Next Colloquia

The Milky Way experienced a major satellite merger 10 Gyr ago which altered, but did not destroy, the early high-alpha disk and created both an accreted and an in situ inner halo. The low-alpha disk that formed subsequently became bar-unstable 8 Gyr ago, creating the b/p bulge that also contains the inner high-alpha disk stars. M31 experienced a similar major satellite merger 3 Gyr ago which greatly heated and mixed the pre-existing high-metallicity disk, and also caused a massive inflow of gas and the formation of a dynamically hot secondary inner disk. Such a merger is consistent with the wide-spread star formation event 2-4 Gyr ago seen in disk colour-magnitude diagrams, and with the major substructures and metal-rich stars in the inner halo of M31 , when comparing photometric and recent spectroscopic data with available models. The merged satellite must have had a broad metallicity distribution and would have been the third most massive galaxy in the Local Group before the merger.

• Speaker: Ortwin Gerhard, MPE (Garching)
• Thursday 15 May 2025, 16:00-17:00
• Venue: Hoyle Lecture Theatre, Institute of Astronomy.
• Series: Institute of Astronomy Colloquia; organiser: .

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Gravitational-wave observations have revealed the population of stellar remnants from a new angle. Yet their stellar progenitors remain uncertain, in particular in the case of black holes. At least a fraction of these stars is believed to form in isolated binary systems. In this talk, I will discuss how binary mass transfer affects the late evolution and final fate of massive stars. The focus will be on stars that transfer their outer layers to a companion star and become binary-stripped. Binary-stripped stars develop systematically different core structures compared to single stars. I will discuss consequences for supernovae, black hole formation, and gravitational-wave observations.

• Speaker: Eva laplace, University of Leuven, Belgium
• Thursday 22 May 2025, 16:00-17:00
• Venue: Hoyle Lecture Theatre, Institute of Astronomy.
• Series: Institute of Astronomy Colloquia; organiser: ag2017.

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The Milky Way experienced a major satellite merger 10 Gyr ago which altered, but did not destroy, the early high-alpha disk and created both an accreted and an in situ inner halo. The low-alpha disk that formed subsequently became bar-unstable 8 Gyr ago, creating the b/p bulge that also contains the inner high-alpha disk stars. M31 experienced a similar major satellite merger 3 Gyr ago which greatly heated and mixed the pre-existing high-metallicity disk, and also caused a massive inflow of gas and the formation of a dynamically hot secondary inner disk. Such a merger is consistent with the wide-spread star formation event 2-4 Gyr ago seen in disk colour-magnitude diagrams, and with the major substructures and metal-rich stars in the inner halo of M31 , when comparing photometric and recent spectroscopic data with available models. The merged satellite must have had a broad metallicity distribution and would have been the third most massive galaxy in the Local Group before the merger.

• Speaker: Ortwin Gerhard, MPE (Garching)
• Thursday 15 May 2025, 16:00-17:00
• Venue: Hoyle Lecture Theatre, Institute of Astronomy.
• Series: Institute of Astronomy Colloquia; organiser: .

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Abstract not available

• Speaker: Ortwin Gerhard, MPE (Garching)
• Thursday 15 May 2025, 16:00-17:00
• Venue: Hoyle Lecture Theatre, Institute of Astronomy.
• Series: Institute of Astronomy Colloquia; organiser: .

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The gravitational pull of a black hole attracts gas and forms an accretion disk where the interplay between hydromagnetic processes and the warping of space-time releases gravitational energy in the form of radiation, relativistic jets, and winds. Most gas falls into supermassive black holes when the accretion rate approaches the Eddington limit (L=Ledd), at which point radiation pressure overcomes gravity. To date, our knowledge of such `luminous’ black hole accretion disks mostly relies on semi-analytical models, supplemented by a limited set of numerical simulations. In my talk I will discuss new insights gained from state-of-the-art radiative general relativistic magnetohydrodynamics (GRMHD) simulations of accretion near the Eddington limit such as the formation of a hot corona, disk truncation, and other physical processes driving the spectral evolution of luminous black holes. I will finish my talk by discussing the challenges and opportunities the next-generation of GRMHD simulations will bring in developing a comprehensive understanding of black hole accretion across the luminosity spectrum.

• Speaker: Matthew Liska
• Friday 09 May 2025, 11:30-12:30
• Venue: Hoyle Lecture Theatre, Institute of Astronomy.
• Series: Institute of Astronomy Colloquia; organiser: Debora Sijacki.

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Brown dwarfs are often described as failed stars, however the flip side of this description is that they can also be described as over-ambitious planets. With masses between 13-70 Jupiter masses they have cool atmospheres dominated by cloud features, molecules and show features due to weather. These atmospheres have a lot of similarities with atmospheres we see in planets in our solar system, and also directly imaged exoplanets. The question then is: How like hot Jupiters are irradiated brown dwarfs? In this seminar I will describe the known irradiated brown dwarfs and how they evolve into post-common envelope systems containing a white dwarf. These rare binaries have very short periods (~hrs) and the brown dwarf is irradiated by the white dwarf companion, often with large amounts of UV radiation. I will discuss the atmospheres of these highly irradiated brown dwarfs and their similarities with irradiated exoplanets.

• Speaker: Dr Sarah Casewell
• Thursday 01 May 2025, 16:00-17:00
• Venue: Hoyle Lecture Theatre, Institute of Astronomy.
• Series: Institute of Astronomy Colloquia; organiser: Jan Scholtz.

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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.

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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.

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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.

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Astronomy of the Milky Way Galaxy has entered a transformative era. The Gaia mission and an ensemble of ground-based spectroscopic surveys are delivering element abundances and velocities for millions of stars. These data provide both an opportunity to deepen our understanding of galaxy formation and to test the “limits of knowledge.” There have been several surprises that have come out of the large stellar surveys and data-driven methodologies built to analyse them. We have learned that up to 1 in 100 stars in the disk are “abundance doppelgangers” – chemically identical but unrelated – limiting the prospect of reconstructing the disk’s star cluster building blocks. Furthermore, for stars in the disk, most of the element abundances measured for most of the stars can be predicted to a precision of better than 10 percent given only two key abundances. However, this is not the case for stars in the stellar halo. These findings frame how we can most effectively work with the data to turn photons into a quantified description of Galactic history and provide strong constraints on the star formation and mixing processes that have set the Galactic environment.

• Speaker: Melissa Ness, Research School of Astronomy and Astrophysics (RSAA), Australian National University, Canberra, Australia
• Thursday 13 March 2025, 16:00-17:00
• Venue: Hoyle Lecture Theatre, IoA (tea at 3:30 pm).
• Series: The Eddington Lectures ; organiser: .

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