skip to content
Home

Cavendish Astrophysics

 

Upcoming talks

Subscribe to Upcoming talks feed
Description to be confirmed
URL: http://talks.cam.ac.uk/show/index/54089
Updated: 48 min 52 sec ago

Thu 20 Mar 16:00: Exoplanet Clouds and Chemistry: A WASP-17b case study

Tue, 11/02/2025 - 08:50
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.

Add to your calendar or Include in your list

Thu 06 Mar 16:00: The Death Throes of Massive Stars

Tue, 11/02/2025 - 08:48
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.

Add to your calendar or Include in your list

Thu 20 Mar 16:00: Exoplanet Clouds and Chemistry: A WASP-17b case study

Mon, 10/02/2025 - 14:36
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.

Add to your calendar or Include in your list

Mon 24 Feb 14:00: Instabilities and the remarkable survivability of AGN jets.

Mon, 10/02/2025 - 11:05
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.

Add to your calendar or Include in your list

Wed 12 Feb 10:00: Towards Habitable Worlds: Detailed Characterization of the Nearest Planetary Systems Note new Zoom details

Mon, 10/02/2025 - 10:48
Towards Habitable Worlds: Detailed Characterization of the Nearest Planetary Systems

Over the past thirty years, astronomers have made extraordinary progress in detecting planets around other stars. We now know that stars commonly host planets with a wider range of physical properties and system architectures than exist in our own solar system, and that planets likely outnumber stars in our galactic neighborhood. Now, planet detection and characterization technologies have advanced to the point that it should be possible to search for signs of life in the atmospheres of Earth-like exoplanets around Sun-like stars within a few decades. These observations will give us our first glimpse at how common—or rare—life is in the universe. However, before we can carry out these observations and understand the implications for the abundance of life outside the Solar system, we must first find the nearest habitable planets to observe, learn their detailed properties, and refine our understanding of habitability. In this talk, I will describe my group’s work to fill in these knowledge gaps by developing new tools and methods to detect and characterize exoplanets. First, I will show how cutting-edge machine learning methods could help reveal the closest potentially habitable planets to Earth—ideal for biosignature searches in the 2040s. Next, I will show how we can learn about extrasolar geochemistry by studying planetary accretion onto white dwarf stars—allowing us to see whether geological processes important for habitability on Earth take place in other systems. And finally, I will describe our work to understand what happens to planets when stars run out of nuclear fuel and find out whether life can continue in a system after the host star’s death.

Note new Zoom details

Add to your calendar or Include in your list

Tue 11 Feb 11:15: The capacity of Constant Torsion Emergent Gravity to resolve cosmological tensions

Fri, 07/02/2025 - 11:07
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.

Add to your calendar or Include in your list

Fri 14 Feb 13:00: Third law of black hole mechanics for supersymmetric black holes

Fri, 07/02/2025 - 10:41
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.

Add to your calendar or Include in your list

Wed 12 Feb 13:40: Kaleidoscope of irradiated disks: VLT/MUSE observations of proplyds

Thu, 06/02/2025 - 14:06
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.

Add to your calendar or Include in your list

Fri 14 Feb 11:30: The history of the Milky Way's bar

Thu, 06/02/2025 - 13:07
The history of the Milky Way's bar

The emergence of barred galaxies is a sensitive indicator of the conditions in the early Universe. Current cosmological simulations now routinely produce realistic barred galaxies but reproducing the precise distributions of morphology and properties remains challenging. One route to understanding how bars form and evolve is to look close to home at our own Galaxy’s bar. I will describe work on measuring the epoch of bar formation in the Milky Way using data from Gaia and a ground-based astrometric catalogue VVV /VIRAC from the VISTA telescope. I will describe how the bar formation can be dated by studying the star formation history in the Milky Way’s nuclear stellar disc, a central structure intimately related to the bar, and describe the broader implications of the derived bar formation epoch for the history of our Galaxy.

Add to your calendar or Include in your list

Wed 12 Feb 13:15: Fact or FABLE: predictions for SMBH merger rates from cosmological simulations

Wed, 05/02/2025 - 16:09
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.

Add to your calendar or Include in your list

Mon 10 Feb 14:00: Uncovering the physical origin of quasi-periodic oscillations from black hole X-ray binaries

Wed, 05/02/2025 - 08:34
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).

Add to your calendar or Include in your list

Thu 06 Feb 16:00: TBC

Tue, 04/02/2025 - 16:01
TBC

Abstract not available

Add to your calendar or Include in your list

Mon 10 Feb 13:00: Spurious secular growth from loops in de Sitter

Tue, 04/02/2025 - 15:58
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.

Add to your calendar or Include in your list

Thu 20 Feb 16:00: The importance of being wide: The key role of wide binaries, from GW sources to Pluto

Mon, 03/02/2025 - 19:04
The importance of being wide: The key role of wide binaries, from GW sources to Pluto

Dense stellar clusters are known to be hotbeds of collisional stellar dynamics, driving a diverse array of phenomena, from gravitational-wave sources and X-ray binaries to blue stragglers. While the Galactic field is typically considered too sparse for such interactions, this view overlooks the significant role of ultra-wide binaries and triples (separations > 1000 AU). These systems possess large cross-sections for encounters, leading to surprisingly high interaction rates even in low-density environments. Cumulative effects from repeated flybys can trigger strong interactions between system components, effectively enabling collisional dynamics and associated phenomena within the field.

Shifting focus to smaller scales, wide binary Kuiper Belt objects can also undergo mergers and collisions. However, instead of direct collisions, these events are driven by secular evolution within hierarchical triple systems. This mechanism offers a compelling explanation for the formation of objects like Arrokoth and the Pluto-Charon system.

Add to your calendar or Include in your list

Fri 07 Feb 13:00: Unimodular JT gravity and de Sitter quantum cosmology

Mon, 03/02/2025 - 18:51
Unimodular JT gravity and de Sitter quantum cosmology

In this talk, I will show how a gauge-theoretic approach to Jackiw–Teitelboim (JT) gravity naturally yields a two-dimensional Henneaux–Teitelboim (HT) unimodular theory, applicable to both flat and curved spacetimes. Under a mini-superspace reduction, the Wheeler–DeWitt equation becomes a Schrödinger-like equation admitting a consistent, unitary quantum description. The resulting wavefunction describes a quantum distribution for the scale factor, illuminating cosmic expansion and contraction, and allowing topology change at a=0.

Add to your calendar or Include in your list

Fri 04 Apr 11:30: Title to be confirmed

Mon, 03/02/2025 - 16:31
Title to be confirmed

Abstract not available

Add to your calendar or Include in your list

Wed 12 Feb 10:00: Towards Habitable Worlds: Detailed Characterization of the Nearest Planetary Systems

Mon, 03/02/2025 - 10:34
Towards Habitable Worlds: Detailed Characterization of the Nearest Planetary Systems

Over the past thirty years, astronomers have made extraordinary progress in detecting planets around other stars. We now know that stars commonly host planets with a wider range of physical properties and system architectures than exist in our own solar system, and that planets likely outnumber stars in our galactic neighborhood. Now, planet detection and characterization technologies have advanced to the point that it should be possible to search for signs of life in the atmospheres of Earth-like exoplanets around Sun-like stars within a few decades. These observations will give us our first glimpse at how common—or rare—life is in the universe. However, before we can carry out these observations and understand the implications for the abundance of life outside the Solar system, we must first find the nearest habitable planets to observe, learn their detailed properties, and refine our understanding of habitability. In this talk, I will describe my group’s work to fill in these knowledge gaps by developing new tools and methods to detect and characterize exoplanets. First, I will show how cutting-edge machine learning methods could help reveal the closest potentially habitable planets to Earth—ideal for biosignature searches in the 2040s. Next, I will show how we can learn about extrasolar geochemistry by studying planetary accretion onto white dwarf stars—allowing us to see whether geological processes important for habitability on Earth take place in other systems. And finally, I will describe our work to understand what happens to planets when stars run out of nuclear fuel and find out whether life can continue in a system after the host star’s death.

Add to your calendar or Include in your list

Wed 12 Feb 10:00: Towards Habitable Worlds: Detailed Characterization of the Nearest Planetary Systems

Mon, 03/02/2025 - 10:33
Towards Habitable Worlds: Detailed Characterization of the Nearest Planetary Systems

Over the past thirty years, astronomers have made extraordinary progress in detecting planets around other stars. We now know that stars commonly host planets with a wider range of physical properties and system architectures than exist in our own solar system, and that planets likely outnumber stars in our galactic neighborhood. Now, planet detection and characterization technologies have advanced to the point that it should be possible to search for signs of life in the atmospheres of Earth-like exoplanets around Sun-like stars within a few decades. These observations will give us our first glimpse at how common—or rare—life is in the universe. However, before we can carry out these observations and understand the implications for the abundance of life outside the Solar system, we must first find the nearest habitable planets to observe, learn their detailed properties, and refine our understanding of habitability. In this talk, I will describe my group’s work to fill in these knowledge gaps by developing new tools and methods to detect and characterize exoplanets. First, I will show how cutting-edge machine learning methods could help reveal the closest potentially habitable planets to Earth—ideal for biosignature searches in the 2040s. Next, I will show how we can learn about extrasolar geochemistry by studying planetary accretion onto white dwarf stars—allowing us to see whether geological processes important for habitability on Earth take place in other systems. And finally, I will describe our work to understand what happens to planets when stars run out of nuclear fuel and find out whether life can continue in a system after the host star’s death.

Add to your calendar or Include in your list

Fri 02 May 11:30: Title to be confirmed

Mon, 03/02/2025 - 09:33
Title to be confirmed

Abstract not available

Add to your calendar or Include in your list

Fri 07 Feb 13:00: Unimodular JT gravity and de Sitter quantum cosmology

Thu, 30/01/2025 - 11:42
Unimodular JT gravity and de Sitter quantum cosmology

In this talk, I will show how a gauge-theoretic approach to Jackiw–Teitelboim (JT) gravity naturally yields a two-dimensional Henneaux–Teitelboim (HT) unimodular theory, applicable to both flat and curved spacetimes. Under a mini-superspace reduction, the Wheeler–DeWitt equation becomes a Schrödinger-like equation admitting a consistent, unitary quantum description. The resulting wavefunction describes a quantum distribution for the scale factor, illuminating cosmic expansion and contraction, and allowing topology change at a=0.

Add to your calendar or Include in your list

Contact us

Battcock Centre for Experimental Astrophysics
Cavendish Laboratory
JJ Thomson Avenue
Cambridge CB3 0HE

Site Privacy & Cookie Policies

Quick links

Study at Cambridge

About the University

Research at Cambridge