2021 / 2022

Friday at ICE means Pizza Seminar!

These seminars have been going on for 10 years now and even though we cannot have the pizza right now due to Covid-19 pandemic, we're happy to see you every Friday at 12 pm online.

Jun 3

Understanding the high-energy emission of pulsars with synchro-curvature radiation models

Daniel Íñiguez (ICE-CSIC)

Out of the several hundreds of gamma-ray pulsars known nowadays, only a few tens have been detected to emit also non-thermal X-ray radiation. Some aspects of the high-energy magnetospheric radiation are still unclear, such as the location of emission. In this talk I will present a radiative model which aims at explaining the high-energy emission of pulsars in an effective way, relying on only three free physical parameters: the electric field, the local magnetic field, and the size of the emitting region. The model computes the dynamics of an ensemble of charged particles traveling in peculiar regions of a pulsar’s magnetosphere and calculates their spectral emission via synchro-curvature radiation losses. The model successfully fits the entire gamma-ray pulsar population. It also reproduces satisfactorily both the X-ray and gamma-ray bands of the spectral energy distribution of a majority of those gamma-ray pulsars emitting also non-thermal X-rays, describing their spectra across eight orders of magnitude. He will show the most relevant results of the systematic spectral fitting of our model to the known population of high-energy pulsars, after improving the injection region assumptions. Finally, I will present how the spectral fitting can constrain the probable range of the spin period for unidentified pulsar candidates.

Jun 3

Powerful outflows from AMXPs: the case of Swift J1749.4-2807

Alessio Marino (ICE-CSIC)

Swift J1749.4-2807 is the only known eclipsing Accreting Millisecond X-ray Pulsar. On March 2021, the source underwent a short (11-days) and relatively faint outburst. I will present the first ever broadband spectral characterisation of the system throughout the whole outburst, analysing 11 NICER observations and XMM-Newton and NuSTAR single observations. According to this analysis, the disc is moderately truncated away from the Neutron Star and does not contribute directly to the X-ray spectrum. The spectral emission is instead well modelled with a black body component, most likely due to a hot spot on the Neutron Star surface, and a Comptonisation spectrum arising from a hot electron corona. During the outburst decay, as the spectral shape hardened, the hot spot on the Neutron Star surface cooled down and shrinked, possibly disclosing the dawn of a pure quiesence power-law spectrum. Finally, the significant detection of a blue-shifted Fe XXVI absorption line at ∼7 keV indicates weakly relativistic disk winds. The discovery of such outflows, typically absent in the hard state of X-ray binaries, is presented in the context of unexpected and powerful outflows in accreting millisecond pulsars.

May 27

Searches for continuous gravitational waves and dark matter signatures with LIGO and Virgo

Ornella Piccinni (IFAE)

The gravitational-wave detections provided by the LIGO-Virgo network of Advanced interferometers, had a significant impact in many fields of science: astrophysics, cosmology, nuclear physics and fundamental physics. Compact binaries coalescence signals, the only type of signals detected so far, are only a small fraction of possible detectable gravitational waves. An interesting family of yet undetected signals, and the ones that I will consider in this talk, are the so-called continuous waves. The main sources of continuous signals are galactic, fast-spinning isolated neutron stars or potential dark matter candidates. In this talk, she will review some of the latest results from Advanced detector data in this field.

May 13

A Plan to Exploit Future X-ray Data with Timing and Machine Learning

Alessandro Patruno (ICE-CSIC)

Accretion-related phenomena observed in X-ray binaries constitute a physical setting through which is possible to constrain extreme physics. For example, detecting the spin of fast-rotating neutron stars might be important to constraining the equation-of-state of ultradense matter, and understanding the origin of quasi-periodic oscillations can be crucial to inferring the physical parameters of black holes and neutron stars. 

With the advent of new instrumentation in the X-ray band, there will be many opportunities to advance our understanding in several key areas related to compact objects (and beyond). 

He will discuss the possibilities offered by future instrumentation, with a particular focus on the Wide-Field-Monitor aboard eXTP, which is currently being built under the lead of scientists and engineers at our institute. In particular, I will discuss which techniques might be more promising and outline a plan to develop a core group for creating an automated analysis tool able to analyze data in nearly real-time. Some basic methods rely on timing techniques coupled with the exploitation of machine learning methods in the natural language processing area, which of course are also applicable to many astrophysical objects and wavelengths beyond binaries and X-rays.

May 6

Probing BH-accretion via X-ray spectral-timing

Barbara de Marco (UPC)

Black hole X-ray binaries (BHXRB) show complex, non-stationary behaviour during an outburst, characterized by significant changes of their spectral and timing properties. The origin of such behaviour is currently unknown, although evolution of the geometry of the innermost accretion flow is thought to play a major role. I will discuss open questions related to understanding the evolution of the inner structure of the accretion flow throughout an outburst, and present recent results obtained through the application of X-ray spectral-timing techniques to data from the latest generation of high throughput X-ray detectors.

Apr 29

Binary systems as gravitational wave detectors

Diego Blas (IFAE/UAB)

The passage of gravitational waves (GWs) through a binary perturbs the trajectories of the two bodies, potentially causing observable changes to their orbital parameters. In the presence of a stochastic GW background (SGWB) these changes accumulate over time, causing the binary orbit to execute a random walk through parameter space. In this talk I will present a new formalism for calculating the full statistical evolution of a generic binary system in the presence of a SGWB, capturing all six of the binary's orbital parameters.

He will show how this formalism can be applied to timing of binary pulsars and lunar laser ranging, thereby setting novel upper limits on the SGWB spectrum in a frequency band that is currently inaccessible to all other GW experiments.

Apr 22

Long-period pulsars as possible outcomes of supernova fallback accretion

Michele Ronchi (ICE-CSIC)

For about half a century the radio pulsar population was observed to spin in the ∼ 0.002–12 s range, with different pulsar classes having a spin-period evolution that differs substantially depending on their magnetic fields or past accretion history. The recent detection of several slowly rotating pulsars has re-opened the long-standing question of the exact physics, and observational biases, driving the upper bound of the period range of the pulsar population. In this talk, we will examine the spin-period evolution of pulsars interacting with supernova fallback matter and specifically look at the fallback accretion disk scenario. This evolution can differ substantially from the typical dipolar spin-down, and is very dependent on the ranges of initial parameters at formation (in particular the initial magnetic field and disk accretion rate), resulting in pulsars that evolve towards spin periods longer than their coeval peers. In addition, in light of our model, we will study the case of a recently discovered peculiar radio transient GLEAM-X J162759.5-523504.3 which has a rotation period of 1091 s. The supernova fallback scenario could represent a viable channel to produce a population of long-period isolated pulsars that only recent observation campaigns are starting to unveil.

Apr 8

MHD simulations and synthetic observations of the magnetised ISM

Evangelia Ntormousi (Scuola Normale Superiore di Pisa/FORTH)

Magnetic fields are of paramount importance for understanding the evolution and dynamics of galaxies. However, even the magnetic field of our own Galaxy is still elusive, since its strength and direction are impossible to measure simultaneously. It is therefore essential that we complete our knowledge with numerical simulations of galaxy and magnetic field co-evolution.

In the first part of this talk, she will show results from a series of high-resolution numerical models, aimed at deciphering the effect of the initial conditions and of stellar feedback on the evolution of the galactic magnetic field in isolated, Milky Way-like galaxies. The models include a dark matter halo, a stellar and a gaseous disk, star formation and supernova feedback, so that the dynamical evolution of the galaxy is self-consistent. The galaxies develop a turbulent velocity field and a random magnetic field component very early in their evolution.

In the second part of the talk, she will show synthetic dust polarization maps taken from various locations within these simulated galaxies. As is done for the characterization of the Galactic foregrounds in observations of the thermal dust polarization sky, we use these maps to derive angular power spectra. By statistically comparing spectra taken from different locations and different models, we are able to quantify the effect of cosmic variance on the power spectral characteristics. We find that the polarization power spectra sensitively depend on the observer's location, impeding a distinction between different simulation setups.

Apr 1

The nature of gamma-ray binaries

Diego F. Torres (ICE-CSIC & IEEC)

LS I +61 303 303 is one of the rare gamma-ray binaries, emitting most of their luminosity in photons with energies beyond 100 MeV. The ~26.5 d orbital period is clearly detected at many wavelengths. Additional aspects of its multi-frequency behavior make it the most interesting example of the class. The morphology of high-resolution radio images changes with orbital phase displaying a cometary tail pointing away from the high-mass star. LS I +61 303 303 also shows superorbital variability. A couple of energetic (~ 10^{37} erg s^{-1}), short, magnetar-like bursts have been plausibly ascribed to it. LS I +61 303 303's phenomenology has been put under theoretical scrutiny for decades, but the lack of certainty regarding the nature of the compact object in the binary has prevented advancing our understanding of the source. Here, using observations done with the Five-hundred-meter Aperture Spherical radio Telescope (FAST), we report on the existence of transient radio pulsations from the direction of LS I +61 303 303. We find a period P=269.15508 \pm 0.00016 ms at a significance of 20 sigma$ This is the first evidence for pulsations from this source at any frequency, and strongly argues for the existence of a rotating neutron star in LS I +61 303 303.

Mar 25

Drivers of stellar metallicity in galaxies

Justus Neumann (Institute of Cosmology and Gravitation, University of Portsmouth)

The distribution of stellar metallicities within and across galaxies is an excellent relic of the chemical evolution across cosmic time. Spatially resolved spectroscopic surveys offer the unique opportunity to study global and local drivers of stellar populations in galaxies. In this talk, I present results from a detailed analysis of spatially resolved stellar populations based on > 2.6 million spatial bins from 8109 nearby galaxies in the SDSS-IV MaNGA survey. Our study goes beyond the well-known global mass-metallicity relation and radial metallicity gradients by providing a statistically sound exploration of local relations between stellar metallicity, stellar surface mass density (SMD) and galactocentric distance across a wide variety of galaxy masses and morphologies.

Mar 18

A new finite-volume code for the magnetic field evolution of neutron stars in 3D

Clara Dehman (ICE-CSIC)

An important problem in astrophysics is the numerical modelling of the evolution of a magnetic field in neutron magnetars. The observed diversity of magnetars indicates that their magnetic topology is rather complex. Three-dimensional simulations of the magnetic induction equation are required to explain the observed bursting mechanisms and surface hotspots of magnetars. Up to now, most attempts to study magnetic evolution were based on spectral or semi-spectral methods. Here, we employ the cubed-sphere system of coordinates: a peculiar gridding technique for the solution of partial differential equations in spherical geometry, which is widely used in several branches of physics. A three-dimensional numerical code based on the finite volume scheme is presented to study the evolution of the magnetic field in the star’s crust via the Hall effect.

To provide realistic results, we have implemented fits of the Hall pre-factor and the magnetic resistivity, taken from the 2D magneto-thermal code developed by our group over the last decade. The code can follow the evolution of intense three-dimensional fields with non-axisymmetric topologies, low magnetic diffusivity, and is suitable for studying the formation of sharp current sheets during the evolution. In this talk, I will present the preliminary results obtained using our new code, which aims to generalize the axisymmetric magneto-thermal finite volume code previously developed by our group.

Mar 11

A new finite-volume code for the thermal evolution of magnetized neutron stars in 3 d

Stefano Ascenzi (ICE-CSIC)

The study of the thermal and magnetic evolution of neutron stars (NSs) in time is fundamental to understand the spectral and temporal properties of these sources and shed light on the origin of the different NS populations. To this aim, a numerical study of the heat diffusion and magnetic evolution equation is required, coupled with a detailed calculation of the microphysical property of the star, such as neutrino emissivity and heat and electric conductivity. Moreover, in order to account for the non-axisymmetric Hall instabilities, which are expected to lead to the formation of small scales regions with high magnetic energy density, a solution of the equation in 3D is required.

In this talk, I present the preliminary implementation of the thermal evolution part of our new 3D magneto-thermal evolution code, which aims to generalize the axisymmetric magneto-thermal finite-volume code previously developed by our group.

Mar 04

How to resist extreme temperatures: a new semiconductor flying to Mercury

Philippe Godignon (IMB-CNM, CSIC)

Electronic components based on semiconductors are widely used in scientific Spacecraft and Satellites. Silicon is the main semiconductor used for electronic devices integration, representing around 95% of the market. However, silicon exhibits several physical limitations when operating in harsh environments or extreme performances, namely at high temperature, high radiation ambient, high frequency or high voltage operation. Then, other semiconductors such as III-V or Wide Band Gap families, are considered to cover applications requiring these extreme conditions or performances. In the BepiColombo mission, defined to study Mercury, the proximity of Sun will strongly impact the Spacecraft electronics, especially the solar panels. We have used an innovative WBG semiconductor, Silicon Carbide, to develop a solar panel protection components able to operate in the extreme temperature and radiation environments of the mission. The device has been developed from scratch, as no equivalent device was available worldwide. A qualification test campaign has been defined and performed, adapting the ESA test standards to the unprecedented specificities of the BepiColombo mission. Finally, flight parts have been produced and delivered to the Solar Panel manufacturer for their integration. This is the first Wide Band Gap semiconductor active device used in a Space mission.

Feb 25

What can we learn from the oscillations of stars?

Kuldeep Verma (ICE-CSIC)

The extremely small amplitude oscillations of the Sun were discovered about half a century ago. The study of these oscillations -so-called helioseismology- allowed us to probe the solar interior in great detail and led to several fundamental discoveries such as neutrino oscillation. The potential of the study of oscillations in distant stars or asteroseismology was realized during the late 1980s, and the quest to detect solar-like oscillations began shortly after that. The major revolution in this field came in 2006 with the advent of the French-led CoRoT space mission, which detected oscillations in several solar-type stars and also measured the corresponding frequencies with very high precision.

We currently have high-fidelity asteroseismic data for thousands of stars from the NASA Kepler/K2 and TESS satellites, providing unique opportunity to study stellar internal structure and measure fundamental stellar properties such as mass, radius, age and helium abundance of field stars to unprecedented precision. These stellar properties are of paramount importance to several disciplines of modern astrophysics including the study of exoplanets and formation and evolution of our host Galaxy. In this talk, I shall briefly introduce the subject and give some concrete examples, from my research, of the kinds of things we can learn about stars and the Milky Way using solar-like oscillations.

Feb 18

Extending the utility of Type Ia Supernovae as Cosmological Probes

Tomás Müller (ICE-CSIC)

Since the discovery of the accelerating expansion of the universe more than two decades ago, type Ia supernovae (SNe Ia) have been extensively used as standardisable candles. The current focus of the field is on decreasing the scatter in the Hubble Diagram by improving the precision of these cosmological distance indicators. However, we are reaching a point where systematic uncertainties are starting to dominate the error budget. In this seminar, I will talk about PISCOLA, a data-driven SN Ia light-curve fitter, and an analysis method I developed during my PhD in search of an improved standardisation of SNe Ia. I will also talk about my contribution to FLOWS and the use of SNe Ia in the near-infrared to measure the local expansion rate of the universe (H0) and map our local supercluster Laniakea.

Feb 11

Why is our universe inside a black hole?

Enrique Gaztañaga (ICE-CSIC and IEEC)

The standard model of cosmology assumes that our Universe began 14 Gyrs (billion years) ago with a hot Big Bang expansion out of nothing. However successful this model is, we have no direct evidence or fundamental understanding of some key assumptions: low entropy start, Inflation, Dark Matter and Dark Energy. Here we present a simpler and more physical explanation for the same observations that do not require such assumptions or new laws of Physics. How did the Big Bang end up inside such a Blac Hole? We propose that 25 Gyrs ago, a very low density dust cloud collapsed and form such BH. As there was no pressure support, the collapse continued inside until it reached neutron energy densities (GeV).

Feb 04

Cornering the Hubble tension by studying systematics and reconstructing the local Universe with supernovae (HOSTFLOWS)

Lluís Galbany (ICE-CSIC)

The expansion rate of the Universe parameterized by the Hubble-Lemaitre parameter H(z) has been a major endeavor in cosmology since the discovery of the expanding Universe. In the last years, significant effort has been put forth to measure with high precision the local value of the Hubble-Lemaitre parameter known as the Hubble constant (H0).

Find more about his project Hostflows here.

Jan 20

The quest for exoplanetary radio emission

Daniele Viganò (ICE-CSIC)

During the last years, the observational campaigns aimed at detecting radio emission from extrasolar planets are gaining momentum. A first tentative detection was announced some months ago, being, if confirmed, the most direct estimate of magnetic fields in exoplanets so far. On the other hand, indirect estimates based on the star-planet interaction point to a scenario in which magnetism appears as a mass-dependent continuum, linking giant planets to brown dwarfs. I will present the future prospects and observational proposals.

Jan 14

HydroGNSS: monitoring parameters related to essential climate variables with GNSS reflectometry

Estel Cardellach (ICE-CSIC & IEEC)

Scout missions are a new Element in ESA's Future EO Programme, demonstrating science from small satellites. HydroGNSS has been selected as the second ESA Scout Earth Observation mission, primed by Surrey Satellite Technology Ltd. The microsatellite uses established and new GNSS-Reflectometry techniques to take four land-based hydrological climate variables; soil moisture, freeze/thaw, inundation and biomass. The initial project is for a single satellite in a near-polar sun synchronous orbit at 550 km altitude that will approach global coverage monthly, but an option to add a second satellite has been proposed that would halve the time to cover the globe, and eventually a future constellation could be affordably deployed to achieve daily revisits. Phases B to E have kicked off during the fourth quarter of 2021, and the launch is expected by 2024. This seminar will explain the mission and ICE-CSIC/IEEC participation.

Dic 17

Special Xmas Pizza Seminar: Limits

Giorgos Kallis, Institute of Environmental Science and Technology (ICTA-UAB)

Western culture is infatuated with the dream of going beyond, even as it is increasingly haunted by the specter of apocalypse: drought, famine, nuclear winter. How did we come to think of the planet and its limits as we do? In this talk, Kallis reclaims, redefines, and makes an impassioned plea for limits—a notion central to environmentalism—clearing them from their association with Malthusianism and the ideology and politics that go along with it. Kallis separates limits and scarcity, two notions that have long been conflated in both environmental and economic thought. Taking us from ancient Greece to Malthus, from hunter-gatherers to the Romantics, from anarchist feminists to 1970s radical environmentalists, this lecture shows us how an institutionalized culture of sharing can make possible the collective self-limitation we so urgently need.

Dic 10

On the distance-redshift relation in an inhomogeneous Universe

Michel-Andrès Breton (ICE-CSIC)

The interpretation of cosmological observations relies on a notion of an average Universe, which is usually considered as the homogeneous and isotropic Friedmann-Lemaître-Robertson-Walker (FLRW) model. However, inhomogeneities may statistically bias the observational averages with respect to FLRW, notably for distance measurements, due to a number of effects such as gravitational lensing and redshift perturbations. In this talk, I will review the main historical theoretical advances on the distance-redshift relation, and perform a numerical analysis using high-resolution N-body simulations and relativistic ray-tracing in order to study the possible biases that can arise from highly non-linear scales when considering CMB or supernovae observations.

Nov 26

Disentangling the formation path(s) of S0 galaxies

Josep Tous (ICCUB)

Lenticular (S0) galaxies occupy a pivotal position in the Hubble tuning fork diagram. Classically, S0s are envisaged as quiescent objects with intermediate structural characteristics between those of spiral and elliptical galaxies. Eighty years after their discovery, however, the evolutionary mechanisms that shape these members of the galaxy zoo are relatively poorly understood and are still subject to debate. In this talk I will review some of the current scenarios in which we think these galaxies form and the most important results from our recent studies in the quest for their origin.

Nov 05

Cosmology ensuing from Machine Learning

Martiros Khurshudyan (Institute of Space Sciences, ICE-CSIC)

This time, I will discuss some of our new results when specific Machine Learning techniques have been applied. In particular, I will discuss the results when Gaussian Processes and Probabilistic Machine Learning have been applied. One of the interesting results to mention when Probabilistic Machine Learning has been used is a deviation from the cold dark matter paradigm. In its turn, it allows solving the H0 tension problem too. On the other hand, it can be a starting point for a better understanding of why interacting dark energy models work. Based on obtained results recently we initialized a massive search to find a confirmation for this using classical tools (or understand why we do not see it). Hopefully, some good news would be possible to share on this issue during upcoming seminars.

Oct 22

On my Book: The True Story of Modern Cosmology

Enrique Gaztañaga (Institute of Space Sciences (ICE-CSIC and IEEC)

I describe how, over the past century, dedicated observers and pioneering scientists achieved our current understanding of the universe. It is reflected that it was already in antiquity that humankind first attempted to explain the universe, but often with the help of myths and legends. The focus, however, is on the time when cosmology finally became a true science. This was actually a slow process, extending over a large part of the 20th century and involving many astronomers, cosmologists and theoretical physicists.

Oct 08

The Black Hole Universe (BHU)

Enrique Gaztañaga (Institute of Space Sciences (ICE-CSIC)

Recent observations show that cosmic expansion is dominated by an effective cosmological constant. This means that we live inside a trapped surface, which corresponds to a Black Hole (BH) event horizon. Such Black Hole Universe (BHU) is a solution to classical GR, where two nested FLRW metrics are connected by a BH event horizon. CMB observations show some anomalies which are consistent with this BHU idea. This new solution can be used to model our full Universe or a stellar BH inside.

Oct 01

Inflationary magnetogenesis (non-helical and helical) with reheating phase from higher curvature coupling

Tanmoy Paul, Department of Physics at Chandernagore College (Hooghly, India)

We investigate the generation of magnetic fields from inflation, which occurs via breakdown of the conformal invariance of the electromagnetic (EM) field, when coupled with the Ricci scalar and the Gauss-Bonnet invariant. It is demonstrated that if a reheating phase with non-zero e-fold numbers following inflation is taken into account, the energy density of the magnetic fields as well as their helicity spectrum evolve differently compared to those for the instantaneous reheating case. As a result, it is shown that in presence of the reheating phase, both the field strength of the generated magnetic fields and the resultant baryon asymmetry of the universe can be compatible with the observations.

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