Thu 27 Feb 16:00: What makes a planet “giant”?
The formation history of giant planets, both within and beyond our solar system, remains an open question. I propose a new pathway for giant planet formation, where runaway gas accretion begins only when a planet reaches about 100 Earth masses and occurs only after a few million years (Myrs). This suggests that the transition to a gas giant—defined as a planet primarily composed of hydrogen and helium—occurs at around Saturn’s mass. The delay in runaway gas accretion to later stages and higher planetary masses results from an intermediate phase of efficient heavy-element accretion. This process generates enough energy to hinder rapid gas accretion. Consequently, Saturn may never have undergone runaway gas accretion, classifying it as a “failed giant planet.” This proposed transition to a gas giant planet above Saturn’s mass naturally explains the distinct bulk metallicities and internal structures of Jupiter and Saturn, as well as the unique characteristics of Uranus and Neptune. In the context of giant exoplanets, postponing runaway gas accretion to planets exceeding Saturn’s mass explains the transitions in the mass-radius (M-R) relations of observed exoplanets, the relatively low occurrence of gas giants, and the high metallicity of intermediate-mass exoplanets.
- Speaker: Ravit Helled
- Thursday 27 February 2025, 16:00-17:00
- Venue: Hoyle Lecture Theatre, Institute of Astronomy.
- Series: Institute of Astronomy Colloquia; organiser: Matthew Grayling.
Thu 06 Feb 16:00: Star-forming Galaxies at Cosmic Noon and Beyond
Lookback studies over the past two decades have assembled a fairly complete census of galaxies over 85% of cosmic time and established that the bulk of stars, which today reside in massive ellipticals and spirals, formed rapidy at redshift z~1-3, “cosmic noon”. An exciting new era has now begun, with dramatic advances driven by facilities such as JWST , the Very Large Telescope, ALMA and NOEMA . I will summarize the state-of-the-art and discuss recent key insights in our understanding of galaxy evolution at and beyond cosmic noon, with a focus on the assembly and transformations of galactic structure and kinematics. I will highlight emerging frontiers for science with the Extremely Large Telescope and other upcoming transformative capabilities towards the end of the decade.
- Speaker: Natascha M. Foerster Schreiber
- Thursday 06 February 2025, 16:00-17:00
- Venue: Hoyle Lecture Theatre, Institute of Astronomy.
- Series: Institute of Astronomy Colloquia; organiser: Jan Scholtz.
Tue 04 Feb 13:00: Uncovering the stellar impact on planetary systems through population demographics
Host stars play a huge role in shaping the planetary systems they host, both through their evolution and through the influence they have over planet formation. While the exact processes through which stars influence their planetary systems remain unclear, these processes are all expected to imprint signatures on the overall population of planets that exist throughout the galaxy. The all sky coverage of the TESS mission provides enables us to study these populations and uncover the influence of the star. In this talk I will discuss how I use the TESS Full-Frame-Image light curves to measure the occurrence rates of different planets and planetary systems, and what these occurrence rates can teach us about the impact of the host star on planet formation and evolution. In particular I will present the results from studying two populations. The first is the population of giant planets around low-mass stars, through which we can probe an extreme of giant planet formation. The second is the population of giant planets around post-main sequence stars. By studying this population we can better understand the impact of the early stages of post-main sequence stellar evolution on close-in planets, including strong tidal interactions and rapid orbital decay.
- Speaker: Ed Bryant (UCL)
- Tuesday 04 February 2025, 13:00-14:00
- Venue: Ryle seminar room + ONLINE - Details to be sent by email.
- Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.
Mon 10 Mar 13:00: Title to be confirmed
Abstract not available
- Speaker: Alkistis Pourtsidou (University of Edinburgh)
- Monday 10 March 2025, 13:00-14:00
- Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
- Series: Cosmology Lunch; organiser: Louis Legrand.
Wed 05 Feb 13:15: The WEAVE-TwiLight Survey: Implementing and Testing a New Low Field Density Observing Mode
Bright exoplanet host stars provide highly precise stellar and planetary parameters, as well as chemical abundances. However, modern multi-object spectroscopic surveys often neglect stars brighter than 11 visual magnitudes due to their relatively low on-sky number density, resulting in significant observational overhead. The WEAVE -TwiLight Survey (WTLS) will address this gap by employing a groundbreaking observing mode, that allows for observations of low-density/bright star fields, without compromising survey efficiency. With an input catalogue derived primarily from the northern PLATO long-duration phase field, WEAVE -TwiLight will result in a highly homogeneous spectral dataset, characterizing approximately 6,000 future PLATO targets, including 68 confirmed planet hosts. In this talk, I will present the progress made in implementing the new observing mode, alongside preliminary results from test observations obtained in late summer 2024, using WEAVE ’s high-resolution setup. Full-scale science operations for WEAVE -TwiLight are expected to begin in Q2 of 2025.
- Speaker: Thomas Hajnik / IoA
- Wednesday 05 February 2025, 13:15-13:40
- Venue: The Hoyle Lecture Theatre + Zoom .
- Series: Institute of Astronomy Seminars; organiser: Xander Byrne.
Fri 31 Jan 11:30: Galaxy-halo connection in current CMB cross-correlation science
In this talk we will review models and constraints on halo occupation distribution (HOD) statistics in Cosmic Microwave Background (CMB) cross-correlation studies. We will focus on CMB lensing and kinetic Sunyavev Zeldovich cross-correlations. As we will see, HOD degeneracies are a limiting aspect of our measurements of the gas distributions around massive halos. We will discuss current constraints on the gas derived from recent ACT data and prospects for SO, as well as the significance of these constraints in the context of hydrodynamical simulations.
- Speaker: Boris Bolliet (Cavendish)
- Friday 31 January 2025, 11:30-12:30
- Venue: Ryle Seminar Room, KICC + online.
- Series: Galaxies Discussion Group; organiser: Sandro Tacchella.
Fri 31 Jan 13:00: The Maxwell equations on the full Kerr black hole family
We discuss a proof of uniform boundedness and decay statements for solutions to the Maxwell equations on Kerr black holes. The proof is unconditional in the full subextremal |a| less than M family, in view of earlier joint work with Yakov Shlapentokh-Rothman. For extremal |a|=M Kerr, it is conditional on a conjecture for the spin ±1 Teukolsky equations motivated by work of Gajic and Casals—Gralla—Zimmerman. This is joint work with Gabriele Benomio (GSSI).
- Speaker: Rita Teixera da Costa
- Friday 31 January 2025, 13:00-14:00
- Venue: Potter Room / https://cam-ac-uk.zoom.us/j/87235967698.
- Series: DAMTP Friday GR Seminar; organiser: Daniela Cors.
Mon 03 Feb 13:00: Results from the Dark Energy Spectroscopic Instrument (DESI) year-one data release.
DESI represents the culmination of multi-years efforts and advanced spectroscopic techniques. Placed at Mayall 4-meter Telescope, DESI harnesses the power of 5,000 robotic fiber positioners, coupled with state-of-the-art spectrographs, to capture the spectral signatures of millions of galaxies and quasars with unprecedented precision. DESI success is also based on the collaborative spirit of its community, more than 400 scientists over 70 institutions in 5 continents.
This data release (DR1) corresponds to the first year of observations; it holds immense scientific promise across a multitude of fronts: from constraining cosmological parameters, mapping the expansion history of the Universe, to the properties of dark energy, gravity and neutrinos.
In this talk I will focus on the results from the first data release of DESI based on the baryon acoustic oscillations (BAO) and redshift space distortions (RSD) analyses, and their impact in cosmology. On one hand, the BAO signal allows us to trace the expansion history of the universe through the last 11 billion years; and on the other hand the RSD allows us to test GR at cosmological scales over a similar period of time. In addition if baryon density information is added, DESI can also infer the rate of expansion today, the Hubble constant at 1% level (H0=68.56 ± 0.75) km/s/Mpc. All these results seem to be in good agreement with the standard model of cosmology, the LCDM model. When combined with external datasets such as the SuperNovae data and Cosmic Microwave Background anisotropy observations (CMB), we have observed in some cases interesting hints towards evolving dark energy. Furthermore, DESI data in combination with CMB is able to put constraints on the sum of neutrino masses reaching an upper bound of 0.071 eV at 95% confidence level within the LCDM model.
- Speaker: Héctor Gil-Marín (ICC, Barcelona U.)
- Monday 03 February 2025, 13:00-14:00
- Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
- Series: Cosmology Lunch; organiser: Thomas Colas.
Fri 24 Jan 13:00: Geometric Characterizations of Kerr-de Sitter and Related Metrics in All Dimensions
The Kerr-de Sitter metric, originally proposed by Carter in four dimensions and later extended by Gibbons, Lü, Page and Pope to all dimensions, is likely to play a relevant role among Lambda positive vacuum spacetimes. To better understand what makes it special, we calculate the asymptotic data characterizing the metric near conformal infinity. This requires a review of tools in conformal geometry, such as the Fefferman-Graham expansion, and its relation with the asymptotic initial value problem in arbitrary dimensions. The asymptotic data obtained for Kerr-de Sitter admits a straightforward generalization to a broader class of spacetimes that depends on a set of parameters, which we refer to as Kerr-de Sitter-like class. This class of metrics is obtained explicitly as limits or analytic extensions of Kerr-de Sitter and the space of parameters inherits a natural topological structure from the asymptotic data. Furthermore, we discuss additional characterizations within the Kerr-Schild type metrics and the algebraically special metrics that highlight the geometrical significance of the class.
- Speaker: Carlos Peón Nieto (UPM, Madrid)
- Friday 24 January 2025, 13:00-14:00
- Venue: Potter Room / https://cam-ac-uk.zoom.us/j/84511154241?pwd=B778JtHEd8Vb7aTOdsygQhBdXWbybI.1.
- Series: DAMTP Friday GR Seminar; organiser: Daniela Cors.
Mon 17 Mar 14:00: TBD
TBD
- Speaker: Malcolm Druett (Sheffield)
- Monday 17 March 2025, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Loren E. Held.
Mon 10 Mar 14:00: TBD
TBD
- Speaker: Paul Barrere (Geneva)
- Monday 10 March 2025, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Loren E. Held.
Mon 03 Mar 14:00: TBD
TBD
- Speaker: James Rogers (Institute of Astronomy, Cambridge)
- Monday 03 March 2025, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Loren E. Held.
Mon 24 Feb 14:00: TBD
TBD
- Speaker: Serguei Komissarov (Leeds)
- Monday 24 February 2025, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Loren E. Held.
Mon 17 Feb 14:00: TBD
TBD
- 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.
Mon 10 Feb 14:00: TBD
TBD
- Speaker: Adam Ingram (Newcastle)
- Monday 10 February 2025, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Loren E. Held.
Sun 02 Feb 14:00: TBD
TBD
- Speaker: Guiseppe Lodato (Milan)
- Sunday 02 February 2025, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Loren E. Held.
Mon 27 Jan 14:00: Formation, Evolution and Radiation of Magnetized Accretion Disks around Black Holes
The role that magnetic fields play in shaping the evolution and the radiative signature of accretion disks around black holes is very uncertain. This uncertainty is mainly due to the scarcity of direct observational constraints on the magnetic field’s geometry or strength in black hole disks. However, even from a theoretical point of viewour understanding of magnetized disks remains relatively poor. Indeed, analytic models of magnetized disks often need inputs from numerical simulations and numerical simulations of magnetized disks are difficult to perform and/or interpret. Because of this lack of magnetized disk models, standard disk models often reduce the magnetic field to a source of turbulence; turbulence through which the accretion can happen. While this simplification may hold for weakly magnetized disks, a large number of numerical simulations have shown that the role of a strong magnetic field goes far beyond producing turbulence. In particular, a strong magnetic field can produce powerful outflows, induce accretion through vertically elevated layers or non-axisymmetric structures, modify the time scales of accretion, enhance dissipation of gravitational energy in the disk and accelerate particles to very high energies. All of these effects will dramatically affect the evolution and the observational signature of accretion disks and open up new and exciting avenues to resolve outstanding problems of the standard accretion disk theory. In this talk, I will present an overview of my recent results on how strongly magnetized disks form, evolve and radiate. I will show in particular how strongly magnetized disks could explain events of very strong variability in AGNs, the flaring behavior of the Galactic center and the hardest emission in X-ray binaries.
- Speaker: Nicolas Scepi (Grenoble)
- Monday 27 January 2025, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Loren E. Held.
Mon 09 Jun 13:00: Title to be confirmed
Abstract not available
- Speaker: Etienne Camphuis
- Monday 09 June 2025, 13:00-14:00
- Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
- Series: Cosmology Lunch; organiser: Louis Legrand.
Mon 03 Mar 13:00: Title to be confirmed
Abstract not available
- Speaker: Sadra Jazayeri (Imperial College)
- Monday 03 March 2025, 13:00-14:00
- Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
- Series: Cosmology Lunch; organiser: Thomas Colas.
Thu 23 Jan 16:00: Zwicky Transient Facility Cosmology Science Working Group: Results and Perspectives
I will present the second data release of the Zwicky Transient Facility (ZTF) Cosmology Science Working Group: the largest Type Ia Supernovae release to date (by far!). It contains more than 3000+ good light curves of Type Ia Supernovae. After a brief introduction of the ZTF survey, I will present the characteristics of this unique dataset and show key results of recently submitted papers as part of the ZTF SN Ia DR2 Astronomy and Astrophysics special issue. I will then present our working program to derive brand new cosmological parameter constraints from Type Ia Supernova distances and the perspective for the next ZTF Cosmology releases.
- Speaker: Mickael Rigault
- Thursday 23 January 2025, 16:00-17:00
- Venue: Hoyle Lecture Theatre, Institute of Astronomy.
- Series: Institute of Astronomy Colloquia; organiser: Matthew Grayling.