Tue 25 Feb 11:15: Exoplanet Detection with SPIRIT: Infrared CMOS Photometry and the Discovery of the Hot Neptune TOI-2407b
The SPECULOOS project is dedicated to the discovery of transiting exoplanets around ultracool dwarfs using high-precision ground-based observations. To enhance sensitivity to these cool stars, we have implemented SPIRIT , a new infrared detector utilizing CMOS technology instead of traditional CCDs. In this talk, I will present my work on developing the data pipeline for SPIRIT and optimizing its performance for detecting exoplanet transits. I will also highlight the discovery of TOI -2407b, a Neptune-like planet observed with this system.
- Speaker: Clàudia Janó Muñoz (University of Cambridge)
- Tuesday 25 February 2025, 11:15-12:00
- Venue: Coffee area, Battcock Centre.
- Series: Hills Coffee Talks; organiser: Charles Walker.
Mon 24 Feb 13:00: Total derivatives in cosmological perturbations: implications for decoherence and Bell violation
We examine the role of total time derivatives (boundary terms) in the action of cosmological perturbations and their impact on momentum-space entanglement, including the processes of decoherence and two-mode squeezing. We also discuss the necessity of considering such terms from several perspectives: the well-defined variational principle in gravity, the integration-by-parts procedure in cosmological perturbations and the WKB limit of the Wheeler-DeWitt equation. Finally, we explore their relevance in a proposed cosmological Bell test utilizing momentum-space entanglement, suggesting a possible window for Bell violation in minimal single-field inflation.
References: 2405.07141, 2305.08071 and 2207.04435
- Speaker: Chon Man Sou 蘇俊文 (Tsinghua U., Beijing)
- Monday 24 February 2025, 13:00-14:00
- Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
- Series: Cosmology Lunch; organiser: Thomas Colas.
Fri 21 Feb 13:00: Free conformally-rescaled hyperboloidal evolution: status and applications
Gravitational wave radiation is only unambiguously defined at future null infinity – the location in spacetime where light rays arrive and where global properties of spacetimes can be measured. Reaching future null infinity is thus very important for extracting correct waveforms. A convenient way to include it in numerical relativity simulations is via hyperboloidal foliations. I will focus on conformal compactification as method to implement free hyperboloidal evolution, in the BSSN / conformal Z4 formulations. After illustrating its advantages, I will report on some ongoing applications in spherical symmetry: an extension to include the Maxwell equations, scattering simulations on a given background, and wave equation(s) evolved on some FLRW -type spacetimes with time-dependent scale factor. I will conclude giving an update on ongoing work in 3D evolutions.
- Speaker: Alex Vañó-Viñuales (IST Lisbon)
- Friday 21 February 2025, 13:00-14:00
- Venue: Potter room.
- Series: DAMTP Friday GR Seminar; organiser: Daniela Cors.
Tue 04 Mar 11:15: Cygnus X-3 in 2024: many giant radio flares!
Cygnus X-3 is a `high mass X-ray binary’, which was first detected in the early days of X-ray astronomy, in 1966. It is also seen in the radio and the infra-red (but not optically due to obscuration). The emission is due to accretion from the companion star onto the compact source, thought to be a Wolf-Rayet star and a black hole respectively. It occasionally shows giant fares, and has been monitored—approximately daily—for several years with the Arcminute Microkelvin Image (AMI) at Lord’s Bridge, SW of Cambridge. During 2022 and 2023 was placid, with little variation in its radio (or X-ray) emission, but in 2024 it showed five giant radio flares, brightening from a few mJy to > 10 Jy over a few days.
- Speaker: Prof. Dave Green (Cavendish Astrophysics)
- Tuesday 04 March 2025, 11:15-12:00
- Venue: Martin Ryle Seminar Room, Kavli Institute.
- Series: Hills Coffee Talks; organiser: Charles Walker.
Wed 19 Feb 13:40: Probing the early history of the Milky Way through ancient carbon-rich stars
The oldest, most metal-poor stars we find in the Milky Way today were born in pristine environments in the early Universe. These local, ancient stars contain unique clues about the First Stars and the early formation and evolution of our Galaxy. At low metallicity, many stars have been found to be enhanced in carbon, coming in two main types: some contain the fingerprints of the First Stars and others have experienced binary interaction with an evolved companion. I recently built a homogeneous sample of C-rich metal-poor stars using the Gaia XP spectra, employing a neural network and a dedicated training sample. I will present this recent paper and discuss how the change in frequency of C-rich stars with Galactic environment relates to globular clusters and clustered star formation in the early Universe.
- Speaker: Anke Ardern-Arentsen / IoA
- Wednesday 19 February 2025, 13:40-14:05
- Venue: The Hoyle Lecture Theatre + Zoom .
- Series: Institute of Astronomy Seminars; organiser: Xander Byrne.
Mon 17 Feb 13:00: Explainable deep learning models in cosmology
Machine learning has significantly improved the way cosmologists model and interpret cosmological data; yet, its “black box” nature often limits our ability to trust and understand its results. In this talk, I will present an explainable deep learning framework designed to rely on a minimal set of physically interpretable parameters which describe the data. I will first discuss applications to dark matter halos, demonstrating how these neural networks can be used to model their final properties — such as their density profiles — and connect them to the underlying physics. Additionally, I will present applications to the cosmic microwave background, revealing to which parameters the CMB temperature power spectrum is sensitive in the context of early dark energy models.
- Speaker: Luisa Lucie-Smith (University of Hamburg)
- Monday 17 February 2025, 13:00-14:00
- Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
- Series: Cosmology Lunch; organiser: Thomas Colas.
Mon 17 Feb 13:00: Title to be confirmed
Abstract not available
- Speaker: Luisa Lucie-Smith (University of Hamburg)
- Monday 17 February 2025, 13:00-14:00
- Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
- Series: Cosmology Lunch; organiser: Thomas Colas.
Mon 17 Feb 14:00: Making waves in Stars: Bridging modern asteroseismology and numerical simulations
Stars and their evolution underpin most of modern astrophysics, enriching the galaxy with heavy elements and producing the progenitors of gravitational wave sources. Yet modern asteroseismology has shown that standard 1D stellar evolution models, used widely in astrophysics fall short when confronted with these detailed observations. The discrepancies lie in the 1D treatment of 3D processes, such as convective overshoot, waves and magnetism. In this talk I will review some of the important results from asteroseismology, my groups work over the years on these processes and the various ways in which we can make contact with the observations and (possibly) improve 1D models.
- Speaker: Tamara Rogers (Newcastle)
- Monday 17 February 2025, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Loren E. Held.
Thu 20 Mar 16:00: Exoplanet Clouds and Chemistry: A WASP-17b case study
In the short time since the start of JWST ’s science operations, it has caused a paradigm shift in the information and understanding of giant planet atmospheres. The spectroscopic IR capabilities have revealed absorption from H2O , CO2, and CO with exquisite precision, provided the first look at elusive methane absorption, and shown a diversity of photochemistry and disequilibrium processes at play in giant planet atmospheres. Previously obscuring aerosols that plagued UV-optical spectra are revealing themselves via distinct absorption and emission in the mid-IR confirming for the first time in irradiated exoplanets theoretical predictions of cloud formation. I will present a case study of one such planet which is revealing the roles of clouds and chemistry in exoplanet atmospheres and the feedback imparted between composition, dynamics, and detectability.
- Speaker: Hannah Wakeford
- Thursday 20 March 2025, 16:00-17:00
- Venue: Hoyle Lecture Theatre, Institute of Astronomy.
- Series: Institute of Astronomy Colloquia; organiser: Matthew Grayling.
Thu 06 Mar 16:00: The Death Throes of Massive Stars
Core collapse supernovae play many important roles in astronomy and astrophysics. They trigger and regulate star formation through the energy they inject into the interstellar medium and they forge and disperse elements that seed the next generation of stars. On much more compact scales, which is the focus area of this talk, core collapsing stars are the birth sites of neutron stars and black holes, and therefore they are the gateway to the compact Universe. Numerical simulations of the core collapse have rapidly progressed in the last decade. Explosions are now readily obtained, the key ingredient being multidimensionality. This colloquium will review recent progress in understanding the central engines at the heart of core-collapse supernovae. I’ll touch upon how we can still use 1D simulations to understand the population as a whole, 2D simulations to systematically study theoretical uncertainties and explore the multimessenger signals, and 3D simulations to push our understanding of these extreme events.
- Speaker: Evan O'Connor
- Thursday 06 March 2025, 16:00-17:00
- Venue: Hoyle Lecture Theatre, Institute of Astronomy.
- Series: Institute of Astronomy Colloquia; organiser: Matthew Grayling.
Thu 20 Mar 16:00: Exoplanet Clouds and Chemistry: A WASP-17b case study
In the short time since the start of JWST ’s science operations, it has caused a paradigm shift in the information and understanding of giant planet atmospheres. The spectroscopic IR capabilities have revealed absorption from H2O , CO2, and CO with exquisite precision, provided the first look at elusive methane absorption, and shown a diversity of photochemistry and disequilibrium processes at play in giant planet atmospheres. Previously obscuring aerosols that plagued UV-optical spectra are revealing themselves via distinct absorption and emission in the mid-IR confirming for the first time in irradiated exoplanets theoretical predictions of cloud formation. I will present a case study of one such planet which is revealing the roles of clouds and chemistry in exoplanet atmospheres and the feedback imparted between composition, dynamics, and detectability.
- Speaker: Dr Hannah Wakeford
- Thursday 20 March 2025, 16:00-17:00
- Venue: Hoyle Lecture Theatre, Institute of Astronomy.
- Series: Institute of Astronomy Colloquia; organiser: Matthew Grayling.
Mon 24 Feb 14:00: Instabilities and the remarkable survivability of AGN jets.
Jets powered by active galactic nuclei (AGN) appear impressively stable in comparison to their terrestrial and laboratory counterparts – they can be traced from their origin to distances exceeding their injection radius by up to a billion times. However some of them, the Fanaroff-Riley class I (FR-I) jets in particular, get disrupted and lose their coherence on the scale of host galaxy. It has been suggested that the survivability of AGN jets is related to their rapid expansion, and that the instabilities develop only when they eventually become confined/recollimated by the surrounding plasma.
Motivated by this hypothesis, we carried out 3D computer simulations of jets propagating through plasma with rapidly declining pressure and jets recollimated by galactic coronas with flat pressure distribution. The results support the stabilising role of jet expansion and show that the recollimation of unmagnetized jets by external pressure is indeed accompanied by a rapid development of instability and transition to a turbulent state. This instability is driven by the inertial force associated with the curved streamlines of recollimated jets and hence relates to the well-known centrifugal instability. Simulations of magnetised jets show that even relatively weak azimuthal magnetic field can suppress the recollimation instability, with the critical relativistic magnetisation parameter sigma about 0.01. These results are consistent with our heuristic analysis of the relativistic centrifugal instability (CFI) and the computer simulations of relativistic rotating fluids.
- Speaker: Serguei Komissarov (Leeds)
- Monday 24 February 2025, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Thomas Jannaud.
Thu 15 May 11:00: LCLU Coffee - TBA
TBA
- Speaker: TBA
- Thursday 15 May 2025, 11:00-12:00
- Venue: tba.
- Series: LCLU Coffee Meetings; organiser: Paul B. Rimmer.
Tue 11 Feb 11:15: The capacity of Constant Torsion Emergent Gravity to resolve cosmological tensions
Despite the success of the ΛCDM model in explaining a wide range of cosmological phenomena, observational discrepancies such as the Hubble tension and curvature tension, as well as theoretical challenges such as the inability to unify General Relativity with other fundamental forces in particle physics, have prompted a reevaluation of our current cosmological model and an exploration of other theories of gravity. We investigate the constant torsion emergent gravity (CTEG) model, a specific case of Poincare Gauge Theory (PGT) of gravity. This model introduces two extra cosmological parameters in addition to the six parameters in ΛCDM, and can be treated as a standard extension to ΛCDM with modified dark energy. This modification is then implemented with CAMB and the constraints of the cosmological parameters of PGT is obtained through nested sampling using Polychord and Cobaya. Our results offer a comparative analysis against the ΛCDM model, looking at the possibility of CTEG to resolve key observational tensions.
- Speaker: Sinah Legner (University of Cambridge)
- Tuesday 11 February 2025, 11:15-12:00
- Venue: Coffee area, Battcock Centre.
- Series: Hills Coffee Talks; organiser: Charles Walker.
Fri 14 Feb 13:00: Third law of black hole mechanics for supersymmetric black holes
The third law of black hole mechanics asserts that it is impossible for a non-extremal black hole to become extremal in finite time (in classical General Relativity). A proof of this law was claimed in the 1980s. However, counterexamples to this law were found recently: gravitational collapse of a massless charged scalar field can produce an exactly extremal Reissner-Nordstrom black hole in finite time, passing through an intermediate phase in which the solution is exactly Schwarzschild at the horizon. These examples involve matter with a large charge to mass ratio. What about theories, such as supersymmetric theories, with an upper bound on the charge to mass ratio of matter? In this case I have proved that one cannot form a supersymmetric black hole (such as extremal Reissner-Nordstrom) in finite time. Thus a third law holds for supersymmetric black holes. The proof involves ideas related to quasi-local energy. In this talk I shall review all of these developments.
- Speaker: Harvey Reall, DAMTP, Cambridge
- Friday 14 February 2025, 13:00-14:00
- Venue: Potter room/Zoom: https://cam-ac-uk.zoom.us/j/86544434784?pwd=dE3XiqwmaWGPz9w5pXNkKk93XsmtJv.1.
- Series: DAMTP Friday GR Seminar; organiser: Xi Tong.
Wed 12 Feb 13:40: Kaleidoscope of irradiated disks: VLT/MUSE observations of proplyds
The evolutionary pathways of protoplanetary disks differ depending on the surrounding environment. In massive star clusters, UV radiation affects disks via external photoevaporative winds, depleting the disks of their material and shortening their lifetimes. Known as proplyds, such irradiated disks are typically surrounded by a teardrop-shaped cloud of ionized gas and observed in forbidden emission lines.
While external photoevaporation of disks is unique to clusters such as the Orion Nebula Cluster (ONC), internal photoevaporative winds may be present in both high UV environments, and low-mass star forming regions with weak external UV fields. In the latter case, the winds arise due to radiation from the central star and can also be studied via forbidden line emission. It is therefore crucial to determine how to disentangle external winds from internal ones.
I will present the results based on the visually striking VLT /MUSE IFU data of a dozen proplyds in the ONC . This sample allows us to study the morphology of proplyds in a wealth of emission lines and determine their physical parameters. Among the results, I will present a proxy for unambiguously identifying externally driven winds with a forbidden line of neutral atomic carbon.
- Speaker: Mari-Liis Aru
- Wednesday 12 February 2025, 13:40-14:05
- Venue: The Hoyle Lecture Theatre + Zoom .
- Series: Institute of Astronomy Seminars; organiser: Xander Byrne.
Wed 12 Feb 13:15: Fact or FABLE: predictions for SMBH merger rates from cosmological simulations
The co-evolution of massive black holes and their host galaxies is well established within ΛCDM cosmology. The repeated mergers, accretion, and feedback that conspire to regulate this process can be studied in large-scale cosmological simulations, such as Illustris, FABLE , MillenniumTNG and Flamingo. These simulations resolve key galaxy formation processes at ~kpc scales, but are plagued with numerical inaccuracies at the smaller scales of black holes. This scale discrepancy presents significant challenges for investigating black hole properties and generating testable predictions, e.g. for future JWST , Gaia, LISA and IPTA observations of isolated and binary black holes. In this talk I will discuss the black hole population in FABLE . Our results show that the numerical treatment of black holes in cosmological simulations leads to a misleading picture, even at the well-resolved large scale of galaxies. In particular, a large fraction of black holes coalesce well before their host galaxies merge and thus require extra delays on the order of a few Gyrs. These delays, governed by the dynamical timescale of the merging host galaxies, occur before and in addition to any delays arising from unresolved ‘sub-grid’ physics describing BH hardening mechanisms on parsec scales. This effect has profound implications for the black hole merger rates predicted from these large-scale cosmological simulations as well as for the multi-messenger predictions, once black hole growth during these dynamical galaxy merger delays is accounted for.
- Speaker: Stephanie Buttigieg / IoA
- Wednesday 12 February 2025, 13:15-13:40
- Venue: The Hoyle Lecture Theatre + Zoom .
- Series: Institute of Astronomy Seminars; organiser: Xander Byrne.
Mon 10 Feb 14:00: Uncovering the physical origin of quasi-periodic oscillations from black hole X-ray binaries
Black hole X-ray binary systems consist of a black hole stripping material from its stellar companion to generate a large X-ray flux. Quasi-periodic oscillations (QPOs) with a period in the range 0.1 to 10 seconds are routinely observed in the X-ray flux from these systems. Despite being strong signals that have been detectable for around 40 years, the physical origin of these QPOs is still debated. The leading theory associates the QPO with the relativistic effect of Lense-Thirring precession. This model requires the black hole spin axis to be moderately misaligned with the binary rotation axis, in which case the frame dragging effect is expected to induce precession in the inner accretion flow. I will review the precession model and the observational evidence in support of it, as well as discussing alternative theories. I will focus on two key predictions of the precession model. First, I will show that the iron line emitted from the inner accretion disk oscillates between red and blue shifted with QPO phase. Second, I will describe our work to determine whether the X-ray polarization angle oscillates with QPO phase, which has recently been made possible by the launch of the Imaging X-ray Polarimetry Explorer (IXPE).
- Speaker: Adam Ingram (Newcastle)
- Monday 10 February 2025, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Thomas Jannaud.
Thu 06 Feb 16:00: TBC
Abstract not available
- Speaker: Speaker to be confirmed
- Thursday 06 February 2025, 16:00-17:00
- Venue: Hoyle Lecture Theatre, Institute of Astronomy.
- Series: Institute of Astronomy Colloquia; organiser: Jan Scholtz.
Mon 10 Feb 13:00: Spurious secular growth from loops in de Sitter
A well-established result in QFT in four-dimensional de Sitter spacetime states that the vacuum of a massless scalar field lacks a normalizable inner product. This has often been interpreted as evidence that the vacuum cannot remain invariant under the full de Sitter isometry group, suggesting the emergence of time-dependent (secular) growth in correlation functions computed in inflationary coordinates. However, the standard quantization of scalar fields in de Sitter spacetime using inflationary coordinates yields a vacuum state for the massless scalar field that explicitly preserves de Sitter symmetries, albeit with infrared divergences. In this talk, I will discuss the computation of n-point correlation functions and demonstrate that loop corrections do not further enhance the secular growth of these functions for massless scalars. I will also address the discrepancies between our findings and those reported in previous studies.
- Speaker: Gonzalo Palma (Universidad de Chile, Santiago)
- Monday 10 February 2025, 13:00-14:00
- Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
- Series: Cosmology Lunch; organiser: Thomas Colas.