Harald Pfeiffer (Max Planck Institute for Gravitational Physics, Potsdam)
Gravitational waves from neutron star-black hole binaries
Friday, July 2nd, 2021, 11am – streaming

Abstract The LIGO and Virgo Gravitational wave detectors operated at higher than ever sensitivity during their third observing run, which lasted from 2019 to 2020. Several notable gravitational wave detections were already announced, while some of the recorded data is still being analysed. In this colloquium, I will give an overview of the most exceptional gravitational wave events that have been published so far.

Contact: Enrico Barausse
VideoHarald Pfeiffer’s webpage

Luigi Iapichino (Leibniz-Rechenzentrum, Garching)
Quantum Computing and its potential applications in astrophysics and astronomy
Friday, June 18th, 2021, 11am – streaming

Abstract Quantum Computing (QC) is a computing paradigm with disruptive potential in many areas of computational sciences and large projected impact in industry and society. In my talk I will provide a general overview of the main concept of QC and how it can be integrated into the HPC ecosystem as a suitable tool for astronomy and astrophysics. Although application areas in these disciplines have to be identified yet, a few promising directions will be presented and discussed.

Contact: Stefano Borgani
VideoSlidesLuigi Iapichino’s website – Slides

Elisabeth Krause (University of Arizona)
Recent cosmology results from the Dark Energy Survey
Friday, June 4th, 2021, 11am – streaming

Abstract Over the next decade, large galaxy surveys will map billions of galaxies and probe cosmic structure formation with high statistical precision. This talk will focus on the opportunities and challenges of cosmological analyses in the presence of complex systematic effects, using recent results from the Dark Energy Survey as pathfinder examples. In particular, I will describe different cosmological probes measured from DES data and summarize recent analyses combining galaxy clustering, weak lensing, cluster clustering and cluster abundances, as well as constraints on baryons and galaxy biasing from small scales.

Contact: Alex Saro, Emiliano Sefusatti
VideoElisabeth Krause’s Website

Alis Deason (Durham University)
The Edge of the Galactic Halo
Friday, May 21st, 2021, 11am – streaming

Abstract We are currently witnessing a golden age in Galactic halo science. Largely thanks to the Gaia mission, we now have phase-space plus chemical information for significant numbers of halo stars, globular clusters, and satellite dwarf galaxies in the Milky Way. I will discuss recent results utilizing the dynamics of these halo populations to i) measure the total Milky Way mass, and ii) measure the edge of the Galactic halo. This latter quantity is closely related to the physical boundary of the dark matter halo, and I will discuss how the stellar edge depends on the halo mass and assembly history. Finally, I address how unusual the Milky Way’s assembly history is, and relate this to the search for Milky Way mass progenitors with the James Webb Space Telescope.

Contact: Piero Ullio
VideoSlidesAlis Deason’s Website

Tim Linden (Stockholm University)
Thermal WIMPs on the Brink
Friday, May 7th, 2021, 11am – streaming

Abstract Weakly Interacting Dark Matter Particles (WIMPs) are among the most well-motivated models for particle dark matter. While these particles can be detected through direct, indirect, or collider experiments, only their indirect annihilation produces a guaranteed signal. Intriguingly, experimental searches using both gamma-rays and cosmic-rays are beginning to close in on this coveted “thermal annihilation cross-section”. Intriguingly, several excesses in Galactic center gamma-rays and cosmic-ray antiprotons have been discovered. Even more intriguingly, these excesses may be consistent with each other. In this talk, I will summarize the current state of the field, and argue that there is hope of resolving this puzzle within the next five years.

Contact: Piero Ullio
VideoSlidesTim Linden’s webpage

Elisa Chisari (Utrecht University)
Galaxy Shapes as a Cosmological Tool
Friday, April 23rd, 2021, 11am – streaming

Abstract Two phenomena contribute to correlating galaxy shapes across the Universe: the deviation of photons from a straight path due to the spacetime curvature (“gravitational lensing”), and “ intrinsic alignments” from physical interactions (e.g. gravitational tides). Modeling both accurately is crucial to obtaining unbiased constraints on the cosmological model from forthcoming surveys, particularly in the context of elucidating the origin of accelerated expansion of the Universe. In this talk, I will cover recent advances in our understanding of the intrinsic alignments of galaxies. While these alignments are typically regarded as a contaminant to gravitational lensing, I will also discuss how they might become a cosmological and astrophysical probe in their own right in the near future.

Contact: Paolo Creminelli
VideoSlidesElisa Chisari’s webpage

Laura Wolz (University of Manchester)
Cold gas constraints via HI Intensity Mapping
Friday, April 9th, 2021, 11am – streaming

Abstract Intensity mapping surveys of neutral hydrogen (HI) are a new way to measure the large-scale matter distribution of our Universe over a wide range of redshifts, and thus constrain cosmological parameters describing the Universal expansion. The next generation of radio telescopes and interferometers are being designed and built to optimise the detection of the HI line at low spatial resolution allowing efficient mapping of large volumes. The impact of instrumental systematics of radio observations on cosmological measurements can be significantly reduced by cross-correlating the HI signal with galaxy surveys. The cross-correlation also offers new ways to measure correlations between HI and properties of the optically-selected galaxy samples. I will give an introduction into the HI intensity mapping technique and prospects of the on-going and future experiments, such as the Square Kilometre Array (SKA). I will showcase studies on the potential of future intensity mapping experiments in constraining HI properties, such as the global HI density as well as HI scaling relations in galaxies. I will also present the latest HI intensity mapping detection of Green Bank Telescope data in cross-correlation with the SDSS eBOSS galaxy survey samples.

Contact: Marta Spinelli
VideoSlidesLaura Wolz’s webpage

Enrico Pajer (DAMTP, University of Cambridge)
A Timeless History of Time
Friday, March 26th, 2021, 11am – streaming

Abstract We have overwhelming evidence that the distribution of everything on very large scales is of primordial origin, i.e. it was determined in the first fraction of a second of the Big Bang. According to the leading paradigm of inflation, the statistics of these primordial perturbations can be traced back to correlators of quantum fields on a curved quasi-de Sitter spacetime. This gives us the unique opportunity to probe the fundamental laws of physics at very high energies as well as the perturbative regime of quantum gravity.
Unfortunately, due to the creativity of theorists and the paucity of data about the primordial universe, there is a huge number of models compatible with all measurements, featuring a wide variety of mechanisms, symmetries, and spectra of particles.The reason can be traced back to the fact that we don’t observe the time evolution during inflation, but only its final outcome.
In this talk I will report on the recent progress in developing a completely new “bootstrap” approach to derive predictions from the very early universe that make no reference to time and the un-observable time evolution. The bootstrap approach builds directly upon the fundamental pillars of physics, namely unitarity, locality and symmetries and is highly model independent. I will show how these principles can be used to derive many well-known and new inflationary predictions associated with primordial non-Gaussianity in a way that is both computationally simpler and conceptually more transparent.

Contact: Paolo Creminelli
VideoSlidesEnrico Pajer’s webpage

Simeon Bird (UC Riverside)
Simulations of Cosmological Structure and Machine Learning
Friday, March 12th, 2021, 5pm – streaming

Abstract The large scale distribution of gas in the Universe contains the answers to many mysteries, such as the nature of dark matter, the sources of ionizing photons, and global trends in star formation. Cosmological simulations are the only way to understand these questions. I will talk about our current simulation models, especially our implementation of helium reionization and massive neutrinos, as well as the way in which we combine simulations to infer the properties of the physics of the Universe. I will close by discussing a new machine learning technique for increasing the effective size of each simulation.

Contact: Elisa Boera
VideoSlidesSimeon Bird’s webpage

Volker Springel (Max-Planck-Institute for Astrophysics, Garching)
Supercomputer insights into the messy physics of galaxy formation
Friday, February 26st, 2021, 11am – streaming

Abstract Simulations of cosmic structure formation have come a long way. Nowadays, they are not only accurately predicting the dark matter backbone of the cosmic web and the internal structure of halos and their satellites far into the non-linear regime, but are also capable of following the baryonic sector with rapidly improving physical fidelity. In my talk, I will review the methodology and selected successes of recent hydrodynamical galaxy formation simulations, and critically discuss some of the primary uncertainties in modelling strong, scale-dependent feedback processes. I will also highlight predictions for the structure of magnetic fields in galaxies and the importance of cosmic rays in galaxy evolution. Finally, I discuss some of the challenges lying ahead in this field in the coming years.

Contact: Matteo Viel
VideoSlidesVolker Springel’s webpage

Anna Franckowiak (DESY & Ruhr University, Bochum)
Neutrino astronomy with IceCube
Friday, February 12th, 2021, 11am – streaming

Abstract High-energy neutrinos are solely produced in interactions of cosmic rays with ambient matter or photon fields and are therefore a smoking-gun signature for hadronic acceleration. A diffuse flux of cosmic neutrinos was first discovered by the cubic-kilometer-sized IceCube detector located at the South Pole in 2013. I will present the ongoing search for the origin of those neutrinos and discuss promising candidate sources including the gamma-ray blazar TXS 0506+056, the tidal disruption event AT2019dsg and the nearby Seyfert galaxy NGC 1068.

Contact: Gabrijela Zaharijas
VideoSlidesAnna Franckowiak’s Multi-Messenger Group

Josquin Errard (CNRS, APC Paris)
Future observations of the primordial, polarized Cosmic Microwave Background: expected science and challenges
Friday, January 29th, 2021, 11am – streaming

Abstract Testing inflation has become one of the main goals in observational cosmology, and one of the scientific priorities for the new generation of Cosmic Microwave Background projects. A race to more sensitive focal planes, combined to a high control of the instrumental and astrophysical systematic effects, is at play across the globe. In this talk, I will review some of the current and future observational efforts which are all aiming at detecting the inflationary, primordial gravitational waves. I will provide more details on two of them: the Simons Observatory, which will achieve its first light in 2021-2022, and the LiteBIRD satellite, expected to be launched in 2028. I will finally illustrate some of the current challenge that the scientific community has to face, and its plans to overcome them.

Contact: Davide Poletti
VideoSlidesJosquin Errard’s webpage

Subir Sarkar (Oxford University)
Reexamining Cosmic Acceleration
Friday, December 18th, 2020, 11am – streaming

Abstract Type Ia supernovae are standard(isable) candles so observing them out to cosmological distances reveals the change of the Hubble parameter with redshift. Such observations have been interpreted to mean that the expansion rate of the universe is accelerating, as if driven by a Cosmological Constant. However reanalysis of the data shows that the inferred cosmic acceleration is anisotropic and aligned with the CMB dipole. Moreover the usual kinematic interpretation of the CMB dipole is suspect since the corresponding dipole in the distribution of distant quasars is much bigger than is expected. Possible reasons for these surprising findings will be discussed.

Contact: Paolo Molaro
VideoSlidesSubir Sarkar’s webpage

Michael Murphy (Swinburne University of Technology)
Testing Fundamental Physics with Solar Twin Stars
Friday, November 20th, 2020, 11am – streaming

Abstract The Standard Model of nature’s laws cannot explain fundamental constants, like electromagnetism’s strength, alpha. Therefore, searches for variations in alpha are key tests of new physics. Using twins of our Sun – a new probe that unlocks a 100-fold sensitivity gain – we aim to test alpha’s constancy across our Galaxy in a new project. By discovering distant solar twins, we will probe alpha in regions of very different Dark Matter density, which opens an unexplored discovery space. Utilising new and existing high-precision instruments at the European Southern Observatory, we expect to make the most precise astronomical measurement of a fundamental constant, and obtain the first test of variations in alpha across our Galaxy’s Dark Matter field. As background, I will first review the observational status of the quasar absorption line searches for cosmological variations in alpha, then outline our solar twin methods and provide the first results from local solar twins which will act as a reference sample for testing alpha’s constancy across the Milky Way.

Contact: Valentina D’Odorico
VideoMichael Murphy’s webpage

Dimitrios Psaltis (University of Arizona)
Testing General Relativity with the Event Horizon Telescope
Friday, September 25th, 2020, 5pm – streaming

Abstract The imaging of black-hole shadows with the Event Horizon Telescope has opened a new window into the strong-field spacetimes of these extreme astrophysical objects. For the Kerr spacetime, the shadow of a black hole is nearly circular with a size that depends almost entirely on its mass. I will discuss first the astrophysics of shadow formation in the images of black holes and the properties of the EHT data that allow us to perform null-hypothesis tests of General Relativity. I will discuss metrics that deviate from Kerr and their signatures related to the shapes and sizes of black-hole shadows. I will conclude with a prognosis on what ground-based observations of shadows can tell us about black-hole metrics and the underlying theory of gravity.

Contact: Enrico Barausse
VideoSlidesDimitrios Psaltis’ webpage