Noemie Globus, NYU-CCA

Although their astrophysical sources remain a mystery, new measurements brought by experiments such as the Pierre Auger Observatory and Telescope Array, have radically improved our knowledge of the ultra-high energy cosmic-rays (UHECRs). I will review the current observational status (spectrum, composition, and arrival directions) and present new results on the interpretation of the first 5 sigma anisotropy in the UHECR sky: a "dipole" for UHECRs with energies above 8 EeV, reported in 2017 by the Pierre Auger Observatory.

Kyle Parfrey, NASA Goddard

Black holes of all masses drive powerful relativistic jets, using magnetic fields dragged in by their accretion flows. The jets' plasma should be so diffuse as to be effectively collisionless, and self-consistently supplied by pair creation near the horizon. I will present the first general-relativistic kinetic plasma simulations of collisionless black-hole magnetospheres, showing the launching of electromagnetic jets by the Blandford-Znajek mechanism. The simulations reveal a population of particles with negative effective energy, which can contribute significantly to black-hole rotational-energy extraction. The kinetic approach will be useful for studying the accretion flows of the primary Event Horizon Telescope targets, M87 and Sgr A*, where the plasma is likewise of low density and collisionless, and for probing black holes' nonthermal X-ray and gamma-ray emission from first principles.

Dimitri Veras, University of Warwick

Connecting planetary systems at different stages of stellar evolution helps us understand their formation, evolution, and fate, and provides us with exclusive and crucial insights about their dynamics and chemistry. Post-main-sequence white dwarf and giant branch stars host planetary systems which include a variety of observed objects and phenomena, such as planetary debris discs, disintegrating and embedded asteroids, exo-comets, and photospheric metal pollution. Here, I provide a review of both our current knowledge of these systems and models which have been used to explain them. I also highlight the transformative advances expected in upcoming years with the current and next generation of ground-based and space-based initiatives. Looming orders-of-magnitude increases in available data must be accompanied by novel theories and simulations in order to understand the results from this interdisciplinary and expanding research field.

David Nataf, Johns Hopkins University

Globular clusters are now well-established to host "Second-generation" stars, which show anomalous abundances in some or all of He, C, N, O, Na, Al, Mg, etc. The simplest explanations for these phenomena typically require the globular clusters to have been ~20x more massive at birth, and to have been enriched by processes which are not consistent with the theoretical predictions of massive star chemical synthesis models. The library of observations is now a vast one, yet there has been comparatively little progress in understanding how globular clusters could have formed and evolved. In this talk I discuss two new insights into the matter. I first report on a meta-analysis of globular cluster abundances that combined APOGEE and literature data for 42 globular clusters, new trends with globular cluster mass are identified. I then discuss the chemical properties of former globular cluster stars that are now part of the field population, and what can be learned. I demonstrate that globular clusters were the predominant sites of star formation in the first epoch of star formation.

Ruediger Pakmor, MPA-Garching

Only very recently cosmological zoom simulations of galaxies have started to be able to include the evolution of magnetic fields and the treatment of relativistic cosmic ray particles. I will present recent results from the Auriga simulations of high resolution cosmological zoom simulations of Milky Way-like galaxies and show how the magnetic field in these galaxies is amplified and ordered during cosmic evolution. Moreover, I will discuss how the inclusion of cosmic rays in the cosmological simulations changes the properties of disk galaxies and their circumgalactic medium.

Kareem El-Badry, University of California- Berkeley

Population statistics of wide binaries encode the end state of turbulent core fragmentation and can thus constrain aspects of the star formation process that are theoretically poorly understood. Because the orbits of wide binaries are fragile, they are also sensitive probes of the dynamical history of a stellar population. The Gaia mission has recently revolutionized the wide binary field, making it possible to assemble large, homogenous, and pure catalogs of binaries with a well-understood selection function. I will discuss several recent discoveries enabled by Gaia, focusing in particular on the unexpected discovery of an excess population of equal-mass "twin" binaries at wide separations that challenges our understanding of the star formation process. I will also discuss tests of gravity in the low-acceleration regime with wide binaries.

Damiano Caprioli, University of Chicago

The life of Supernova Remnants (SNRs) offers exquisite laboratories for Astrophysics, Plasma Physics, and Astroparticle Physics. I consider three SNR stages, childhood, adulthood, and old age, and outline how non-thermal processes in each stage are essential to address three fundamental questions: How do massive stars end their life? How are cosmic rays generated? How does stellar feedback work in galaxy formation? In particular, I use a combination of analytical calculations and ab-initio kinetic plasma simulations to study how electrons and ions are accelerated in SNR shocks, discussing (and challenging) the state of the art in the light of recent multi-wavelength observations.