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URL: http://talks.cam.ac.uk/show/index/54089
Updated: 39 min 48 sec ago

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.

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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.

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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.

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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.

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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.

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Fri 20 Jun 13:00: TBC

Sat, 26/04/2025 - 13:44
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Fri 30 May 13:00: TBC

Sat, 26/04/2025 - 13:42
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Fri 16 May 13:00: TBC

Sat, 26/04/2025 - 13:41
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Fri 09 May 13:00: TBC

Sat, 26/04/2025 - 13:40
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Mon 16 Jun 14:00: Title to be confirmed

Fri, 25/04/2025 - 10:30
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Thu 05 Jun 14:00: Title to be confirmed

Fri, 25/04/2025 - 10:28
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Mon 02 Jun 14:00: Title to be confirmed

Fri, 25/04/2025 - 10:24
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Mon 12 May 14:00: Title to be confirmed

Fri, 25/04/2025 - 10:22
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Mon 19 May 14:00: Title to be confirmed

Fri, 25/04/2025 - 10:22
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Tue 27 May 14:00: Title to be confirmed

Fri, 25/04/2025 - 10:21
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Thu 29 May 14:00: Title to be confirmed

Fri, 25/04/2025 - 10:21
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Tue 29 Apr 13:00: Formation of planetary cores in spontaneously generated dust traps during the secular evolution of magnetized protoplanetary disks

Fri, 25/04/2025 - 03:32
Formation of planetary cores in spontaneously generated dust traps during the secular evolution of magnetized protoplanetary disks

An outstanding gap in the current planet formation theory is about the first steps of the planet formation process; namely how, when and where the initially ISM like solid dust particles grow into pebbles and planetesimals, the building blocks of planetary cores. Protoplanetary disks provide the initial conditions for the planet formation process. They are weakly magnetized accretion disks that are subject to the magnetorotational instability (MRI), one of the main magnetized processes responsible for their angular momentum transport and gas turbulence. The nonideal magnetohydrodynamic (MHD) effects prevent the MRI from operating everywhere in PPDs, leading to a complex dichotomy between MRI active regions with higher gas turbulence and non-MRI regions with lower gas turbulence. In this talk,  I will present the first numerical framework that describes the evolution of PPDs over millions of years powered by the MRI . It captures the MRI driven gas evolution via nonideal MHD calculations, which accounts for the dynamics and growth of the solid dust particles. An MRI powered mechanism that can spontaneously generate short- and long-lived pressure maxima in the PPD is unveiled. Within the long-lived pressure maxima, solid dust particles can be efficiently trapped, grow into pebbles, and reach high enough dust-to-gas mass ratios to potentially trigger the formation of planetesimals via the streaming instability. These planetesimals and pebbles can further rapidly interact to form planetary cores.

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Fri 25 Apr 11:30: The Thesan-Zoom simulations: Studying high-redshift galaxy formation with cosmological radiation-hydrodynamics simulations

Wed, 23/04/2025 - 15:59
The Thesan-Zoom simulations: Studying high-redshift galaxy formation with cosmological radiation-hydrodynamics simulations

Abstract not available

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Mon 09 Jun 13:00: Title to be confirmed

Wed, 23/04/2025 - 09:58
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Fri 25 Apr 13:00: Black hole radiation from non-vacuum initial states

Tue, 22/04/2025 - 23:10
Black hole radiation from non-vacuum initial states

Hawking derived the black hole thermal radiation state by comparing the vacuum state at the future null infinity I+ with that at the past null infinity I-. We revisit Hawking’s computation, considering a non-vacuum initial state at the past of the black hole geometry. We show in which cases the black hole radiation arising from the initial matter state differs from the well-known thermal state. We moreover classify what initial states are distinguishable from one another through measurements on the black hole radiation in this framework. Finally we provide a physical interpretation of the classification, using Algebraic Quantum Field Theory localisation.

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