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arXiv:2405.00113v1 Announce Type: new Abstract: We present extensive observations of the Type II supernova (SN II) 2023ufx which is likely the most metal-poor SN II observed to-date. It exploded in the outskirts of a low-metallicity ($Z_{\rm host} \sim 0.1~Z_\odot$) dwarf ($M_g = -13.23\pm0.15$~mag; $r_e\sim 1$~kpc) galaxy. The explosion is luminous, peaking at $M_g\approx -18.5~$mag, and shows rapid evolution. The $r$-band (pseudo-bolometric) light curve has a shock-cooling phase lasting 20 (17) days followed by a 19 (23)-day plateau. The entire optically-thick phase lasts only $\approx 55~$days following explosion, indicating that the red supergiant progenitor had a thinned H envelope prior to explosion. The early spectra obtained during the shock-cooling phase show no evidence for narrow emission features and limit the pre-explosion mass-loss rate to $\dot{M} \lesssim 10^{-3}~\rm M_\odot$/yr. The photospheric-phase spectra are devoid of prominent metal absorption features, indicating a progenitor metallicity of $\lesssim 0.1~Z_\odot$. The semi-nebular ($\sim 60-130~$d) spectra reveal weak Fe II, but other metal species typically observed at these phases (Ti II, Sc II, Ba II) are conspicuously absent. The late-phase optical and near-infrared spectra also reveal broad ($\approx 10^4~\rm{km}~\rm s^{-1}$) double-peaked H$\alpha$, P$\beta$, and P$\gamma$ emission profiles suggestive of a fast outflow launched during the explosion. Outflows are typically attributed to rapidly-rotating progenitors which also prefer metal-poor environments. This is only the second SN II with $\lesssim 0.1~Z_\odot$ and both exhibit peculiar evolution, suggesting a sizable fraction of metal-poor SNe II have distinct properties compared to nearby metal-enriched SNe II. These observations lay the groundwork for modeling the metal-poor SNe II expected in the early Universe.

The cometary delivery of prebiotic feedstock molecules to the early-Earth and rocky exoplanets

The delivery of prebiotic feedstocks molecules, such as hydrogen cyanide (HCN), during cometary impacts may have significantly influenced prebiotic chemistry on the early Earth, motivated by the discovery of a rich diversity of CHN - and CHS -bearing molecules on solar system comets. Numerical experiments have demonstrated that HCN survival during cometary impacts is however only possible in oblique impacts at very low velocities. In this talk I will discuss the effects of stellar mass, and planetary architecture on minimum cometary impact velocities onto rocky exoplanets. Using both an analytical model and numerical N-body simulations, we show the lowest impact velocities occur for low-mass planets in tightly-packed planetary systems around high-mass (i.e., Solar-mass) stars, enabling the intact delivery of prebiotic feedstock molecules. I will finish by discussing a specific origins scenario, proposed to achieve favourable conditions for subsequent prebiotic chemistry, which invokes the arrival of a secondary impactor in the same location. We consider the atmospheric fragmentation of cometary impactors, and use the lunar crater record to quantitatively evaluate the likelihood of these `double impact’ scenarios on the early-Earth. These scenarios are found to be extremely unlikely settings for the initial stages of prebiotic chemistry, unless there was a particularly high impact rate on the early-Earth, and global environmental conditions conducive to successful cometary delivery.

• Speaker: Richard Anslow (University of Cambridge)
• Wednesday 08 May 2024, 13:15-13:40
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Hannah Uebler.

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Results of beamline testing at the MROI

TBC

• Speaker: Dr. John Young (Cavendish Astrophysics)
• Tuesday 26 November 2024, 11:15-12:00
• Venue: Coffee area, Battcock Centre.
• Series: Hills Coffee Talks; organiser: Charles Walker.

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Title to be confirmed

Abstract not available

• Speaker: Siyi Xu (NOIRlab, USA)
• Thursday 13 June 2024, 16:00-17:00
• Venue: Hoyle Lecture Theatre, Institute of Astronomy.
• Series: Institute of Astronomy Colloquia; organiser: eb694.

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Title to be confirmed

Abstract not available

• Speaker: Siyi Xu (NOIRlab, USA)
• Thursday 13 June 2024, 16:00-17:00
• Venue: Hoyle Lecture Theatre, Institute of Astronomy.
• Series: Institute of Astronomy Colloquia; organiser: eb694.

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Insights into cosmological simulations from modified initial conditions

I will discuss the GMGalaxies programme, which is pursuing a new ‘hybrid’ approach to cosmological galaxy formation simulations combining the best of cosmological zooms and idealised approaches of the past. By customising (‘genetically modifying’) our initial conditions, we can construct controlled tests of structure formation within a fully cosmological environment. This approach has allowed us to obtain new and unique insights into ultra-faint dwarf galaxy formation, AGN -driven galaxy quenching, large scale structure formation and — in soon-to-be-released ultra-high-resolution simulations — the Milky Way fossil record seen by Gaia. In this talk, I will summarise some of these results but focus especially on recent insights into dwarf galaxy formation.

• Speaker: Andrew Pontzen (UCL)
• Thursday 09 May 2024, 16:00-17:00
• Venue: Hoyle Lecture Theatre, Institute of Astronomy.
• Series: Institute of Astronomy Colloquia; organiser: eb694.

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Black hole accretion in the TDAMM Era

Most of the power from an Active Galactic Nucleus is released close to the black hole, and thus studying accretion at event horizon scales—at the intersection of inflow and outflow—is essential for understanding how much matter accretes and grows the black hole vs. how much matter is ejected, thus effecting the black hole’s large-scale environments. In the past decade, we have had a breakthrough in how we probe the inner accretion flow, through the discovery of X-ray Reverberation Mapping, where X-rays produced close to the black hole reverberate off inflowing gas. By measuring reverberation time delays, we can quantify the effects of strongly curved space time and measure black hole spin, which is key for understanding how efficiently energy can be tapped from the accretion process. In this talk, I will give an overview of this field, and will show how extending these spectral-timing techniques to extreme, transient (and possibly multi-messenger) accretion events like Tidal Disruption Events and Quasi Periodic Eruptions can help us understand the growth and impact of black holes in galactic centers.

• Speaker: Erin Kara (MIT)
• Thursday 06 June 2024, 16:00-17:00
• Venue: Hoyle Lecture Theatre, Institute of Astronomy.
• Series: Institute of Astronomy Colloquia; organiser: eb694.

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Title to be confirmed

Abstract not available

• Speaker: Anshu Gupta (Curtin)
• Friday 05 July 2024, 11:30-12:30
• Venue: Ryle seminar room + online.
• Series: Galaxies Discussion Group; organiser: Sandro Tacchella.

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Black Hole Entropy for Higher Curvature Gravity with Higher Spin Fields

Assuming a Killing horizon background, we generalise the linear null Raychaudhuri equation to higher curvature gravity with spin s ≥ 2 bosonic fields, and we attempt to extract the black hole entropy from the Raychaudhuri equation at the linear order of dynamical perturbation. Unlike pure gravity, scalar fields, and vector fields, we show that an additional “integrability condition” must be satisfied by the higher spin theory/field in order to extract a “sensible” entropy formula. We test this condition in several examples and speculate about its role for higher spin theories.

• Speaker: Zihan Yan, DAMTP, University of Cambridge
• Friday 03 May 2024, 13:00-14:00
• Venue: Potter room/Zoom.
• Series: DAMTP Friday GR Seminar; organiser: Xi Tong.

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Title to be confirmed

Abstract not available

• Speaker: Kenta Kiuchi (Max Planck Institute for Gravitational Physics)
• Monday 20 May 2024, 14:00-15:00
• Venue: MR14 DAMTP and online.
• Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.

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Title to be confirmed

Abstract not available

• Speaker: Antti Rantala (Max Planck Institute for Astrophysics)
• Tuesday 21 May 2024, 14:00-15:00
• Venue: MR14 DAMTP and online.
• Series: DAMTP Astrophysics Seminars; organiser: Loren E. Held.

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Blue Phase Liquid Crystals & Their Potential for Astronomy

Adaptive optics is a technique used to reduce the effects of aberration on wavefront propagation, used to correct for the light distortion which appears due to atmospheric turbulence. Customarily, in astronomy, systems employed for this purpose use deformable or adaptive mirrors as correctors, which are costly and mechanically actuated.

As opposed to a classic deformable mirror, which requires actuators to change its shape, a Liquid Crystal Wavefront Corrector (LCWFC) uses its inherent birefringence to act as a phase modulator and correct the incoming wavefront. Despite its reduced size and cost, LCWF Cs have historically suffered from a large response time, which makes them less desirable over typical solutions.

Blue Phases will be introduced as an alternative correcting medium. They have the potential to overcome the usual limitations of liquid crystal devices. Their working principle and typical design considerations will be presented, as well as progress made in making these devices a reality.

• Speaker: Oana Niculescu (University of Cambridge)
• Tuesday 14 May 2024, 11:15-12:00
• Venue: Coffee area, Battcock Centre.
• Series: Hills Coffee Talks; organiser: Charles Walker.

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Title to be confirmed

TBA

• Speaker: Alexandros Papageorgiou (IFT, Madrid)
• Tuesday 28 May 2024, 13:00-14:00
• Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
• Series: Cosmology Lunch; organiser: Thomas Colas.

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arXiv:2404.17043v1 Announce Type: new Abstract: We present a JWST MIRI/MRS spectrum (5-27 $\mathrm{\mu}$m) of the Type Ia supernova (SN Ia), SN 2021aefx at $+415$ days past $B$-band maximum. The spectrum, which was obtained during the iron-dominated nebular phase, has been analyzed in combination with previous JWST observations of SN 2021aefx, to provide the first JWST time series analysis of an SN Ia. We find the temporal evolution of the [Co III] 11.888 $\mathrm{\mu}$m feature directly traces the decay of $^{56}$Co. The spectra, line profiles, and their evolution are analyzed with off-center delayed-detonation models. Best fits were obtained with White Dwarf (WD) central densities of $\rho_c=0.9-1.1\times 10^9$g cm$^{-3}$, a WD mass of M$_{\mathrm{WD}}$=1.33-1.35M$_\odot$, a WD magnetic field of $\approx10^6$G, and an off-center deflagration-to-detonation transition at $\approx$ 0.5 $M_\odot$ seen opposite to the line of sight of the observer. The inner electron capture core is dominated by energy deposition from $\gamma$-rays whereas a broader region is dominated by positron deposition, placing SN 2021aefx at +415 d in the transitional phase of the evolution to the positron-dominated regime. The formerly `flat-tilted' profile at 9 $\mathrm{\mu}$m now has significant contribution from [Ni IV], [Fe II], and [Fe III] and less from [Ar III], which alters the shape of the feature as positrons excite mostly the low-velocity Ar. Overall, the strength of the stable Ni features in the spectrum is dominated by positron transport rather than the Ni mass. Based on multi-dimensional models, our analysis strongly supports a single-spot, close-to-central ignition with an indication for a pre-existing turbulent velocity field, and excludes a multiple-spot, off-center ignition.

Resolution: New Insights from Modular Symmetry in Conformal Field Theory

I will explain how tools from the theory of modular forms may be used to resolve operator spectra of conformal field theories. This leads to a quantitative framework for diagnosing quantum chaos and random matrix behavior in field theory and gravity.

• Speaker: Eric Perlmutter, IPhT
• Wednesday 01 May 2024, 14:00-15:00
• Venue: MR2.
• Series: Theoretical Physics Colloquium; organiser: Ronak M Soni.

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The Conditions for Warping and Breaking Protoplanetary Discs

The study of warped discs was once limited to the viscous accretion discs around black holes. Now, high resolution observations indicate that the warping and breaking of protoplanetary discs is not uncommon and there is growing interest from the planet formation community in these effects. Warping and breaking alter the evolution of the disc, for example by enhancing the accretion rate and changing the chemical composition. However, our understanding of the conditions under which protoplanetary discs warp and/or tear remains far more limited than for black hole discs. I will present the conclusions from our high-resolution simulations and discuss what factors affect whether and where a protoplanetary disc will break and how this differs from the commonly referenced theoretical predictions. Finally, I will share some examples of observed disc systems that we still can’t explain and suggest avenues for future research.

• Speaker: Alison Young (Edinburgh)
• Monday 29 April 2024, 14:00-15:00
• Venue: MR14 DAMTP and online.
• Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.

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arXiv:2404.16805v1 Announce Type: new Abstract: The early dark energy (EDE) extension to $\Lambda$CDM has been proposed as a candidate scenario to resolve the "Hubble tension". We present new constraints on the EDE model by incorporating new data from the Dark Energy Spectroscopic Instrument (DESI) Baryon Acoustic Oscillation (BAO) survey and CMB lensing measurements from the Atacama Cosmology Telescope (ACT) DR6 and \textit{Planck} NPIPE data. We do not find evidence for EDE. The maximum fractional contribution of EDE to the total energy density is $f_\mathrm{EDE}

arXiv:2404.16428v1 Announce Type: new Abstract: Nested sampling parameter estimation differs from evidence estimation, in that it incurs an additional source of error. This error affects estimates of parameter means and credible intervals in gravitational wave analyses and beyond, and yet, it is typically not accounted for in standard error estimation methods. In this paper, we present two novel methods to quantify this error more accurately for any chain based nested sampler, using the additional likelihood calls made at runtime in producing independent samples. Using injected signals of black hole binary coalescences as an example, we first show concretely that the usual error estimation method is insufficient to capture the true error bar on parameter estimates. We then demonstrate how the extra points in the chains of chain based samplers may be carefully utilised to estimate this error correctly, and provide a way to check the accuracy of the resulting error bars. Finally, we discuss how this error affects $p$-$p$ plots and coverage assessments.

The next-generation Event Horizon Telescope: from Still Images to Video.

The next-generation Event Horizon Telescope (ngEHT) is a transformative upgrade to the EHT that will realize black hole “cinema”: real-time and time-lapse movies of supermassive black holes on event horizon scales. These movies will resolve complex structure and dynamics on Schwarzschild radius dimensions, bringing into focus not just the persistent strong-field gravity features predicted by General Relativity (GR), but details of active accretion and relativistic jet launching that drive large scale structure in the Universe. This effort builds upon recent results by the Event Horizon Telescope (EHT): the first image of M87 ’s supermassive black hole and its magnetic field structure, as well as resolved images of SgrA*, the central black hole at the heart of the Milky Way. These images are scientifically rich, and show that evolution of the EHT to a more capable array can address even deeper questions across physics and astronomy. The central concept behind the ngEHT is that the addition of modest-diameter dishes at new geographic locations and multi-color observations over a range of frequencies will enable the next revolution in horizon-resolved black hole studies. This talk will cover the ngEHT technical plans and scientific goals.

• Speaker: Speaker to be confirmed
• Wednesday 01 May 2024, 15:00-16:00
• Venue: Battcock coffee area + ONLINE - Details to be sent by email.
• Series: Kavli Institute for Cosmology Seminars; organiser: Steven Brereton.

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Nature, Published online: 24 April 2024; doi:10.1038/d41586-024-01023-6

Observations have revealed a galaxy that stopped forming stars earlier than expected. This discovery offers clues about when the first galaxies emerged and sheds light on how stars formed when the Universe was in its infancy.