2022 / 2023

Friday at ICE-CSIC means Pizza Seminar!

These seminars have been going on for 10 years now. We gather at the patio of the institute to eat pizza after the seminar as a nice way of ending the week. Since the last few months, the seminars are a hybrid event and we're happy to see you every Friday at 12 pm online.

Jun 23

Harnessing the opportunities in the approaching radio astronomy renaissance

Jessica Dempsey (ASTRON, Netherlands Institute for Radio Astronomy)

Radio astronomy is about to step into a new era of technical and scientific capability. ASTRON leads the expansion of LOFAR, while SKA enters construction of the largest radio observatory ever built. On the horizon, to complement and compete, are the ngVLA and DSA-2000. ASTRON, as the Netherlands centre for radio astronomy, looks now to its role in this renaissance, and in its opportunities with our LOFAR and SKA partners. ASTRON is developing a science data centre to lead the world in providing the broadest accessibility to science-ready data products in the radio regime, committed to lowering the barrier of access to the radio universe for the widest community of astronomers possible, in advance of hosting the upcoming SKA regional centre. The coming renaissance is not without challenge – particularly in facing and overcoming the daunting data collection, processing and storage bottlenecks and to develop green solutions for our expanding environmental impacts. ASTRON is developing its long-look strategic plan around these goals with our national and international community, focusing on ensuring in this decade of world-spanning facilities, we maintain agency and opportunity for our researchers to lead impactful science and technology developments.

Jun 16

The scientific context of Einstein’s visit to Catalonia and Spain

Emilio Elizalde (ICE-CSIC, IEEC)

On November 25, 1915, in a speech at the session of the Prussian Academy of Sciences, entitled "Die Feldgleichungen der Gravitation", Albert Einstein announced his General Theory of Relativity; on which he had been working tirelessly for nearly ten years. One and a half later, on February 8, 1917, in another speech at the same Academy ̶ this one with the title "Kosmologische Betrachtungen zur allgemeinen Relativitatstheorie" ̶ he applied his new theory to the description of the Universe. Something later, exactly one hundred years ago, Albert Einstein visited Barcelona, as well as other places in Catalonia and Spain. And just around the same time, very interesting solutions to his field equations for the General Theory of Relativity were found by Alexander Friedmann; among which, the family that corresponds to our universe (a unique theory with a unique solution!). In this presentation, I will discuss the conceptual significance of all these events, among other first episodes ̶ indeed very relevant and corresponding to astronomical observations ̶ which culminated in the birth of Cosmology as a modern science.

Jun 9

The Snake of Physics: The Indispensable Role of Programming in Physics

Froilan Enriquez (ICE-CSIC)

Like mathematics, science, and engineering..., programming is a vital, important, and in fact, indispensable, weapon in the armory of any professional researcher, scientist, and physicist. I will discuss the role that programming plays in our day to day work. I will enunciate what are the good, the bad, and the ugly coding practices in science. Finally, I will share with you what you can do now to become a better programmer and ergo a better researcher/scientist/physicist. Among these, we will examine variable/method semantic conventions, correct business keyboarding, program sequence flow, code repetition and encapsulation, and rubber duck debugging. This will be a participatory talk, with real code examples from official documentation, and examples from real hardcore PhD research. It is encouraged that those attending bring paper and pencils, and a phone to the seminar to get the most out of this opportunity. This talk is aimed at all levels, form undergrads to masters, to PhD's and perhaps postdocs.

Jun 2

Insights about binary's common envelope evolution with Luminous Red Nova transients

Nadia Blagorodnova Mujortova (Universitat de Barcelona)

Common envelope evolution (CEE) is a critical step in the evolution of binary stars. In those binary configurations where mass transfer becomes unstable, a fraction of the matter will eventually leave the system, causing a quick loss of angular momentum and a tightening of the binary’s orbit. In some cases, the stars will end up in a merger, but it others the orbital energy of the secondary star will allow to fully expel the primary star’s envelope, resulting in a compact binary configuration. This channel is necessary for the formation of numerous exciting astrophysical phenomena: X-ray binaries, supernova progenitors, sources of ionizing radiation, or progenitors of gravitational wave sources. Despite its importance, very little is still known about the CEE phase, as its complexity prevents a holistic theoretical approach. Fortunately, within the last three decades, a new class of astrophysical transients called Luminous Red Novae (LRNe) has been associated with the merger of massive stars, providing new observational clues about the physics occurring at the onset of the common envelope. In my talk, I will explain what LRNe can teach us about the different phases of CEE, such as loss of angular momentum, envelope ejection, and post-CE evolution of the system.

May 26

Compact Binaries through a lens: silent vs. detectable lensing with the LIGO-Virgo-Kagra Gravitational Wave Observatories

Ruxandra Bondarescu (Institut de Ciències del Cosmos, Universitat de Barcelona, ICCUB))

Massive objects located between the Earth and a compact binary merger can act as a magnifying glass improving the sensitivity of gravitational wave detectors to distant events. A point mass lens between the detector and the source can manifest itself either through an amplification of the gravitational wave signal in a frequency dependent manner that is maximum at merger, or through magnification combined with the appearance of a second image that interferes with the first creating a regular, predictable pattern. Many sources will be lensed, which complicates parameter estimation. However, if the lens mass is low, it will not affect the waveform in a visible manner. Similarly, if the lens is far from the line of sight it will not be detectable. We look for events that are likely to produce detectable evidence of lensing by computing the mismatch between lensed and unlensed waveforms, and the SNR increase due to lensing. We map the parameter space as a function of lens mass and source position. We find that most microlensing is likely to be silent with a mismatch of under 10% and may never be identified as lensed.

May 12

The time-dependent B-rho relation in galaxy simulations with chemistry

Anna Kontantinou (University of Crete)

Magnetic fields play a key role in nature, as they can impact various essential processes in galaxies, including star formation, the expansion of feedback regions, and the propagation of cosmic rays. In this talk, I will present our recent galaxy simulations that include gravity, star formation, and supernova feedback, starting with different magnetic field morphologies: toroidal or random. Our main motivation for this project is to investigate the B-rho relation, which is a metric used to quantify the importance of magnetic fields in the interstellar medium and to understand star formation. First, I will discuss our results regarding the morphology of the galaxies and their star formation rates. Then, I will talk about our investigations of the characteristics of the gas, such as the plasma beta parameter, pressure, and temperature. Finally, I will focus on the time evolution of the B-rho relation.

May 5

Swarms of nanosats: new opportunities for observational science

Estel Cardellach (ICE-CSIC & IEEC)

The success of the cost-effective nanosats and CubeSats and the development of communication links between them has opened the door to new concepts based on clusters of such small platforms. These clusters, also known as swarms, aim to expand the observational capabilities of the nanosats while keeping the costs below the 'traditional' larger platform solutions. Sharing information at high rates, the disperse units can act as a single much larger sensor. The technology to implement these ideas is ready, and the Agencies started to look into its possibilities. For example, in 2020 NASA selected a mission to dispatch six CubeSats, each the size of a toaster oven, to an orbit more than 20,000 miles from Earth to study massive particle ejections from the sun (Sun Radio Interferometer Space Experiment, or SunRISE), and ESA is selecting ideas for swarm applications in astronomy, heliophysics, Earth observation and telecommunication, under ESA's OSIP scheme. For example, in the OSIP call we read: "a swarm could function as a large in-space telescope, or it could measure how solar wind varies across space. This can be done either close to Earth or in deep space. Swarms could also provide improved, cheaper or novel forms of telecommunication and remote sensing for Earth science and commercial applications". The Earth Observation group participates in two swarm-related activities. On the one hand, under the GLITTER Doctoral Network project, a EU funded project involving 10 PhD students to jointly investigate the possibilities of swarms of GNSS-R nanosatellites. On the other hand, we have passed the first phase of the OSIP competition on 'Innovative Mission Concepts Enabled by Swarms of CubeSats', and we are now preparing for the second round. Finally, this approach could be also suggested in the frame of an ESA Earth Explorer 12 proposal we have recently joined. This talk will present a basic overview of the swarm concept, example applications and the EO group's activities on the topic.

April 28

Chandra studies of the globular cluster M28

Eda Vurgun

We present a detailed spectral and temporal study of the neutron star population in the globular cluster M28, after analyzing the dataset from the Chandra X-ray Observatory. We discover an orbital modulation in the X-ray flux of the redback and transitional millisecond pulsar PSR J1824-2452I during the pulsar state. Its orbital X-ray light curve shows a double-peaked maximum centered on the inferior conjunction of the pulsar, which suggests that the intrabinary shock is wrapped around the pulsar. We present improved mass and radius constraints from spectral fits of the quiescent LMXB in M28, using both hydrogen and helium neutron star atmosphere models. We also discover six new variable X-ray sources in the cluster.

April 21

How we transfer knowledge at CSIC

Isabel Gavilanes

CSIC is the first public institution in patent filing in Spain and the third in Europe. In 2022 it signed more than 108 exploitation and patents licence agreements with third parties. Transfer the research results to innovations that improve people's lives and benefit society, is one of the main missions of CSIC. Technology transfer is a process to transform scientific-technical knowledge into new products and services. This process, known as technology transfer (TT): is multiagent and multidirectional and requires of a high compromise of effort and commitment, and above all, of a great dose of trust between all the actors involved: researchers, TT managers, IP agents, industrial licensees, investors, business agents, end-users. All of them will transform, with their expertise and experience, the scientific-technical knowledge into a new product and service. Since the execution of the technology transfer involves time (medium to long term) and a high investment, it is very important to take care of the technical, legal and strategic aspects from the beginning until the end of the process. The VATC (Vicepresidencia Adjunta de Transferencia del Conocimiento) is the Technology Transfer Office at CSIC. Their staff gives support to CSIC´s researchers in all the process. I will illustrate how this works in the different steps, what are CSIC policies, and a few success stories.

April 14

Radio emissions from exoplanets and a young stellar object

Simranpreet Kaur

With the increasing uGMRT, LOFAR and VLA campaigns and the recent claims pertaining to the tentative detection of low-frequency bursting emission (hundreds mJy at 15-30 MHz) from the Tau Boötis system, the quest for exoplanetary radio signals is gaining momentum. Based on the behavior of Solar System planets, radio emissions from exoplanets are expected to be produced by the Electron Cyclotron Maser Instability, a coherent emission mechanism which needs the presence of a magnetic field, a source of energetic(keV) electrons and an anisotropy in the electron distribution function. I will begin by talking about different mechanisms leading to radio emissions, followed by the planetary systems we are aiming to look at for radio signatures. I will also talk briefly about the observed radio emission from another object, BHB07-01, which is a young stellar object with an ongoing data analysis.

March 31

Chiral Transport Phenomena and Compact Stars

Cristina Manuel

In systems made up of (almost) massless fermions new transport phenomena emerge as a consequence of the so called quantum chiral anomaly that have relevant implications in the dynamical evolution of those systems. I will review all these ideas as well as the tools needed to study these effects. These quantum effects might have relevant implications in situations of extreme conditions of temperature and/or density, such as in cosmology and in compacts stars. I will also show how a new conservation law that emerges in perfect classical fluids, that has the same for as the chiral anomaly equation, but it expresses that the magnetic, fluid and mixed helicities for isentropic fluids is conserved.

March 24

Environments of SNe Ia using IFS

Cristina Jiménez

Type Ia supernovae have standarizable light curves using empirical relations. The analysis of SNe Ia environments properties is a crucial tool to understand how this standardization is affected by the place of the explosion and to constrain its progenitors. In this talk, I will describe the analysis of the local and global environments of type Ia supernovae using Integral Field Spectroscopy (IFS) data cubes from a sample of +1000 host galaxies from PMAS, MUSE and MaNGA surveys.

March 17

Dynamo action and turbulence from localized random expansion waves / Long-term evolution of planetary magnetic fields

Albert Elias López

The main driving forces supplying energy to the interstellar medium are supernova explosions and stellar winds. Such localized irrotational sources must be combined with other physical processes to replicate real galactic environments, as interstellar medium possesses both turbulence and a dynamo-sustained magnetic field. We have performed three-dimensional periodic box magnetohidrodinamical (MHD) simulations with a simple forcing function that naively resembles a supernova. The flow created reaches up Reynolds numbers of 300 and Mach numbers of 1. We have evaluated the appearance of small scale dynamo when the system is influenced by rotation, baroclinicity or a shear profile. We have only found dynamo in the shearing case. I will also give an introduction to planetary magnetism in the Solar System, some of the latest 3D numerical planetary simulations and give an overview of our starting project about the gigayear evolution of planetary magnetic fields.

March 10

The effect of host-galaxy environment on type Ia supernova standardisation

Tomás Müller Bravo

Type Ia supernovae (SNe Ia) are excellent cosmological probes in the local Universe given their high precision as distance indicators. This precision is only achievable by standardising their light curves using empirical relations found between their optical peak brightness and other light-curve parameters, such as stretch and colour. Although SNe Ia have been used to estimate distances for quite some time, only in the last decade or so have we started to understand how the environment in which they explode can affect their standardisation. In this talk, I will explain how host-galaxy properties are used to further standardise SNe Ia and the new developments there have been to understand the connection between these transients and their environment to improve their usefulness as cosmological probes.

March 03

Type Ia supernovae with the James Webb Space Telescope

Chris Ashall (Virginia Tech)

Type Ia Supernovae (SNe Ia) mark the demise of white dwarfs (WD). These cosmic explosions release as much luminous energy as the sun produces over its entire lifetime. As cauldrons of nucleosynthesis, SNe Ia provide the interstellar medium with Fe-group elements and are key to its isotopic composition. They are also accurate cosmological distance rulers, which were vital in the discovery of the acceleration of the universe. Yet somehow the exact details of their progenitor scenario (e.g. single degenerate vs double degenerate) and explosion mechanism (e.g. Chandrasekhar mass vs. sub-Chandrasekhar mass) still eludes us. Understanding the origin of SNe Ia is critical if we are to reduce systematics in future cosmological experiments. Here, I will discuss the latest results from my Cycle1 JWST program, GO-2114. In particular I will show how late time MIR observations can accurately measure the mass of the primary WD, as well as chemical asphericities within the explosion. I will demonstrate how this data can be used to show that the nearby SN 2021aefx (the first SN Ia observed with JWST) was produced by an explosion of a near Chandrasekhar mass WD.  I will also show preliminary results from my other JWST Cycle1 JWST program, GO-2122, where I will present the first ever JWST spectra of a core collapse, SN 2022acko.  Overall, JWST is a truly exciting time for astronomy and promises to revolutionize SN physics.

Feb 24

Towards a statistical understanding of the star formation process

Álvaro Sánchez-Monge (ICE-CSIC)

Stars are the fundamental building blocks of galaxies and hosts of planetary systems. Therefore, studying their formation is not only key to understanding the most abundant luminous objects in the Universe, but also the properties of galaxies as well as planetary systems. Characterizing the process of formation of stars requires understanding the effects of gravity, turbulence and magnetic fields among others, over several orders of magnitude in spatial scale and temporal evolution, in heavily-obscured environments. With this talk I will take the opportunity to introduce my research, which covers different aspects of the star formation process from the 100-pc size molecular clouds where star formation begins down to 100-AU size circumstellar disks surrounding newly-born stars, where planetary systems will eventually form. Moreover, obtaining general conclusions about the star formation process requires observing not only a few selected regions, but a large number of them. Based on this, I will also present the efforts that we are carrying out in order to characterize statistically-significant samples of star-forming regions.

Feb 17

Magnetic White Dwarfs

Clàudia Soriano Guerrero (ICE-CSIC)

The number of discovered exoplanets has increased significantly in the recent years. Up to the date, there are more than 5000 confirmed exoplanets. However, not all of them show the same characteristics. In this talk we are going to present Hot Jupiters, gas giants which orbit really close to their host start. This proximity makes this exoplanets an excellent scenarios to study their dynamics, thermal properties and chemical composition. One of the most outstanding questions regarding them is why they have an inflated radii. Several theories have been proposed, but ohmic dissipation is one of the promising to explain this anomaly. In this talk we will travel through Hot Jupiters and show our on-going projects to explain the inflated radii anomaly via generation and dissipation of magnetic fields.

Feb 10

Magnetic White Dwarfs


White dwarfs are the descendants of stars with masses smaller than ~8 Mo. Their evolution is just a gravothrmal process of cooling. A fraction of them, not all of them, display magnetic fields with intensities in the range of kilo to giga Gauss and the incidence changes when moving from single to binary white dwarfs. In this seminar I will review the status of the problem.

Feb 03

New Diagnostics for the optical identification of Supernova Remnants

Maria Kopsacheili (Institute of Space Sciences, ICE-CSIC)

Study of Supernova Remnant (SNR) demographics and their physical properties (density, temperature, shock velocities) is very important in order to understand their role in galaxies. Many photometric and spectroscopic studies of SNRs, have been carried out in our Galaxy but also in extragalactic environments. The most common means for the SNR identification in the optical regime, is the use of the flux ratio of the [S II] (λλ6717, 6731) to Hα (λ6563) emission lines. However, this diagnostic is biased against low excitation SNRs. For this reason, we have developed new diagnostics that combine 2 and 3 emission line ratios along with a Support Vector Machine model, that efficiently differentiate SNRs from HII regions. These diagnostics recover up to 35% of the SNRs that we miss using the traditional diagnostic tool, which is very important in order to obtain more complete samples of SNRs (e.g. SNRs of different physical properties) and consequently to more efficiently explore the feedback processes to the host galaxy. We present the application of these diagnostics on IFU data that not only provide the necessary emission lines, but also the opportunity to study the properties of SNRs and their environments.

Jan 27

X-ray Binary Populations in Galaxies Across Cosmic History

Bret D. Lehmer (Department of Physics, University of Arkansas, USA)

Studies of the extragalactic Universe, from ultraviolet to infrared wavelengths, have been extremely effective at piecing together a basic picture of how stars in galaxies evolved throughout cosmic history. At X-ray wavelengths, galaxy emission is dominated by hot gas and populations of X-ray binaries, the latter of which consist of black holes and neutron stars accreting material from normal stellar companions. Hot gas in star-forming galaxies traces energetics from young and massive stars and X-ray binaries provide unique and important information regarding the star-formation histories and chemical evolution (metallicities) of their host galaxies.  These energetic phenomena have been proposed to play roles in the ionization of nebulae and long-range heating of the intergalactic medium in the early Universe. Furthermore, some X-ray binaries are expected to be predecessors and tracers of the gravitational-wave source populations that are now being detected by LIGO/VIRGO.  Using X-ray and multiwavelength observations (e.g., from Chandra, GALEX, Hubble, NuSTAR, Spitzer, Herschel, and other telescopes) of nearby and distant galaxies, as well as large-scale theoretical modeling, we are developing a framework detailing how X-ray binary populations and their host galaxies evolved together over the last 12 billion years (~90%) of cosmic history.  In this talk, I will describe some of the exciting new insights from our work, and I will highlight how new data sets, future observational facilities, and improved theoretical modeling will continue to improve our understanding of X-ray binaries, compact objects, and galaxies.

Jan 20

Unsupervised galaxy classification reveals new evolutionary pathways

Malgorzata Siudek, Polish National Agency for Academic Exchange (NAWA)

A complete and satisfactory understanding of the processes that led to the formation of all the variety of today’s galaxy types is still beyond our reach. To solve this problem, we need both large datasets reaching high redshifts and novel methodologies for dealing with them. The statistical power of the VIPERS survey, which observed ~90,000 galaxies at intermediate redshifts (z>0.5), and the application of an unsupervised clustering algorithm, allowed us to distinguish between passive galaxies, star-forming galaxies and galaxies hosting active galactic nuclei (AGN), among other types. A follow-up study of their environmental dependence indicates that this classification may actually reflect different galaxy evolutionary paths, revealing for instance a rare population of small and passive red galaxies. In my talk, I will discuss the clustering methodology and emerging scenarios of galaxy evolution.

Dec 02

Characterizing ASAS-SN core-collapse supernova environments with VLT+MUSE

Thallis Pessi, European Southern Observatory (ESO) & Universidad Diego Portales (UdP, Chile)

The study of supernova (SN) environments is an important method for understanding and constraining the progenitors of the different SN types. In this talk, he will present the analysis of 114 galaxies observed by the All-weather MUse Supernova Integral field Nearby Galaxies survey (AMUSING) that hosted core-collapse supernovae (CCSNe) detected or discovered by the All-Sky Automated Survey for Supernovae (ASAS-SN) survey, between 2014 and 2018. This is the largest analysis to date of CCSN host galaxies observed by the MUSE instrument at the Very Large Telescope (VLT). The use of a homogeneous SN sample from ASAS-SN, an untargeted and spectroscopically complete panoramic survey of transients, allowed us to perform a minimally biased statistical analysis of CCSN environments. The talk will describe our sample, the capabilities of the MUSE instrument in investigating SN environments, our main results, and prospects for future projects.

Nov 25

Visualizing the pulsar population using graph theory

Carlos R. García (ICE-CSIC)

The PPdot-diagram is a cornerstone of pulsar research. It is used in multiple ways for classifying the population, understanding evolutionary tracks, identifying issues in our theoretical reach, and more. However, we have been looking at the same plot for more than five decades. A fresh appraisal may be healthy. Is the PPdot-diagram the most useful or complete way to visualize the pulsars we know? Here we pose a fresh look at the information we have on the pulsar population. First, we use principal component analysis over magnitudes depending on the intrinsic pulsar’s timing properties (proxies to relevant physical pulsar features), to analyse whether the information contained by the pulsar’s period and period derivative is enough to describe the variety of the pulsar population. Even when the variables of interest depend on P and Pdot, we show that PPdot are not principal components. Thus, any distance ranking or visualization based only on P and Pdot is potentially misleading. Next, we define and compute a properly normalized distance to measure pulsar nearness, calculate the minimum spanning tree of the population, and discuss possible applications. The pulsar tree hosts information about pulsar similarities that go beyond P and Pdot, and are thus naturally difficult to read from the P Pdot-diagram. We use this work to introduce the pulsar tree website containing visualization tools and data to allow users to gather information in terms of MST and distance ranking.

Nov 18

A data-driven approach to non-linear dynamos

Anna Guseva (University of Leeds)

Organized, large-scale magnetic fields are frequently encountered in the Universe, from planets and stars to accretion disks and galactic clusters. It is widely accepted that these fields are created through dynamo action, which is supported by turbulent motions of conducting fluid inside astrophysical objects and opposed by Ohmic dissipation. These dynamos can be considered as nonlinear chaotic dynamical systems, whose saturated states depend on nonlinear interactions between the flow and the magnetic field. A rigorous description of these saturation mechanisms is important for a better understanding of long-term evolution and variations in large-scale stellar and planetary flows.

Nov 11

The mass of the interstellar dust reservoir in galaxies

Francisca Kemper (ICE-CSIC, IEEC, ICREA)

The evolution of interstellar dust reservoirs, and the evolution of galaxies themselves go hand-in-hand, as the presence of dust alters evolutionary drivers, such as the interstellar radiation field and the star formation history, while at the same time, the dust is being formed and altered by processes taking place in galaxies. However, far-infrared and submillimeter studies have revealed enormous dust masses at high redshifts that are difficult to explain with dust production from evolved stars (the so-called "dust budget problem"), while in the nearby universe there is also a significant mismatch between the dust production rate and the dust mass observed in the interstellar medium of galaxies. I will go over some possible explanations in an attempt to find a way forward towards a solution to this seeming discrepancy.

Oct 28

Ultraluminous X-ray source populations: observational constraints and theoretical modelling

Konstantinos Kovlakas (ICE-CSIC)

Ultraluminous X-ray sources (ULXs) are thought to be X-ray binary systems exhibiting super-Eddington luminosities. They challenge our understanding of accretion physics at extreme accretion rates, while their nature and evolution has not yet been fully explored. Since ULXs are rare and usually found at large distances, only a few systems have been studied thoroughly, nevertheless providing useful information on their accretion states. On the other hand, having extreme luminosities, numerous ULXs have been detected at different galactic environments, allowing demographic ULX studies to indirectly access the properties of ULXs, but most importantly, to directly explore the formation and evolution of ULX populations via the comparison with binary population synthesis models. In this seminar, we will talk about a census of ULXs designed for this purpose (HECATE-ULX), and a new binary population synthesis code (POSYDON) providing reliable modelling of mass-transfer sequences. We will see how they will be combined with cosmological simulations, giving access to the properties of ULX populations (X-MARCS-THE-SPOT). Furthermore, we will discuss on ULXs as local Universe ionizing sources, and important players in heating the early Universe.

Oct 21

What Moves the Heavens Above?

Enrique Gaztañaga (ICE-CSIC & IEEC)

Aristotle proposed that Aether, a divine substance, moved the heavenly spheres of stars and planets. It took two millennia to discovered that such Aether was just the universal law of Gravity. Yet, according to the current lore, cosmic expansion can not be explained by Gravity. The standard model of cosmology assumes that everything started in a singular Big Bang out of Cosmic Inflation, a mysterious form of modern Aether. But there is no direct evidence that this ever occurred. Measurements of cosmic acceleration also seem to requiere a cosmological constant (Λ), yet another form of such Aether. We will argue instead that these are just indications that our Universe has a finite mass. If this is the case, we live inside a large local Black Hole (BH) Universe (BHU) whose event horizon plays the role of Λ. This BHU has the same metric as the standard cosmology (ΛCDM) . A comoving observer, anywhere inside such BHU, measures the same background as an observer in the standard ΛCDM. This solution to the Λ conundrum opens new questions about the origen of expansion and structure and could also help us understand other recent puzzling observations.

Oct 14

Unification of inflation with dark energy in axion F(R) gravity. How fundamental is entropy

Sergei D. Odintsov (ICREA, ICE-CSIC, IEEC, Barcelona)

The detection of gravitational waves (GWs) has opened a completely new window on the Universe. At nHz frequencies, pulsar timing arrays (PTAs) promise to detect the signal coming from the cosmological population of supermassive black hole binaries (SMBHBs) within the next few years. After reviewing the astrophysics of SMBHBs, I will describe the pulsar timing technique, the current status of the PTA effort, present the most recent results, and discuss their astrophysical implications.

Oct 07

A pulsar wind population: issues and prospects (with a status of CTA)

Diego F. Torres (ICREA & ICE-CSIC)

During the last few years, I have been promoting a line of research centered on analyzing and modelling pulsar wind nebulae. I have put special emphasis to the theoretical challenges, issues, opportunities and risks that will be brought in by the new generation of instruments. I will provide an update of how this research line goes, including some of the recent results, and explain at once the status of the Cherenkov Telescope Array.

Sept 30

Ultraviolet Explosions

Peter Brown (Texas A&M University)

The quick response of the Neil Gehrels Swift Observatory has led to an explosion in the number of ultraviolet observations of supernova explosions.  I will summarize the zoo of stellar explosions and the knowledge gained from ultraviolet observations.  Key Swift discoveries include the ultraviolet diversity of Type Ia supernova "standard candles" and the extreme UV luminosity of superluminous supernovae -- detectable all the way to the edge of the observable universe.

Sept 23

Extreme Occultations of a Sun-like Star

Jonathan Marshall (Institute of Astronomy and Astrophysics, Academia Sinica, Taipei, Taiwan)

The discovery of deep, quasiperiodic transits of KIC 8642852 (Boyajian's star) revealed substantial amounts of optically thick material on an eccentric orbit residing around an otherwise ordinary main sequence star. Since this discovery, a dozen such stars have been identified and are referred to collectively as "little dippers". The dimming of these objects are thought to be caused by large clouds of circumstellar material related to comet swarms or disintegrating planet(esimal)s. Here we report on the recent dimming event of the Sun-like star ASASSN-21qj, which dropped from SDSS g = 13.8 mag to > 16 mag over the course of several weeks. We present LCO time series photometry of the star in SDSS griz bands, tracing the evolution of the occultation after its initial discovery back to its quiescent state. We identify two separate major dimming events in the observations, down to depths of 20 mag and 17 mag, respectively, along with a large number of intermediate events of varying depth and duration. We use multi-wavelength monitoring to capture for the first time the onset of such occultations and characterize the dusty material responsible. From these observations we infer the spatial distribution of the occulting material to be a compact clump within a broader diffuse cloud based on the shape and duration of the eclipses. The typical grain size of the dust grains, derived from the photometric colours, is 0.4 micron for the general obscuration and 2 micron for the deepest eclipses

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