Feed aggregator

Scientists say they have discovered what lies at the heart of the cosmos's most famous explosion.

Positronium has the potential to revolutionise physics but the elusive substance had been too hot to handle.

arXiv:2310.07767v2 Announce Type: replace Abstract: Confronting measurements of the Lyman-$\alpha$ forest with cosmological hydrodynamical simulations has produced stringent constraints on models of particle dark matter and the thermal and ionization state of the intergalactic medium. We investigate the robustness of such models of the Lyman-$\alpha$ forest, focussing on the effect of particle initial conditions on the Lyman-$\alpha$ forest statistics in cosmological SPH simulations. We study multiple particle initialization algorithms in simulations that are designed to be identical in other respects. In agreement with the literature, we find that the correct linear theory evolution is obtained when a glass-like configuration is used for initial unperturbed gas particle positions alongside a regular grid configuration for dark matter particles and the use of non-identical initial density perturbations for gas and dark matter. However, we report that this introduces a large scale-dependent distortion in the one-dimensional Lyman-$\alpha$ transmission power spectrum at small scales ($k > 0.05$ s/km). The effect is close to $50\%$ at $k\sim 0.1$ s/km, and persists at higher resolution. This can severely bias inferences in parameters such as the dark matter particle mass. By considering multiple initial conditions codes and their variations, we also study the impact of a variety of other assumptions and algorithmic choices, such as adaptive softening, background radiation density, particle staggering, and perturbation theory accuracy, on the matter power spectrum, the Lyman-$\alpha$ flux power spectrum, and the Lyman-$\alpha$ flux PDF. This work reveals possible pathways towards more accurate theoretical models of the Lyman-$\alpha$ forest to match the quality of upcoming measurements.

arXiv:2206.02729v2 Announce Type: replace Abstract: Results of the mathematical treatment of the radiation by the superluminally moving current sheet in the magnetosphere of a neutron star, which was presented in Ardavan (2021, {\it MNRAS}, {\bf 507}, 4530), are explained here in more transparent physical terms with the aid of illustrations. Not only do these results provide an all-encompassing explanation for the salient features of the radiation received from pulsars (its brightness temperature, polarization, spectrum, profile with microstructure and with a phase lag between the radio and gamma-ray peaks, and the discrepancy between the energetic requirements of its radio and gamma-ray components), but they also shed light on the putative energetic requirements of magnetars and the sources of fast radio bursts and gamma-ray bursts.

arXiv:2402.18773v1 Announce Type: new Abstract: Observations with the James Webb Space Telescope (JWST) have revealed active galactic nuclei (AGN) powered by supermassive black holes with estimated masses of $10^7-10^8$ M$_\odot$ at redshifts $z\sim7-9$. Some reside in overmassive systems with higher AGN to stellar mass ratios than locally. Understanding how massive black holes could form so early in cosmic history and affect their environment to establish the observed relations today are some of the major open questions in astrophysics and cosmology. One model to create these massive objects is through direct collapse black holes (DCBHs) that provide massive seeds ($\sim10^5-10^6$ M$_\odot$), able to reach high masses in the limited time available. We use the cosmological simulation code GIZMO to study the formation and growth of DCBH seeds in the early Universe. To grow the DCBHs, we implement a gas swallowing model that is set to match the Eddington accretion rate as long as the nearby gaseous environment, affected by stellar and accretion disk feedback, provides sufficient fuel. We find that to create massive AGN in overmassive systems at high redshifts, massive seeds accreting more efficiently than the fiducial Bondi-Hoyle model are needed. We assess whether the conditions for such enhanced accretion rates are realistic by considering limits on plausible transport mechanisms. We also examine various DCBH growth histories and find that mass growth is more sustained in overdense cosmological environments, where high gas densities are achieved locally. We discuss the exciting prospect to directly probe the assembly history of the first SMBHs with upcoming, ultra-deep JWST surveys.

arXiv:2402.18641v1 Announce Type: new Abstract: The Early Data Release (EDR) of the Dark Energy Spectroscopic Instrument (DESI) comprises spectroscopy obtained from 2020 December 14 to 2021 June 10. White dwarfs were targeted by DESI both as calibration sources and as science targets and were selected based on Gaia photometry and astrometry. Here we present the DESI EDR white dwarf catalogue, which includes 2706 spectroscopically confirmed white dwarfs of which approximately 1630 (roughly 60 per cent) have been spectroscopically observed for the first time, as well as 66 white dwarf binary systems. We provide spectral classifications for all white dwarfs, and discuss their distribution within the Gaia Hertzsprung-Russell diagram. We provide atmospheric parameters derived from spectroscopic and photometric fits for white dwarfs with pure hydrogen or helium photospheres, a mixture of those two, and white dwarfs displaying carbon features in their spectra. We also discuss the less abundant systems in the sample, such as those with magnetic fields, and cataclysmic variables. The DESI EDR white dwarf sample is significantly less biased than the sample observed by the Sloan Digital Sky Survey, which is skewed to bluer and therefore hotter white dwarfs, making DESI more complete and suitable for performing statistical studies of white dwarfs.

arXiv:2402.18624v1 Announce Type: new Abstract: We use rest-frame optical and near-infrared (NIR) observations of 42 Type Ia supernovae (SNe Ia) from the Carnegie Supernova Project at low-$z$ and 37 from the RAISIN Survey at high-$z$ to investigate correlations between SN Ia host galaxy dust, host mass, and redshift. This is the first time the SN Ia host galaxy dust extinction law at high-$z$ has been estimated using combined optical and rest-frame NIR data ($YJ$-band). We use the BayeSN hierarchical model to leverage the data's wide rest-frame wavelength range (extending to $\sim$1.0-1.2 microns for the RAISIN sample at $0.2\lesssim z\lesssim0.6$). By contrasting the RAISIN and CSP data, we constrain the population distributions of the host dust $R_V$ parameter for both redshift ranges. We place a limit on the difference in population mean $R_V$ between RAISIN and CSP of $-1.16

Nature, Published online: 29 February 2024; doi:10.1038/d41586-024-00623-6

Thirty Meter Telescope and Giant Magellan Telescope might need to compete for survival in face of federal spending limit.

Nature, Published online: 29 February 2024; doi:10.1038/d41586-024-00564-0

The surface of a white dwarf is marked with metallic patches — souvenirs of its encounter with an asteroid or planet.

Science, Volume 383, Issue 6686, Page 988-992, March 2024.

Reassessing the Evidence for Time Variability in the Atmosphere of the Exoplanet HAT-P-7b

We reassess the claimed detection of variability in the atmosphere of the hot Jupiter HAT -P-7 b, reported by Armstrong et al. (2016). Although astronomers expect hot Jupiters to have changing atmospheres, variability is challenging to detect. We looked for time variation in the phase curves of HAT -P-7 b in Kepler data using similar methods to Armstrong et al. (2016), and identified apparently significant variations similar to what they found. Numerous tests show the variations to be mostly robust to different analysis strategies. However, when we injected unchanging phase curve signals into the light curves of other stars and searched for variability, we often saw similar levels of variations as in the HAT -P-7 light curve. Fourier analysis of the HAT -P-7 light curve revealed background red noise from stellar supergranulation on timescales similar to the planet’s orbital period. Tests of simulated light curves with the same level of noise as HAT -P-7’s supergranulation show that this effect alone can cause the amplitude and phase offset variability we detect for HAT -P-7 b. Therefore, the apparent variations in HAT -P-7 b’s atmosphere could instead be caused by non-planetary sources, most likely photometric variability due to supergranulation on the host star.

• Speaker: Maura Lally (Cornell)
• Tuesday 05 March 2024, 13:00-14:00
• Venue: Ryle seminar room + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Dr Emily Sandford.

Add to your calendar or Include in your list

arXiv:2402.18515v1 Announce Type: new Abstract: We introduce a model for dust evolution in the {\sc ramses} code for simulations of galaxies with a resolved multiphase interstellar medium. Dust is modelled as a fluid transported with the gas component, and is decomposed into two sizes, 5 nm and $0.1 \, \mu\rm m$, and two chemical compositions for carbonaceous and silicate grains. Using a suite of isolated disc simulations with different masses and metallicities, the simulations can explore the role of these processes in shaping the key properties of dust in galaxies. The simulated Milky Way analogue reproduces the dust-to-metal mass ratio, depletion factors, size distribution and extinction curves of the Milky Way. Galaxies with lower metallicities reproduce the observed decrease in the dust-to-metal mass ratio with metallicity at around a few $0.1\,\rm Z_\odot$. This break in the DTM corresponds to a galactic gas metallicity threshold that marks the transition from an ejecta-dominated to an accretion-dominated grain growth, and that is different for silicate and carbonaceous grains, with $\simeq0.1\,\rm Z_\odot$ and $\simeq 0.5\,\rm Z_\odot$ respectively. This leads to more Magellanic Cloud-like extinction curves, with steeper slopes in the ultraviolet and a weaker bump feature at 217.5 nm, in galaxies with lower masses and lower metallicities. Steeper slopes in these galaxies are caused by the combination of the higher efficiency of gas accretion by silicate relative to carbonaceous grains, and by the low rates of coagulation that preserves the amount of small silicate grains. Weak bumps are due to the overall inefficient accretion growth of carbonaceous dust at low metallicity, whose growth is mostly supported by the release of large grains in SN ejecta. We also show that the formation of CO molecules is a key component to limit the ability of carbonaceous dust to grow, in particular in low-metallicity gas-rich galaxies.

For the seventh year in a row, observations conducted at ESO’s observatories have led to more than 1000 scientific publications in a year. Recently, the ESO Library, Documentation, and Information Services Department has updated their detailed statistics on publications using ESO data, presenting each facility's contributions in 2023 [1]. 

The most significant contributions to these publications come from ESO’s Very Large Telescope (VLT) and the VLT Interferometer (VLTI) at Paranal Observatory, which yielded data included in over 600 studies. Highlights include the detection of distant gas clouds with leftovers from the first stars in the Universe and the most distant fast radio burst to date. For the last four years, the Multi Unit Spectroscopic Explorer (MUSE) has been the most productive VLT instrument, producing data for over 200 papers in 2023 alone.  

Also located at Paranal Observatory, the Visible and Infrared Telescope for Astronomy (VISTA) and the VLT Survey Telescope (VST) [2] contributed to over 120 publications. As a highlight, astronomers created an infrared atlas of five nearby stellar nurseries using the VISTA telescope. Further south, the telescopes at ESO’s La Silla Observatory contributed to approximately 185 studies; for example, an observational campaign including the New Technology Telescope (NTT), as well as other ESO telescopes, helped unravel the mystery of a mode-switching pulsar’s behaviour. 

Over the year, the Atacama Large Millimeter/Submillimeter Array (ALMA), in which ESO is a partner, provided data for almost 500 papers. As in the last three years, approximately half of them (53%) used data obtained through observing time granted to astronomers based in Europe. In particular, in 2023 astronomers using ALMA detected the magnetic field of a galaxy 11 billion years away and contributed to imaging the black hole at the centre of the M87 galaxy expelling a jet.  

Until December 2022, ESO was also a partner of the Atacama Pathfinder Experiment (APEX) [3], located close to ALMA on the Chajnantor plateau in Chile’s Atacama region. In 2023, observations obtained during ESO observing time at APEX contributed to 24 papers, more than half (57%) of the studies from all APEX observing time. 

The number of papers that partly or exclusively used archival data has increased continuously during recent years and remained high in 2023, making up almost 45% of all publications. In particular, almost 24% of papers relied on archival data alone, without any ESO observations obtained by the authors themselves. Even data from instruments that were decommissioned years ago still actively contribute to the pool of data papers. These figures demonstrate the important legacy value of the ESO Science Archive Facility. 

The impressive publication numbers described above highlight ESO’s important role in helping astronomers advance our understanding of the Universe. 

Notes 

[1] Papers can use data from more than one facility, therefore the total number cannot be calculated by adding all publications of the individual sites. 

[2] The VST project was a joint venture between ESO and the Capodimonte Astronomical Observatory, part of the Italian National Institute for Astrophysics (INAF). As of 1 October 2022, this is a sole project of INAF, hosted by ESO at Paranal. 

[3] As of 1 January 2023, ESO hosts and operates APEX on behalf of the Max Planck Institute for Radio Astronomy. 

More Information 

The statistics presented here are derived from the ESO Telescope Bibliography (telbib), a database of refereed papers published by the ESO users community. Telbib is developed and curated by the ESO Library, Documentation, and Information Services Department. Whilst text-mining scripts are applied when screening the literature for ESO data papers, articles are carefully examined by the curators before they are added to the database to ensure that all telbib papers use partly or exclusively data from ESO facilities for which observing time was recommended by ESO. The public telbib interface provides visualisations of search results including on-the-fly graphs and predefined charts. 

New Space & the CubeSat Revolution

CubeSats stand at the forefront of the New Space Revolution, a paradigm shift in space exploration characterised by reduced launch costs and increased accessibility to space. These miniature satellites, defined by their standardised dimensions and modular design, have emerged as a pivotal technology with some implications for research in astronomy. With their standardised dimensions and modular design, these Nanosatellites enable a wide range of experiments that were previously the domain of larger, more costly missions. In my talk, I aim to introduce you to valuable opportunities that can emerge by leading a CubeSat project with a special interest in payloads dedicated to astrophysics research. As a cost-effective space instrument, CubeSats unlock observational windows across the ultraviolet, far-infrared, and low-frequency radio spectra, which are inaccessible from Earth’s surface. Beyond their technical capabilities, these satellites enable sustained observations of celestial bodies over extended periods, free from the scheduling constraints of larger telescopes.

• Speaker: Dolev Bashi
• Tuesday 05 March 2024, 11:15-12:00
• Venue: Coffee area, Battcock Centre.
• Series: Hills Coffee Talks; organiser: Dolev Bashi.

Add to your calendar or Include in your list

Applying Quantum Computing to HEP

In this talk I will discuss several studies in which quantum computers have been proposed as tools for studying particle theories. The first study uses quantum annealers to implement simple scalar field theories and observe quantum tunnelling, which follows the expected analytic behaviour: for example the decay rate follows the WKB approximation. The second more recent idea uses photonic devices to implement quantum tunnelling. In principle in both of these studies we are observing non-perturbative effects, suggesting that these and similar methods may be of interest in understanding a wide range of phenomena. The talk will be pedagogical.

• Speaker: Steve Abel (IPPP)
• Wednesday 06 March 2024, 14:00-15:00
• Venue: MR2.
• Series: Theoretical Physics Colloquium; organiser: Hannah Banks.

Add to your calendar or Include in your list

Nature, Published online: 28 February 2024; doi:10.1038/s41586-024-07043-6

An analysis of eight ultra-faint galaxies during the epoch of reionization with absolute magnitudes between −17 mag and −15  mag shows that most of the photons that reionized the Universe come from dwarf galaxies.

Nature, Published online: 28 February 2024; doi:10.1038/d41586-024-00594-8

Some of the faintest objects ever observed suggest that small galaxies get the credit for clearing the ‘fog’ pervading the early cosmos.

Nature, Published online: 28 February 2024; doi:10.1038/d41586-024-00613-8

The Odysseus spacecraft gathered data successfully from the lunar surface.

Ahead of the total solar eclipse in North America, here is everything you need to know about solar and lunar eclipses

An exoplanet called K2-18b has been suggested as a good place to look for alien life, but a new analysis shows it is probably made from gas