Thu 23 May 16:00: Some Disassembly Required
Planetary systems are shaped as much by destructive processes— N-body instabilities, catastrophic impacts, and atmospheric loss— as by accretionary ones. We examine the histories of violence written in: (a) the orbital architectures of super-Earths and sub-Neptunes; (b) the scattered light morphologies of debris disks; (c) chondritic meteorites and high-temperature minerals in comets; and (d) the chaotically variable light curves of disintegrating planets.
- Speaker: Eugene Chiang, Professor of Astronomy and Earth & Planetary Science, University of California, Berkeley
- Thursday 23 May 2024, 16:00-17:00
- Venue: Hoyle Lecture Theatre, Institute of Astronomy.
- Series: Institute of Astronomy Colloquia; organiser: .
Thu 30 May 16:00: New results about black hole feedback in galaxy clusters
Clusters of galaxies serve as excellent laboratories for exploring the physics of black hole feedback, illustrating how AGN -driven jets can deliver substantial energy to their surroundings via shock fronts, sound waves, and turbulence. These jets can also drive powerful molecular outflows and expel metals from galaxies. In this talk, I will review the current state of the field, focusing on how these powerful AGN -driven jets influence the properties of galaxy clusters over cosmic time. Additionally, I will present new observations of the giant multiphase nebula within the Perseus galaxy cluster and share insights into the pivotal role machine learning can—and will—play in advancing our understanding of galaxy clusters.
- Speaker: Julie Hlavacek-Larrondo, Université de Montréal
- Thursday 30 May 2024, 16:00-17:00
- Venue: Hoyle Lecture Theatre, Institute of Astronomy.
- Series: Institute of Astronomy Colloquia; organiser: .
Mon 20 May 13:00: Cosmology with the CMB: from Planck to SPT-3G
The observation of the Cosmic Microwave Background (CMB) is one of the most powerful probes of our universe. ESA ’s Planck satellite confirmed that the ΛCDM model works astonishingly well to describe the CMB anisotropies, measuring cosmological parameters with percent-level accuracy. Nevertheless, the Planck results reveal a number of outstanding inconsistencies that might hint at cracks in this very successful model. The most critical one is the Hubble tension, the difference between the expansion rate of the universe measured by the CMB and other early universe probes, versus the rate measured by Type Ia supernovae calibrated with Cepheids. In this talk I will present the current efforts to shed light on these problems using the South Pole Telescope. SPT is a ground-based CMB experiment which is observing the sky with its latest camera, SPT -3G. It is expected to provide ground-breaking CMB measurements over 25% of the sky. I will show SPT -3G early results, the several innovations we are introducing in the analysis pipeline for our upcoming second data release, and the expectations for the future.
- Speaker: Silvia Galli (Institut Astrophysique de Paris)
- Monday 20 May 2024, 13:00-14:00
- Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
- Series: Cosmology Lunch; organiser: Fiona McCarthy.
Tue 28 May 13:00: Phenomenology of axion-gauge field interactions in the early universe
In this talk, I will give a brief overview of my work on the phenomenology of axion-gauge interactions in the early universe. Couplings between axion-like particles (ALPs) and gauge fields arise naturally in UV-complete theories such as string theory. Moreover, their phenomenology is rich and potentially within reach of current or future experimental probes. For the aforementioned reasons there has been a considerable and systematic effort to uncover the phenomenology of such couplings and I will be providing a review of past results with a focus on couplings between axions and massless U(1) gauge fields as well as SU(2) gauge fields (chromo-natural inflation etc.). In the context of inflation, these models in particular produce strong gravitational waves, potentially observable with current of future interferometers or PTA experiments. Additionally, they predict strongly sourced scalar perturbations, scalar induced gravitational waves, primordial black holes and more. Finally, I will emphasize a regime of these models which is only recently beginning to be explored, namely the “strong backreaction” regime and give a detailed breakdown of the unique signatures of such a regime during infllation.
- Speaker: Alexandros Papageorgiou (IFT, Madrid)
- Tuesday 28 May 2024, 13:00-14:00
- Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
- Series: Cosmology Lunch; organiser: Thomas Colas.
Fri 24 May 11:30: The Extremes of Resolved Stellar Spectroscopy
The study of local star clusters and galaxies with existing spectroscopic instruments and techniques has reached the point of diminishing returns. Breakthroughs require new instruments or innovation in spectral analysis. I will describe the measurement of radial velocities and abundances of individual stars at the threshold of spectral resolution and signal-to-noise ratio. First, I will address measurements from Keck/DEIMOS and KCWI . I will discuss the “backsplash” galaxy Andromeda XVIII (at 1.33 Mpc!), neutron-capture abundances in Milky Way satellites, and the “fundamental” stellar mass-stellar metallicity relation of low-mass field galaxies. New spectrograph innovations, like the upgrade to DEIMOS and the Subaru Prime Focus Spectrograph, will lead stellar spectroscopy into the future.
- Speaker: Evan Kirby (Notre Dame)
- Friday 24 May 2024, 11:30-12:30
- Venue: Ryle seminar room + online.
- Series: Galaxies Discussion Group; organiser: Sandro Tacchella.
Tue 21 May 11:15: Diffusion meets Nested Sampling
Sampling techniques are a stalwart of reliable inference in the physical sciences, with the nested sampling paradigm emerging in the last decade(s) as a ubiquitous tool for model fitting and comparison. Parallel developments in the field of generative machine learning have enabled advances in many applications of sampling methods in scientific inference pipelines. This work explores the synergy of the latest developments in diffusion models and nested sampling. I will review the challenges of precise model comparison in high dimension, and explore how score based generative models can provide a solution. This work builds towards a public code that can apply out of the box to many established hard problems in fundamental physics, as well as providing potential to extend precise inference to problems that are intractable with classical methods. I will motivate some potential applications at the frontiers of inference that can be unlocked with these methods.
- Speaker: David Yallup (University of Cambridge)
- Tuesday 21 May 2024, 11:15-12:00
- Venue: Coffee area, Battcock Centre.
- Series: Hills Coffee Talks; organiser: David Buscher.
Tue 21 May 13:00: Exploring the atmospheric structure of water-rich sub-Neptunes
Population studies and planetary formation models predict a class of water-rich sub-Neptunes consisting of a rocky core overlain by a water-rich envelope. Characterising such planets is difficult since differing interior structures often lead to degenerate mass and radii. Recent JWST observations aim to break some of these degeneracies by retrieving atmospheric composition, however accurate atmospheric models are required to interpret data. For example, separate analyses of the JWST transmission spectrum of water world candidate TOI -270 d predicted different interior structures – a “Hycean world” scenario with a liquid water surface and a “miscible sub-Neptune” where the water in the envelope is in a supercritical state. To distinguish these scenarios, I have developed a radiative-convective model specifically designed to model water-rich sub-Neptunes. In particular, the model accounts for the inhibition of convection due to mean molecular weight gradients induced by the condensation of water vapour in a less dense background gas. I show that this can warm a liquid water surface significantly, moving the traditional habitable zone of the planet outwards and disfavouring the presence of water oceans for sub-Neptunes with Earth-like instellations. Following on from this, I will explore the possible equilibrium states of a sub-Neptune with a supercritical water envelope. Lastly, I will discuss attempts to decipher whether sub-Neptunes have surfaces using atmospheric chemistry and the implications this has on interpreting present and future observations.
- Speaker: Hamish Innes (Freie Universität - Berlin)
- Tuesday 21 May 2024, 13:00-14:00
- Venue: Hoyle Committee Room + ONLINE - Details to be sent by email.
- Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.
Mon 20 May 14:00: A large-scale dynamo via MRI-driven alpha Omega dynamo in binary neutron star mergers
We challenge the magnetar scenario for short gamma-ray bursts by performing a high-resolution neutrino magnetohydrodynamics numerical relativity simulation of a binary neutron star merger. We find the alpha Omega dynamo mediated by the magnetorotational instability generates the large-scale magnetic field in the merger remnant. The resultant large-scale field is efficiently wrapped and drives a relativistic Poynting-flux dominated outflow from the merger remnant.
- Speaker: Kenta Kiuchi (Max Planck Institute for Gravitational Physics)
- Monday 20 May 2024, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.
Tue 21 May 12:00: The dynamics of parsec-scale eccentric stellar disks around SMBHs in galactic nuclei: disk disruption mechanisms, tidal disruption events and milliparsec stars
We study the dynamics of eccentric parsec-scale stellar disks around supermassive black holes (SMBHs) in galactic nuclei using our novel post-Newtonian N-body code BIFROST . The simulated eccentric disks (Mdisk
- Speaker: Antti Rantala (Max Planck Institute for Astrophysics)
- Tuesday 21 May 2024, 12:00-13:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Thomas Jannaud.
Tue 21 May 12:00: The dynamics of parsec-scale eccentric stellar disks around SMBHs in galactic nuclei: disk disruption mechanisms, tidal disruption events and milliparsec stars
We study the dynamics of eccentric parsec-scale stellar disks around supermassive black holes (SMBHs) in galactic nuclei using our novel post-Newtonian N-body code BIFROST . The simulated eccentric disks (Mdisk
- Speaker: Antti Rantala (Max Planck Institute for Astrophysics)
- Tuesday 21 May 2024, 12:00-13:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Thomas Jannaud.
Fri 17 May 11:30: Machine Learning enhanced Bayesian Workflows for Galaxies
Abstract not available
- Speaker: Harry Bevins (KICC)
- Friday 17 May 2024, 11:30-12:30
- Venue: Ryle seminar room + online.
- Series: Galaxies Discussion Group; organiser: Sandro Tacchella.
Thu 13 Jun 16:00: Title to be confirmed
Abstract not available
- Speaker: Georges Maynet (Geneva)
- Thursday 13 June 2024, 16:00-17:00
- Venue: Hoyle Lecture Theatre, Institute of Astronomy.
- Series: Institute of Astronomy Colloquia; organiser: eb694.
Fri 12 Jul 11:30: Title to be confirmed
Abstract not available
- Speaker: Suhail Dhawan (KICC)
- Friday 12 July 2024, 11:30-12:30
- Venue: Ryle seminar room + online.
- Series: Galaxies Discussion Group; organiser: Sandro Tacchella.
Fri 06 Sep 11:30: Title to be confirmed
Abstract not available
- Speaker: Mark Krumholz (ANU)
- Friday 06 September 2024, 11:30-12:30
- Venue: Ryle seminar room + online.
- Series: Galaxies Discussion Group; organiser: Sandro Tacchella.
Wed 15 May 13:15: Prototyping a Sparse-Aperture, Segmented, Parabolic Primary Mirror Telescope for SUPERSHARP
The motivation for my research comes from the SUPERSHARP mission concept for large, unfolding, lightweight space telescopes which take advantage of unfolding segmented optics and a sparse aperture primary mirror to generate powerful observations while maintaining limited cost, mass, and volume requirements. The original motivation for the SUPERSHARP design comes from the ongoing search for life in the universe, but the technology has wider applications in both space and Earth observation. Prototyping of the optical system is integral to ensuring technological readiness of key aspects of the telescope design – in particular, the active control and maintenance of optics alignment. In this talk, I will present the work I have done designing and building a prototype of a sparse-aperture, segmented, parabolic primary mirror telescope using two mirror segments. I will also outline the immediate improvements and next steps required for the prototype to more accurately model an effective imaging system.
- Speaker: Zoe Horvath
- Wednesday 15 May 2024, 13:15-13:40
- Venue: The Hoyle Lecture Theatre + Zoom .
- Series: Institute of Astronomy Seminars; organiser: .
Fri 17 May 13:00: Non-smooth horizons in Kerr black hole mergers
Dynamical black holes are known to develop non-smooth structures on their horizon. We begin by reviewing a classification of all generic non-smooth structures that may appear on black hole horizons in four-dimensional spacetimes. Introducing a time function, we describe how two of these features – namely creases and caustics – evolve, and in particular discuss processes known as ‘perestroikas’, where the non-smooth structure on a horizon cross-section changes qualitatively. We then study the merger of two Kerr black holes in the extreme mass ratio limit, and focus on the creases and caustics that are present on the horizon. We explain how our results differ from an older analysis of the same system by Emparan et al., and show that these novel results are consistent with the properties of creases expected generically. This talk is based on work done with Harvey Reall and Robie Hennigar.
- Speaker: Maxime Gadioux, DAMTP, University of Cambridge
- Friday 17 May 2024, 13:00-14:00
- Venue: Potter room/Zoom.
- Series: DAMTP Friday GR Seminar; organiser: Xi Tong.
Tue 14 May 13:00: Attractor reconstruction of active stellar light curves
Stellar activity is notoriously difficult to model, being neither periodic nor purely stochastic. In light curves, the interplay between the stellar rotation period and the birth and death of spots and faculae gives rise to quasi-periodic modulation over time scales of hours to weeks. Despite the complexity of this interplay, the resulting light curves bear strong qualitative resemblance to systems known to exhibit low-dimensional dynamical chaos, such as the Rössler attractor.
In the 1980s and 1990s, a suite of techniques for nonlinear dynamical analysis, called attractor reconstruction, evolved to study exactly this type of system. Attractor reconstruction works by embedding a 1-dimensional time series, such as stellar light curve, in a higher-dimensional phase space capable of capturing its full dynamical behavior: too low a dimensionality, and the system’s trajectory will self-intersect and tangle, which we know to be physically unrealistic given the non-periodicity of the observed signal. This technique has been used successfully to model the historical sunspot record and the light curves of variable stars (both simulated and observed) and to recover important features of their underlying dynamics, including their dimensionality and the time scales over which they can be meaningfully forecast into the future. Here, I discuss the application of attractor reconstruction to the light curve of the Sun over Solar cycles 23-25, as observed by the Solar and Heliospheric Observatory.
- Speaker: Emily Sandford (Cavendish)
- Tuesday 14 May 2024, 13:00-14:00
- Venue: Ryle seminar room + ONLINE - Details to be sent by email.
- Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.
Mon 13 May 14:00: Convection, waves and mixing in stars: insights and challenges from numerical simulations
The lifecycle of stars is profoundly shaped by the internal transport and mixing of chemical elements. Within most stars, regions of convective motions and stable stratification coexist, separated by so-called convective boundaries. While convective regions are very efficient at mixing chemical species, stably stratified regions mostly inhibit the vertical transport of elements. Current models suggest that mixing beyond convective regions is needed to explain observed stellar properties. Waves, excited by convection at convective boundaries, could play a crucial role by providing additional mixing in the vertical direction.
In this talk, I will highlight results from recent numerical simulations with the MUSIC code on the study of waves, convection, and mixing in stars. I will discuss challenges in measuring vertical mixing and transport by waves in numerical simulations, and present some prospects for improving our understanding of mixing mechanisms through numerical experiments.
- Speaker: Thomas Guillet (Exeter)
- Monday 13 May 2024, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.
Fri 14 Jun 11:30: Title to be confirmed
Abstract not available
- Speaker: Sergio Martin Alvarez (Stanford)
- Friday 14 June 2024, 11:30-12:30
- Venue: Ryle seminar room + online.
- Series: Galaxies Discussion Group; organiser: Sandro Tacchella.
Fri 14 Jun 13:00: TBC
TBC
- Speaker: William Biggs, DAMTP, University of Cambridge
- Friday 14 June 2024, 13:00-14:00
- Venue: Potter room/Zoom.
- Series: DAMTP Friday GR Seminar; organiser: Xi Tong.
