discovered in the 1980’s. Very high velocity motions were detected in the line wings of the carbon monoxide molecule, seen towards Orion-KL. With the subsequent detection of the bipolar outflows in many sources, they became recognized as a ubiquitous stage in star formation. Excess angular momentum was carried outwards by the molecular outflow, which allowed the remaining material to fall onto the protostar. However, around 10 years ago, our paradigm changed radically, the eponymous outflow in Orion-KL turned out to be an explosive outflow. These explosive flows are possibly powered by the release of gravitational energy related with the formation of a massive (proto)stellar merger or a close stellar binary, a totally different process from the classical bipolar outflows. In this talk, I will review this new phenomenon, and show the latest efforts to reveal more cases where possible mergers events could led the violent flows.

	Main Colloquium
Prof. Guido Müller	ORATED

Max Planck Institute for Gravitational Physics (Hannover)

Since their first detection, gravitational waves (GW) have become a major part of current and future plans to study the universe. The current ground based observatories opened an observational channel which allows us to listen to GW from mergers between neutron stars and black holes up to about 100 solar masses. The first space-based observatory, the Laser Interferometer Space Antenna (LISA), will enable us to listen to the mHz gravitational wave band which is the natural frequency of GW sources involving a million solar mass black holes. LISA is currently passing through the first project phases and is expected to be adopted by ESA as its next L-class mission later this year with a launch anticipated in the mid 2030s. I will discuss the science case for LISA as well as its technology and also initial ideas about ‘beyond LISA’ missions.

	Main Colloquium
Dr. Roberto Neri	CANCELED

IRAM Grenoble (France)

TBD

	Special Colloquium
Prof. Biwei Jiang	ORATED

Beijing University

Interstellar extinction increases with distance and presents a significant jump at the position of dense medium. This property makes it an important indicator of distance to the extended objects such as supernova remnants and molecular clouds. By taking the bluest color as the intrinsic color for a given set of stellar parameters, the interstellar extinction is calculated with relatively high accuracy for millions of stars from the stellar parameters derived in large-scale spectroscopic surveys including LAMOST and APOGEE. With the Gaia distance, the distances to several tens of SNRs and molecular clouds. Accordingly, the dust properties implied in the extinction law are discussed.

	Main Colloquium
Prof. Alessandra Corsi	ORATED

Texas Tech University, Lubbock, USA

The births and mergers of neutron stars and black holes, the most exotic objects in the universe, can launch the fastest cosmic jets and shake the very fabric of space-time with gravitational waves. GW170817, the merger of two neutron stars witnessed through both its gravitational wave siren and its glow at all wavelengths of light, marked the beginning of a golden age in multi-messenger astrophysics. Starting from the example of GW170817, I will show how observations at radio wavelengths can probe the ejecta and environments of compact binary mergers and help unveil their progenitors and remnants. I will then discuss opportunities and challenges ahead, as new observational facilities will transform a trickle of multi-messenger discoveries into a flood. I will conclude by highlighting prospects for extending the reach of radio and gravitational wave studies to the heaviest black holes in merging galaxies.

	Special Colloquium
Dr. Michal Zajaček	ORATED

Department of Theoretical physics and Astrophysics, Faculty of Science, Masaryk University, Brno, Czech Republic

Over the last decades, tight correlations between the time delays of prominent broad lines - Hbeta, MgII, CIV - and corresponding underlying monochromatic luminosities at 510, 300, 135 nm were established thanks to reverberation mapping (RM). For optical Hbeta broad line, RM has been performed for more than 120 sources, for UV MgII line, we currently have time delays for 94 sources, and for the UV CIV broad line, 38 sources were reverberation mapped. The radius-luminosity relation implies that RM quasars can in principle be standardized, i.e. by measuring the time delay, we can determine monochromatic luminosity, and from the measured flux density, we can infer the luminosity distance. I will demonstrate the method how to constrain both radius-luminosity relation parameters and cosmological parameters from the measured time delay, the measured flux density, and the source redshift, thus avoiding the circularity problem. So far uur analysis shows that the RM quasars are standardizable, i.e. the radius-luminosity parameters do not change significantly for different cosmologies. Specifically, MgII and CIV quasars (on average more distant) give results that are weaker but fully consistent with better established cosmological probes (BAO+H(z)). In contrast, closer Hbeta quasars do show a small, 2sigma tension with the better established probes.

	Special Colloquium
Prof. Nirupam Roy	ORATED

Indian Institute of Science, Bangalore

The redshifted 21 cm signal from neutral hydrogen is a very useful probe of cosmic evolution. A particularly interesting phase of this evolution is the Epoch of Reionization (EoR), when the first ionizing sources were born in the early universe. The current and the upcoming low frequency radio telescopes, like the upgraded GMRT (Giant Metrewave Radio Telescope) or the Square Kilometre Array (SKA), are expected to play a crucial role in studying cosmic evolution during the EoR and the post-EoR era, and thus addressing many important but unresolved issues. One of the challenging aspects in this regard is the fast and efficient data processing necessary for weak EoR/post-EoR signal detection in presence of the strong, confusing foreground. However, the foreground is interesting in its own right. In this talk, I plan to share some of our recent efforts to study the low radio frequency foreground using the uGMRT data. This work may help us to understand the near-future pathways of studying the atomic hydrogen power spectrum from the cosmological EoR/post-EoR, but it also allows us to study, in details, the properties of a large population of extragalactic sources as well as of the interstellar medium of the Milky Way.

	Special Colloquium
Dr. Barak Zackay	ORATED

Weizmann Institute of Science, Israel

Since its very beginning, discoveries in pulsar astronomy had required algorithmic sophistication and ingenuity. The basic problem, detecting a pulsar by its periodicity modulated by intrinsic, orbital or barycentric modulation is computationally prohibitive as the number of combinations of all of these parameters can be as large as 10^40. While there had been substantial developments in algorithms for pulsar detection in the last 50 years, the state of the art algorithms trade sensitivity (in some cases, orders of magnitude) for computational tractability. In this talk, I will show a road map for solving the pulsar detection problem in observationally relevant regimes using algorithms that are prevalent in the field of cryptography. I will show in detail how to take the discrete timing problem, relevant for gamma-ray pulsar astronomy, and transform it to the problem of finding a short vector in a lattice, that is then solved in seconds using standard implementations. I will then outline in rough sketches three different algorithms for detecting pulsars, creating a roadmap for unlocking the full potential of pulsar surveys to detect "holy grail" systems - a tight pulsar black hole system and a pulsar in the vicinity of the galactic center.

	Promotionskolloquium
Hans Nguyen	ORATED

MPIfR

High-mass stars (>8 msol) are not as numerous as their less massive counterparts but have a much more profound impact on their environment within their native galaxies. Despite their importance, our understanding of their formation process is not as developed as that of low-mass stars. As such, the GLObal view on STAR formation (GLOSTAR) Galactic Plane survey aims to address this question of how high-mass stars form by finding all sites of high-mass star formation at different evolutionary stages in the Milky Way and characterising their physical properties in order to develop a complete view of massive star formation. In the first half of this talk, I present our findings of 5.8 GHz radio continuum observations of the region known as the Central Molecular Zone (CMZ) using the Karl G. Jansky Very Large Array (VLA) to detect HII regions, which are known tracers of high-mass star formation. We investigated the presence of young stellar object (YSO) candidates with HII regions as it is unknown how many of the near-infrared (NIR) identified YSOs trace HII regions. Our results show that the majority of these NIR-identified YSOs lack VLA radio counterparts. We found that most of these sources also lack dust emission (using data from ATLASGAL), and it is likely that they are older and have dispersed their natal clouds. The second half of this talk focuses on 6.7 GHz methanol masers as they have been shown to be an exclusive tracer of the earliest stages of high-mass star formation. Many surveys have already been conducted, however, with the upgraded VLA, GLOSTAR can provide the most sensitive unbiased survey of 6.7 GHz methanol masers to date. I present the results of this catalogue where we detect many new masers. To study the environments of early high-mass star formation we used ancillary dust continuum and radio continuum data. We find that the newly detected masers are more likely to be associated with less massive stars. Furthermore, by comparing the radio source and the maser flux distributions, we find no correlation with respect to angular offset, suggesting that the maser and the radio source are powered by unrelated mechanisms.

	Promotionskolloquium
Huanchen Hu	ORATED

MPIfR

General relativity has so far passed all experimental tests, with some of the most stringent tests in strong fields coming from observations of pulsars — magnetised rotating neutron stars that form from the collapsed cores of massive stars during supernovae. Such compact objects contain some of the densest forms of matter in the Universe and therefore produce a strong gravitational field in their vicinity. Thanks to their excellent rotational stability, these cosmic clocks are powerful tools for studying a wide range of topics in fundamental physics. These include the equation of state of matter at supranuclear densities, tests of general relativity and its alternatives, and the search for nanohertz gravitational waves with pulsar timing arrays, all of which are investigated in this dissertation using the new-generation of radio telescopes. In this talk, I will focus on two aspects based on studies of the unique Double Pulsar system, PSR J0737-3039A/B. Firstly, I will highlight the timing results of the Double Pulsar using data from the MeerKAT telescope, in particular the (so far) best test of higher-order signal propagation effects predicted by general relativity. Secondly, I will introduce a new approach to constrain the equation of state by measuring the neutron star moment of inertia through pulsar timing and show predictions for future measurements.

	Special Colloquium
Dr. Vardha N. Bennert	ORATED

CalPoly, San Luis Obispo

Supermassive black holes (BHs) are ubiquitous in the center of massive galaxies. When actively growing through accretion, Active Galactic Nuclei (AGNs) become some of the brightest objects in the universe. It has been two decades that relations between BH mass and the properties of their host galaxies (such as luminosity, stellar mass and stellar velocity dispersion) were first discovered. Interpreted as evidence for a co-evolution between BHs and galaxies, these scaling relations remain a hot topic for contemporary studies with many open questions remaining, including the role of AGN feedback or hierarchical merging, and the nature of the host galaxies (elliptical versus spiral galaxies, bars, pseudo-bulges and mergers). While reverberation mapping has been the gold standard for BH mass measurements in AGNs, traditional methods yield only sample-average recipes for BH mass estimates. Recent advances include dynamical modeling of reverberation-mapped data to obtain BH mass for individual objects and directly resolving the broad emission around AGNs spatially. Studying the co-evolution as a function of cosmic history can shed light onto origin and fundamental drivers, but relies on AGNs for which host-galaxy properties are intrinsically difficult to measure. Thus, a robust local baseline for AGN MBH-scaling relations is the key. I will review our understanding of the nature and origin of the scaling relations between supermassive black holes and their host galaxies.

	Main Colloquium
Prof. Thorsten Kleine	CANCELED

Max Planck Institute for Solar System Research

TBD

	Special Colloquium
Professor Tomas Brage	ORATED

Lund University

Physics is often seen, by Physicists not the least, as objective and we believe we are surrounded by a "culture with no culture". At the same time our history, class and board rooms are dominated by men. This is a paradox that should awaken the curiosity of anyone. In this talk I will give some examples on how you can approach the question in the title. There have been several studies of Scientists and I will combine a discussion of these with some general theory and personal experiences, to paint a picture on how gender transgresses Physics, like all other fields. By using the levels of change introduced by Schiebinger, I refer to studies of e.g. Anthropologists, Sociologists and Psychologists. The bias against women, since Science is stereotypically male, combined with the "myth of meritocracy" could be key to understand the lack of women in the field. The talk is intended as a translation of results from recent progress in Gender Science to an audience of non-experts in the field, especially people within STEM-fields. The aim is to give some answers to the question in the title, but also to show that this is an extremely interesting and active field of research.

	Master Colloquium
Evdokia Makroleivaditi	ORATED

MPIfR

The main mechanisms that suppress the star-formation in nearby galaxies, known as “star-formation quenching” processes, are considered to play a key role in galaxy evolution. Nearby galaxies across the Hubble sequence exhibit various quenching patterns based on the distribution of the ionised gas and the resolved maps of the equivalent width of Hα, WHα. In Kalinova et al., 2021 they found six repetitive patterns for their sample of 238 Calar Alto Legacy Integral Field Area (CALIFA) galaxies and defined the following “stages”: star-forming (SF) – systems, dominated by star formation; quiescent-nuclear-ring (QnR) – galaxies that have a quiescent ring within 0.5 effective radius (Re); centrally quiescent (cQ) – objects that are fully quiescent within 0.5Re and star-forming in the outskirts; mixed (MX) – galaxies with no clear pattern of the star-forming; nearly retired (nR) – retired systems in which small star-formation regions can be found within 2Re, and fully retired (fR) – objects that are completely retired within 2Re with no sign of star-formation. A further categorisation based on their nuclear activity, lead to two groups: active systems that host a weak or strong active galactic nucleus (wAGN or sAGN) at their centre, and non-active objects. In our work, we analyze the molecular gas properties by using resolved data from the CARMA Extragalactic Database for Galaxy Evolution (EDGE)- CAL- IFA survey, (see Bollato et al. 2017) for 115 galaxies across quenching stage and nuclear activity. Our sample includes 104 non-Active galaxies and 11 AGN- hosting galaxies (2 wAGN and 9 sAGN). We explore the radial variation of the CO gas, star formation rate (SFR), star formation efficiency (SFE) and stellar-mass surface density as well as the age, metallicity, stellar velocity, stel- lar velocity dispersion, specific star formation rate (sSFR) and gas mass fraction of our sample. Additionally, we build-up resolved (pixel-by-pixel) relations be- tween quenching indexes of the galaxies (defined as thresholds in the equivalent width of the Hα line) and molecular gas properties.

	Special Colloquium
Dr. Daniela Doneva	ORATED

Theoretische Astrophysik Eberhard-Karls-Universitat Tuebingen

Gravity models admitting scalarization are attracting considerable attention due to their natural ability to evade constraints from weak field observations. In the present talk, I will discuss one such modified theory of gravity, namely the scalar-Gauss-Bonnet gravity. It offers the possibility for spontaneous growth of scalar hair both for neutron stars and black holes with a trigger of the process being the curvature of the spacetime itself. I will discuss the sectors of the theory that have already been tested with binary pulsar observations and what is the implication on black hole scalarization. Special attention will be paid to future prospects of testing further Gauss-Bonnet gravity in terms of theory development and pulsar observations.

	Special Colloquium
Prof. Subir Sarkar	ORATED

University of Oxford

In the ΛCDM cosmological model the Universe is assumed to be isotropic & homogeneous when averaged on large scales. That the CMB has a dipole anisotropy is interpreted as due to our peculiar motion because of local inhomogeneity. There should then be a similar dipole in the sky distribution of high redshift sources. Using catalogues of radio sources and quasars we find that this expectation is rejected at >5σ, i.e. the distribution of distant matter is not isotropic in the 'CMB frame’. This calls into question the standard practice of boosting to this frame to analyse cosmological data, in particular to infer isotropic acceleration of the Hubble expansion rate from Type Ia supernovae, which is interpreted as due to Λ.

	Main Colloquium
Dr. Ronald Drimmel	ORATED

Osservatorio astrofisico di Torino, INAF (Italy)

Galactic studies is undergoing a renaissance in the current decade, thanks not only to Gaia, but to ground-breaking astrometry in the NIR and radio. I will give an update on the latest Gaia results following on the it's last data release about the structure of our Galaxy, with particular focus on the disk. Thanks to a recent Lorentz Center workshop with the same title as this talk, I will attempt to put Gaia's contribution in the context of other recent results from the NIR and radio. Integrating all these together I hope to share what we are learning and hope to soon learn about the Milky Way.

	Master Colloquium
Anahat Cheema	ORATED

MPIfR

In our work, we investigate the high mass star formation activity in the region centered at (l,b)=(358.69°, 0.03°) near the Galactic center. In order to identify and characterise the HII regions, we use data from the GLOSTAR survey, which is a wideband radio (4-8 GHz) survey of the Milky Way combining data from the Karl G. Jansky Very Large Array (VLA) and the Effelsberg 100m telescope. Using BLOBCAT source extraction software which uses flood-fill algorithm to detect sources in 2 dimensional astronomical images, we identified 46 radio sources in the region. Candidate HII regions are cataloged based on association with at least one multiwavelength counterpart. For this, we used mid-infrared (GLIMPSE, MIPSGAL and WISE), far-infrared (Hi-GAL) and submillimeter (ATLASGAL) archival data. In total, we have identified 43 HII region candidates. We compute the properties of these HII regions, such as the Lyman continuum photon rate, ZAMS spectral type, dynamical age etc. The HII region candidates are distributed in a ring-like formation. We also observe enhancement of ATLASGAL clumps and infrared sources towards south-east of the ring, suggesting triggered star formation in the region.

	Special Colloquium
Dr. Willem Baan	CANCELED

ASTRON, The Netherlands

TBD

	Informal Colloquium
Dr. Sheperd S. Doeleman	ORATED

Center for Astrophysics | Harvard & Smithsonian

The next-generation Event Horizon Telescope (ngEHT) is a transformative instrument that will be capable of making real-time and time-lapse movies of supermassive black holes on event horizon scales. These movies will resolve complex structure and dynamics on Schwarzschild radius dimensions, bringing into focus not just the persistent strong-field gravity features predicted by General Relativity (GR), but details of active accretion and relativistic jet launching that drive large scale structure in the Universe. This effort builds upon recent results by the Event Horizon Telescope (EHT): the first image of M87’s supermassive black hole and its magnetic field structure, as well as resolved images of SgrA*, the central black hole at the heart of the Milky Way. These images are scientifically rich, and show that evolution of the EHT to a more capable array can address even deeper questions across physics and astronomy. The central concept behind the ngEHT is that the addition of many modest-diameter dishes at new geographic locations will enable high-dynamic-range imaging and time-resolved dynamical studies of the black hole boundary that extend beyond planned upgrades to the existing global mm/submm VLBI array.

	Main Colloquium
Prof. Lukasz Wyrzykowski	ORATED

Warsaw University (Poland)

Most of about 60 known stellar-mass black holes were found in binaries (X-ray binaries and GW mergers). Gravitational microlensing is the only tool capable of detecting single black holes, which are not interacting with anything. I will present our long-term project aiming at discovering and studying the microlensing black holes with the OGLE, Gaia and forthcoming Rubin/LSST surveys. Microlensing non-detections towards the Magellanic Clouds have put strong limits on the compact dark matter content in the Galaxy Halo, while the statistical studies of microlensing events towards the Galactic Centre, revealed a continuum of masses of dark lenses and hint at a lack of the mass gap between neutron stars and black holes. However, in order to study individual events and obtain the masses of individual lenses it is crucial to measure the size of the Einstein Radius, which defines a separation between the lensed images and is a physical parameter degenerated in the classical microlensing light curve model. This is possible en masse only with the Gaia space mission, which scans the entire sky and is providing not only brightness and colour temporal evolution for nearly 2 billion stars but also positional time series with sub-milliarcsecond precision. I will describe how we search for on-going microlensing events within daily Gaia data using Gaia Science Alerts system and how their photometric, spectroscopic and interferometric follow-up is conducted. I will present the first candidates for dark lenses from Gaia and then describe how these lessons learnt can be applied to the forthcoming Rubin/LSST survey and GRAVITY+ instrument.

	Main Colloquium
Dr. Dominic Pesce	ORATED

Center for Astrophysics - CfA Harvard

Water megamasers residing in the accretion disks around supermassive black holes in active galactic nuclei (AGN) provide unique tools for bypassing the distance ladder and making one-step, geometric distance measurements to their host galaxies. The Megamaser Cosmology Project (MCP) is a multiyear campaign to find, monitor, and map such AGN accretion disk megamaser systems, with the goal of constraining the Hubble constant to a precision of several percent. In this talk I will cover the latest results from the MCP. We have systematically applied an updated disk modeling technique to measure the distances to six megamaser-hosting galaxies, which together constrain the Hubble constant to 73.9 +/- 3.0 km/s/Mpc. This value relies solely on maser-based distance and velocity measurements, and it does not use any peculiar velocity corrections. We have explored a variety of different approaches for correcting peculiar velocities, none of which modify this constraint by more than 1-sigma. Our measurement is independent of distance ladders, the cosmic microwave background, and gravitational lenses, and it corroborates prior indications that the local Hubble constant exceeds the early-Universe prediction.

	Master Colloquium
Kathrin Grunthal	ORATED

MPIfR

We will explore the method of precision pulsar timing as a tracer of space-time deformations both in the vicinity of the pulsar, caused by ist host system, as well as a probe of gravitational waves (GWs) crossing the lines-of-sight between multiple pulsars and the Earth. Subsequently, this work is set up in a two-fold manner: In the first part, we present an analysis of the millisecond pulsar (MSP) J1618-3921 using radio observations from MeerKAT, Parkes and Nancay. We investigate its emission behavior, comprising a change of its mean stable profile, as well as a Rotating-Vector-Model fit of the linear polarisation position angle swing. The main focus lies on the following timing analysis using the 23-year long timing baseline stretching back to the discovery observations in 1999. We present the first timing solution of this pulsar containing a binary model and a mass estimate for both the pulsar and its companion. We also discuss the measurement of the change of the orbital period, which strongly diverges from its expected value, indicating the presence of a third massive object in the pulsar's vicinity. With J1618-3921 belonging to the class of eccentric MSPs, all these results shed new light on this enigmatic pulsar population, raising new questions to current stellar evolution models. The second part holds a theoretical approach to the detection of continuous GWs with current pulsar timing arrays (PTAs). We discuss the mathematical framework of PTA sensitivity curves and its impementation. We apply it to the European Pulsar Timing Array (EPTA) using its latest 25 pulsar data set, followed by a comparison with the Northern American Nanohertz Observatory for Gravitational Waves (NANOGrav), as well as the full GW detector network available in the mid 2030s.

	Main Colloquium
Prof. Nanase Harada	ORATED

National Astronomical Observatory of Japan

ALMA Comprehensive High-resolution Extragalactic Molecular Inventory (ALCHEMI) is a spectra scan towards the nearby starburst galaxy NGC 253. It covers a wide frequency range of ALMA Bands 3-7, and was conducted as an ALMA Large Program in Cycle 5. The interstellar medium (ISM) in starburst galaxies is expected to have different physical properties from the ISM in the Milky Way due to the high star formation activity. This difference should also appear in chemical composition. The ALCHEMI survey aims to analyze this ISM property in one of the nearest starburst galaxies. The survey detected about 1500 transitions and more than 100 species. They include complex organic molecules that originated from the hot and dense starburst region. Comparing chemical models and observed chemical abundances, our results show 1-2 orders of magnitude higher cosmic-ray ionization rates than the Galactic Center. They also demonstrate multiple signs of shocks. A statistical study to extract physical features from the survey images is also on the way.

	Main Colloquium
Prof. Stephen Taylor	ORATED

Vanderbilt University, Nashville, USA

The nanohertz-frequency band of gravitational waves should be awash with signals from supermassive black-hole binaries, as well as cosmological signatures of phase transitions, cosmic strings, and other relics of the early Universe. Pulsar-timing arrays (PTAs) are poised to chart this new frontier of gravitational-wave discovery within the next several years using precision timing data recorded by flagship radio telescopes from dozens of pulsars in the Milky Way. I will present exciting new results from recent cutting-edge searches, discuss some milestones on the road to the next decade of PTA discovery, and how these results will influence and shape other fields.

	Master Colloquium
Nipesh Dulal	ORATED

MPIfR

In this work, we examined the properties of the molecular gas in the Central Molecular Zone (CMZ) of our Galaxy from the APEX CMZ survey data, which imaged the 13CO(2-1) emission from CMZ at an unprecedented sensitivity. We employed the automatic algorithms dendrograms and SCIMES to segment clouds and construct a catalog of the integrated properties of almost 4200 clouds in the CMZ. Our catalog contains clouds ranging from small (1 pc) scale clouds to large cloud complexes, with a distribution of sizes similar to that of the inner Galaxy. However, the clouds in the CMZ appear more turbulent than those of the inner Galaxy. The average molecular cloud surface mass densities estimated were lower than in previous catalogs, and we found a lower CO-to-H2 conversion factor (X_CO) in the CMZ, which was calculated using local thermodynamic equilibrium assumptions. Additionally, the star formation efficiency and the dense gas mass fraction are significantly lower for the clouds in the CMZ compared to those in the inner part of the Galaxy. Overall, the extreme ambient environment of the CMZ prevents its surrounding molecular gas from forming stars.

	Special Colloquium
Alejandro Mus	ORATED

Universitat de Valencia

The Galactic Center (GC) presents one of the highest stellar densities in our Galaxy, making its surroundings an environment potentially rich in radio transients, such as pulsars and different kinds of flaring activity. In this talk, I will present the first study of transient activity in the region of the GC based on Atacama Large Millimeter/submillimeter (mm/submm) Array (ALMA) continuum observations at 230 GHz. This search is based on a new self-calibration algorithm, especially designed for variability detection in the GC field. Using this method, we have performed a search of radio transients in the effective field of view of ∼30arcseconds of the GC central supermassive black hole Sagittarius A* (SgrA*) using ALMA 230 GHz observations taken during the 2017 Event Horizon Telescope (EHT) campaign, which span several observing hours (5-10) on 2017 April 6, 7, and 11. This calibration method allows one to disentangle the variability of unresolved SgrA* from any potential transient emission in the wider field of view and residual effects of the imperfect data calibration. Hence, a robust statistical criterion to identify real transients can be established: the event should survive at least three times the correlation time and it must have a peak excursion of at least seven times the instantaneous root-mean-square between consecutive images. Our algorithms are successfully tested against realistic synthetic simulations of transient sources in the GC field. Having checked the validity of the statistical criterion, we provide upper limits for transient activity in the effective field of view of the GC at 230 GHz.

	Special Colloquium
Dr. Nicolas Aimar	ORATED

LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université

For the past two decades, flares (i.e. outbursts of radiation) have been observed from the centre of the Milky Way where a massive compact object of 4.3 millions solar masses resides at only 8.3 kpc. This makes this object called Sgr A* the closest supermassive black hole candidate to Earth and an unique laboratory for relativistic astrophysics. Recent observations have shown that the source of these outbursts is close to the event horizon and has an orbital motion around the black hole. Many scenarios are envisaged to explain this phenomenon without reaching a consensus. Among these scenarios, magnetic reconnection is one of the most promising, supported by many GRMHD and PIC studies. During this presentation I will present a realistic semi-analytical magnetic reconnection model based on kinetic simulations. I will examine the diversity of observables associated to these models and discuss them in the light of the recent VLTI/GRAVITY observations of Sgr A* flares

	Main Colloquium
Prof. Ralf Klessen	ORATED

Universität Heidelberg

Stars and star clusters form by gravitational collapse in regions of high density in the dynamically evolving magnetised multi-phase interstellar medium. The process of stellar birth is controlled by the intricate interplay between the self-gravity of the star-forming gas and various opposing agents, such as supersonic turbulence, magnetic fields, radiative feedback, cosmic rays, and gas pressure. I will discuss examples of recent progress and controversy, specifically, I will focus on current attempts to bring numerical simulations and theoretical models closer to the observational domain. In this context, I would like to report on efforts to model magnetic field evolution and generate synthetic polarisation and Faraday rotation maps for comparison with the observational data.