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Description to be confirmed
URL: http://talks.cam.ac.uk/show/index/54089
Updated: 1 hour 11 min ago

Tue 07 May 11:15: Interferometric measurements of the 21-cm signal with SKA

Tue, 16/04/2024 - 00:44
Interferometric measurements of the 21-cm signal with SKA

The Cosmic Dawn marks the first star formations and preceded the Epoch-of-Reionization, when the Universe underwent a fundamental transformation propelled by the radiation from these first stars and galaxies. Interferometric 21-cm experiments aim to probe redshifted neutral hydrogen signals from these periods, constraining the conditions of the early Universe. The SKA -LOW instrument of the Square Kilometre Array telescope is envisaged to be the largest and most sensitive radio telescope at m and cm wavelengths. In this talk we present a data analysis pipeline that was used in the SKA Science Data Challenge 3a: Epoch of Reionisation (SKA SDC3a) to process the novel data products expected from the SKA . To determine whether a successful 21-cm detection is possible with the envisaged SKA , we implement predictive foreground and Bayesian Gaussian Process Regression models alongside a foreground avoidance strategy to isolate the 21-cm signal from that of the astrophysical radio frequency (RF) foregrounds.

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Tue 30 Apr 11:15: Radio observations of extra-galactic transients with the AMI-LA telescope

Tue, 16/04/2024 - 00:31
Radio observations of extra-galactic transients with the AMI-LA telescope

TBC

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Tue 30 Apr 13:00: Title to be confirmed

Sun, 14/04/2024 - 12:47
Title to be confirmed

Abstract not available

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Tue 28 May 13:00: Title to be confirmed

Sun, 14/04/2024 - 12:44
Title to be confirmed

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Tue 21 May 13:00: Title to be confirmed

Sun, 14/04/2024 - 12:44
Title to be confirmed

Abstract not available

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Tue 23 Apr 13:00: The physical mechanism of the streaming instability, and whether it works in vortices

Sun, 14/04/2024 - 12:41
The physical mechanism of the streaming instability, and whether it works in vortices

A major hurdle in planet formation theory is that we do not understand how small pebbles congregate into big planetesimals. A promising way to overcome this metre-scale barrier involves a fluid dynamics phenomenon called the streaming instability (SI). It concentrates the pebbles into clumps that are dense enough to collapse gravitationally, thereby forming planetesimals.

Unfortunately, the mechanism responsible for the onset of the instability remains mysterious. This makes it hard to evaluate the robustness of the instability, or to understand how it saturates. It has recently been shown that the SI is a Resonant Drag Instability (RDI) involving inertial waves. In the first part of this talk, I build on this insight to produce a clear physical picture of how the SI develops.

Another problem is that the SI can only devellop in regions containing a high density of similar-sized pebbles. Those conditions are met in large-scale vortices, but no one knows if the SI can feed on vorticial flows. Indeed, any instability can only devellop in specific flows, and a priori the SI is tailored to Keplerian disc flows, not vortex flows. I answer this question in the second part of the talk. To do so, I develop a simple pen-and-paper model of a dust-laden vortex in a protoplanetary disc. I find that if the vortex is weak and anticyclonic, dust drifts towards its centre. I then build a vortex analog of the shearing box to analyse the local linear stability of my dusty vortex. I find that the dust’s drift powers an instability which closely resembles the SI. This result strengthens the case for vortex-induced planetesimal formation.

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Thu 02 May 16:00: Experimental Studies of Black Holes: Status & Prospects

Fri, 12/04/2024 - 11:45
Experimental Studies of Black Holes: Status & Prospects

More than a century ago, Albert Einstein presented his general theory of gravitation. One of the predictions of this theory is that not only particles and objects with mass, but also the quanta of light, photons, are tied to the curvature of space-time, and thus to gravity. There must be a critical mass density, above which photons cannot escape. These are black holes. It took fifty years before possible candidate objects were identified by observational astronomy. Another fifty years have passed, until we finally can present detailed and credible experimental evidence that black holes of 10 to 10^10 times the mass of the Sun exist in the Universe. Three very different experimental techniques have enabled these critical experimental breakthroughs. It has become possible to investigate the space-time structure in the vicinity of the event horizons of black holes. I will summarize these interferometric techniques, and discuss the spectacular recent improvements achieved with all three techniques. In conclusion, I will sketch where the path of exploration and inquiry may lead to in the next decades.

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Fri 19 Apr 11:30: Probing the epoch of galaxy assembly with MUSE

Thu, 11/04/2024 - 13:14
Probing the epoch of galaxy assembly with MUSE

Abstract not available

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Fri 31 May 11:30: Title to be confirmed

Tue, 09/04/2024 - 17:11
Title to be confirmed

Abstract not available

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Wed 22 May 11:30: Hierarchical star cluster assembly boosts intermediate-mass black hole formation

Mon, 08/04/2024 - 09:08
Hierarchical star cluster assembly boosts intermediate-mass black hole formation

Observations and high-resolution hydrodynamical simulations indicate that massive star clusters assemble hierarchically from sub-clusters with a universal power-law cluster mass function. We study the consequences of such assembly for the formation of intermediate-mass black holes (IMBHs) and massive black hole (MBH) seeds at low metallicities (1% of the solar value) with our updated direct N-body code BIFROST in simulations up to N = 2.35 million stars. The GPU -accelerated code BIFROST is based on the hierarchical fourth-order forward integrator. Few-body systems are treated using secular and regularized techniques including post-Newtonian equations of motion up to order PN3 .5 and gravitational-wave recoil kicks for merging BHs. Stellar evolution is provided by the fast population synthesis code SEVN . IMBHs with masses up to 2200 solar masses form rapidly mainly via the collapse of very massive stars (VMSs) assembled through repeated collisions of massive stars followed by growth through tidal disruption events (TDEs) and BH mergers. Later the IMB Hs form subsystems resulting in gravitational-wave BH-BH, IMBH -BH and IMBH -IMBH mergers with a 1000 solar mass gravitational-wave detection being the observable prediction. Our simulations indicate that the hierarchical formation of massive star clusters in metal poor environments naturally results in formation of potential seeds for supermassive black holes.

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Thu 16 May 16:00: Inside Astronomically Realistic Black Holes

Fri, 05/04/2024 - 23:35
Inside Astronomically Realistic Black Holes

I will use a real-time general relativistic Black Hole Flight Similator to show what really happens inside astronomically realistic black holes. The inner horizon of a rotating black hole is the most violent place in the Universe, easily reaching and surpassing energy densities attained in the Big Bang. What does Nature do at this extraordinary place?

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Tue 07 May 11:30: KICC Special Seminar (Title TBC)

Fri, 05/04/2024 - 13:29
KICC Special Seminar (Title TBC)

Abstract not available

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Fri 07 Jun 11:30: Title to be confirmed

Fri, 05/04/2024 - 12:26
Title to be confirmed

Abstract not available

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Fri 21 Jun 11:30: Modelling supermassive black holes: accretion, spin evolution, jets and winds

Fri, 05/04/2024 - 12:22
Modelling supermassive black holes: accretion, spin evolution, jets and winds

Abstract not available

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Tue 07 May 11:30: TBD

Fri, 05/04/2024 - 10:51
TBD

Abstract not available

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Fri 03 May 11:30: TBD (have to move to May 7?)

Thu, 04/04/2024 - 22:16
TBD (have to move to May 7?)

Abstract not available

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Fri 12 Apr 11:30: Chemo-dynamical evolution of disks over cosmic time

Thu, 04/04/2024 - 13:35
Chemo-dynamical evolution of disks over cosmic time

Abstract not available

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Fri 14 Jun 11:30: Title to be confirmed

Wed, 03/04/2024 - 10:23
Title to be confirmed

Abstract not available

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Fri 19 Apr 13:00: Dynamical Gravastars

Sun, 31/03/2024 - 15:47
Dynamical Gravastars

I give new results for ``gravastars’’, which are horizonless compact objects that closely mimic mathematical black holes in their exterior geometry, but for which $g_{00}$ is always positive. In my initial formulation, they result from solving the Tolman-Oppenheimer-Volkoff (TOV) equations for relativistic stellar structure, which require continuous pressure, but with an interior density jump from a normal matter equation of state, to an equation of state where pressure plus density approximately sum to zero. We present Mathematica notebooks solving the TOV equations, in which the structure of the gravastar is entirely governed by the Einstein-Hilbert gravitational action (with zero cosmological constant) together with the matter equation of state, with radii where structural changes occur emerging from the dynamics, rather than being specified in advance as in the original Mazur-Mottola gravastars.

My more recent work with a student shows that the interesting ``simulated horizon’’ structure of dynamical gravastars is a property solely of the exterior TOV equations for relativistic matter with appropriate small radius boundary conditions, and will be present for a large class of interior equations of state. The exterior TOV equations can be rewritten in rescaling-invariant form, leading to a two dimensional autonomous system of differential equations which are now being studied numerically and analytically , and for which hopefully some rigorous results can be proved.

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Tue 23 Apr 13:00: Title to be confirmed

Sat, 30/03/2024 - 08:42
Title to be confirmed

Abstract not available

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