2020
A&A Colloquium - Lorenzo Sironi (Columbia)
3:30–4:30 pm ERC 161
Fast and furious: magnetic reconnection in relativistic jets and black hole coronae
Relativistic jets of blazars and magnetized coronae of low-luminosity accretion flows, like Sgr A* at our Galactic Center, routinely display fast and bright flares of high-energy emission. Yet, the “engine” responsible for accelerating the emitting particles to ultra-relativistic energies is still unknown. With fully-kinetic particle-in-cell (PIC) simulations, we argue that magnetic reconnection — a process by which magnetic field lines of opposite polarity annihilate, releasing their energy to the particles — can satisfy all the basic conditions for the emission. In blazar jets, we show that reconnection can naturally explain the puzzling ultra-fast bright flares observed at GeV and TeV energies, whose duration can be even shorter than the light-travel time across the black hole that powers the jet. In low-luminosity accretion flows like Sgr A*, we show that reconnection — potentially seeded by turbulence — can power both thermal and non-thermal emission, and we produce physically-grounded synthetic images and spectra to be compared with infrared and X-ray observations and with the upcoming results of the Event Horizon Telescope.
Special A&A Colloquium: Benjamin Fulton (Caltech)
12:00–1:00 pm ERC 576
Is our Solar System Unique? A Holistic View of Exoplanet Demographics
The Kepler and K2 missions blessed the community with a plethora of planet transit detections which enabled studies of exoplanet size demographics. Much of the recent progress in this field is driven by improved characterization of the stellar hosts. Our group recently used precise radius measurements from the California-Kepler Survey (CKS) to detect a gap in the distribution of planet radii. The paucity of planets with sizes between 1.5 and 2.0 Earth radii supports the emerging picture that close-in planets smaller than Neptune are composed of small, rocky cores enveloped by varying amounts of low-density gas that determine their total sizes. This result demonstrated the value of precise and homogeneous stellar parameters. I will discuss implications of the radius distribution and our ongoing and complimentary work to measure the frequency of giant planets orbiting well beyond the snow line. The occurrence of close-in planets from Kepler combined with the latest results from long-baseline radial velocity surveys allow us to construct a comprehensive picture of planetary system architectures spanning three orders of magnitude in orbital separation and planet mass.
KICP seminar: Jessica M Turner (Fermilab)
12:00–1:00 pm ERC 401
“Heavy neutrinos and their role in the early Universe”
KICP colloquium: Abigail Crites (University of Toronto)
3:30–4:30 pm ERC 161
“Measuring the Epoch of Reionization with Line Intensity Mapping using TIME”
Special A&A Colloquium: Jaehan Bae (Carnegie Institution of Washington)
12:00–1:00 pm ERC 576
Toward a More Complete Picture of Planet Formation
Abstract: The studies of planet formation have long been dominated by theoretical work because observing planets in formation has been challenging. The situation is, however, gradually changing. Thanks to increasingly powerful observing facilities and techniques, we are now able to peer into the birthplaces of planets - protoplanetary disks, routinely finding signposts of ongoing planet formation. I will introduce state-of-the-art observations of protoplanetary disks, made available by the Atacama Large Millimeter/submillimeter Array and ground-based optical/IR telescopes equipped with adaptive optics. I will discuss how planet formation theories are being tested with and improved by observational data in conjunction with supercomputer simulations. I will conclude with a discussion of prospects for future directions, focusing on how we can connect studies of protoplanetary disks to those of solar and extrasolar planetary systems and develop a more complete picture of planet formation.
KICP seminar: Raymond T Co (University of Michigan)
12:00–1:00 pm ERC 401
“X-ray Search for Axions from Nearby Isolated Neutron Stars”
KICP open group seminar: Ethan Nadler (Stanford University)
1:30–2:30 pm ERC 401
“The Galaxy—Halo Connection Including the Impact of the Large Magellanic Cloud”
Special A&A Colloquium: Alexander Ji (Carnegie Observatories)
3:30–4:30 pm ERC 161
Accessing the First Stars and Galaxies with Near-Field Cosmology
In the first billion years of the universe, stars and galaxies formed in the smallest dark matter halos, produced high-energy photons that reionized the intergalactic medium, and polluted the universe with the first heavy elements. Near-field cosmology probes this early era by observing nearby relic galaxies that have survived from ancient times. In particular, the elemental abundances of their old, metal-poor stars encode otherwise inaccessible information about the first stellar populations and first galaxy formation histories. Decoding these abundances requires connecting nuclear and stellar astrophysics to galaxy formation and hierarchical assembly. In this talk, I will use elements synthesized in the rapid neutron-capture process (r-process) to illustrate how I have used stellar abundances in dwarf galaxies to study the first stars and galaxies. My work has shaped our current understanding of the origin of r-process elements, informed future multi-messenger observations of neutron star mergers, produced unique constraints on gas dynamics in the first galaxies, and now enables reconstruction of the hierarchical assembly of our Milky Way’s stellar halo. I will conclude with a blueprint for how to measure the old stellar populations and early star formation histories of galaxies across the Local Group, making near-field cosmology an observational pillar for accessing the high-redshift universe.
Special A&A Colloquium: Matteo Fasiello (University of Portsmouth)
12:00–1:00 pm ERC 401
Probing Inflation with Primordial Messengers
Some of our best ideas on early universe physics are about to be put to the test by an unprecedented array of cosmological probes. The data these will collect span a vast range of scales, from the CMB to large scale structure, from pulsar timing arrays all the way to laser interferometers. This combined wealth of new information holds the potential to transform not just our understanding of cosmology, but also particle physics. Probing the earliest accessible epoch, the accelerated expansion known as inflation, is absolutely crucial: inflation can provide a cosmological portal to otherwise unaccessible energy scales. This is the “cosmological collider” idea. The spectacular success of the inflationary paradigm in explaining the origin of cosmic structure demands that we tackle a number of compelling questions still in need of an answer: what is the energy scale of inflation? what fields were active during inflation?
In this talk I will review recent progress on the inflationary field content. I will survey different approaches to address the most pressing challenges and provide examples including axion-inflation models and the so-called effective theory approach. I will then focus on the key observables, starting with primordial gravitational waves, and discuss their prospects for detection.