It was back in 1979 that I began a series of time-resolved optical observations of the X-ray burst source 4U 1636-536 (aka MXB 1636-53 and V801 Ara), resulting in the detection of several bursts in common with X-ray satellites.

Perhaps for reason of technical difficulties, there have been few attempts to improve on these results. During the talk, I shall go over the scientific case, and suggest ways ahead.

"The bigger picture of dwarf galaxy alignments in the Local Group and beyond", Marcel Pawlowski (Leibniz Institut fur Astrophysik)

Abstract: The satellite galaxy systems of several well-studied galaxies, in particular the Milky Way and Andromeda, have been found to show signs of correlated Planes of Satellites. These structures might be related on even larger scales. Two surprisingly symmetric planar arrangements can be identified among the more isolated dwarf galaxies in the Local Group, and satellite planes appear to show some alignment with the larger-scale cosmic web around their hosts. I will provide a brief overview of the observed satellite and non-satellite planes in relation to each other, to the Local Group dynamics, possible backsplash galaxies, and the larger-scale cosmic web, all of which might hold clues to understand the origin of these structures.

and

"Solving the problem of disks of satellites with modified gravity", Michal Bilek (LERMA)

Abstract: Simulations in standard cosmology leave only a small chance for disks of satellites being comprised of primordial galaxies. The observed distribution of satellites would be more natural if the satellites were tidal dwarf galaxies, that is small galaxies that form by gravitational collapse in tidal arms of interacting galaxies. If so, then the observed internal dynamics of the satellites indicates that gravity is not Newtonian. We run a simulation of the history of the Local Group in the leading alternative, the MOND modified gravity theory. The simulation was tuned only to reproduce the observed relative distance, velocities and disk orientations of the Milky Way and Andromeda galaxies. It showed that the two galaxies had a close fly-by 6.8 Gyr ago that produced long tidal arms. The remnants of the arms resemble the observed disks of satellites. The simulated Milky Way developed a warp resembling the observed one.

"Dynamical Friction in Barred Spiral Galaxies", Francesca Fragkoudi (ESO)

Abstract: The formation and properties of stellar bars in spiral galaxies are both tightly linked to the properties of their dark matter halos. For example, it has been shown that dynamical friction induced by a massive dark matter halo will slow down the rotation speed of bars. While numerous observational studies have found that bars tend to rotate fast, numerical simulations within the LCDM framework tend to find that bars slow down excessively. This has given rise to an apparent tension between fast bars and the LCDM cosmological paradigm, which has been highlighted over the past years in the literature. I will present recent findings from cosmological simulations that help to shed light on this longstanding issue, and discuss this within the context of recent claims in the literature of a > 10sigma tension between fast bars and LCDM.

and

"Cosmological Voids", Eelco van Kampen (ESO)

Abstract: A large local under-density (void) would provide the simplest explanation for the mismatch between local determinations of the Hubble constant and those derived from cosmological probes, which results in smaller estimates than the local ones. Such a large local void acts like an under-dense mini-Universe with a correspondingly higher Hubble constant (a 'Hubble bubble'). There is some observational evidence for this, but the question is whether the claimed local void is large and/or empty enough to remove the Hubble tension between local and cosmological estimates.

I will continue the discussion started on Friday 29/10 at coffee regarding the preprint by J. Kormendy (https://arxiv.org/abs/2110.14115v1) who aims at calibrating citations count metrics against the evaluation of the researcher's research impact by senior astronomers, with the goal of building "prediction machines". In a short presentation, I will introduce the methodology and main arguments of the paper and argue that this is not a very useful study, and that in my opinion its results should not be used.

In this talk I will tell you about the exciting ESA space science missions that we are currently working on with our science communications team: such as JWST, JUICE and Euclid. In the second half I will talk about storytelling. Storytelling is an important tool for communicating with the public and with your scientific community. Storytelling is not only useful to prepare for outreach talks or media interviews, but for example also for writing grant proposals or giving a (poster) presentation at a conference. During this talk I will share a few tips and tricks that can help you to define your story about your research or preferred topic in an engaging way.

Following a dynamical encounter with Sgr A*, binaries in the Galactic Centre (GC) can be tidally separated and one member star ejected as a hyper-velocity star (HVS). As GC-born objects located in more observationally accessible regions of the sky, HVSs can provide insight into the stellar population(s) within the inner parsecs of the Milky Way. In this talk I will show that the absence of confident HVS candidates in the radial velocity catalogue of Gaia Data Release 2 offers constraints on still-uncertain properties of the GC environment, namely the shape of the stellar initial mass function in the GC and the ejection rate of HVSs. Forecasting ahead, I will illustrate how these constraints will improve if/when more HVS candidates are unearthed in future Gaia data releases.

Current detection limits struggle to find exoplanets around hot (A/B-type) stars. Searching for planets in this regime provides crucial information on how planet occurrence rate scales with stellar mass. We are carrying out an interferometric survey to detect au-regime giant planets via differential astrometry orbiting individual stars of sub-arcsecond hot binary systems. The combination of milli-arcsecond resolution with stable wavelength calibration provides precision at the few tens of micro-arcsecond level in short observations at CHARA/MIRCX and VLTI/GRAVITY. This allows us to detect the wobble of a star from orbiting companions down to a few Jupiter masses. I will present the status of our survey and astrometric results, including newly detected tertiary stellar companions and some substellar candidate detections. We show that we are beginning to probe down to planetary masses on a number of targets with non-detections. This data will be used to constrain demographic models of low mass companions around hot stars.

Modified Newtonian dynamics (MOND) can successfully predict, without any free parameters, rotation curves or velocity dispersions of most galaxies. Nevertheless, analytic calculations suggested that globular clusters (GCs) of low-surface-brightness galaxies experience extremely strong dynamical friction in MOND. The friction would cause the GCs to quickly sink in the centers of the galaxies, which contradicts observations. The problem was underlined by the discovery of ultra-diffuse galaxies (UDGs) with large numbers of massive GCs. We therefore decided to test the MOND analytic formulas for dynamical friction by self-consistent N-body simulations of GCs moving in UDGs. It turned out that the formulas work very well as long as the GC is far from the center of the galaxy. Close to the center, dynamical friction becomes ineffective. Similar behavior had already been reported in Newtonian simulations and is called "core stalling". UDGs with GCs thus do not currently seem to pose a problem for MOND.

Finding a black hole, especially a nearby one, is a dream of almost every astronomer. But it is not easy as the black holes are pitch black. One of the promising methods is gravitational microlensing, in which a background source gets brighter temporarily due to its light being bent and magnified by a foreground object. Gaia space mission provides unique data which can be used for discovering black holes thanks to its superb accuracy time-series astrometric measurements. However, in order to efficiently use Gaia data, a long-term monitoring and follow-up of candidate microlensing events is necessary. I will describe our programme of coordinated time-domain observations of candidates for lensing events reported by Gaia, including long-term photometry collected by a global network of robotic and manual telescopes, as well as spectroscopic and astrometric follow-up using the largest telescopes in the world. I will conclude with the future plans for the forthcoming era of the VRO/LSST observatory as well as NRST/WFIRST and GaiaNIR space missions and their potential impact on the black hole hunt.

Through their strong stellar winds, massive OB-type stars act as galactic engines, influencing star formation and galaxy evolution. The loss of mass and associated angular momentum during the life of massive stars determines their explodability and the formation of a compact object at the end of their evolution. Despite its importance, mass-loss is still one of the most elusive parameters in stellar astrophysics. The lack of understanding of the eruptive and extreme mass-loss of stars in the upper part of the HR diagram makes stellar evolutionary models highly uncertain. This is especially the case of the enigmatic Luminous Blue Variable (LBV)  stars.

In this informal discussion I will first present an overview of the upper HR diagram, focusing particularly on the instabilities and observational properties of LBV stars. I will then summarize different diagnostics (and related challenges) to estimate the mass-loss rates. I will show the importance of multiwavelength observations of the central star and associated circumstellar nebula to recover the mass-loss history. I will finally present some recent results showing the contribution of LBVs to dust in galaxies.

Our leading model of galaxy formation hinges on strong energy injection by active galactic nuclei (AGN) powered by accreting supermassive black holes in order to explain the observed properties of galaxy populations. Even though "AGN feedback" is widely accepted as the chief source of energy operating in massive galaxies, the dominant physical mechanisms through which supermassive black holes supposedly shape galaxy evolution remain unidentified. This poor grasp of the physics underlying AGN feedback remains a major obstacle limiting (i) a conclusive assessment of the role of AGN in galaxy evolution, (ii) the interpretation and constraining power of observational data and (iii) the development of realistic models for AGN feedback in state-of-the-art cosmological simulations. In this talk, I will present results from numerical, (radiation-)hydrodynamic, cosmological simulations designed to test an array of specific AGN physical processes in massive galaxies at high-redshift (z > 2). These simulations make a strong case against "momentum-driven" feedback, ruling out direct radiation pressure from the AGN or large-scale outflows suffering strong cooling losses. The associated feedback is too weak, requiring unrealistically high black hole masses to effectively launch outflows. Our simulations single out two effective AGN feedback mechanisms. One is associated to radiation pressure arising from infrared photons trapped in dusty regions of the interstellar medium. This process has a strong impact on galactic nuclei, but can only operate effectively when AGN are highly obscured by dust. The most effective AGN feedback mechanism, I will argue, corresponds to "energy-driven" winds. Such outflows operate through hot, over-pressurised bubbles capable of ejecting gas from galaxies and of halting halo gas inflow through adiabatic expansion. The talk will conclude with a discussion on the expected observational imprints of energy-driven bubbles, an analysis of their multi-phase structure as well as its origin, and an assessment of their impact on galaxy evolution.

Galaxies evolve under the influence of gas exchanges with their surrounding gaseous halos, the so-called circumgalactic medium (CGM), extending over tens of kpc. A solid characterisation of both galactic gas flows and chemical composition of the CGM is thus crucial to understand galaxy evolution, especially in the first few Gyrs of cosmic time, when galaxies rapidly assembled their masses and reached their chemical maturity.  I will review recent studies on galactic feedback and CGM metal enrichment in the early Universe, mainly exploiting ALMA observations of galaxies at z>4. These works find evidence that star-formation-driven outflows and (in case of dense environments) tidal stripping can efficiently contribute to the metal pollution of the CGM, as suggested by the detection of large [CII]-halos extended on ~20 kpc around massive galaxies. Also, I will discuss pros and cons of the currently adopted observational techniques, the importance of cosmological simulations in guiding the interpretation, and some of the possibilities offered by future telescopes for improving our understanding of the baryon cycle in early galaxies.

ESO is regularly updating its science-driven perspective with the goal to provide the best facilities and services for its community. As part of this exercise, ESO polled its users between January and February 2020. Questions were inspired by the previous poll (Primas et al. 2015), to probe any evolution of community opinions and profile, with an emphasis on the future of the VLT/I - following the “VLT in 2030” workshop (Mérand & Leibundgut, 2019). Of 14,000 registered unique users polled, from the ESO and European ALMA portals, 1,674 complete responses were received, a response rate comparable to the 2015 poll. The present poll was split into three parts: 1) profile of respondents; 2) current and future observing facilities; 3) ESO in the coming decade.

I will present the main results of the polls which will appear in the upcoming issue of the ESO Messenger.

I will offer an informal discussion on the Observatory Operations during the pandemic. What are the constraints we operate under? How do we decide the level at which we operate? How do we deal with Covid cases on-site? What lessons have we learnt up to now? ‘Your questions’...

The dynamical properties of bars in disc galaxies — such as their rotation (or pattern) speed — are sensitive to the attributes of their dark matter halos. In particular, it has been shown that dynamical friction induced by a massive dark matter halo will slow down the rotation of bars. Numerous observational studies have found that bars tend to rotate fast, suggesting that the stellar component is dominant over the dark matter in the inner regions of barred galaxies. On the other hand, numerical simulations within the LCDM framework tend to find that bars slow down excessively. This has given rise to a tension between fast bars and the LCDM cosmological paradigm. In this informal discussion I will give a historical overview of this tension, and show recent results from cosmological simulations that offer clues on how to solve it.

Wide-field extragalactic surveys have revealed a population of extremely luminous Lyman-alpha emitters observed at the end stages of reionisation (z>6). These objects represent the phase in the life of massive galaxies when they experience their most luminous star-burst and/or supermassive blackhole accretion event before the onset of significant dust production. Currently, spatially resolved observations of these galaxies allow us to probe the emission from young stars, the interstellar medium and the properties of surrounding hydrogen gas. I will present spatially resolved (spectroscopic) follow-up studies of lluminous galaxies at z>6 with ALMA, HST/WFC3 and MUSE on the VLT. We find that these galaxies likely reside in early ionised bubbles and are complex systems, consisting of multiple components where traces of metals and outflows are already present. I will address the difficulty in addressing the nature of the ionising sources and discuss in particular the unique value of ALMA observations, even when JWST and the ELTs will be available.

The detection of phosphine (PH3), a pre-biotic molecule, in the atmosphere of Venus was published on Nature. This paper got a lot of attention from the press, due to the interesting implications for the possible presence of life on Venus in September 2020. The publication was then followed by a series of other papers questioning either the detection of the PH3 line or its interpretation. In this Informal Discussion we would like to summarize the Saga of the detection of PH3 on Venus and give some detail on the reprocessing of the ALMA data, that have been re-reduced and re-ingested in the ALMA Archive in November 2020.

Astrophysical observations at (sub-)mm wavelengths (λ from ~300 μm to ~3mm) allow us to study the cold and dense material in the Universe, hence probing the formation of stars and planets, and the interstellar and circumgalactic medium within galaxies across cosmic time. The current generation of 10-meter-class single dish telescopes has delivered some of the first surveys at (sub-)mm wavelengths, allowing us to go far beyond the previously optical-biased view of the Universe. Follow-up observations with interferometers then revealed in exquisite detail the morphology and kinematics of such (sub-)mm sources, enabling tests and revisions of theoretical models for the formation and evolution of planets, stars, and galaxies. However, it is now clear that without a transformative change in the capabilities of single-dish facilities in the 2030s, interferometers (like the ALMA observatory) will soon become source-starved. The current generation of 10-m class single dish telescopes, with their limited fields of view, spatial resolutions, and sensitivities, can only reveal the ‘tip of the iceberg’ of the (sub-)mm source population, both for Galactic and extragalactic studies. These limitations cannot be fully mitigated by interferometers, which are all intrinsically affected by a low mapping speed and by the loss of diffuse extended signals.

The Atacama Large Aperture Submillimeter telescope (AtLAST; http://atlast-telescope.org/; https://ui.adsabs.harvard.edu/abs/2020SPIE11445E..2FK/abstract) project is a concept for a 50-meter diameter single dish observatory to be built near the ALMA site. With its extremely large field of view (the goal is ~ 2 degrees), spatial resolution (up to ~1.5” at 350 μm), and sensitivity to both point sources and large-scale structures, AtLAST will be transformational for all fields of Astronomy in the 2030s. Here we will describe the recently approved EU Horizon2020 project to deliver a comprehensive design study for such a next-generation single-single dish facility. AtLAST is community-driven, so get involved!

In this informal discussion, ESO students and fellows will present the Nobel Prizes awarded in 2020.
There will be a short presentation on each prize, focusing on the main results which led to it.
The list of presentations is:

Medicine
Harvey J. Alter, Michael Houghton and Charles M. Rice
Presentation by Avinash Chaturvedi

Chemistry
Emmanuelle Charpentier and Jennifer A. Doudna
Presentation by Rosita Kokotanekova

Literature
Louise Glück
Presentation by Dominika Itrich

Peace
World Food Program
Presentation by Teresa Paneque Carreno

Bank of Sweden Prize in Economic Sciences in Memory of Alfred Nobel
Paul R. Milgrom and Robert B. Wilson,
Presentation by Samuel Ruthven Ward