Our current view of the interstellar medium (ISM) is as a multiphase environment where magnetohydrodynamic (MHD) turbulence affects many key processes: star formation, cosmic ray acceleration, and the evolution of structure in the diffuse ISM. In part 1 of this talk, I shall review the fundamentals of galactic turbulence and discuss progress in the development of new techniques for comparing observational data with numerical MHD turbulence simulations. In part 2, I will focus on how turbulence affects the long-standing problem of star formation. From scales of giant molecular clouds (GMCs), I will demonstrate how the star formation efficiency can be analytically calculated from our understanding of how turbulence, gravity, and stellar feedback induce density fluctuations in the ISM via a probability distribution function analysis. This analytic calculation predicts star formation rates from pc size scales (GMCs) to kpc size scales in galaxies.

The Milky Way’s Galactic Center black hole Sagittarius A* is the closest to us supermassive black hole. It is an ideal candidate to explore near horizon effects, to test alternative theories of gravity, and to learn the mechanics of black hole feeding, accretion, and feedback -- forces shaping galaxies and the Universe as a whole. Despite its proximity, the accretion flow onto it is not well understood. At large scales (10^5 R_sch and beyond), the primary source of information about accretion flow comes from observations of hot X-ray emitting gas. At near horizon scales, the density of the flow is constrained by polarization measurements. At intermediate scales, there are too few model-independent probes to reliably determine physical properties of the gas. In 2019, using ALMA observations I discovered a disk of cool gas at intermediate distances (10^4 R_sch) from the black hole, which provides new clues to the physics of the inner accretion flow of the Sagittarius A*. In this talk, I will review what is known about the structure of the accretion flow around the black hole. I will discuss the properties of the cool disk and what we can learn from it about the structure of the accretion flow. I will show our new realistic simulations of the inner two parsecs of the Galactic Center which, for the first time, captures Sagittarius A*’s multiphase accretion physics.

The term “Great Observatory” was once a piece of programmatic branding for four space telescopes launched between 1990 and 2003. No longer. While Hubble, Chandra, Compton, and Spitzer will reign as everlasting triumphs of science, the term “Great Observatory” has transcended these missions alone. It now reflects a vision for transformationally powerful, flexible, and long-lived facilities enabling panchromatic synergy, near-simultaneity, and acting as force multipliers for ground-based facilities around the world. With extended missions that can span decades, Great Observatories become something other than a pursuit of important but narrowly-defined science goals. They become discovery platforms for the questions we have not yet thought to ask. In this talk, I’ll review the past, present, and future of the Great Observatories program, particularly in the wake of Astro2020.

Are we alone in the Universe? 60 years ago, Frank Drake posed a unique answer to that question, positing that, given a handful of statistics about the local galaxy, one could calculate the number of intelligent civilizations currently residing in the Milky Way. Today, that equation poses a serious question to astrophysics: how can we better constrain those statistics? First, I will introduce the concept of exoplanet spectroscopy and discuss the latest methods and challenges of the field. Then, I will talk about the "n_e" factor: the number of planets which could support life. My present work studying the atmospheres of hot- and ultra-hot Jupiters at multiple orbital phases serves as a perfect testing ground for the statistical methods which will one day constrain the atmospheres of Earth-sized planets, answering the question: Is it Earth-like? Venus-like? Mars-like? I will also discuss the "f_l" factor, the fraction of habitable planets which could support life. One of the biggest challenges faced by the next generation of telescopes will be the massive degeneracy of possible atmospheres on Earth- and super-Earth-sized worlds. I will discuss new and intriguing techniques for characterizing both biosignatures and anti-biosignatures in the very-low signal-to-noise regime and address the question: Could life develop on a given planet?

Since the detection of the first gravitational wave transient in 2015 there has been a small revolution in our understanding of the mass distribution of black holes. But there are still many unknowns and theory is still struggling to understand how the observed distribution is determined. There are also other windows onto black holes that are showing that the GW transient masses are only have the story. I'll present the main samples of black holes that are available to us today and in the not-too-distant future. Then describe how theoretical work will allow us to understand what physics is in play in determining the birth and evolution of black holes, their ecology within galaxies and the Universe.

What are the processes that govern the formation evolution and assembly of galaxies across cosmic time? This question is among the most fundamental in modern astronomy yet the answer still eludes us to this day. The Milky Way is an optimal laboratory for answering the questions of galaxy formation and assembly because it is one of the only systems to date where we can obtain detailed and precise data on the positions motions and chemical composition for billions of individual stars. Using our Galaxy as a sandbox for exploring galaxy formation and assembly is the essence of Galactic archaeology. In this context I will present my ongoing work in Galactic and stellar archaeology using large spectroscopic photometric and astrometric surveys together with high resolution spectroscopy. I aim to cover the process of chemo-dynamic tagging metal-poor stars in the Galactic bulge as tracers of the first stars what we can learn from industrial-scale spectroscopic surveys and the future of Galactic archaeology.

Mapping the Milky Way has been a seventy year long painful slog, and the picture that many researchers currently use for Milky Way structure is more of a “model" than it is a “map". But the combination of (a) high precision parallaxes of radio masers from the BeSSeL and VERA programs and (b) stellar parallaxes for a billion sources from Gaia are drastically reshaping our picture of the structure of the Milky Way Galaxy. In this talk, I will trace the development of the current model of Milky Way spiral structure from its origins in 1951 through to the current day, with a focus on the three nearest spiral arm segments: Perseus, Orion/Local, and Sagittarius. In the modern era, we now have five principal tracers of the star forming structure of the Milky Way: (a) individual “upper main sequence” stars (or just spectroscopically selected OB) stars with Gaia parallaxes, (b) young stellar clusters with Gaia parallaxes, (c) masers in high mass star forming regions with radio parallaxes, (d) three dimension dust extinction maps using main sequence stars with Gaia parallaxes, and (e) YSOs in high mass star forming regions with Gaia parallaxes. I will show a comparison of these maps with each other and discuss how well they compare with the historical model. It is clear that current models of MW star forming structure are in need of some revision. I will provide some speculations on where I see this whole process going in the next few years.

Metal poor stars are key to understanding the history of our Galaxy. In their element abundances pattern is encoded the chemical composition of the first stars and therefore, when the stellar age is available, hints on the chemical enrichment and evolution of the Milky Way. However, to obtain precise ages for field metal poor stars is a challenging task: at present only an handful very metal-poor stars have ages, derived by using nucleo-cosmo-chronology (e.g. via Thorium and Uranium abundances). Asteroseismology in recent years has demonstrated to be a powerful tool to derive masses, and hence ages, of red giant stars. When this technique is applied to metal poor stars,it is possible to increase the number of metal poor stars with a precise age measurement. For this purpose I am leading a project combining asteroseismology and high resolution spectroscopy of metal-poor halo giants ([Fe/H]<-1.5 dex). Targets have been identified in RAVE and APOGEE surveys. We obtained seismic information from the light curves collected by the Kepler,K2, and TESS space missions, and detailed chemical abundances, from ESO-UVES and HARPS-N high resolution spectra. We derived iteratively the atmospheric parameters, by taking into account the seismic surface gravity. We then derived precise abundances taking into account NLTE effects. The final atmospheric parameters and abundances, together with the seismic information and, when available, Gaia parallaxes, were used for interfere stellar masses, radii and ages, via Bayesian fitting on a set of isochrones. We obtained a unique set of metal poor stars, for which we determined precise ages. For the first time a consistent and complete approach have been adopted, in order to quantify the impact of temperature shifts, different mass-loss approaches, alpha-enrichment and corrections on seismic scaling relations. Our project shows how it is possible to obtain precise ages for field metal poor giants, and therefore to reconstruct the history of the Galactic halo.

The first, Population III stars ignited several hundred million years after the Big Bang. While we know they formed from primordial metallicity gas in 10^5 - 10^7 solar mass dark matter halos, and are thought to be more massive than later generations of stars, their detailed properties remain unconstrained. Current unknowns include; when the first Pop III stars ignited, how massive they were, and when and how the era of the first stars ended. Investigating these questions requires a exploration of a multi-dimensional parameter space including, the slope of the Pop III stellar initial mass function (IMF), and the strength of the non-ionizing UV background. We have developed a novel model which treats these relative unknowns as true free parameters. Our simple model reproduces the results from hydrodynamic simulations, but with a computational efficiency which allows us to investigate the observable differences between a wide range of potential Pop III IMFs. The upcoming launch of the James Webb Space Telescope (JWST) provides us with a unprecedented opportunity to marry theoretical predictions to observations and determine the astrophysics which governs the formation of the first stars. Here we suggest constraining the masses of the first stars with JWST will require a multi-pronged approach. In addition to direct detection via gravitation lensing, this also includes understanding how the Pop III IMF affects observed rates of highly luminous pair instability supernova.

Two years ago, in April 2019, the Event Horizon Telescope (EHT) released the first images of a black hole, resolving the shadow of the supermassive black hole M87* at the center of the nearby active galaxy M87. Furthermore, the EHT recently captured the polarization of the photon ring in M87*, resolving the magnetic field near the event horizon. The EHT uses very long baseline interferometry at 1.3 mm wavelength, allowing to image supermassive black holes at horizon-scale resolutions. In this talk, I will present an overview of the past, present, and future of black hole imaging with the EHT. I will first discuss the major breakthroughs enabling to provide these results and also provided by these horizon-scale image. Finally, I will introduce our next decadal forecast of the forthcoming exciting era to study black holes through direct imaging.

Stellar feedback plays an important role in regulation of star formation and stellar mass growth on cosmological timescales. Direct inclusion of this feedback in cosmological simulations has proven difficult but a new generation of cosmological zoom-in simulations shows significant promise. For example, simulations from the FIRE project model stellar feedback on spatial scales of molecular clouds and achieve local self-regulation of star formation and self-consistent driving of galactic outflows via careful treatment of the supernova momentum and energy injected to the surrounding ISM. A prominent feature of these simulations is bursty star formation and spatial clustering of supernovae that drive significant outflows from galaxies, especially in low mass objects. Star formation-driven galactic outflows become inefficient at late times for galaxy masses similar to the Milky Way, which leads to significant buildup of galactic stellar mass. Interestingly, if only a moderate fraction of supernova energy is imparted to the surrounding gas in the form of cosmic rays, this can significantly modify the structure and properties of the circum-galactic medium (CGM), drive large scale winds, and slow down gas infall and growth of L* galaxies. The magnitude of these effects is sensitive to the transport of cosmic rays that can be constrained with diffuse gamma ray emission from galaxies. Potential significant role of cosmic rays in galaxy evolution motivates increased interest in understanding of their transport.