Tue 17 Jun 11:15: Love Bites: The Deadly Romance of Spider Pulsars
Pulsars in binary systems are fantastic physics laboratories, primarily because their orbital dynamics allow us to probe binary evolution, test gravity theories, measure neutron star masses, etc. Among them are the “black widows” and “redbacks”, which are nicknamed after the deadly arachnids because the millisecond pulsar they contain gradually destroys their low mass companion. The strongly irradiated dayside displayed by the low-mass companions in these systems is reminiscent of what is observed in exoplanets called “hot jupiters”. In the last decade, the number of known spiders has grown exponentially to the point of becoming the most prevalent type of fast rotating binary pulsars. In this talk, I will present some of the recent efforts undertaken with the MeerKAT telescope to uncover these pulsars and review some of the key advances they have provided for our understanding of binary evolution, stellar physics under extreme irradiation, and measurement of neutron star masses.
- Speaker: Prof. Rene Breton (University of Manchester)
- Tuesday 17 June 2025, 11:15-12:00
- Venue: Martin Ryle Seminar Room, Kavli Institute.
- Series: Hills Coffee Talks; organiser: Charles Walker.
Fri 20 Jun 13:00: Well-posed initial value formulation of general effective field theories of gravity
In this talk, I will show that all higher-derivative effective field theories (EFTs) of vacuum gravity admit a well-posed initial value formulation when augmented by suitable regularising terms. These regularising terms can be obtained by field redefinitions and do not affect the dynamics in the regime of validity of EFT . I will explain how our result applies to the quadratic, cubic, and quartic truncations of the EFT of gravity and to various truncations of a simple EFT of a scalar field. Finally, I will also discuss some numerical results on the non-linear dynamics of this simple scalar field theory.
- Speaker: Aron Kovacs, Queen Mary University of London
- Friday 20 June 2025, 13:00-14:00
- Venue: Potter room/Zoom.
- Series: DAMTP Friday GR Seminar; organiser: Daniela Cors.
Tue 06 May 13:00: The Dynamic Chemistry of Planet-Forming Disks
The chemical composition of a planet’s atmosphere is intimately tied to the volatile inventory of the protoplanetary disk in which it forms. Establishing this connection requires detailed measurements of elemental abundances in disks at small spatial scales relevant to planet formation. In this talk, I will present two targeted studies of well-known Herbig Ae/Be systems, combining ALMA observations with chemical modelling to probe disk chemistry. In HD 100546 , we detect complex molecular asymmetries, interpreted as the result of shadowing from planet-induced structures within the inner cavity, generating azimuthal temperature variations that drive chemical diversity. In HD 169142 , we investigate the first detection of SiS emission from a protoplanetary disk—nearly a billion times brighter than predicted under typical conditions—indicative of planet-induced shocks that release silicon from dust grains into the gas phase. These findings reveal that planet formation can significantly reshape the chemical environment of disks, with direct implications for how emerging planets accrete their atmospheres. Together, these studies emphasise the dynamic and heterogeneous nature of disk chemistry and provide new insights into the origins of the wide diversity observed in exoplanetary atmospheres.
- Speaker: Luke Keyte (UCL)
- Tuesday 06 May 2025, 13:00-14:00
- Venue: Ryle seminar room + ONLINE - Details to be sent by email.
- Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.
Tue 06 May 13:00: The Dynamic Chemistry of Planet-Forming Disks
The chemical composition of a planet’s atmosphere is intimately tied to the volatile inventory of the protoplanetary disk in which it forms. Establishing this connection requires detailed measurements of elemental abundances in disks at small spatial scales relevant to planet formation. In this talk, I will present two targeted studies of well-known Herbig Ae/Be systems, combining ALMA observations with chemical modelling to probe disk chemistry. In HD 100546 , we detect complex molecular asymmetries, interpreted as the result of shadowing from planet-induced structures within the inner cavity, generating azimuthal temperature variations that drive chemical diversity. In HD 169142 , we investigate the first detection of SiS emission from a protoplanetary disk—nearly a billion times brighter than predicted under typical conditions—indicative of planet-induced shocks that release silicon from dust grains into the gas phase. These findings reveal that planet formation can significantly reshape the chemical environment of disks, with direct implications for how emerging planets accrete their atmospheres. Together, these studies emphasise the dynamic and heterogeneous nature of disk chemistry and provide new insights into the origins of the wide diversity observed in exoplanetary atmospheres.
- Speaker: Luke Keyte (UCL)
- Tuesday 06 May 2025, 13:00-14:00
- Venue: Ryle seminar room + ONLINE - Details to be sent by email.
- Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.
Tue 06 May 13:00: Updates on fundamental science from the secondary CMB
A major frontier in cosmic microwave background (CMB) science is the study of secondary anisotropies—temperature and polarization anisotropies induced by the gravitational, electromagnetic, or beyond-standard-model (BSM) interactions of CMB photons with large-scale structure (LSS) over cosmic history. Leveraging their distinct statistical properties and cross-correlations with LSS enables us to isolate these secondary anisotropies from the primary CMB and extract new astrophysical and cosmological information. In this talk, I discuss how secondary anisotropies from electromagnetic interactions (Sunyaev-Zel’dovich effects) and hypothetical BSM particles (dark screening) can serve as probes of fundamental physics. I present a general formalism for capturing the information content of secondary anisotropies. I then give a summary of existing measurements of the kinetic Sunyaev-Zel’dovich (kSZ), polarized Sunyaev-Zel’dovich (pSZ), and dark screening effects. Next I provide an update on how these measurements constrain large-scale homogeneity, primordial non-Gaussianity, isocurvature, and BSM particles (axions and dark photons). Looking ahead to the high-resolution, low-noise, large-volume frontier, I discuss how upcoming observations from the Simons Observatory, combined with LSS surveys like DESI and LSST , will significantly improve these results and allow for novel tests of fundamental physics.
- Speaker: Matthew Johnson (Perimeter Institute and York University)
- Tuesday 06 May 2025, 13:00-14:00
- Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
- Series: Cosmology Lunch; organiser: Thomas Colas.
Thu 15 May 16:00: Title to be confirmed
Abstract not available
- Speaker: Ortwin Gerhard, MPE (Garching)
- Thursday 15 May 2025, 16:00-17:00
- Venue: Hoyle Lecture Theatre, Institute of Astronomy.
- Series: Institute of Astronomy Colloquia; organiser: .
Fri 30 May 13:00: Gravitational Wave Signatures of Dark Matter in Neutron Star Mergers
Binary neutron star mergers provide insights into strong-field gravity and the properties of ultra-dense nuclear matter. These events offer the potential to search for signatures of physics beyond the standard model, including dark matter. We present the first numerical-relativity simulations of binary neutron star mergers admixed with dark matter, based on constraint-solved initial data. Modeling dark matter as a non-interacting fermionic gas, we investigate the impact of varying dark matter fractions and particle masses on the merger dynamics, ejecta mass, post-merger remnant properties, and the emitted gravitational waves. Our simulations suggest that the dark matter morphology – a dense core or a diluted halo – may alter the merger outcome. Scenarios with a dark matter core tend to exhibit a higher probability of prompt collapse, while those with a dark matter halo develop a common envelope, embedding the whole binary. Furthermore, gravitational wave signals from mergers with dark matter halo configurations exhibit significant deviations from standard models when the tidal deformability is calculated in a two-fluid framework neglecting the dilute and extended nature of the halo. This highlights the need for refined models in calculating the tidal deformability when considering mergers with extended dark matter structures. These initial results provide a basis for further exploration of dark matter’s role in binary neutron star mergers and their associated gravitational wave emission and can serve as a benchmark for future observations from advanced detectors and multi-messenger astrophysics.
- Speaker: Violetta Sagun, University of Southampton
- Friday 30 May 2025, 13:00-14:00
- Venue: MR9/Zoom.
- Series: DAMTP Friday GR Seminar; organiser: Xi Tong.
Fri 16 May 13:00: TBC
Abstract not available
- Speaker: Benjamin Elder, Imperial College London
- Friday 16 May 2025, 13:00-14:00
- Venue: MR20/Zoom.
- Series: DAMTP Friday GR Seminar; organiser: Xi Tong.
Fri 09 May 13:00: TBC
Abstract not available
- Speaker: Robbie Hennigar, Durham University
- Friday 09 May 2025, 13:00-14:00
- Venue: MR9/Zoom.
- Series: DAMTP Friday GR Seminar; organiser: Xi Tong.
Fri 06 Jun 13:00: A Spacetime Interpretation of the Confluent Heun Functions in Black Hole Perturbation Theory
In Black Hole Perturbation Theory, confluent Heun functions appear as solutions to the radial Teukolsky equation, which governs perturbations in black hole spacetimes. While these functions are typically studied for their analytic properties, their connection to the underlying spacetime geometry has received less attention. In this talk, I will propose a spacetime interpretation of the confluent Heun functions, demonstrating how their behaviour near their singular points reflects the structure of key surfaces in Kerr spacetimes. By interpreting homotopic transformations of these functions as changes in the spacetime foliation, I will establish a connection between these solutions and various regions of the black hole’s global structure. I will also explore their relationship with the hyperboloidal formulation of the radial Teukolsky equation.
- 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 30 May 13:00: Gravitational Wave Signatures of Dark Matter in Neutron Star Mergers
Binary neutron star mergers provide insights into strong-field gravity and the properties of ultra-dense nuclear matter. These events offer the potential to search for signatures of physics beyond the standard model, including dark matter. We present the first numerical-relativity simulations of binary neutron star mergers admixed with dark matter, based on constraint-solved initial data. Modeling dark matter as a non-interacting fermionic gas, we investigate the impact of varying dark matter fractions and particle masses on the merger dynamics, ejecta mass, post-merger remnant properties, and the emitted gravitational waves. Our simulations suggest that the dark matter morphology – a dense core or a diluted halo – may alter the merger outcome. Scenarios with a dark matter core tend to exhibit a higher probability of prompt collapse, while those with a dark matter halo develop a common envelope, embedding the whole binary. Furthermore, gravitational wave signals from mergers with dark matter halo configurations exhibit significant deviations from standard models when the tidal deformability is calculated in a two-fluid framework neglecting the dilute and extended nature of the halo. This highlights the need for refined models in calculating the tidal deformability when considering mergers with extended dark matter structures. These initial results provide a basis for further exploration of dark matter’s role in binary neutron star mergers and their associated gravitational wave emission and can serve as a benchmark for future observations from advanced detectors and multi-messenger astrophysics.
- Speaker: Violetta Sagun, University of Southampton
- Friday 30 May 2025, 13:00-14:00
- Venue: Potter room/Zoom.
- Series: DAMTP Friday GR Seminar; organiser: Xi Tong.
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
- Friday 09 May 2025, 11:30-12:30
- Venue: Hoyle Lecture Theatre, Institute of Astronomy.
- Series: Institute of Astronomy Colloquia; organiser: Debora Sijacki.
Fri 02 May 13:00: The Black Hole Threshold
Numerical evolutions show that, in spherical symmetry, as we move through the solution space of GR to the threshold of black hole formation, the resulting spacetimes tend to display a surprising degree of simplicity. A heuristic description of this behavior, called critical collapse, has been built around this empirical fact. Less is known when symmetry is dropped. In this presentation I will review the current status of the topic, focusing in particular on the struggle to understand the situation in axisymmetry.
- Speaker: David Hilditch, IST Lisbon
- Friday 02 May 2025, 13:00-14:00
- Venue: Potter room/Zoom https://cam-ac-uk.zoom.us/j/87235967698.
- Series: DAMTP Friday GR Seminar; organiser: Daniela Cors.
Thu 01 May 16:00: Irradiated brown dwarfs
Brown dwarfs are often described as failed stars, however the flip side of this description is that they can also be described as over-ambitious planets. With masses between 13-70 Jupiter masses they have cool atmospheres dominated by cloud features, molecules and show features due to weather. These atmospheres have a lot of similarities with atmospheres we see in planets in our solar system, and also directly imaged exoplanets. The question then is: How like hot Jupiters are irradiated brown dwarfs? In this seminar I will describe the known irradiated brown dwarfs and how they evolve into post-common envelope systems containing a white dwarf. These rare binaries have very short periods (~hrs) and the brown dwarf is irradiated by the white dwarf companion, often with large amounts of UV radiation. I will discuss the atmospheres of these highly irradiated brown dwarfs and their similarities with irradiated exoplanets.
- Speaker: Dr Sarah Casewell
- Thursday 01 May 2025, 16:00-17:00
- Venue: Hoyle Lecture Theatre, Institute of Astronomy.
- Series: Institute of Astronomy Colloquia; organiser: Jan Scholtz.
Fri 20 Jun 13:00: TBC
Abstract not available
- Speaker: Aron Kovacs, Queen Mary University of London
- Friday 20 June 2025, 13:00-14:00
- Venue: Potter room/Zoom.
- Series: DAMTP Friday GR Seminar; organiser: Xi Tong.
Fri 30 May 13:00: TBC
Abstract not available
- Speaker: Violetta Sagun, University of Southampton
- Friday 30 May 2025, 13:00-14:00
- Venue: Potter room/Zoom.
- Series: DAMTP Friday GR Seminar; organiser: Xi Tong.
Fri 16 May 13:00: TBC
Abstract not available
- Speaker: Benjamin Elder, Imperial College London
- Friday 16 May 2025, 13:00-14:00
- Venue: Potter room/Zoom.
- Series: DAMTP Friday GR Seminar; organiser: Xi Tong.
Fri 09 May 13:00: TBC
Abstract not available
- Speaker: Robbie Hennigar, Durham University
- Friday 09 May 2025, 13:00-14:00
- Venue: Potter room/Zoom.
- Series: DAMTP Friday GR Seminar; organiser: Xi Tong.
Mon 16 Jun 14:00: Title to be confirmed
Abstract not available
- Speaker: Gavin Coleman [Queen Mary University London]
- Monday 16 June 2025, 14:00-15:00
- Venue: Venue to be confirmed.
- Series: DAMTP Astrophysics Seminars; organiser: Thomas Jannaud.
Thu 05 Jun 14:00: Title to be confirmed
Abstract not available
- Speaker: Jonathan Squire [Otago, New Zealand]
- Thursday 05 June 2025, 14:00-15:00
- Venue: MR20 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Loren E. Held.