The seminar of the Astro & Theory Section takes place normally on Thurdays in D5-106, starting at 14.00. If you would like to suggest a seminar speaker or want to be added to the email list, please contact the organizer (maksat.satybaldiev@ntnu.no).

The (planned) seminars in 2025 are


  • 14.01. Matteo Imbrogno (Università di Tor Vergata of Rome): A tale of serendipity: quasi-periodic oscillations in pulsating ULXs and a search for new X-ray pulsators

Abstract: The discovery of pulsating ultraluminous X-ray sources (PULXs) has revealed that accreting neutron stars can shine at extreme luminosities, well above their Eddington limit. This finding has caused a shift in the ULX paradigm and poses significant challenges to our understanding of the physics of accretion onto compact objects. Given their rarity, every new insight into their complex phenomenology can bring us closer to a deeper understanding of these sources. A possible way to find more PULXs is by searching the archives of X-ray missions with good imaging and timing capabilities using a data mining approach. In the process, serendipitous sources are always behind the corner. Both the study of PULXs and the search for new X-ray pulsators through data mining have defined the course of my PhD. I will report my discovery of mHz QPOs in the X-ray flux of the PULXs. These mHz QPOs could represent a signature of super-Eddington accretion. I will also talk about a new pulsar (likely a new candidate magnetar) I discovered in the Large Magellanic Cloud thanks to a data mining project aimed at searching for new pulsators in the XMM-Newton archive. Slides available here: https://www.ntnu.no/wiki/download/attachments/195538250/NTNU_seminar_Imbrogno.pdf?api=v2


  • 13.02. Yan-Chuan Cai (University of Edinburgh): Peculiar velocities in cosmology

Abstract: On large scales, peculiar velocities refer to the motions of extragalactic objects relative to the background expansion of the Universe, known as the Hubble flow. Coupled with the initial density perturbations of the Universe, peculiar velocities are influenced by the expansion history of the Universe and the strength of gravity. They encode information about the matter-energy content of the Universe and the law of gravity. I will summarise how peculiar velocities of galaxies can be observed, and what we can learn about cosmology from observing them using data from galaxy redshift surveys and the cosmic-microwave background.


  • 10.04. Devina Misra (IFY, NTNU): Investigating cannibalistic millisecond pulsar binaries using MESA: New constraints from pulsar spin and mass evolution

Abstract: Compact binary millisecond pulsars (MSPs) with orbital periods less than 1d are key to understanding binary evolution involving massive neutron stars (NSs). Due to the ablation of the companion by the rapidly spinning pulsar, these systems are also known as spiders and categorized into two main branches: redbacks (RBs; companion mass in the range of 0.1 to 0.5Msun) and black widows (BWs; companion mass less than 0.1 Msun ). We present models of low- and intermediate-mass X-ray binaries and compare them with observations of Galactic spiders (including the presence or absence of hydrogen lines in their optical spectra), and we constrain and quantify the interaction between the pulsar and the companion. For the first time in MESA, we also included the detailed evolution of the pulsar spin and modeled the irradiation of the companion by the pulsar wind. Efficient mass accretion onto the NS (i.e., at least 70% of the mass transferred is accreted) with an X-ray irradiated disk followed by strong irradiation of the companion can explain most of the properties of the observed spiders. Our RB evolutionary tracks continue to the BW regime, connecting the two branches of spiders. Our models explain the lack of hydrogen in some observed BWs with ultra-light companions. During accretion-induced spin up, the mass required to spin up an NS to sub-milliseconds is high enough to collapse into a black hole. Cannibalistic MSP binary formation depends heavily on the interplay between accretion onto the pulsar and pulsar wind irradiation. Our work supports earlier claims that RBs evolve into BWs. We also show that the fastest-spinning pulsars may collapse before reaching sub-millisecond spin periods. 


  • 15.05. Hosein Gholami (TU Darmstadt): Renormalization Group Consistent Treatment of Color Superconductivity in the NJL Model

Abstract: The Nambu–Jona-Lasinio (NJL) model—and particularly its extension to color superconductivity—is a powerful framework for investigating dense quark matter. However, its reliability is limited by regularization artifacts that emerge near the cutoff energy scales. In this talk, we present a mean-field Functional Renormalization Group (FRG) approach, referred to as the RG-consistent treatment, which effectively eliminates these artifacts. Our study reveals substantial modifications to the previously established phase diagram of three-flavor, neutral, color superconducting matter within the NJL model. Notably, the RG-consistent treatment not only removes the regularization artifacts but also aligns with earlier Ginzburg-Landau analyses, suggesting the emergence of a so-called dSC phase in the melting pattern of the Color-Flavor Locked (CFL) phase. Finally, I present our recent results on the renormalized Quark-Meson-Diquark (QMD) model and compare them with those obtained via the RG-consistent treatment of the QMD framework.


  • tba. Vittoria Vecchiotti (IFY, NTNU): tba

Abstract: tba









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