Mon 20 Oct 13:00: What do acoustic scale observations tell us about dark energy?
I explore how cosmic microwave background (CMB) and baryon acoustic oscillation (BAO) measurements constrain cosmological models. The CMB angular scale provides robust constraints on the ratio of sound horizon to angular diameter distance, limiting possible deviations from the standard ΛCDM model. The null energy condition for a separate dark energy component imposes strict inequalities on BAO observables relative to ΛCDM predictions, restricting the freedom to fit new data within standard cosmological frameworks. I’ll discuss what this means for latest BAO results and other possible interpretations.
- Speaker: Antony Lewis (University of Sussex)
- Monday 20 October 2025, 13:00-14:00
- Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
- Series: Cosmology Lunch; organiser: Louis Legrand.
Mon 20 Oct 16:00: Dynamics of nearly isolated, lenticular vortices: From waves to bulk instabilities?
In geophysical and astrophysical settings, rotating stratified flows often exhibit large-scale, nearly isolated vortices. Examples include the Mediterranean eddies in the Atlantic ocean, or the Great Red Spot (GRS) in Jupiter. These vortices have been widely studied using shallow-water or quasi-geostrophic models for decades. In particular, these models have successfully explained why these vortices maintain nearly lenticular shapes through time. However, prior reduced models have a blind spot when it comes to predicting the internal dynamics of such vortices, despite the fact that they are far from being motionless in their bulk (e.g. as observed for the GRS ). Various instabilities may sustain small-scale turbulence and accelerate the decay of large-scale vortices on long time scales.
Here, I will present a reduced model accounting for the bulk dynamics of large-scale pancake-like vortices. This model, which is developed in the framework of an interdisciplinary collaboration between pure and applied mathematics, is largely inspired by some ideas and methods pioneered by astrophysicists (e.g. S. Chandrasekhar or N. Lebovitz). First, I will describe the properties of the normal modes, because wave motions are often key to understanding the transition to turbulence in geophysical flows. As in the rotating non-stratified case, it will be shown that the wave spectrum solely consists of eigenvalues, and that the eigenvectors are all smooth. Moreover, it will be explained why some low-frequency waves/modes, which are governed by a mixed hyperbolic-elliptic problem for the velocity, can exist below the usual cutoff frequency of inertia-gravity waves. Next, by combining local and global stability methods, I will discuss whether some bulk instabilities could sustain small-scale bulk turbulence in strongly deformed stratified vortices.
- Speaker: Jérémie Vidal (ENS Lyon)
- Monday 20 October 2025, 16:00-17:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Mattias Brynjell-Rahkola.
Wed 22 Oct 13:15: Hydrogen-deficient binary stars with magnetic braking
Hydrogen-deficient binary stars comprise one star which has been stripped of its hydrogen through mass transfer to a binary companion. Observations show that the companion is able to accrete several solar masses without spinning up to critical rotation, and so there must be a mechanism to drain spin angular momentum from the accretor. We test magnetically coupled winds and magnetic star-disc coupling as possible mechanisms and find that, while the disc coupling is negligible, the winds are sufficient to allow the accretor to gain mass without spinning up to critical rotation. However, in order to fully replicate observations, time-dependent scalings of the dynamo-generated magnetic field are needed.
- Speaker: David Bour / IoA
- Wednesday 22 October 2025, 13:15-13:40
- Venue: Hoyle Lecture theatre + Zoom .
- Series: Institute of Astronomy Seminars; organiser: Xander Byrne.
Wed 15 Oct 13:15: Miscibility in sub-Neptunes
Sub-Neptunes are found around 50% of Sun-like stars in our galaxy. Despite their ubiquity, we lack a comprehensive understanding of their interior structure. I will present the first evolving interior structure model for sub-Neptunes that accounts for the expected miscibility between silicate magma and hydrogen. I will discuss the concept of “binodal surfaces”, which represent phase transitions within sub-Neptunes and provide a physically/chemically informed boundary between a planet’s “interior”’ and “envelope”. I will discuss the many implications of miscibility, and a potential observational route to testing its prevalence.
- Speaker: James Rogers / IoA
- Wednesday 15 October 2025, 13:15-13:40
- Venue: Hoyle Lecture theatre + Zoom .
- Series: Institute of Astronomy Seminars; organiser: Xander Byrne.
Fri 24 Oct 13:00: Strong cosmic censorship for de Sitter black holes
We discuss modern formulations of the strong cosmic censorship conjecture (SCCC) and possible resolutions supported by rigorous non-linear results for the spherically symmetric Einstein-Maxwell-scalar field system. We show that the presence of a positive cosmological constant suggests a violation of the SCCC at a fundamental level of regularity. Indeed, the blueshift mechanism occurring at the Cauchy horizon can be counterbalanced by the dispersive effects encoded in the exponential Price law along (cosmological) black hole event horizons. On the other hand, we show that, if non-smooth black hole solutions are allowed, then the aforementioned violations are non-generic in a positive co-dimension sense.
- Speaker: Flavio Rossetti (Gran Sasso Science Institute)
- Friday 24 October 2025, 13:00-14:00
- Venue: Potter Room / Zoom .
- Series: DAMTP Friday GR Seminar; organiser: Daniela Cors.
Forecasts and Simulations for Relativistic Corrections to the Sunyaev-Zeldovich Effect
SN 2021lwz: Another Exotic Luminous and Fast Evolving Optical Type Ic Broad-Lined Supernova ?
Mon 13 Oct 16:00: Tracking subcritical dynamo transitions and minimal dynamo seeds
In some astrophysical flows known to be linearly stable, finite-amplitude perturbations with favourable spatial structure can nonlinearly trigger a transition from a non-magnetic, non-turbulent state to self-sustained dynamo action and turbulence. Such transitions are suspected to significantly impact spin-down in radiative stellar layers or accretion rates in stellar discs. I will first present numerical examples of nonlinearly-triggered Tayler-Spruit dynamos in a spherical shell and zero-net-flux MRI dynamos in a quasi-Keplerian plane flow. I will then discuss how optimal control can identify stable, nontrivial (M)HD equilibria without requiring prior knowledge of the transition mechanisms.
- Speaker: Florence Marcotte (Université Côte d'Azur, INRIA, CNRS)
- Monday 13 October 2025, 16:00-17:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Mattias Brynjell-Rahkola.
Testing Lens Models of PLCK G165.7+67.0 Using Lensed SN H0pe
Introducing the THESAN-ZOOM project: radiation-hydrodynamic simulations of high-redshift galaxies with a multi-phase interstellar medium
Evidence for Supermassive Black Hole Binaries
$\texttt{geko}$: A tool for modelling galaxy kinematics and morphology in JWST/NIRCam slitless spectroscopic observations
Mon 20 Oct 13:00: Title to be confirmed
Abstract not available
- Speaker: Antony Lewis (University of Sussex)
- Monday 20 October 2025, 13:00-14:00
- Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
- Series: Cosmology Lunch; organiser: Louis Legrand.
Tue 14 Oct 13:00: The Nature of Rocky Exoplanets Via Study of White Dwarf Stars
Venerable Exoplanetary Systems, a brief history: Revelations from 100 years ago to some new discoveries via an unusual, entirely unanticipated, observational technique. The discussion will include the first ever observational evidence for the existence of an extrasolar planetary system, the first observational evidence for the existence of a differentiated extrasolar planet (i.e., one with a crust and mantle), and the remarkable discovery of objects with 100s of times larger abundances of the light elements Be and B than previously seen in any astronomical object.
- Speaker: Prof. Ben Zuckerman
- Tuesday 14 October 2025, 13:00-14:00
- Venue: HOYLE LECTURE THEATRE + ONLINE - Details to be sent by email.
- Series: Exoplanet Seminars; organiser: Dr. Mariona Badenas Agusti.
Prospects for disentangling dark matter with weak lensing
RFSoC receiver calibration system for 21-cm global spectrum experiments from space: The CosmoCube case
Beyond the stars: Linking H$\alpha$ sizes, kinematics, and star formation in galaxies at $z\approx 4-6$ with JWST grism surveys and $\texttt{geko}$
Thu 09 Oct 12:00: Einstein Metrics, Interacting QFT’s and Confinement in Four and Five Dimensions
M-theory provides a geometric framework to describe a variety of interesting quantum field theories in which the QFT ’s arise from Einstein metrics. We motivate a precise definition of this framework which (partly) takes the form of the space of complete, asymptotically conical Ricci flat manifolds in various dimensions. We show how this provides insights into various strongly coupled systems such as non-Abelian gauge theories in four and more dimensions and leads to confining string theories in four and five dimensions. The four dimensional strings can be compared to flux tubes in Yang-Mills theories.
- Speaker: Bobby Acharya (ICTP Trieste)
- Thursday 09 October 2025, 12:00-13:00
- Venue: MR9/Zoom https://cam-ac-uk.zoom.us/j/81827907718.
- Series: DAMTP Friday GR Seminar; organiser: Daniela Cors.
Fri 17 Oct 13:00: Dust cosmological collapse
Cosmological collapse, where gravitational pull overcomes the universe’s expansion, can create primordial black holes or other bound structures. The ultimate fate of such a collapse depends on the initial distribution of matter and its equation of state, as pressure counteracts the gravitational infall. Then, in the dust case, where there is no pressure, shouldn’t a black hole always form? In this talk, I will attempt to answer this question using numerical relativity simulations, discussing the challenges of this problem and the progress we have made so far. Additionally, as this is in full GR, it presents an opportunity to characterise the cosmological spacetime; therefore, I will also describe this using gravito-electromagnetism and Weyl invariants.
- Speaker: Robyn Munoz (Sussex University)
- Friday 17 October 2025, 13:00-14:00
- Venue: Potter Room / Zoom .
- Series: DAMTP Friday GR Seminar; organiser: Daniela Cors.
Thu 06 Nov 16:00: An Ever-Evolving Story of the Chemical Composition and Accretion History of the HR 8799 Planets
As the poster child of directly-imaged exoplanets, the HR 8799 system consists of four young gas giant planets that are likely to be in mean motion resonance. Their formation origin and evolutionary history remain uncertain but can be constrained by a rich set of archival and newly-obtained proprietary data. I will present the detection of key molecular species such as H2O and CO in the planetary atmosphere using the combination of high-contrast imaging and high-resolution spectroscopy. Despite solid detections, interpreting the data through spectral retrieval analysis has been controversial, largely due to systematics introduced by inhomogeneous data sets and differing underlying model assumptions. I will present a calibration procedure using benchmark brown dwarfs to understand the systematic errors. This leads to an accurate constraint of atmospheric composition, which in turn allows us to robustly trace the formation history. Moreover, using a sample of directly-imaged exoplanets including the HR 8799 planets, we convert their atmospheric metallicities to the accreted mass of solid during formation through a Bayesian framework that marginalizes the probabilities of disk conditions, formation locations, planetary interior structures, and accretion physics. We show that more than 50 M⊕ solid mass has been accreted, pointing to an extremely early formation time scale (
- Speaker: Ji Wang
- Thursday 06 November 2025, 16:00-17:00
- Venue: Hoyle Lecture Theatre, Institute of Astronomy.
- Series: Institute of Astronomy Colloquia; organiser: Jan Scholtz.