Mon 28 Apr 13:00: String axions: the hot and the fuzzy
String axions have been proposed as candidates for solving several puzzles in cosmology. In this talk, I will focus on axions as dark matter. After reviewing how string axions can occur in our universe, I will provide a string theoretical explanation of dark matter as composed of axions coming from type IIB string theory. Based on the latest bounds, I will show how likely it is for dark matter to be composed of such particles and in which abundance, and I will provide predictions on the preferred ranges of masses and decay constants. On the contrary, requiring the axions to lie in a particular range of the parameter space imposes constraints on the UV theory. I will focus both on the role of moduli stabilization and the landscape of string vacua. Finally, I will discuss axion production at the end of inflation and the implications for the proposed cosmic axion background.
- Speaker: Nicole Righi (King's College London)
- Monday 28 April 2025, 13:00-14:00
- Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
- Series: Cosmology Lunch; organiser: Thomas Colas.
Wed 14 May 16:00: Spacetime Singularities and Black Holes
After a brief introduction to Einstein’s theory of general relativity and its most profound prediction of black holes, I will focus on spacetime singularities, i.e., regions where general relativity breaks down and must be replaced by a quantum theory of gravity. I first discuss singularities inside black holes. This is the usual case and is an old story, but there have been some recent developments. I will next describe some new results which show that some black holes have singularities on their surface. Finally, I will discuss the possibility of singularities outside black holes.
- Speaker: Professor Gary Horowitz - University of California, Santa Barbara
- Wednesday 14 May 2025, 16:00-17:00
- Venue: MR3.
- Series: Theoretical Physics Colloquium; organiser: Amanda Stagg.
Tue 15 Apr 11:00: Growing pains: the dining habits of stars, planets and black holes
To make planets, stars and supermassive black holes, one must rapidly accrete material onto central objects. But the tiniest tangential motion combined with angular momentum conservation sends material into orbit, rather than accreting. Since work at the IoA in the 1970s we have understood that Nature solves the angular momentum problem by forming accretion discs, but the angular momentum transport mechanism remains unclear. The past 10 years have given us spectacular resolved observations of discs around both young and old stars, bringing fresh clues. In this talk I’ll explain how pairing 3D simulations with observations helps us solve the problem of accretion, revealing how stars and planets form, black holes grow and how accretion powers tidal disruption events.
- Speaker: Daniel Price, Monash University
- Tuesday 15 April 2025, 11:00-12:00
- Venue: The Hoyle Lecture Theatre + Zoom .
- Series: Institute of Astronomy Seminars; organiser: Cristiano Longarini.
Fri 09 May 11:30: How do the most luminous black holes accrete and expel gas?
The gravitational pull of a black hole attracts gas and forms an accretion disk where the interplay between hydromagnetic processes and the warping of space-time releases gravitational energy in the form of radiation, relativistic jets, and winds. Most gas falls into supermassive black holes when the accretion rate approaches the Eddington limit (L=Ledd), at which point radiation pressure overcomes gravity. To date, our knowledge of such `luminous’ black hole accretion disks mostly relies on semi-analytical models, supplemented by a limited set of numerical simulations. In my talk I will discuss new insights gained from state-of-the-art radiative general relativistic magnetohydrodynamics (GRMHD) simulations of accretion near the Eddington limit such as the formation of a hot corona, disk truncation, and other physical processes driving the spectral evolution of luminous black holes. I will finish my talk by discussing the challenges and opportunities the next-generation of GRMHD simulations will bring in developing a comprehensive understanding of black hole accretion across the luminosity spectrum.
- Speaker: Matthew Liska (Georgia Tech)
- Friday 09 May 2025, 11:30-12:30
- Venue: Hoyle Lecture Theatre .
- Series: Galaxies Discussion Group; organiser: Sandro Tacchella.
Tue 27 May 11:15: JAX-powered Bayesian anomaly detection for supernovae analysis
Abstract TBC
- Speaker: Samuel Leeney (University of Cambridge)
- Tuesday 27 May 2025, 11:15-12:00
- Venue: Martin Ryle Seminar Room, Kavli Institute.
- Series: Hills Coffee Talks; organiser: Charles Walker.
Tue 15 Apr 11:00: Growing pains: the dining habits of stars, planets and black holes
To make planets, stars and supermassive black holes, one must rapidly accrete material onto central objects. But the tiniest tangential motion combined with angular momentum conservation sends material into orbit, rather than accreting. Since work at the IoA in the 1970s we have understood that Nature solves the angular momentum problem by forming accretion discs, but the angular momentum transport mechanism remains unclear. The past 10 years have given us spectacular resolved observations of discs around both young and old stars, bringing fresh clues. In this talk I’ll explain how pairing 3D simulations with observations helps us solve the problem of accretion, revealing how stars and planets form, black holes grow and how accretion powers tidal disruption events.
- Speaker: Daniel Price, Monash University
- Tuesday 15 April 2025, 11:00-12:00
- Venue: The Hoyle Lecture Theatre + Zoom .
- Series: Institute of Astronomy Seminars; organiser: Cristiano Longarini.
Fri 13 Jun 13:00: TBC
Abstract not available
- Speaker: Panos Giannadakis, Queen Mary University of London
- Friday 13 June 2025, 13:00-14:00
- Venue: Potter room/Zoom.
- Series: DAMTP Friday GR Seminar; organiser: Xi Tong.
Fri 06 Jun 13:00: TBC
Abstract not available
- Speaker: Marica Minucci, Bohr Inst., Copenhagen
- Friday 06 June 2025, 13:00-14:00
- Venue: Potter room/Zoom.
- Series: DAMTP Friday GR Seminar; organiser: Xi Tong.
Fri 02 May 13:00: TBC
Abstract not available
- Speaker: David Hilditch, Lisbon
- Friday 02 May 2025, 13:00-14:00
- Venue: Potter room/Zoom.
- Series: DAMTP Friday GR Seminar; organiser: Xi Tong.
Fri 25 Apr 13:00: TBC
Abstract not available
- Speaker: Ali Akil, Hong Kong University
- Friday 25 April 2025, 13:00-14:00
- Venue: Potter room/Zoom.
- Series: DAMTP Friday GR Seminar; organiser: Xi Tong.
Tue 20 May 11:15: A 21-cm Cosmologist’s Journey: From Cambridge to North America and Back Again
Abstract TBC
- Speaker: Dr. Peter Sims (University of Cambridge)
- Tuesday 20 May 2025, 11:15-12:00
- Venue: Martin Ryle Seminar Room, Kavli Institute.
- Series: Hills Coffee Talks; organiser: Charles Walker.
Tue 27 May 11:15: Jax-powered Bayesian anomaly detection for supernovae analysis
Abstract TBC
- Speaker: Samuel Leeney (University of Cambridge)
- Tuesday 27 May 2025, 11:15-12:00
- Venue: Martin Ryle Seminar Room, Kavli Institute.
- Series: Hills Coffee Talks; organiser: Charles Walker.
Tue 20 May 11:15: TBC
TBC
- Speaker: Dr. Peter Sims (University of Cambridge)
- Tuesday 20 May 2025, 11:15-12:00
- Venue: Martin Ryle Seminar Room, Kavli Institute.
- Series: Hills Coffee Talks; organiser: Charles Walker.
Tue 27 May 11:15: Jax-powered Bayesian anomaly detection for supernovae analysis
TBC
- Speaker: Samuel Leeney (University of Cambridge)
- Tuesday 27 May 2025, 11:15-12:00
- Venue: Martin Ryle Seminar Room, Kavli Institute.
- Series: Hills Coffee Talks; organiser: Charles Walker.
Fri 11 Apr 11:30: Unveiling AGN Outflows: A High Resolution Morphological Study with LOFAR-VLBI
How AGN (Active Galactic Nuclei) feedback operates is one of the unsolved mysteries plaguing modern day astronomy. AGN outflows could explain how this feedback operates and, to investigate this, I use the [O III ] emission line as a tracer of ionised outflows. In this talk, I will present work investigating the link between low-frequency radio emission, using the LOFAR Two-meter Sky Survey Deep Fields at 144 MHz, and [O III ] kinematics, measured from SDSS spectroscopy, for a sample of optically selected AGN . We discover that radio detected AGN are more likely to host an [O III ] outflow compared to radio non-detected AGN . We observe a stronger broad, blue-shifted component in the radio-detected AGN , implying a profound link between low-frequency radio emission and [OIII] outflows. To further link AGN outflows to low-frequency radio emission, we harness the power of widefield VLBI (Very Long Baseline Interferometry) processing and imaging by incorporating the international stations of LOFAR into the data reduction process, to obtain sub-arcsecond radio images. To conclude this talk, I will present the first 0.3” resolution image at 144 MHz of the Boötes Deep Field and early results linking high resolution radio morphologies at 144 MHz to the presence of [O III ] outflows.
- Speaker: Emmy Escott (Durham)
- Friday 11 April 2025, 11:30-12:30
- Venue: Ryle Seminar Room, KICC + online.
- Series: Galaxies Discussion Group; organiser: Sandro Tacchella.
Thu 08 May 14:00: How common are misaligned accretion disks around black holes?
Accretion disks around black holes emit across the electromagnetic spectrum, providing a window into strong-field gravity and extreme plasma environments. By analyzing their light curves and spectra, astrophysicists aim to probe fundamental questions about relativistic dynamics and high-energy astrophysics. Traditionally, models of black hole accretion have assumed that the disk’s angular momentum is aligned with the black hole’s spin axis. However, both observations and theoretical considerations increasingly suggest that misalignment—or tilt—is common. In this talk, I will present new insights from cutting-edge radiative general relativistic magnetohydrodynamic (GRMHD) simulations of tilted accretion disks. These simulations reveal that radiative cooling can induce a dramatic nonlinear response: disk warping leads to tearing, breaking the flow into discrete, misaligned sub-disks. The resulting dynamics naturally drive disk precession, which may underlie the quasi-periodic oscillations frequently observed in X-ray binaries and active galactic nuclei. In the second part of the talk, I will question the prevailing view that accretion is primarily driven by magnetorotational instability (MRI)-induced turbulence. I will show that in tilted, warped disks, accretion can instead be mediated by large-scale hydrodynamic shocks—specifically, nozzle shocks—offering a possible explanation for rapid luminosity variability in certain active galactic nuclei.
- Speaker: Matthew Liska (Georgia Tech)
- Thursday 08 May 2025, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Loren E. Held.
Thu 10 Apr 11:30: Probing Black Hole Winds with SimBAL: Mapping the Physics of Broad Absorption Line Quasar Outflows KICC Special Seminar
Broad absorption line (BAL) quasars provide striking evidence of energetic winds driven by accreting supermassive black holes. These outflows are thought to play a crucial role in regulating black hole growth and the host star formation rate, as well as shaping the evolution of galaxies; however, their physical properties—such as radius and energetics—remain poorly constrained. Our group has developed SimBAL, a spectral synthesis tool that enables detailed, physically motivated modeling of BAL quasar spectra. It has allowed us to perform a detailed spectral analysis of a large sample of BAL quasars for the first time and to characterize multi-phase outflows in a quasar discovered at the Epoch of Reionization. I will demonstrate SimBAL’s unique strengths by discussing the results from several projects and how our group has taken a systematic approach to investigate the physics of black hole winds. Lastly, I will introduce the 4MOST–Gaia Purely Astrometric Quasar Survey, an upcoming spectroscopic survey uniquely designed to deliver the first large-scale, color-independent quasar reference sample.
KICC Special Seminar
- Speaker: Hyunseop (Joseph) Choi (Université de Montréal)
- Thursday 10 April 2025, 11:30-12:00
- Venue: Ryle Meeting Room, KICC.
- Series: Kavli Institute for Cosmology Seminars; organiser: Steven Brereton.
Thu 10 Apr 11:30: Probing Black Hole Winds with SimBAL: Mapping the Physics of Broad Absorption Line Quasar Outflows KICC Special Seminar
Broad absorption line (BAL) quasars provide striking evidence of energetic winds driven by accreting supermassive black holes. These outflows are thought to play a crucial role in regulating black hole growth and the host star formation rate, as well as shaping the evolution of galaxies; however, their physical properties—such as radius and energetics—remain poorly constrained. Our group has developed SimBAL, a spectral synthesis tool that enables detailed, physically motivated modeling of BAL quasar spectra. It has allowed us to perform a detailed spectral analysis of a large sample of BAL quasars for the first time and to characterize multi-phase outflows in a quasar discovered at the Epoch of Reionization. I will demonstrate SimBAL’s unique strengths by discussing the results from several projects and how our group has taken a systematic approach to investigate the physics of black hole winds. Lastly, I will introduce the 4MOST–Gaia Purely Astrometric Quasar Survey, an upcoming spectroscopic survey uniquely designed to deliver the first large-scale, color-independent quasar reference sample.
KICC Special Seminar
- Speaker: Hyunseop Choi (Université de Montréal)
- Thursday 10 April 2025, 11:30-12:00
- Venue: Ryle Meeting Room, KICC.
- Series: Kavli Institute for Cosmology Seminars; organiser: Steven Brereton.
Fri 04 Apr 11:30: The first stars: window to cosmic dawn
The era of cosmic dawn began with the first stars that formed in the Universe a mere 200 – 300 million years after the Big Bang. These stars produced the first supernovae and black holes, enriched the interstellar medium (ISM) with metals, were the building blocks of the first galaxies, and significantly contributed to cosmic reionization. However, compared to star formation and feedback in metal-rich environments today, the lack of direct observations at low metallicities as well as high redshifts has posed a significant challenge for understanding the physics behind their formation and evolution. In this talk, I will introduce POPSICLE , a new framework for high resolution simulations that caters to star formation and feedback in low metallicity ISM reminiscent of redshift > 10 galaxies. I will describe how incorporating the full spectrum of ISM physics coupled to stellar evolution is crucial to constrain the stellar initial mass function (IMF) and feedback in such environments. I will particularly focus on Population III stars, and discuss their potential as seed black holes in the early Universe. I will conclude by showcasing the capability of GPU -accelerated simulations to revolutionize our understanding of the astrophysics of cosmic dawn, and to bring theory at par with state of the art observations from JWST .
- Speaker: Piyush Sharda (Leiden)
- Friday 04 April 2025, 11:30-12:30
- Venue: Ryle Seminar Room, KICC + online.
- Series: Galaxies Discussion Group; organiser: Sandro Tacchella.
Mon 09 Jun 13:00: Title to be confirmed
Abstract not available
- Speaker: Etienne Camphuis (Institut d'Astrophysique de Paris)
- Monday 09 June 2025, 13:00-14:00
- Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
- Series: Cosmology Lunch; organiser: Louis Legrand.