Tue 16 Jan 11:15: The History of MRAO
Abstract not available
- Speaker: Malcolm Longair (Cavendish Astrophysics)
- Tuesday 16 January 2024, 11:15-12:00
- Venue: Coffee area, Battcock Centre.
- Series: Hills Coffee Talks; organiser: David Buscher.
Fri 08 Dec 13:00: Observational evidence of cosmological coupling in black holes
Over the past ten years, observational evidence has continued to mount that astrophysical black holes grow too quickly or are more massive than easily explained by physical processes such as merger and accretion. With the advent of gravitational wave astronomy, this evidence now spans all observational channels, over ten orders of magnitude in mass, and over cosmological timescales. The simplest black hole model, Kerr, cannot be applied over cosmological timescales because it has non-cosmological boundary conditions. Aspects of non-singular and horizon-free black hole models in General Relativity suggest dynamics on cosmological timescales that can help to ease these observational tensions. We review recent formal advances in General Relativity that permit investigation of candidate black hole models through their possible cosmological interactions, and present the first observational evidence for cosmologically coupled mass growth in the supermassive black holes of quiescent elliptical galaxies. The measured growth is consistent with a vacuum energy equation of state for astrophysical black hole contributions in aggregate, leading to the striking prediction that astrophysical black holes may well be the material source that drives accelerated late-time expansion.
- Speaker: Kevin Croker, University of Hawaii at Manoa
- Friday 08 December 2023, 13:00-14:00
- Venue: Potter room/Zoom.
- Series: DAMTP Friday GR Seminar; organiser: Xi Tong.
Mon 04 Dec 13:00: Beyond perturbation theory in inflation
Deviations from Gaussianity in inflation are usually calculated using perturbation theory. This method, however, fails for unlikely events on the tail of the probability distribution, like the formation of a primordial black hole. I explain how one can explore these unlikely events using semiclassical methods and then discuss the case of resonant non-Gaussianity.
- Speaker: Paolo Creminelli (ICTP, Trieste)
- Monday 04 December 2023, 13:00-14:00
- Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
- Series: Cosmology Lunch; organiser: Dr Dong-Gang Wang.
Tue 05 Dec 14:00: Positivity Constraints on Lorentz-breaking EFTs
The coefficients of the operators of an effective field theory (EFT) are constrained to satisfy certain inequalities, under the (mild) assumption that the UV completion satisfies general requirements of causality and unitarity. I discuss the extension of these ideas to theories where the Lorentz symmetry is spontaneously broken, as it happens in cosmology and condensed matter physics. I explain why the use of the S-Matrix run into immediate problems. Constraints can be derived using dispersive arguments for the 2-point function of conserved currents and applied to models of interest in high-energy and condensed matter.
- Speaker: Paolo Creminelli (ICTP, Trieste)
- Tuesday 05 December 2023, 14:00-15:00
- Venue: CMS, Pav. B, Meeting Room 11 (MR11).
- Series: Cosmology Lunch; organiser: Dr Dong-Gang Wang.
Fri 01 Dec 13:00: The Cosmological Tree Theorem
In recent years, there has been an increasing interest in the interplay between amplitudes and cosmological correlators, particularly in how amplitudes techniques can constrain cosmological correlators. In this talk, I will give an overview of the formalism of the wavefunction of the universe and how it relates to cosmological correlators. We will focus on how a new set of cutting rules, derived from causality, explains the analytic structure of wavefunction coefficients. These cutting rules further constrain the analytic structure of cosmological correlators, making explicit the absence of a particular kind of singularities. Finally, I will address future research in the rich interplay between amplitudes and cosmology.
- Speaker: Santiago Agui-Salcedo, University of Cambridge
- Friday 01 December 2023, 13:00-14:00
- Venue: Potter room/Zoom.
- Series: DAMTP Friday GR Seminar; organiser: Xi Tong.
Thu 14 Mar 16:00: How Did Cassiopeia A Explode?
Abstract not available
- Speaker: Martin Laming (US Naval Research Laboratory)
- Thursday 14 March 2024, 16:00-17:00
- Venue: Hoyle Lecture Theatre, Institute of Astronomy.
- Series: Institute of Astronomy Colloquia; organiser: eb694.
Wed 29 Nov 13:40: Probing galactic growth through the study of Low Surface Brightness tidal features
In hierarchical models, the assembly history of galaxies can be probed through the study of their Low Surface Brightness (LSB) stellar structures, which are remnants of past interactions and accretion events. These LSB tidal features are sensitive to the type of merger that occurred, but also to the environment and properties of their host galaxies. Using a dedicated annotation tool, we investigated of the properties of LSB tidal features around a sample of 475 nearby massive galaxies located in the Virgo cluster and in the field. We used deep images obtained with the Canada-France-Hawaii Telescope: MATLAS , CFIS/UNIONS, VESTIGE and NGVS . From our database of LSB structures we computed quantitative properties such as geometry and luminosity using automated aperture photometry. I will present results on the evolution of the fraction of galaxies with tidal debris and the fraction of luminosity in haloes as a function of the mass of the host galaxy and of its environment.
- Speaker: Elisabeth Sola
- Wednesday 29 November 2023, 13:40-14:05
- Venue: The Hoyle Lecture Theatre + Zoom .
- Series: Institute of Astronomy Seminars; organiser: .
Wed 29 Nov 13:15: Heavily Obscured AGN, a radio vs X-ray challenge
Heavily obscured AGN represent a fundamental phase in the MBH -galaxy coevolution scenario. They are expected to constitute a major fraction of the whole AGN population, in particular at high-z, but their statistics and evolution across cosmic time are still highly uncertain. A promising way to select most obscured AGN is through radio emission, which is largely unaffected by obscuration and can be used as a proxy for nuclear activity. In this talk, I will present a detailed investigation of the effectiveness of radio selection to discover heavily obscured AGN , I will compare their radio and X-ray detectability, and present predictions for current and future radio surveys. Our results show that, while X-ray selection is generally more effective in detecting unobscured AGN , radio selection is significantly more effective in detecting the most heavily obscured, Compton-thick AGN . Thousands of Compton-thick nuclei are indeed expected to hide among the sources of popular radio catalogs, escaping any detection in the corresponding X-ray observations. I will finally present expectations for the number of AGN to be detected by the continuum surveys of the Square Kilometer Array Observatory (SKAO). SKAO is expected to detect more than 2000 AGN at z>6, and even some tens at z>10: half of them Compton-thick.
- Speaker: Giovanni Mazzolari
- Wednesday 29 November 2023, 13:15-13:40
- Venue: The Hoyle Lecture Theatre + Zoom .
- Series: Institute of Astronomy Seminars; organiser: .
Mon 12 Feb 14:00: On the life of erupting flux ropes
Abstract not available
- Speaker: Jaroslav Dudik (Czech Academy of Sciences)
- Monday 12 February 2024, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.
Mon 11 Mar 14:00: Title to be confirmed
Abstract not available
- Speaker: Karen Meyer (Dundee)
- Monday 11 March 2024, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.
Mon 04 Mar 14:00: Title to be confirmed
Abstract not available
- Speaker: Martin Laming (NRL)
- Monday 04 March 2024, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.
Mon 26 Feb 14:00: Title to be confirmed
Abstract not available
- Speaker: Isobel Romero-Shaw (DAMTP)
- Monday 26 February 2024, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.
Mon 19 Feb 14:00: Title to be confirmed
Abstract not available
- Speaker: Alison Young (Edinburgh)
- Monday 19 February 2024, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.
Mon 12 Feb 14:00: Title to be confirmed
Abstract not available
- Speaker: Jaroslav Dudik (Czech Academy of Sciences)
- Monday 12 February 2024, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.
Mon 29 Jan 14:00: Title to be confirmed
Abstract not available
- Speaker: Peter Young (NASA Goddard)
- Monday 29 January 2024, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.
Mon 05 Feb 14:00: Title to be confirmed
Abstract not available
- Speaker: Frank Stefani (Helmholtz-Zentrum Dresden)
- Monday 05 February 2024, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.
Mon 22 Jan 14:00: Title to be confirmed
Abstract not available
- Speaker: Dan D'Orazio (Niels Bohr Institute)
- Monday 22 January 2024, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.
Tue 28 Nov 14:00: Understanding the initial stages of planet-driven gap formation
When planets form in protoplanetary discs, they interact gravitationally with the gas in the disc. This interaction excites spiral density waves which, when they dissipate, can cause the formation of gaps and rings. These gaps can be seen in observations from ALMA and JSWT , and could be used to infer the existence and location of planets. However, interpreting these observations requires robust models of how the planet and disc interact and how gaps form. I will show new work that provides a linear relationship between the angular momentum deposition caused by a planet and the resultant surface density evolution. I will discuss how this analytic model can help us understand the evolution of gap structures in viscous and inviscid discs.
- Speaker: Amelia Cordwell (DAMTP)
- Tuesday 28 November 2023, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.
Mon 27 Nov 14:00: Metastability of magnetohydrodynamic atmospheres and their relaxation
Motivated by explosive releases of energy in space and fusion plasmas, this talk considers the nonlinear convective stability of stratified magnetohydrodynamic (MHD) equilibria in 2D. We demonstrate that, unlike the Schwarzschild criterion in hydrodynamics (“entropy must increase upwards for convective stability”), the so-called modified Schwarzschild criterion for 2D MHD (or in any kind of fluid dynamics with more than one source of pressure) is a guarantor only of linear stability. As a result, in 2D MHD (unlike HD) there exist metastable equilibria that are unstable to nonlinear perturbations despite being stable to linear ones. We show that the minimum-energy configurations attainable by these atmospheres via non-diffusive reorganisation can be obtained by solving a combinatorial optimisation problem — these ground states are usually 2D and are fairly well reproduced by direct numerical simulations at small Reynolds number. For the case of relaxation at large Reynolds number, we construct a statistical mechanical theory based on the maximisation of Boltzmann’s mixing entropy (this is analogous to the Lynden-Bell statistical mechanics of self-gravitating systems and collisonless plasmas and the Robert-Sommeria-Miller theory of 2D vortices) — the minimum-energy states described above are the low-temperature limit of this theory. We show that the predictions of the statistical mechanics are in reasonable agreement with direct numerical simulations.
- Speaker: David Hosking (Princeton)
- Monday 27 November 2023, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.
Mon 27 Nov 13:00: Dissipative Inflation via Scalar Production
I will describe a new mechanism that gives rise to dissipation during cosmic inflation. In the simplest implementation, the mechanism requires the presence of a massive scalar field with a softly-broken global U(1) symmetry, along with the inflaton field. Particle production in this scenario takes place on parametrically sub-horizon scales, as opposed to the case of dissipation into gauge fields. Consequently, the backreaction of the produced particles on the inflationary dynamics can be treated in a local manner, allowing us to compute their effects analytically. I will show the parametric dependence of the power spectrum and its deviation from the usual slow-roll expression. I will show that non-Gaussianities are always sizeable whenever perturbations are generated by the noise induced by dissipation.
- Speaker: Luca Santoni (APC, Paris)
- Monday 27 November 2023, 13:00-14:00
- Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
- Series: Cosmology Lunch; organiser: Dr Dong-Gang Wang.