The albedo of a celestial body is the fraction of incident starlight reflected by it. The study of the albedos of Solar System objects is at least a century old, at least in the Western world. As examples: Bond (1861) speculated on the near-unity albedo of Jupiter, while Russell (1916) observed the opposition surge of the Moon near and at full phase. The light of a planet or moon varying with orbital phase is known as its phase curve. Modern astronomical facilities have enabled the measurement of phase curves of reflected light and thermal emission from exoplanets (e.g. Kepler, TESS, CHEOPS, Hubble, Spitzer), which enables the investigation of atmospheric dynamics and aerosols. In the current talk, I will concisely review and discuss historically important work, including seminal contributions by Seeliger (1888), Chandrasekhar (1960), Sobolev (1975) and Hapke (1981). These introductions set the stage for a detailed discussion of our recent work on generalising these classic works to derive closed-form, ab initio solutions for the geometric albedo and reflected light phase curve. This novel theoretical framework is applied to Kepler space telescope data of the hot Jupiter Kepler-7b, where we demonstrate that one may infer fundamental aerosol (single-scattering albedo, scattering asymmetry factor) and atmospheric (geometric albedo, Bond albedo, phase integral) properties from precise photometry alone, thus providing powerful complementary information to spectra. Another case study are the Cassini phase curves of Jupiter, which were measured in the early 2000s by the Cassini space mission but never subjected to Bayesian inference.By inverting the Cassini phase curves, we infer that aerosols in the Jovian atmosphere are large, irregular, polydisperse particles that may be responsible for causing coherent backscattering of sunlight.

The clustered nature of star formation leaves a long-term imprint on galaxies, stars, and planets. At young ages, stellar clustering subdivides galaxies into individual building blocks undergoing vigorous, feedback-driven life cycles that vary with the galactic environment. These units structure the interstellar medium spatially, dynamically and chemically, and collectively define how galaxies form stars. At old ages, the relics of clustered star formation persist as ancient globular clusters, which hold a wealth of information allowing us to reconstruct the assembly histories of galaxies, culminating in the reconstruction of the Milky Way’s merger tree. Towards smaller scales, stellar clustering has a measurable impact on the evolution of protoplanetary discs, the architectures of planetary systems, and the properties of planets themselves. I will discuss how this web of physical processes across a hierarchy of scales defines the cosmic ecosystem that we live in, and demonstrate that stellar clustering is at its focal point.

Li is the element with the largest number of known astrophysical nucleosynthetic processes, but also with several astronomical puzzles. It is  a primordial element produced in the first 3 minutes, but   Li abundance in the old halo population of the Galaxy  is lower by a factor 3 than predicted by Big Bang models when the baryonic density is  either from the CMB or from primordial deuterium.  Also,  the same abundance is seen in metal poor Gaia-Enceladus candidate stars, which are  effectively extragalactic. This disagreement   is known as the Cosmological Lithium problem for which  a satisfactory solution is still to be found. A possible fix by pre-main sequence stellar depletion will be   discussed briefly as an example. Spallation processes in the interstellar medium    also produce Li, but  not enough  to reach the  abundance observed  today, and one or more stellar sources are required  to make most (~ 70%) of the Li in the Galaxy.  Several candidates have been proposed but  none is really satisfactory. Novae were  suggested in the early 70’s but only recently  Be-7, the Li  parent nuclei,  has been detected in novae outburst. Ongoing observations of Be-7 in few recent novae will be reported,   including the first detection of Be-7 in two novae in the Small Magellanic Cloud.   The   Be-7(= Li-7) yields obtained from novae are very high,  higher than model predictions, which represents a matter of concern. Taken at face value the observed   yields overproduce the present meteoritic Li abundance by  four orders of magnitude, and  therefore novae look as  the most promising candidates for "THE" source of Galactic  Li. This is also supported by detailed  chemical evolution models  of  Li evolution in the thick and thin disks of the Galaxy.

Galaxies are known to occupy preferential regions in the star formation versus stellar mass (SFR-M*) plane. More than a decade ago, the existence of two main regimes have been recognised: a so-called main sequence (MS) for star-forming galaxies and a passive cloud for galaxies with negligible instantaneous star formation rates. Since then, the MS has been considered the general rule for galaxy growth from low to high redshifts. Until recently, there was scarce evidence for the presence of starbursts, i.e. galaxies with a star formation activity that is significantly elevated with respect to the MS.
In this talk I will revisit the importance of starburst galaxies in the light of the most recent results in this field. I will argue that there is a clear starburst/MS bimodality for the modes of galaxy star formation, which becomes evident at high redshifts (z>2-3), when the starburst mode dominates the total SFR budget. Interestingly, state-of-the-art galaxy formation models fail to predict the starburst population overall, suggesting that the physics behind the starburst mode may be absent in these models.

The next generation of astronomical observatories bring a realistic prospect of paradigm-shifting constraints on the nature of dark matter and dark energy, both through deeper observations of large scale structure and by pushing to fainter surface brightness galaxies. I will discuss the unique computational challenges that producing simulations for this era pose. On the one hand we wish to simulate large volumes to gain representative samples of galaxies and to understand the cosmological implications of forthcoming survey data from e.g. LSST. On the other, we also want to maintain very high resolution to resolve highly non-linear astrophysical processes and internal kinematics for Gaia, MaNGA and the like. These two requirements result in a tension on how to best spend limited computer time. I will argue that a new approach to simulations, in which we use statistical models to tailor cosmological initial conditions for different questions, can help relieve this tension. I will mainly focus on recent applications to understanding the diversity of dwarf galaxies, and will also give a quicker overview of results for higher mass galaxies and large scale structure.

Our understanding of the motions of stars within our Milky Way and of the many small galaxies that orbit around it has changed dramatically over the past few years owing to new observational surveys and significant advancements in our understanding of galaxy structure. New surveys now enable us to precisely measure the motions of objects that orbit our Galaxy, like clusters of stars, satellite galaxies and stellar streams. The motions of these objects trace the so-called “dark matter” distribution, the unseen material that is expected to exist within and around our Galaxy, making up the bulk of its mass. However, connecting these data to theoretical models requires understanding the influence of the Milky Way’s largest satellite galaxy, the Large Magellanic Cloud (LMC). I will provide an overview of this evolving picture and how we can test the cold dark matter paradigm in the near future using next-generation surveys and simulations that include the LMC.

The archaeological record of the Milky Way is being unveiled through measurements of its stars. This is an endeavour across a huge range of scale, where both individual stellar atmospheres and million star surveys are revealing the connection of present to past. I will present my recent work that makes measurements of stellar ages, and uses these ages as the fundamental variable to learn the formation and evolutionary properties of the Galaxy: where stars were born, how they have moved over time, and how individual abundances can quantify the diversity of the environment in which they formed. The overarching goal of this ensemble of studies is to link the chemical to the structural evolution of the Milky Way, showing relationships that directly enable comparisons to other galaxies.

In this talk, I will review the physics of accretion and outflows, focusing on the relativistic jets, as revealed by 3D general relativistic simulations of magnetized plasma near spinning black holes. I will discuss the conditions necessary for jet formation, what the jets can reveal about the central engine, and the effects the jets can have on their environment.

The Atacama Large Millimeter Array (ALMA) has granted us the sharpest view of protoplanetary disks, the planet formation environment, to date. These disks, reservoirs of planet-forming material, have been found to host a stunning variety of substructure. Gaps, rings and spirals are routinely observed in the distribution of large dust grains, suggestive of dynamical processing by an unseen population of recently formed planets. I will demonstrate how through studies of the gas structure, in concert with the development of new data analysis techniques, we have been able to detect the young planets responsible for the structure we have seen in the dust. I will show how we are now able to conduct a thorough chemical inventory of the planet forming material, and trace the delivery of these materials to young planets during the accretion of their atmospheres. To conclude, I will high how the mapping of the dynamical structure of the disk is providing a unique opportunity to identify the hydrodynamical processes that are driving planet formation and influencing the global evolution of the protoplanetary disks.

IceCube detects more than 100,000 neutrinos per year in the GeV to 10 PeV energy range. Among those, we have isolated a flux of high-energy neutrinos of cosmic origin, with an energy density in the extreme universe similar to that of high-energy photons and cosmic rays. We identified their first source: on September 22, 2017, following an IceCube neutrino alert, observations by other astronomical telescopes pinpointed a flaring active galaxy, powered by a supermassive black hole, as the source of a cosmic neutrino with an energy of 290 TeV. We will review recent progress in measuring the cosmic neutrino spectrum and in identifying its origin.

The Dark Energy Survey (DES) included a six-year, 5000 sq. deg. observing program using the Dark Energy Camera on the 4m Blanco telescope at CTIO. Observations are now complete, but this is just the start of shedding light on the fundamental mysteries of the Universe with DES. I’ll discuss the most recent analysis of weak gravitational lensing and large-scale structure measurements using the first three years of DES data. The power of this data set, which has produced calibrated shape measurements for over 100 million galaxies, has required the development of novel new approaches to calibrating shear and photometric redshift information. I will describe these advances and our measurements, and comment on what we can look forward to with future DES science.

The Perseverance rover landed on the floor of an ancient martian lake on February 18, 2021. After confirming complete functionality of the rover and demonstrating the capabilities of the Ingenuity helicopter, the rover began its science investigations in earnest. The rover has now traversed almost 3 km, exploring rocks on the crater floor. Early data suggest that at least some of these rocks are lava flows with pervasive aqueous alteration. A major milestone was achieved in early September when the first samples for possible Earth return were successfully cored, sealed, and stored on the rover. I will discuss the mission's goals, activities and preliminary results.

In the past decade we have started to explore extragalactic and intergalactic space using millisecond-duration radio flashes called `fast radio bursts' (FRBs).  These cosmological signals are surprisingly abundant: there is likely an FRB occurring somewhere on the sky at least once every minute.  But what is producing them?  Thanks to a new generation of wide-field radio telescopes, several FRBs per day are now being discovered.  Novel high-time-resolution observations using radio interferometers are now also pinpointing FRB locations and providing host galaxy associations.  More than a decade since the famous `Lorimer burst', we are now making rapid progress in our understanding of the enigmatic FRB phenomenon.  In this talk, I will focus on how observations with the European VLBI Network (EVN) and the Low-Frequency Array (LOFAR) are shedding light on the nature of FRB sources.  These observations have provided milli-arcsecond localisations and nanosecond-resolution polarimetry to decode the source model and emission mechanism.

Black holes are solutions of Einstein's equations that were long considered unphysical.  So are white holes.  Advances in quantum gravity suggest that white holes could be generated by a quantum transition at the end of the Hawking evaporation of primordial black holes.  I illustrate the theoretical ground of this scenario and briefly discuss its possible astrophysical relevance. 

ALMA observations of circumstellar disks obtained by the "Disk Substractures at High Angular Resolution Project" (DSHARP) have revealed that the dust distribution in the majority of (large) circumstellar disks is characterized by small-scale structures. Dust rings are the most common features, but crescents
and spiral arms were also observed. Whereas the origin of these structures is still debated, there are many indications that they might be directly connected to the formation of planetary systems. During my talk, I will provide a quick overview of the main results obtained by DSHARP and discuss more recent studies, both theoretical and observational, that highlight the relation between disk substructures and planets.

The first detection of gravitational waves was made in September 2015 with the measurement of the coalescence of two ~30 solar mass black holes at a distance of about 1 billion light years from Earth. The talk will provide some history and description of the detector. A review will be given of more recent measurements of black hole events as well as the first detection of the coalescence of two neutron stars and the beginning of multi-messenger astronomy. The talk will end with a discussion of some prospects for the field.

In 2017 the Event Horizon Telescope (EHT) Collaboration made the first direct image of the light surrounding the black hole in M87. While spectacular, this result was just the beginning of a multitude of projects. By deepening the coverage on M87 in time and polarisation with an improved array, combining with multi-wavelength coverage, and exploring other supermassive black holes, we are building a more complete model of black holes as "central engines".

Our Galactic centre supermassive black hole Sgr A* is a major focus at the moment, but we also have results on several of the brightest nearby radio galaxies, famous for their enormous particle-accelerating plasma jets. I will provide an overview of what we have learned since the first big announcement, with an emphasis on the implications for multiwavelength/multi-messenger science, and what results are close on the horizon, literally.

Planets form in disks around young stars. The resulting planet compositions are intimately linked to the disk chemical structures; the distribution of molecules across disks regulate the elemental compositions of planets, including C/N/O/S ratios and metallicity (O/H and C/H), as well as access to water and prebiotically relevant organics. These molecules are in part inherited from earlier stages of star formation, and in part formed in situ in disks. In this talk I will present our developing view of the molecular cloud and protostellar chemistry that sets the initial chemical conditions in planet forming disks. I will then turn to recent gains made in our understanding of disk chemistry through the Molecules with ALMA at Planet-forming Scales (MAPS) ALMA Large Program. With MAPS we have been exploring disk chemical structures down to 10 au scales in a small sample of disks in which dust substructures are detected and planet formation appears to be ongoing. Some highlights include discoveries of links between dust and chemical sub-structures, large reservoirs of nitriles and other prebiotically interesting organics in the inner disk regions, and elevated C/O ratios across most disks. I will discuss how these results are reshaping our view of the chemistry of planet formation, but also review some open questions that remain and the observations, models and laboratory experiments that will be needed to address them.

A new window into the growth and evolution of large-scale structure has opened up with the recent observations of the thermal and kinetic Sunyaev-Zel’dovich (SZ) effects. I will review recent observations of the SZ signals and highlight their expected rapid growth over the next decade with upcoming cosmic microwave background experiments, like Simons Observatory and CMB-S4. I will present ongoing work to extract SZ signals in data from the Atacama Cosmology Telescope and how they can be used to constrain the important baryonic process that govern galaxy formation. Time permitting, I will conclude by discussing the connections between these SZ observations and mitigating the modeling uncertainties associated with "baryonic effects" in future large-scale structure surveys like LSST.

Evolved stars and their winds play a crucial role for galactic chemical evolution, including the origin of building blocks for planets and life. Essential chemical elements, like carbon, are produced inside these stars, transported to the surface by turbulent gas flows, and ejected into interstellar space by massive outflows of gas and dust. I will present an overview of recent results and ongoing work on stellar winds. In particular, I will describe how project EXWINGS contributes to the field, creating global dynamical star-and-wind-in-a-box simulations. With such models it will be possible to follow the flow of matter, in full 3D geometry, all the way from the turbulent, pulsating interior of an asymptotic giant branch star, through its atmosphere and dust formation zone into the region where the wind is accelerated by radiation pressure on dust. Advanced instruments, which can resolve the stellar atmospheres where the winds originate, provide essential data for testing the models. I will also discuss what the recent dimming event of Betelgeuse may teach us about the still enigmatic mechanisms that drive the winds of red supergiant stars.

Supernovae are explosive endpoints of stellar evolution. The most common two categories are core-collapse supernovae and thermonuclear supernovae. For core-collapse supernovae, the kinetic energy of the explosion is provided by the gravitational energy release when the iron core of an evolved massive star collapses to either a neutron star or a black hole. Open questions include how stripped supernovae lose their envelopes and which core-collapse supernovae make black holes and which make neutron stars.

In part I of my talk, I will present examples of how optical integral field observations of the remnants of certain core-collapse supernovae, such as 1E0102.2-7219 or Puppis A, provide us with puzzling new structures that need to be understood if we want make progress on the nature of their progenitors. For thermonuclear supernovae, the energy source is explosive nuclear fusion in white dwarf stars of lighter elements like helium, carbon, and oxygen, to heavier elements like silicon or nickel and iron. What kind of white dwarfs explode and how they evolve to ignition are still largely open questions.

In part II of my talk, I will present the recently discovered optical coronal line emission of the reverse shocked ejecta in three young thermonuclear (Type Ia) supernova remnants and discuss a new approach how these optical emission lines can be modelled to infer key parameters of the original supernova, such as explosion energy and mass.

In the last decade we have explored the cosmic depths and found a statistically significant number of galaxies well into the Epoch of Reionization. However, our physical knowledge of these pristine objects remains very scant. Investigating the internal structure, interstellar medium and evolution of early galaxies is the next challenge to understand key processes as the cosmic history of baryons, feedback, reionization and metal enrichment of the intergalactic medium, This ambitious plan can be tackled by combining a new generation of physically-rich, high resolution, zoom simulations with data in the sub-mm bands provided by ALMA. This approach will be soon strengthened by the forthcoming JWST power. I will review the present status and the open questions in the field.

Magnetic fields thread our Milky Way Galaxy, influencing interstellar physics from cosmic ray propagation to star formation. The magnetic interstellar medium is also a formidable foreground for experimental cosmology, particularly for the quest to find signatures of inflation in the polarized cosmic microwave background (CMB). Despite its importance across scientific realms, the structure of the Galactic magnetic field is not well understood. Observational tracers like polarized dust emission yield only sky-projected, distance-integrated measurements of the three-dimensional magnetic structure. I will discuss new ways to probe interstellar magnetism in three dimensions, by combining high-resolution observations of Galactic neutral hydrogen with recent insights into how gas morphology encodes properties of the ambient magnetic field. These 3D maps are a new tool for understanding the magnetic interstellar medium and the polarized foreground to the CMB.

SRG spacecraft with German (eRosita) and Russian (ART-XC) X-Ray telescopes was launched by RosKosmos on July 13th of 2019 from Baikonur. During the flight to the L2 point of the Sun-Earth system SRG performed calibrations and long duration Perfomance Verification (PV) observations of a dozen of targets and deep fields. Starting in the middle of December 2019, the SRG scanned the whole sky in half a year and discovered more than a million point X-Ray sources, mainly AGNs and QSOs, stars with hot and bright coronae, and 16 thousand clusters of galaxies. There is a competition and synergy with the search for clusters of galaxies by Atacama Cosmology and South Pole Telescopes sensitive in the microwave spectral band.

We see X-Rays from hundreds of the stars accompanied with exoplanets.

SRG provided the X-Ray map of the whole sky in hard and soft bands, the last is now the best among existing. It reveals a lot of information about the distribution of absorbing gas in the Milky Way and provides a beautiful image of the North Polar Spur and similar bright emitting eRosita Bubble on the Southern side from the Central Part of the Galaxy. I plan to describe the Observatory plans for the future and to demonstrate several exciting results from the PV phase observations as well as from the second and third all-sky survey which is ongoing. The huge samples of the X-ray selected quasars at the redshifts up to z=6.2 and clusters of galaxies will be used for well-known cosmological tests and for detailed study of the growth of the large scale structure of the Universe during and after reionization.  

During all sky survey SRG/eRosita is discovering every day several extragalactic objects which increased or decreased their brightness more than 5-10 times during half of the year after previous scan of the same strip on sky. Significant part of these objects has observational properties similar to the Tidal Disruption Events. 

Our standard model for physical cosmology, with its nonbaryonic dark matter and cosmological constant, passes well-checked tests that make a persuasive case that this model is a good approximation to reality. There are open issues, of course, and research programs in progress to address them. I will discuss some less widely advertised issues that I suspect merit closer attention.

I will report on some of the results emerging from the ALMA large program ASPECS that obtained deep (sub-)millimeter imaging of the Hubble Ultra-Deep Field (H-UDF). The observations provide a census of dust and molecular gas in the H-UDF, down to masses that are typical of main-sequence galaxies at redshifts 1-3. The resulting data enable a great range of studies, from the characterisation of individual galaxies, capitalizing on the unique multi-wavelength database available for the H-UDF, to CO excitation studies that constrain the gas properties. Stacking analyses in dust continuum and CO line emission, using available H-UDF galaxy catalogues and precise redshifts from VLT/MUSE, helped to constrain the emission of galaxy samples that are too faint to be detected individually. The nature of the observations (full ALMA spectral scans) provides a census of dust and molecular gas in the cosmic volume defined by the H-UDF. The resulting cosmic molecular gas density as a function of redshift shows an order of magnitude decrease from z~2 to z=0. This is markably different from the atomic gas phase that shows a rather flat redshift dependence. With other measurements from the literature, these results are used to put additional observational constraints on the gas (net) accretion flows, needed to explain the build-up of stellar mass in galaxies, and are compared to cosmological galaxy formation simulations.  

Massive black holes weighing from a few thousands to tens of billions of solar masses inhabit the centers of today’s galaxies, including our own Milky Way. Massive black holes also shone as quasars in the past, with the earliest detected a mere one billion years after the Big Bang. Massive black holes during their cosmic evolution interact with diverse environments, starting from messy and rapidly evolving galaxies at high redshift to quiescent galaxies today. I will discuss how these changing environments affect the growth of massive black holes and the formation of massive black hole binaries that eventually coalesce by emission of gravitational waves, which can be detected with ESA’s planned satellite LISA and with Pulsar Timing Arrays.

Over the past decade comprehensive and systematic studies of star formation and the gas contents of galaxies during the epochs that are associated with the peak (z~1-3), and subsequent winding down (z<1) of star formation have enabled us to illustrate the important role that cold gas plays in the assembly of galaxies across cosmic time. These studies show that star forming galaxies contained significantly more molecular gas at earlier cosmic epochs than at the present time. Global rates of galaxy gas accretion, which vary with cosmological expansion, primarily drive this increase in cold gas and star formation rates in the dominant main sequence galaxy population. Studies also show that the molecular gas depletion time depends mainly on redshift or Hubble time, and at a given z, on the vertical location of a galaxy relative to the “star formation main sequence”. In this talk, I will discuss various strategies and methods used to determine the evolution of cold gas contents, and discuss the latest gas scaling relations with redshift, star formation and stellar mass. I will also discuss howsimple gas regulator models successfully predict the combined evolution of molecular gas fractions, star formation rates, galactic winds, and gas phase metallicities.

The results of the Gaia astrometric mission have ushered in a new era of "precision Galactic dynamics". Using this new phase-space map of Galactic stars with unprecedented volume, we are beginning to obtain new insights into the dark matter distribution in our Galaxy as well as its formation history. Thanks to significant advances on the computational front, meanwhile, we can now compare these insights directly with, and test our modeling strategies on, simulations of Milky-Way-mass galaxies where the influence of baryons and the cosmological context on the dark matter structure are realistically taken into account. I will demonstrate how this convergence of new data and better models can improve our understanding of the Milky Way's dark matter distribution, leading to better constraints on the nature of dark matter.

Since the discovery of the first extrasolar planet orbiting a Solar-like star in 1995, exoplanet science has been evolving into a highly dynamic field of modern astrophysics. Today we know more than 4000 exoplanets and thanks to ongoing efforts from the ground and from space this number keeps continuously increasing. While most of the planets have been discovered via indirect techniques, such as the radial velocity and transit techniques, the direct detection of (small, terrestrial) exoplanets will be required in order to test hypotheses concerning exoplanet habitability and the possible existence of bio-signatures in a statistically relevant sample of objects. In this talk, I will briefly review the current state of high-contrast exoplanet imaging today, discuss the challenges that need to be overcome in order to directly take a picture or a spectrum of an exoplanet, and present a way forward, how we will eventually be able to search for indications of biological activity in exoplanet atmospheres around nearby stars.