Upcoming Talks

Thu 15 May 16:00: Title to be confirmed

Tue, 29/04/2025 - 13:01

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: .

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Fri 30 May 13:00: Gravitational Wave Signatures of Dark Matter in Neutron Star Mergers

Tue, 29/04/2025 - 12:38

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.

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Fri 16 May 13:00: TBC

Tue, 29/04/2025 - 12:36

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.

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Fri 09 May 13:00: TBC

Tue, 29/04/2025 - 12:34

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.

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Fri 06 Jun 13:00: A Spacetime Interpretation of the Confluent Heun Functions in Black Hole Perturbation Theory

Tue, 29/04/2025 - 12:32

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.

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Fri 30 May 13:00: Gravitational Wave Signatures of Dark Matter in Neutron Star Mergers

Mon, 28/04/2025 - 19:30

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.

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Fri 09 May 11:30: How do the most luminous black holes accrete and expel gas?

Mon, 28/04/2025 - 15:16

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.

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Fri 02 May 13:00: The Black Hole Threshold

Mon, 28/04/2025 - 12:16

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.

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Thu 01 May 16:00: Irradiated brown dwarfs

Mon, 28/04/2025 - 11:25

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.