Feed aggregator

Nature, Published online: 05 February 2024; doi:10.1038/d41586-024-00315-1

Reviewers will likely approve only one in every nine research proposals submitted in latest application cycle.

Stellar populations and dust build-up in the early Universe

We are witnessing an exciting revolution in our understanding of the first galaxies. JWST observations have already revealed galaxies in the first few hundred million years of the Universe and their detailed characterization in terms of chemical enrichment and stellar populations, revealing galaxies as metal poor as 1% of the solar value, and even potential traces of the first (Pop III ) stars at z ≈ 6.5 – 10.5. In addition to the stunning discoveries made recently by JWST , there have also been recent probes of the dust content of galaxies in the first billion years of the Universe with ALMA . This is a key and rapid transition phase for the evolution of dust, as galaxy evolutionary timescales become comparable with the formation timescales of dust. In this talk, I will attempt to provide some indications on the diversity of physical properties of the first galaxies expected by theoretical models, and on the current (limited) understanding of dust enrichment at very early cosmic epochs.

• Speaker: Raffaella Schneider (University of Rome)
• Thursday 08 February 2024, 16:00-17:00
• Venue: Hoyle Lecture Theatre, Institute of Astronomy.
• Series: Institute of Astronomy Colloquia; organiser: eb694.

Add to your calendar or Include in your list

Title to be confirmed

Abstract not available

• Speaker: Jayne Birkby (University of Oxford)
• Thursday 15 February 2024, 16:00-17:00
• Venue: Hoyle Lecture Theatre, Institute of Astronomy.
• Series: Institute of Astronomy Colloquia; organiser: eb694.

Add to your calendar or Include in your list

Scientists have analysed the stars that an upcoming NASA telescope will target in its search for biosignatures, narrowing down the candidates for those that could host potential extraterrestrial life

Disc evolution in young intermediate-mass stars

Planets are born from circumstellar discs and the evolution of these discs determines the final architecture of planetary systems. The stellar mass range between 1.5 and 3.5 solar masses presents a particularly interesting circumstellar disc evolution; most notably, it is dominated by the EUV /FUV photoevaporation regime on the pre-main sequence, it contains the majority of gaseous debris discs, and it also shows the highest giant planet frequency. In our recent spectroscopic VLT /X-Shooter survey (UV to nIR), combined with WISE data (nIR to mIR), we identified 135 pre-main sequence (PMS) intermediate mass stars (IMSs) in the Southern sky. This is the first unbiased sample of IMSs in the PMS , allowing a study of disc evolution. Our sample, encompassing protoplanetary and debris discs, also revealed a significant number of discs between these two evolutionary stages. We find that the IR excess evolution of IMSs differs from that seen for low-mass stars (LMSs), exemplified by samples drawn from nearby star forming regions. We observe that, in IMSs, the inner disc regions are vacated in their entirety, in contrast to the LMSs where we note a more gradual inside-out dissipation. We also investigated the presence of gas absorption features in our sample via optical high-resolution spectroscopy to identify gas-bearing debris discs. This requires detailed comparisons to spectra of nearby stars to eliminate objects with foreground cloud absorption as cause of the absorption features. In particular, we apply this effective method to one such disc, eta Tel, discarding the earlier claim of disc wind as the origin for the absorption features. Finally, we discuss our several ongoing and future surveys investigating the nature of circumstellar discs around IMSs.

• Speaker: Daniela Iglesias Vallejo (Leeds)
• Tuesday 13 February 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

The Lisa project to detect gravitational waves will be one of the most complex ever space missions.

The unprecedented medium-resolution (R~1500-3500) near- and mid-infrared (1-18um) spectrum provided by JWST for the young (140+/-20Myr) low-mass (12-20MJup) L-T transition (L7) companion VHS1256b gives access to a catalogue of molecular absorptions. In this study, we present a comprehensive analysis of this dataset utilizing a forward modelling approach, applying our Bayesian framework, ForMoSA. We explore five distinct atmospheric models to assess their performance in estimating key atmospheric parameters: Teff, log(g), [M/H], C/O, gamma, fsed, and R. Our findings reveal that each parameter's estimate is significantly influenced by factors such as the wavelength range considered and the model chosen for the fit. This is attributed to systematic errors in the models and their challenges in accurately replicating the complex atmospheric structure of VHS1256b, notably the complexity of its clouds and dust distribution. To propagate the impact of these systematic uncertainties on our atmospheric property estimates, we introduce innovative fitting methodologies based on independent fits performed on different spectral windows. We finally derived a Teff consistent with the spectral type of the target, considering its young age, which is confirmed by our estimate of log(g). Despite the exceptional data quality, attaining robust estimates for chemical abundances [M/H] and C/O, often employed as indicators of formation history, remains challenging. Nevertheless, the pioneering case of JWST's data for VHS1256b has paved the way for future acquisitions of substellar spectra that will be systematically analyzed to directly compare the properties of these objects and correct the systematics in the models.

Verifying the fully kinematic nature of the cosmic microwave background (CMB) dipole is of fundamental importance in cosmology. In the standard cosmological model with the Friedman-Lemaitre-Robertson-Walker (FLRW) metric from the inflationary expansion the CMB dipole should be entirely kinematic. Any non-kinematic CMB dipole component would thus reflect the preinflationary structure of spacetime probing the extent of the FLRW applicability. Cosmic backgrounds from galaxies after the matter-radiation decoupling, should have kinematic dipole component identical in velocity with the CMB kinematic dipole. Comparing the two can lead to isolating the CMB non-kinematic dipole. It was recently proposed that such measurement can be done using the near-IR cosmic infrared background (CIB) measured with the currently operating Euclid telescope, and later with Roman. The proposed method reconstructs the resolved CIB, the Integrated Galaxy Light (IGL), from Euclid's Wide Survey and probes its dipole, with a kinematic component amplified over that of the CMB by the Compton-Getting effect. The amplification coupled with the extensive galaxy samples forming the IGL would determine the CIB dipole with an overwhelming signal/noise, isolating its direction to sub-degree accuracy. We develop details of the method for Euclid's Wide Survey in 4 bands spanning 0.6 to 2 mic. We isolate the systematic and other uncertainties and present methodologies to minimize them, after confining the sample to the magnitude range with negligible IGL/CIB dipole from galaxy clustering. These include the required star-galaxy separation, accounting for the extinction correction dipole using the method newly developed here achieving total separation, accounting for the Earth's orbital motion and other systematic effects. (Abridged)

Blue Horizontal Branch (BHB) stars, excellent distant tracers for probing the Milky Way's halo density profile, are distinguished in the $(g-r)_0$ vs $(i-z)_0$ color space from another class of stars, blue straggler stars (BSs). We develop a Bayesian mixture model to classify BHB stars using high-precision photometry data from the Dark Energy Survey Data Release 2 (DES DR2). We select $\sim2100$ highly-probable BHBs based on their $griz$ photometry and the associated uncertainties, and use these stars to map the stellar halo over the Galactocentric radial range $20 \lesssim R \lesssim 70$ kpc. After excluding known stellar overdensities, we find that the number density $n_\star$ of BHBs can be represented by a power law density profile $n_\star \propto R^{-\alpha}$ with an index of $\alpha=4.28_{-0.12}^{+0.13}$, consistent with existing literature values. In addition, we examine the impact of systematic errors and the spatial inhomogeneity on the fitted density profile. Our work demonstrates the effectiveness of high-precision $griz$ photometry in selecting BHB stars. The upcoming photometric survey from the Rubin Observatory, expected to reach depths 2-3 magnitudes greater than DES during its 10-year mission, will enable us to investigate the density profile of the Milky Way's halo out to the virial radius, unravelling the complex processes of formation and evolution in our Galaxy.

The quest for the earliest black holes: a theoretical perspective

Abstract not available

• Speaker: Rosa Valiante (Rome)
• Friday 09 February 2024, 11:30-12:30
• Venue: Ryle seminar room + online.
• Series: Galaxies Discussion Group; organiser: Sandro Tacchella.

Add to your calendar or Include in your list

Problems with (our) galaxy formation simulations and some new angles

Stellar feedback is a crucial component in controlling the baryon cycle in galaxies. However, it is not very clear how this can be done without assuming exotic models of stellar feedback. In this talk I will first discuss why we have not been very successful in producing realistic galaxies in our simulations, and present some attempts to solve this problem. I will also discuss how Lyman alpha profiles can potentially be used to place some constraints on cosmological simulations with cosmic ray feedback. This talk is intended to be thought-provoking rather than a collection of success stories.

• Speaker: Taysun Kimm (Yonsei)
• Thursday 08 February 2024, 11:30-12:30
• Venue: Ryle seminar room + online.
• Series: Galaxies Discussion Group; organiser: Sandro Tacchella.

Add to your calendar or Include in your list

The Crafoord Prize in Astronomy The Crafoord Prize in Astronomy 2024 is awarded to Douglas Gough , University of Cambridge, UK, Jørgen Christensen-Dalsgaard , Aarhus University, Denmark, and Conny Aerts , KU Leuven, Belgium “for developing the methods of asteroseismology and their application to the study of the interior...

Title to be confirmed

Abstract not available

• Speaker: Xuejian (Jacob) Shen (MIT)
• Friday 28 June 2024, 11:30-12:30
• Venue: Ryle seminar room + online.
• Series: Galaxies Discussion Group; organiser: Sandro Tacchella.

Add to your calendar or Include in your list

Title to be confirmed

Abstract not available

• Speaker: Roger de Belsunce (LBNL)
• Monday 18 March 2024, 13:00-14:00
• Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
• Series: Cosmology Lunch; organiser: Fiona McCarthy.

Add to your calendar or Include in your list

Title to be confirmed

Abstract not available

• Speaker: Trevor Mendel (ANU)
• Friday 19 April 2024, 11:30-12:30
• Venue: Ryle seminar room + online.
• Series: Galaxies Discussion Group; organiser: Sandro Tacchella.

Add to your calendar or Include in your list

Title to be confirmed

Abstract not available

• Speaker: Emily Wisnioski (ANU)
• Friday 12 April 2024, 11:30-12:30
• Venue: Ryle seminar room + online.
• Series: Galaxies Discussion Group; organiser: Sandro Tacchella.

Add to your calendar or Include in your list

Photoevaporation from Exoplanet Atmospheres: Understanding the Role of Stellar Winds and Considering Water-rich Atmospheres

The atmospheres of close-in exoplanets are extremely vulnerable to the effects of stellar UV to X-ray radiation. Photoevaporation can significantly alter planetary atmospheres or even strip them entirely, potentially rendering a planet uninhabitable. Understanding how these atmospheres evolve, persist, or fade away remains a fundamental challenge. In this talk, I will discuss two distinct but interconnected areas of photoevaporative research.

Firstly, I will discuss the interaction between the stellar wind and photoevaporating atmospheres. I will present 3D magnetohydrodynamic simulations of the interaction between the stellar wind and the photoevaporating outflow of a planet orbiting an M dwarf. This analysis reveals a diverse range of magnetosphere morphologies and plasma distributions due to the wind-outflow interaction. I consider how these changing morphologies might impact observable hydrogen Lyman-alpha signatures during planetary transits.

In the second part, I will delve into our current understanding of photoevaporation from water-rich atmospheres. Conventional analytic approaches often oversimplify the process, assuming two scenarios: the escape of only lighter hydrogen, or the dragging of oxygen along with escaping hydrogen. These two scenarios lead to two end cases: a planet that has retained its water-rich atmosphere or a planet which has lost its atmosphere, becoming dry and desiccated. I will challenge these oversimplifications by presenting results from a novel 1D multifluid hydrodynamic model of photoevaporation from a water-rich atmosphere, which shows oxygen escape should no longer be described by a simple on/off switch but instead requires careful modelling.

Room changed

• Speaker: Laura Harbach (Imperial)
• Tuesday 06 February 2024, 13:00-14:00
• Venue: Hoyle Committee Room + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Dr Emily Sandford.

Add to your calendar or Include in your list

The INSPIRE project has built the largest sample of ultra-compact massive galaxies (UCMGs) at 0.1<z<0.4 and obtained their star formation histories (SFHs). Due to their preserved very old stellar populations, relics are the perfect systems to constrain the earliest epochs of mass assembly in the Universe and the formation of massive early-type galaxies. The goal of this work is to investigate whether a correlation exists between the degree of relicness (DoR), quantifying the fraction of stellar mass formed at z>2, and the other stellar population parameters.We use the Full-Index-Fitting method to fit the INSPIRE spectra to single stellar population (SSP) models. This allows us to measure, for the first time, the low-mass end slope of the IMF, as well as stellar metallicity [M/H], [Mg/Fe], [Ti/Fe] and [Na/Fe] ratios, and study correlations between them and the DoR. Similarly to normal-sized galaxies, UCMGs with larger stellar masses have overall higher metallicities. We found a correlation between the low-mass end of the IMF slope and the DoR, that, however, breaks down for systems with a more extended SFH. An even stronger dependency is found between the IMF and the fraction of mass formed at high-z. At equal velocity dispersion and metallicity, galaxies with a higher DoR have a dwarf-richer IMF than that of low-DoR counterparts. This might indicate that the cosmic epoch and formation mechanisms influence the fragmentation of the star formation cloud and hence might be the explanation for IMF variations detected in massive ETGs.

We present the discovery and characterization of two warm mini-Neptunes transiting the K3V star TOI-815 in a K-M binary system. Analysis of the spectra and rotation period reveal it to be a young star with an age of $200^{+400}_{-200}$Myr. TOI-815b has a 11.2-day period and a radius of 2.94$\pm$0.05$\it{R_{\rm\mathrm{\oplus}}}$ with transits observed by TESS, CHEOPS, ASTEP, and LCOGT. The outer planet, TOI-815c, has a radius of 2.62$\pm$0.10$\it{R_{\rm\mathrm{\oplus}}}$, based on observations of three non-consecutive transits with TESS, while targeted CHEOPS photometry and radial velocity follow-up with ESPRESSO were required to confirm the 35-day period. ESPRESSO confirmed the planetary nature of both planets and measured masses of 7.6$\pm$1.5 $\it{M_{\rm \mathrm{\oplus}}}$ ($\rho_\mathrm{P}$=1.64$^{+0.33}_{-0.31}$gcm$^{-3}$) and 23.5$\pm$2.4$\it{M_{\rm\mathrm{\oplus}}}$ ($\rho_\mathrm{P}$=7.2$^{+1.1}_{-1.0}$gcm$^{-3}$) respectively. Thus, the planets have very different masses, unlike the usual similarity of masses in compact multi-planet systems. Moreover, our statistical analysis of mini-Neptunes orbiting FGK stars suggests that weakly irradiated planets tend to have higher bulk densities compared to those suffering strong irradiation. This could be ascribed to their cooler atmospheres, which are more compressed and denser. Internal structure modeling of TOI-815b suggests it likely has a H-He atmosphere constituting a few percent of the total planet mass, or higher if the planet is assumed to have no water. In contrast, the measured mass and radius of TOI-815c can be explained without invoking any atmosphere, challenging planetary formation theories. Finally, we infer from our measurements that the star is viewed close to pole-on, which implies a spin-orbit misalignment at the 3$\sigma$ level.

Astronomers have, for the first time, made a direct measurement of the mass of a distant black hole, one so far away that light from its surroundings took 11 billion years to reach us. The team, led by Taro Shimizu at the Max Planck Institute for Extraterrestrial Physics in Germany, found the black hole, called J0920, to have a mass of about 320 million times that of the Sun. This achievement, described in a paper published today in Nature, has been made possible thanks to GRAVITY+, a series of ongoing upgrades to ESO’s Very Large Telescope Interferometer (VLTI) and its GRAVITY instrument.

To directly measure the mass of a black hole, astronomers use telescopes to track the movement of gas and stars around it. The faster these move, the more mass is encased within the material’s orbit. This technique has been used to measure the mass of nearby black holes, including the one at the centre of the Milky Way. At very remote distances, however, this motion is extremely hard to observe. This means similar direct measurements of the mass of distant black holes, which provide a window into a period in the history of the Universe when galaxies and black holes were rapidly growing, have not been possible until now.

The direct measurement of J0920’s mass was only possible with the first set of GRAVITY+ improvements. These upgrades have allowed astronomers to observe the faint, distant gas around the black hole with greater accuracy than ever before by using a technique called wide-field, off-axis fringe tracking. Measuring the mass of J0920 accurately is a first step to help astronomers understand how black holes and galaxies grew together at a time when the Universe was only a couple of billion years old and galaxies were still forming. For J0920, the new mass measurement reveals the black hole is about four times less massive than expected given the mass of its host galaxy; this indicates a delay in the growth of the black hole compared to the surrounding galaxy.

GRAVITY+ uses interferometry to combine the light arriving at the four 8-metre Unit Telescopes (UTs) that are part of VLTI. Once completed, it will include upgraded adaptive optics technology that will enable better correction of the blur caused by the Earth’s atmosphere and improve the contrast of observations. GRAVITY+ will also implement one new laser guide star on each of UT1-3, and will make use of one of the lasers currently installed on UT4, to observe fainter and more distant objects than currently possible.

The upgrades to GRAVITY+ are being implemented incrementally, to ensure that there are limited disruptions to the scientific operations of the VLTI. This also allows for astronomers to continually test the performance of GRAVITY+ as it comes online. The full set of upgrades is anticipated to be completed in 2025. The new features will benefit all present and future VLTI instruments and the scientists who use them.

More Information

This research was presented in a paper to appear in Nature titled “A dynamical measurement of the supermassive black hole mass in a quasar 11 billion years ago”.

The team is composed of R. Abuter (European Southern Observatory, Garching, Germany [ESO]), F. Allouche (Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, France [Lagrange]), A. Amorim (Universidade de Lisboa - Faculdade de Ciências, Portugal and Centro de Astrofísica e Gravitação, IST, Universidade de Lisboa, Portugal [CENTRA]), C. Bailet (Lagrange), A. Berdeu (Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, France [LESIA]), J. P. Berger (Univ. Grenoble Alpes, CNRS, France [UGA]), P. Berio (Lagrange), A. Bigioli (Institute of Astronomy, KU Leuven, Belgium [KU Leuven]), O. Boebion (Lagrange), M.-L. Bolzer (Max Planck Institute for Extraterrestrial Physics, Germany [MPE], Department of Physics, Technical University Munich, Germany [TUM] and Univ. Lyon, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon, France [CRAL]), H. Bonnet (ESO), G. Bourdarot (MPE), P. Bourget (European Southern Observatory, Chile [ESO Chile]), W. Brandner (Max Planck Institute for Astronomy, Germany [MPIA]), Y. Cao (MPE), R. Conzelman (ESO), M. Comin (ESO), Y. Clénet (LESIA), B. Courtney-Barrer (ESO Chile and Research School of Astronomy and Astrophysics, College of Science, Australian National University, Australia [ANU]), R. Davies (MPE), D. Defrère (KU Leuven), A. Delboulbé (UGA), F. Delplancke-Ströbele (ESO), R. Dembet (LESIA), J. Dexter (Department of Astrophysical & Planetary Sciences, JILA, University of Colorado, USA), P. T. de Zeeuw (Leiden University, The Netherlands), A. Drescher (MPE), A. Eckart (Max Planck Institute for Radio Astronomy, Germany [MPIfR] and 1st Institute of Physics, University of Cologne, Germany [Cologne]), C. Édouard (LESIA), F. Eisenhauer (MPE), M. Fabricius (MPE), H. Feuchtgruber (MPE), G. Finger (MPE), N. M. Förster Schreiber (MPE), P. Garcia (Faculdade de Engenharia, Universidade do Porto, Portugal [FEUP] and CENTRA), R. Garcia Lopez (School of Physics, University College Dublin, Ireland), F. Gao (MPIfR), E. Gendron (LESIA), R. Genzel (MPE and Departments of Physics and Astronomy, University of California, USA), J.P. Gil (ESO Chile), S. Gillessen (MPE), T. Gomes (CENTRA and FEUP), F. Gonté (ESO), C. Gouvret (Lagrange), P. Guajardo (ESO Chile), S. Guieu (IPAG), W. Hackenberg (ESO), N. Haddad (ESO Chile), M. Hartl (MPE), X. Haubois (ESO Chile), F. Haußmann (MPE), G. Heißel (LESIA and Advanced Concepts Team, European Space Agency, TEC-SF, ESTEC, The Netherlands), T. Henning (MPIA), S. Hippler (MPIA), S.F. Hönig (School of Physics & Astronomy, University of Southampton, UK [Southampton]), M. Horrobin (Cologne), N. Hubin (ESO), E. Jacqmart (Lagrange), L. Jocou (IPAG), A. Kaufer (ESO Chile), P. Kervella (LESIA), J. Kolb (ESO), H. Korhonen (ESO Chile), S. Lacour (ESO and LESIA), S. Lagarde (Lagrange), O. Lai (Lagrange), V. Lapeyrère (LESIA), R. Laugier (KU Leuven), J.-B. Le Bouquin (IPAG), J. Leftley (Lagrange), P. Léna (LESIA), S. Lewis (ESO), D. Liu (MPE), B. Lopez (Lagrange), D. Lutz (MPE), Y. Magnard (IPAG), F. Mang (MPE and TUM), A. Marcotto (Lagrange), D. Maurel (IPAG), A. Mérand (ESO), F. Millour (Lagrange), N. More (MPE), H. Netzer (School of Physics and Astronomy, Tel Aviv University, Israel [TAU]), H. Nowacki (IPAG), M. Nowak (Institute of Astronomy, University of Cambridge, UK), S. Oberti (ESO), T. Ott (MPE), L. Pallanca (ESO Chile), T. Paumard (LESIA), K. Perraut (IPAG), G. Perrin (LESIA), R. Petrov (Lagrange), O. Pfuhl (ESO), N. Pourré (IPAG), S. Rabien (MPE), C. Rau (MPE), M. Riquelme (ESO), S. Robbe-Dubois (Lagrange), S. Rochat (IPAG), M. Salman (KU Leuven), J. Sanchez-Bermudez (Instituto de Astronomía, Universidad Nacional Autónoma de México, Mexico and MPIA), D.J.D. Santos (MPE), S. Scheithauer (MPIA), M. Schöller (ESO), J. Schubert (MPE), N. Schuhler (ESO Chile), J. Shangguan (MPE), P. Shchekaturov (ESO), T.T. Shimizu (MPE), A. Sevin (LESIA), F. Soulez (CRAL), A. Spang (Lagrange), E. Stadler (IPAG), A. Sternberg (TAU and Center for Computational Astrophysics, Flatiron Institute, USA), C. Straubmeier (Cologne), E. Sturm (MPE), C. Sykes (Southampton), L.J. Tacconi (MPE), K.R.W. Tristram (ESO Chile), F. Vincent (LESIA), S. von Fellenberg (MPIfR), S. Uysal (MPE), F. Widmann (MPE), E. Wieprecht (MPE), E. Wiezorrek (MPE), J. Woillez (ESO), and G. Zins (ESO).

The GRAVITY+ upgrades are designed and built by the following institutes together with ESO:

• Max Planck Institute for Extraterrestrial Physics; Max Planck Institute for Astronomy; the University of Cologne (Germany)
• Institut National des Sciences de l'Univers, French National Center for Scientific Research; Institut de Planétologie et d'Astrophysique de Grenoble; Laboratoire d’Etudes Spatiales et d’Instrumentation en Astrophysique; the Lagrange Laboratory; the Centre de Recherche Astrophysique de Lyon (France)
• Instituto Superior Técnico’s Centre for Astrophysics and Gravitation; University of Lisbon; University of Porto (Portugal)
• University of Southampton (UK)
• Katholieke Universiteit Leuven (Belgium)