2024 Seminar Abstracts

Richard McCracken

Title: Hunting for exoplanets with a fine-toothed comb

Astrocombs are broadband, high-repetition rate optical frequency combs that are used for the calibration of astronomical spectrographs. Their precision and accuracy make astrocombs a critical technology that will enable ground-breaking observations in the fields of exoplanets, cosmology, and fundamental physics. The conflicting requirements of resolvable comb line spacing (usually >10 GHz), broadband spectral coverage (from below 400 to above 2400 nm) and compatibility with low-maintenance operation represents a significant technical challenge. In this talk I will present an overview of these instruments and will highlight our work on developing broadband astrocombs for the Southern African Large Telescope (SALT) and the upcoming Extremely Large Telescope (ELT).

Joseph Barker

Title: Metadynamics calculations of the effect of thermal spin fluctuations on skyrmion stability

The stability of magnetic skyrmions has been investigated in the past, but mostly in the absence of thermal fluctuations. However, thermal spin fluctuations modify the magnetic properties (exchange stiffness, Dzyaloshinskii-Moriya interaction (DMI) and anisotropy) that define skyrmion stability. Thermal magnons also excite internal skrymion dynamics, deforming the skyrmion shape. Entropy has also been shown to modify skyrmion lifetimes in experiments, but is absent or approximated in previous studies. Here we use metadynamics to calculate the free energy surface of a magnetic thin film in terms of the topological charge and magnetization. We identify the free energy minima corresponding to different spin textures and the lowest energy paths between the ferromagnetic and single skyrmion states. We show that at low temperatures the lowest free energy barrier is a skyrmion collapse process. However, this energy barrier increases with temperature. An alternative path, where a singularity forms on the skrymion edge, has a larger free energy barrier at low temperatures but decreases with increasing temperature and eventually becomes the lowest energy barrier. (https://arxiv.org/abs/2310.03169)

Clare Dobbs

Title: The formation of clusters and associations in spiral galaxies

I will present simulations of cluster formation in regions taken from galaxy scale simulations, including photoionization and supernovae feedback. We simulate regions with different densities, and from different galactic environments. In all our simulations, clusters undergo mergers and splits during their formation. More massive clusters form in regions of spiral arms with stronger converging flows, and in bars and inner spiral arm regions. In inter-arm or outer galaxy regions, we tend to see looser groups more characteristic of associations. In all simulations, the most massive clusters are formed by mergers. Feedback has a greater impact on cluster formation at lower densities, where star formation occurs over a longer timescale. In our lowest density case, the resulting clusters (in terms of number, mass) are very different with and without feedback, and one of our simulations forms an association which has a similar size, mass and morphology to the Orion OB1 association. We also show that photoionizing feedback is necessary to produce clusters with the observed cluster mass relation. Initial results with magnetic fields show that magnetic fields can have a strong impact on cluster formation, depending on field strength. We also compare our simulations with the observed Crutcher relation. Lastly, we place our simulated clusters into the GAIA catalogue and try to re-identify them. We find that the spatial properties of clusters are surprisingly robust even at relatively large distances and when relatively few members of the original cluster are observed. However dynamical measurements tend to be much less reliable.

James Mullaney

Title: The Climate of Black Hole Growth

Over the past 30 years, it has become increasingly clear that all massive galaxies contain, at their centers, a supermassive black hole. Over the same period of time, many astronomers have come to the conclusion that the energy released when these black holes accrete matter plays a key role in shaping their host galaxies. As such, understanding what causes supermassive black hole accretion is thought to be fundamental to our understanding of galaxy formation and evolution. Unfortunately, while accretion events are long lasting compared to human timescales, they are extremely short-lived on galactic timescales, making the identification of causal relationships between host and accretion very challenging. In this seminar, I will talk about how a statistical approach can help to uncover the causes of supermassive black hole accretion.

Joe Lyman

Title: Transient astrophysics with the Gravitational wave Optical Transient Observer (GOTO)

Beginning in 2017, with the discovery of GW170817, we moved to the era of gravitational-wave multi-messenger astronomy. This single source, caused by the merging of two neutron stars, was detected both as a gravitational-wave source by the LIGO/Virgo interferometers, and as a multi-wavelength electromagnetic astrophysical transient. In this talk I will briefly recap ground-breaking results from GW170817, and
the scientific potential from observing more multi-messenger events, as motivation for the GOTO project. I will present our telescope array GOTO, designed to search the skies for fast-evolving transients. I’ll show our developments for optimising recovery of multi-messenger events, and introduce some intriguing transient discoveries from a pilot classification programme on La Palma – GOTO-FAST.

Zoë Henderson

Title: Glass Surfaces on the Nanoscale: Surface Analysis at NSG Pilkington

As a member of the NSG Group, Pilkington United Kingdom Limited is one of the leading glass suppliers in the UK, producing glass for the architectural and automotive industries as well as producing glass for creative technology applications. Within Research and Development (R&D), the Surface Analysis team provide analytical expertise and technical support for the company in both R&D projects and commercial products. This talk will aim to take the audience through the glass manufacture process, production methods, and look at how probing nanoscale phenomena with surface analysis techniques supports R&D and the wider business.

Steve Longmore

Title: Early results from the ALMA Large Program, ACES (“ALMA Central Molecular Zone Exploration Survey”)

The extreme environment and relative proximity to Earth make the centre of our Galaxy a unique astrophysical laboratory. The gas properties, radiation field, cosmic ray ionisation rate, etc., are more similar to those in the centre of other galaxies, starbursts and high-z galaxies than the Solar neighbourhood. It is the only such extreme environment in which it is possible to resolve down to size scales of individual forming stars and link the small-scale physics of star formation and feedback with the galactic-scale
processes that together drive the evolution of galaxies. In this talk I will present early results from the ALMA Large Program, ACES (“ALMA Central Molecular Zone Exploration Survey”), which uses ALMA’s combination of sensitivity, resolution, and image fidelity to derive the gas properties from cloud scales down to the size scale of individual forming stars across the inner 100pc of the Galaxy. I will then present initial results from a JWST program to uncover and derive the properties of the previously hidden Young Stellar Object population in Galactic Centre molecular clouds. Finally, I will describe a proposed open Treasury Program of the inner 100pc of the Galaxy with JWST to measure the spatially resolved star formation history, identify recently formed massive stars and candidate Young Stellar Objects down to ∼1 Msun and constrain the 3D structure of the molecular gas, the Nuclear Stellar Disk, and the Nuclear Star Cluster.

Ziri Younsi

Title: Studying Black Holes on Event Horizon-Scales

Black holes possess gravitational fields so strong that not even light can escape their event horizons. For more than a century, black holes were predicted to exist, but direct observational confirmation remained elusive. In April 2019 the Event Horizon Telescope Collaboration (EHTC) published the first ever “image” of a supermassive black hole in the M87 galaxy. In May 2022 the EHTC subsequently published an image of the Galactic Centre supermassive black hole.
In this talk I will present an overview of black hole physics and radiation processes occurring near event horizons, together with an introduction to the EHT. I will discuss how these and other complimentary observations may provide important insights into the properties of black holes and the physical processes occurring in their surrounding environments. Finally, I will touch upon some of the exciting future prospects for these novel new studies of black holes.

Alex Hall

Title: Testing the concordance cosmological model with Euclid

The Lambda-CDM model of cosmology has proven an immensely successful description of our Universe, accounting for a wide range of astrophysical phenomena. At the same time, the model is deeply unsatisfying because it requires Dark Energy and Dark Matter, neither of which are understood at a fundamental level. Dark Energy measurements in particular are vastly at odds with vacuum energy predictions, potentially indicating the need for new fundamental physics. These questions have motivated Euclid, the European Space Agency’s flagship Dark Energy mission. Euclid was launched in July 2023 and is shortly due to start a galaxy survey covering almost the entire accessible extragalactic sky. In the talk, I will describe the Euclid project, its core cosmology probes Weak Lensing and Galaxy Clustering, and discuss what our understanding of the large-scale Universe might look like at the end of its nominal 6-year mission.

Pavel Kroupa

Title: The first star clusters and the formation of super-massive black holes therein

The most massive galaxies started to form earliest and on the shortest time. At their centres the formation began with the first ultra-massive star clusters, weighing 10^7-10^10 Msun. This mass depends on the mass of the post-Big-Bang gas cloud that later (on the downsizing time-scale) evolves to the early-type galaxy or bulge. I will discuss the physical and dynamical processes in these clusters, which, due to the low metallicity, form with top-heavy stellar initial mass functions, and how the formation of the surrounding spheroidal galaxy dictates their evolution. For spheroid masses larger than a few 10^9 Msun, the central cluster implodes to a SMBH seed which can continue to grow as long as the spheroid keeps forming on the downsizing time-scale. The result of these events is the present-day observed strong correlation between the SMBH mass and its hosting spheroid. This theory also explains the existence of quasars at redshifts larger than 9