LUTh seminars

Accurate and efficient modeling of binary black holes (BBHs) is crucial for the detection of gravitational waves (GWs) emitted by them. Closed-form solutions to these systems when they are in the initial inspiral phase are highly sought after and have been worked out by many groups in the post-Newtonian (PN) approximation. Most of these solutions are valid only in certain limits (small eccentricity, no spins, equal mass, etc.). Establishing the integrable nature of PN BBHs opens up the possibility of constructing closed-form solutions since integrability precludes chaos and guarantees the existence of action-angle variables. In this talk, I will discuss our series of efforts in establishing the integrable nature of the most general BBH system (arbitrary masses, spins, and eccentricity) as per the Liouville-Arnold theorem at 2PN order. I will also discuss our recently derived action-angle-based solution for these systems at 1.5PN order.

In this seminar, I will present what are paleo-detectors, how they work, and what they are useful for. I will show the base ideas for their employment in astroparticle physics, with specific cases for neutrino, dark matter, and cosmic ray physics. I will then outline the main challenges that arise in the proposals, in the choice of the target detectors and the measurable quantities. Finally I will briefly describe some personal lines of work.

High-cadence long-term monitoring of the transient sky suggests that most core-collapse supernovae are influenced at some level by interaction with circumstellar material (CSM). Although considered so far a feature in core-collapse supernovae, this observation has led theorists to revise the idealized view of massive star evolution and explosion, and consider additional time-dependent, dynamical, and multi-dimensional effects that remain today poorly understood.

In this talk, I will review the basic features of massive star evolution, the ultimate gravitational collapse of their degenerate core, their explosion as supernova, and the subsequent evolution of the ejecta and radiation properties (i.e., light curves and spectra). I will then describe the variety of signatures that are suggestive of ejecta interaction with CSM and how we can model the radiation and the dynamics of these events. I will consider various configurations for the CSM, including when it is dense but confined to the direct vicinity of the star, when it is dense but extended, when the CSM is more massive than the ejecta that strike it, and finally when the CSM is very distant and gives rise to delayed interaction when the ejecta have expanded for a year or more.

In this seminar, I will present recent results concerning the analysis of gamma-ray bursts (GRB) afterglows and on the formation of binary neutron stars (BNSs). I will show a new model of the very high energy emission of GRB afterglows from the synchrotron self-Compton radiation of laterally-structured jets, and make predictions for GW 170817-like events. Concerning the formation of BNSs, I will present results obtained with population synthesis, that show an evolution of the dominant progenitors evolutionary tracks with redshift.

Il y a près de 13 milliards d’années, notre univers est né, mais ce n’est que depuis le siècle dernier que la théorie du « Big Bang » a été élaborée pour expliquer sa naissance et son évolution.

Cette théorie affirme que l’Univers était extrêmement dense et chaud à ses débuts, et qu’il s’est ensuite étendu. En 1964, la découverte d’un rayonnement fossile, libéré environ 380 000 ans après le Big Bang, a validé cette évolution. Mais bien avant cela, lors des premières secondes et minutes de la vie de l’Univers primordial, la théorie du Big Bang prévoit l’apparition des briques élémentaires de la matière que nous connaissons aujourd’hui. Ces prédictions ont été confirmées grâce à des expériences menées sur des accélérateurs de particules, tels que ceux utilisés au CERN.

L’objectif de cette conférence est de vous faire découvrir les avancées de notre compréhension de l’Univers depuis le Big Bang astrophysique, ainsi que l’étude des briques élémentaires de la matière en laboratoire, notamment au CERN.

Ne manquez pas cette occasion unique d’explorer les profondeurs du cosmos et de plonger dans les découvertes révolutionnaires qui ont façonné notre vision de l’univers et de la matière elle-même. Rejoignez-nous le 14 septembre 2023 pour une expérience scientifique fascinante !

– Reina Coromoto Camacho Toro (Laboratoire de Physique Nucléaire et de Hautes Énergies, Paris)

Les trous noirs sont des astres tellement compacts que même la lumière ne peut leur échapper. Tout ce qui s’en approche trop est condamné a y être englouti.

Si l’existence de ces objets est prédite depuis plus de 100 ans par la théorie de la relativité générale d’Einstein, ils ont tout d’abord été cantonnés au statut de curiosité mathématique. Toutefois, peu a peu, les trous noirs sont sortis de l’ombre ; les preuves observationnelles de leur existence étant de plus en plus convaincantes. A ce titre les dernières années ont été particulièrement fructueuses avec les observations à haute résolution des disques de matière autour de trous noirs ainsi que celles des ondes gravitationnelles émises lors de la fusion de deux tels objets. Après une mise en perspective historique, cette conférence présentera l’état de nos connaissances sur la physique des trous noirs, se basant principalement sur les dernières observations en date.

Orateurs :

La fusion de deux étoiles à neutrons se produit lorsque les deux étoiles en orbite l’une autour de l’autre se rapprochent de plus en plus jusqu’à entrer en collision. Ce processus s’accompagne entre autres de l’émission d’ondes gravitationnelles et d’une contrepartie électromagnétique, dont un sursaut de rayonnement gamma.

Ces différents signaux ont été détectés pour la première fois par différents observatoires (au sol et en orbite) en août 2017. La mise en commun des données collectées a permis d’identifier la fusion d’étoiles à neutrons comme un nouveau site où l’or et les éléments plus lourds présents dans l’Univers sont produits. La conférence mettra en lumière les différents aspects de ce phénomène extraordinaire en abordant des notions couvrant les domaines de l’astrophysique, de la relativité générale et de la physique nucléaire.

Nicolas Arnaud (IJCLab)

Cyg X-3 is a high-mass X-ray binary, and is the only system in the Milky Way consisting of a Wolf-Rayet star and a compact object. The nature of the compact object (neutron star / black hole) is still unclear. Despite numerous studies, Cyg X-3 remains a unique and puzzling system. In our study, we present a detailed physical modeling of Cyg X-3 gamma-ray data, allowing us to drastically improve our understanding of this complex system. We perform fitting of the gamma-ray spectrum and light curve with our complex physical model and firmly establish that the jet of the compact object has to be inclined with respect to the orbital axis. Additionally, we test for the first time the predictions of General Relativity (GR) for the precession of the inclined jet in the system and find the predictions for the black hole compact object hypothesis in disagreement with the 50-year-long sample of observational data in the radio band. Finally, we incorporate in our data set available infrared (IR) measurements that constrain the synchrotron emission from the jet and its modulation, and test a physical scenario where the jet is bent and is precessing due to the influence of the stellar wind, as well as is bent by the Coriolis force.

Since the discovery of neutron stars (NSs) as pulsating sources ∼50 years ago, pulsars have become the perfect laboratories to test the boundaries of theoretical physics, thanks to the extreme astrophysical environments they thrive in. Arguably the most useful of them are millisecond pulsars, extreme neutron stars that have been spun-up to millisecond spin periods by accreting matter from an orbiting companion star, as the measurement of their orbital dynamics allows us to investigate their evolution and test gravity theories. Among them are the “spiders”, a subclass of binary millisecond pulsars with low-mass semi-degenerate companions which are in the process of being ablated by the pulsar, leading to them being named after the deadly “black widows” and “redbacks”. In the last decade, the number of known spiders has grown by over an order of magnitude. They have since been linked to transitional millisecond pulsars which are believed to provide the missing link between binary pulsars and low-mass X-ray binaries. In this talk I will review some of the recent science developments enabled by this growing population, including the quest for measurement neutron star masses, finding the fastest spinning pulsars in our Galaxy and study the role of magnetic fields in accretion physics.

Since the launch of the Fermi/LAT gamma-ray telescope, several hundred radio-loud gamma-ray pulsars have been detected,

In this presentation we show how time-aligned gamma-ray light curve fitting of young and millisecond pulsars constrains their

We find a good agreement between our emission model and the time-aligned single- or double-peaked gamma-ray pulsar observations.