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Tue 14 May 11:15: Liquid Crystal based adaptive optics

Next External Talks - Tue, 16/04/2024 - 00:47
Liquid Crystal based adaptive optics

TBC

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

Next External Talks - 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

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

TBC

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

Next Colloquia - 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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Thu 16 May 16:00: Inside Astronomically Realistic Black Holes

Next Colloquia - 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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Fri 19 Apr 13:00: Dynamical Gravastars

Next External Talks - 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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Thu 02 May 16:00: Experimental Studies of Black Holes: Status & Prospects

Next Colloquia - Mon, 25/03/2024 - 10:18
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 1010 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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Mon 22 Apr 13:00: Title to be confirmed

Next External Talks - Fri, 22/03/2024 - 09:52
Title to be confirmed

Abstract not available

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Mon 25 Mar 13:00: The FLAMINGO project: revisiting the S8 tension and the role of baryonic physics

Next External Talks - Thu, 21/03/2024 - 11:25
The FLAMINGO project: revisiting the S8 tension and the role of baryonic physics

A number of recent studies have found evidence for a tension between observations of large-scale structure (LSS) and the predictions of the standard model of cosmology with the cosmological parameters fit to the cosmic microwave background (CMB). The origin of this ‘S8 tension’ remains unclear, but possibilities include new physics beyond the standard model, unaccounted for systematic errors in the observational measurements and/or uncertainties in the role that baryons play. In this talk, I will examine the latter possibility using the new FLAMINGO suite of large-volume cosmological hydrodynamical simulations. I will discuss how important ‘feedback’ processes that affect the baryons are implemented and calibrated in the simulations and how the simulations are projected onto observable space for comparisons with observational measurements of cosmic shear, CMB lensing, and the thermal Sunyaev-Zel’dovich (tSZ) effect. I will then focus on the dependence of the predictions on the efficiency and nature of baryonic feedback and whether or not it can plausibly resolve the S8 tension. Finally, I will discuss some independent tests that the simulations can be subjected to in order to build confidence (or undermine it!) in our cosmological conclusions.

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Wed 15 May 14:00: Title to be confirmed

Next External Talks - Tue, 19/03/2024 - 17:16
Title to be confirmed

Abstract not available

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Wed 08 May 14:00: Title to be confirmed

Next External Talks - Tue, 19/03/2024 - 17:15
Title to be confirmed

Abstract not available

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Wed 01 May 14:00: Title to be confirmed

Next External Talks - Tue, 19/03/2024 - 17:13
Title to be confirmed

Abstract not available

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Mon 20 May 13:00: Title to be confirmed

Next External Talks - Mon, 18/03/2024 - 17:42
Title to be confirmed

Abstract not available

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Tue 19 Mar 14:00: Primordial black holes in the dark matter halo of our Galaxy

Next Wednesday Seminars - Mon, 18/03/2024 - 11:09
Primordial black holes in the dark matter halo of our Galaxy

If there are primordial black holes in the dark matter halo, they must collide with the Galactic neutron stars (NSs) and produce light black holes (LBHs), with masses below 1.4 M_Sun. This has observational consequences that may be checked by microlensing, by LIGO -Virgo-Kagra interferometers detecting gravitational waves from collisions of LBHs with NSs and BHs, and (possibly) by detecting LBHs in X-ray binaries and from pulsars statistics.

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

Next Colloquia - Thu, 14/03/2024 - 11:19
Experimental Studies of Black Holes: Status & Prospects

Abstract not available

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Tue 19 Mar 11:15: Source dynamics and evolution of low-luminosity FRII radio galaxies

Next External Talks - Thu, 14/03/2024 - 10:10
Source dynamics and evolution of low-luminosity FRII radio galaxies

I will present new VLA observations that reveal the structure of a new population of low-luminosity FRII radio galaxies discovered in LoTSS. Fanaroff and Riley (1974) identified a luminosity break between their two morphological classes. FRIs are defined to be low-luminosity, centre bright jets and the higher luminosity FRI Is have jets that are edge brightened and terminate in hotspots. Using LoTSS DR1 , Mingo et al (2019) demonstrated an overlap in luminosity between FRI and FRII morphology rather than a clear divide, discovering a sub-sample of FRI Is with luminosities up to 3 magnitudes lower than the typical FR break. A population of low-luminosity FRI Is raises questions about their origins; are they older, fading FRI Is, or hosted by lower mass galaxies? Our new VLA observations of a sample of LoTSS-selected low-luminosity FRI Is allow us to make comparisons between the two FRII luminosity populations on the prevalence of hotspots, as well as morphological and spectral differences.

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Fri 15 Mar 13:00: Fully general Cauchy evolution of asymptotically AdS spacetimes: the non-linear instability of Kerr-AdS

Next External Talks - Tue, 12/03/2024 - 10:56
Fully general Cauchy evolution of asymptotically AdS spacetimes: the non-linear instability of Kerr-AdS

In addition to being at the core of the widely employed AdS/CFT correspondence, asymptotically anti-de Sitter (AdS) spacetimes with reflective boundary conditions can serve as the arena for a range of strong gravity effects: arbitrarily small perturbations are bound to remain in the bulk, where they continue to interact and typically become sizeable. Initially, I will review a numerical scheme that enables the Cauchy evolution of these spacetimes to be performed in full generality. Then, I will present the first simulations of the trapping mechanism occurring in the exterior of a Kerr-AdS black hole. This mechanism has been conjectured to cause a non-linear instability, the existence of which remains a topic of debate. The simulations offer insights into this debate, providing new perspectives on the non-linear instability of Kerr-AdS.

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Wed 13 Mar 13:15: A new convection scheme for exoplanet atmospheres

Next Wednesday Seminars - Mon, 11/03/2024 - 09:43
A new convection scheme for exoplanet atmospheres

Convection is an essential process for transporting heat and moisture in planetary atmospheres. The standard Earth picture of moist convection rising from the surface is only one of a number of modes of convection. Notably, convection in atmospheres with a high condensible mass fraction (non-dilute atmospheres), or with a lighter background gas than the condensible species (e.g. water convection in a hydrogen dominated atmosphere) – acts very differently and can be much weaker or even shut down entirely in the latter case. Here I present a new mass-flux scheme which can capture these variations and simulate convection in a wide range of parameter space for use in 3D climate models. A validation using the case of Trappist-1 e is presented.

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Wed 13 Mar 13:40: Constraining physics and astrophysics with multifrequency CMB data

Next Wednesday Seminars - Sun, 10/03/2024 - 21:00
Constraining physics and astrophysics with multifrequency CMB data

The CMB anisotropies are measured in several microwave frequency bands. Having this frequency information allows us to separate signals that are due to different sources. We can easily make maps that are sensitive to specific frequency combinations, and in this way isolate the contribution from the primary CMB (early-Universe) and various other CMB interactions such as the Sunyaev—Zel’dovich (SZ) effect (the scattering of the CMB from electrons in the late Universe). I will talk about constraints on the SZ effect from Planck data using a new frequency-separation code, pyilc, which we use to isolate the signal while removing other late-Universe biases, in particular the infrared emission from star-forming galaxies. I will also show an application to beyond standard model interactions between the CMB and a non-trivial dark sector, and how we can use the CMB to constrain beyond-standard-model particle physics.

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Thu 07 Mar 16:00: Eddington lecture 2024: The Dawn of Galaxy-scale Gravitational Wave Astronomy

Next Colloquia - Thu, 07/03/2024 - 14:36
Eddington lecture 2024: The Dawn of Galaxy-scale Gravitational Wave Astronomy

For more than 15 years, NANO Grav and other pulsar-timing array collaborations have been carefully monitoring networks of pulsars across the Milky Way. The goal was to find a tell-tale correlation signature amid the data from all those pulsars that would signal the presence of an all-sky background of nanohertz-frequency gravitational waves, washing through the Galaxy. At the end of June 2023, the global pulsar-timing array community finally announced its evidence for this gravitational-wave background, along with a series of studies that interpreted this signal as either originating from a population of supermassive black-hole binary systems, or as relics from cosmological processes in the very early Universe. I will describe the journey up to this point (including the integral role that the IoA played), what led to the ultimate breakthrough, how this affects our knowledge of supermassive black holes and the early Universe, and what lies next for gravitational-wave astronomy at light-year wavelengths.

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