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: 1 hour 32 min ago

Mon 13 May 14:00: Title to be confirmed

Wed, 07/02/2024 - 14:39
Title to be confirmed

Abstract not available

Add to your calendar or Include in your list

Tue 07 May 14:00: Title to be confirmed

Wed, 07/02/2024 - 14:38
Title to be confirmed

Abstract not available

Add to your calendar or Include in your list

Mon 29 Apr 14:00: Title to be confirmed

Wed, 07/02/2024 - 14:37
Title to be confirmed

Abstract not available

Add to your calendar or Include in your list

Fri 16 Feb 11:30: Light from the Cosmic Dawn: origin and observational signatures of the first black holes

Tue, 06/02/2024 - 12:56
Light from the Cosmic Dawn: origin and observational signatures of the first black holes

Abstract not available

Add to your calendar or Include in your list

Fri 09 Feb 13:00: Nonlinear stability of Einstein-matter models near the big bang singularity

Mon, 05/02/2024 - 16:59
Nonlinear stability of Einstein-matter models near the big bang singularity

In our recent work, we have made progress in understanding the complex mathematical landscape of the big bang singularity in general relativity. Utilizing Fuchsian partial differential equation techniques, we have established rigorous nonlinear stability results for certain Friedmann cosmological models, particularly focusing on solutions to the fully coupled Einstein-matter equations. This does not only reinforce some of the standard cosmological model’s assumptions in certain scenarios but also brings to light new critical phenomena that have yet to be fully understood. This research was conducted in collaboration with Todd Oliynyk from Monash University.

Add to your calendar or Include in your list

Thu 08 Feb 16:00: Stellar populations and dust build-up in the early Universe

Mon, 05/02/2024 - 16:15
Stellar populations and dust build-up in the early Universe

We are witnessing an exciting revolution in our understanding of the first galaxies. JWST observations have already revealed galaxies in the first few hundred million years of the Universe and their detailed characterization in terms of chemical enrichment and stellar populations, revealing galaxies as metal poor as 1% of the solar value, and even potential traces of the first (Pop III ) stars at z ≈ 6.5 – 10.5. In addition to the stunning discoveries made recently by JWST , there have also been recent probes of the dust content of galaxies in the first billion years of the Universe with ALMA . This is a key and rapid transition phase for the evolution of dust, as galaxy evolutionary timescales become comparable with the formation timescales of dust. In this talk, I will attempt to provide some indications on the diversity of physical properties of the first galaxies expected by theoretical models, and on the current (limited) understanding of dust enrichment at very early cosmic epochs.

Add to your calendar or Include in your list

Thu 15 Feb 16:00: Title to be confirmed

Mon, 05/02/2024 - 11:52
Title to be confirmed

Abstract not available

Add to your calendar or Include in your list

Thu 08 Feb 16:00: Stellar populations and dust build-up in the early Universe

Mon, 05/02/2024 - 11:48
Stellar populations and dust build-up in the early Universe

Abstract not available

Add to your calendar or Include in your list

Tue 13 Feb 13:00: Disc evolution in young intermediate-mass stars

Mon, 05/02/2024 - 09:05
Disc evolution in young intermediate-mass stars

Planets are born from circumstellar discs and the evolution of these discs determines the final architecture of planetary systems. The stellar mass range between 1.5 and 3.5 solar masses presents a particularly interesting circumstellar disc evolution; most notably, it is dominated by the EUV /FUV photoevaporation regime on the pre-main sequence, it contains the majority of gaseous debris discs, and it also shows the highest giant planet frequency. In our recent spectroscopic VLT /X-Shooter survey (UV to nIR), combined with WISE data (nIR to mIR), we identified 135 pre-main sequence (PMS) intermediate mass stars (IMSs) in the Southern sky. This is the first unbiased sample of IMSs in the PMS , allowing a study of disc evolution. Our sample, encompassing protoplanetary and debris discs, also revealed a significant number of discs between these two evolutionary stages. We find that the IR excess evolution of IMSs differs from that seen for low-mass stars (LMSs), exemplified by samples drawn from nearby star forming regions. We observe that, in IMSs, the inner disc regions are vacated in their entirety, in contrast to the LMSs where we note a more gradual inside-out dissipation. We also investigated the presence of gas absorption features in our sample via optical high-resolution spectroscopy to identify gas-bearing debris discs. This requires detailed comparisons to spectra of nearby stars to eliminate objects with foreground cloud absorption as cause of the absorption features. In particular, we apply this effective method to one such disc, eta Tel, discarding the earlier claim of disc wind as the origin for the absorption features. Finally, we discuss our several ongoing and future surveys investigating the nature of circumstellar discs around IMSs.

Add to your calendar or Include in your list

Fri 09 Feb 11:30: The quest for the earliest black holes: a theoretical perspective

Sat, 03/02/2024 - 12:41
The quest for the earliest black holes: a theoretical perspective

Abstract not available

Add to your calendar or Include in your list

Mon 12 Feb 14:00: The life of erupting flux ropes

Fri, 02/02/2024 - 13:31
The life of erupting flux ropes

Unstable magnetic flux ropes represent the primary driver of eruptive solar flares and thus space weather. We summarize the recent developments of the 3D extensions of the Standard model of solar flares, including formation of the flux ropes, identification of the erupting mechanism(s), and processes during the eruption proper. New reconnection geometries are reviewed, both from theoretical as well as observational standpoint, as these lead to re-building of the erupting flux rope once the eruption is underway.

Add to your calendar or Include in your list

Thu 08 Feb 11:30: Problems with (our) galaxy formation simulations and some new angles

Thu, 01/02/2024 - 14:26
Problems with (our) galaxy formation simulations and some new angles

Stellar feedback is a crucial component in controlling the baryon cycle in galaxies. However, it is not very clear how this can be done without assuming exotic models of stellar feedback. In this talk I will first discuss why we have not been very successful in producing realistic galaxies in our simulations, and present some attempts to solve this problem. I will also discuss how Lyman alpha profiles can potentially be used to place some constraints on cosmological simulations with cosmic ray feedback. This talk is intended to be thought-provoking rather than a collection of success stories.

Add to your calendar or Include in your list

Fri 28 Jun 11:30: Title to be confirmed

Wed, 31/01/2024 - 16:38
Title to be confirmed

Abstract not available

Add to your calendar or Include in your list

Mon 18 Mar 13:00: Title to be confirmed

Wed, 31/01/2024 - 15:00
Title to be confirmed

Abstract not available

Add to your calendar or Include in your list

Mon 19 Feb 14:00: Title to be confirmed

Wed, 31/01/2024 - 14:27
Title to be confirmed

TBD

Add to your calendar or Include in your list

Fri 19 Apr 11:30: Title to be confirmed

Wed, 31/01/2024 - 12:24
Title to be confirmed

Abstract not available

Add to your calendar or Include in your list

Fri 12 Apr 11:30: Title to be confirmed

Wed, 31/01/2024 - 12:23
Title to be confirmed

Abstract not available

Add to your calendar or Include in your list

Mon 05 Feb 14:00: Dynamo action, magnetorotational instability, Alfvén waves: Theory and experiments on astrophysical magnetohydrodynamics

Tue, 30/01/2024 - 13:52
Dynamo action, magnetorotational instability, Alfvén waves: Theory and experiments on astrophysical magnetohydrodynamics

The homogeneous dynamo effect in moving electrically conducting fluids, such as liquid metals or plasmas, is responsible for magnetic-field generation in planets, stars and galaxies. Magnetic fields, in turn, can promote cosmic structure formation by destabilizing, via the magnetorotational instability (MRI), rotational flows in accretion disks that otherwise would be hydrodynamically stable.

For a long time, those topics have been the subject of purely theoretical and numerical research. This situation changed in 1999 when the threshold of magnetic-field self-excitation was crossed in two large-scale liquid-sodium experiments in Riga and Karlsruhe. Later, the VKS dynamo experiment in Cadarache successfully reproduced field reversals and excursions that are of great geophysical interest. Various types of the MRI were studied in liquid metal experiments at the Princeton Plasma Physics Laboratory and at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). A liquid-rubidium experiment at the Dresden High Magnetic Field Laboratory (HLD) reached the “magic point” of coinciding Alfvén and sound speeds, which is thought to play a key role for the heating of the solar corona.

After a short introduction to the basic equations of magnetohydrodynamics, the lecture gives an overview about previous and future liquid metal experiments on dynamo action, Alfvén waves, and magnetically triggered flow instabilities such as the MRI . Special focus lies on a precession driven dynamo experiment that is presently being constructed in frame of the DRESDYN project at HZDR . Closely related to this, some emphasis is placed on the potential role of various astronomical forcings in triggering reversals of the geodynamo or even synchronizing the solar dynamo.

Add to your calendar or Include in your list

Fri 02 Feb 13:00: Towards reconciling Cosmology, GR and QFT through non-perturbative Stochastic Inflation

Tue, 30/01/2024 - 11:21
Towards reconciling Cosmology, GR and QFT through non-perturbative Stochastic Inflation

In the context of inflation, we show how to account for quantum modes in general and numerical relativity on scales bigger than the Hubble radius, from where they behave classically and can grow non-perturbatively.

We provide a formulation of Stochastic Inflation in full general relativity that goes beyond the slow-roll and separate universe approximations. Starting from the initial conditions problem in numerical relativity, we show how gauge invariant Langevin source terms can be obtained for the complete set of Einstein equations in their ADM formulation by providing a recipe for coarse-graining the spacetime in any small gauge. These stochastic source terms are defined in terms of the only dynamical scalar degree of freedom in single-field inflation and all depend simply on the first two time derivatives of the coarse-graining window function, on the gauge-invariant mode functions that satisfy the Mukhanov-Sasaki evolution equation, and on the slow-roll parameters.

We validate the efficacy of these Langevin dynamics directly using an example in uniform field gauge, obtaining the stochastic e-fold number without the need for a first-passage-time analysis. As well as investigating the most commonly used gauges in cosmological perturbation theory, we also derive stochastic source terms for the coarse-grained first-order BSSN formulation of Einstein’s equations, which enables a well-posed implementation for 3+1 numerical relativity simulations.

Based on https://arxiv.org/abs/2401.08530v1

Add to your calendar or Include in your list

Tue 06 Feb 13:00: Photoevaporation from Exoplanet Atmospheres: Understanding the Role of Stellar Winds and Considering Water-rich Atmospheres Room changed

Tue, 30/01/2024 - 10:54
Photoevaporation from Exoplanet Atmospheres: Understanding the Role of Stellar Winds and Considering Water-rich Atmospheres

The atmospheres of close-in exoplanets are extremely vulnerable to the effects of stellar UV to X-ray radiation. Photoevaporation can significantly alter planetary atmospheres or even strip them entirely, potentially rendering a planet uninhabitable. Understanding how these atmospheres evolve, persist, or fade away remains a fundamental challenge. In this talk, I will discuss two distinct but interconnected areas of photoevaporative research.

Firstly, I will discuss the interaction between the stellar wind and photoevaporating atmospheres. I will present 3D magnetohydrodynamic simulations of the interaction between the stellar wind and the photoevaporating outflow of a planet orbiting an M dwarf. This analysis reveals a diverse range of magnetosphere morphologies and plasma distributions due to the wind-outflow interaction. I consider how these changing morphologies might impact observable hydrogen Lyman-alpha signatures during planetary transits.

In the second part, I will delve into our current understanding of photoevaporation from water-rich atmospheres. Conventional analytic approaches often oversimplify the process, assuming two scenarios: the escape of only lighter hydrogen, or the dragging of oxygen along with escaping hydrogen. These two scenarios lead to two end cases: a planet that has retained its water-rich atmosphere or a planet which has lost its atmosphere, becoming dry and desiccated. I will challenge these oversimplifications by presenting results from a novel 1D multifluid hydrodynamic model of photoevaporation from a water-rich atmosphere, which shows oxygen escape should no longer be described by a simple on/off switch but instead requires careful modelling.

Room changed

Add to your calendar or Include in your list

Upcoming Talks

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