My name is Alexander, but you can call me Alex or Sasha. Currently, I hold the position of Stephen Hawking Fellow at the University of Oxford, where I am part of the High Energy Astrophysics group led by Prof. Rob Fender. Additionally, I am a visiting scientist at Leiden Observatory in the Netherlands, collaborating with the computational astrophysics group under the guidance of Prof. Simon Portegies Zwart.

  My research revolves around accretion processes onto compact objects, predominantly neutron stars, but also encompassing black holes and white dwarfs. I specialize in radiation hydrodynamics, radiative transfer theory, Quantum Electrodynamics (QED) under extreme field conditions, plasma physics, and computational astrophysics. Currently, my focus is on the study of extreme accretion onto strongly magnetized neutron stars, and I am part of the leading theoretical group contributing to research on accretion onto magnetized neutron stars for the NASA space mission IXPE (the Imaging X-ray Polarimetry Explorer).

   I earned my master's degree from Saint Petersburg State University, where I conducted research under the guidance of Prof. Dmitrij Nagirner. Following this, I spent two years engaged in research at Pulkovo Observatory. Subsequently, I transitioned to Finland and became a member of the Relativistic Astrophysics group at the University of Oulu. My doctoral studies were completed at the University of Turku, under the supervision of Prof. Juri Poutanen. I was honored to receive the Award for the best thesis of 2015 from the Doctoral Programme in Physical and Chemical Sciences for my dissertation.
   In 2015, I embarked on my postdoctoral journey at the Anton Pannekoek Institute for Astronomy at the University of Amsterdam. There, I became a member of a research group spearheaded by Prof. Michiel van der Klis, where we delved into the investigation of timing properties in accreting compact objects. This endeavor aimed to explore analogous accretion phenomena from a different perspective. Collaborating with Prof. van der Klis and Dr. Adam Ingram from the University of Oxford, we developed an analytical model for deciphering aperiodic variability in X-ray binaries, which we detailed in a published paper (see paper). Our research revealed that the geometry of the accretion flow, influenced by the strong magnetic field of a neutron star, shapes the power density spectra of aperiodic variability, giving rise to distinctive features (see paper). Building upon our theoretical framework, we introduced a novel method for probing magnetic field strength and geometry in accreting strongly magnetized neutron stars. Additionally, I proposed a groundbreaking concept of optically thick envelopes in ultra-luminous X-ray pulsars (see paper), which were identified in 2014 as accreting neutron stars exhibiting extraordinary luminosities.



   In collaboration with the high-energy astrophysics groups at the University of Turku (Finland), Tübingen University (Germany), and the Space Research Institute (Russia), we have made significant strides in our understanding of low-level accretion phenomena. Our efforts led to groundbreaking discoveries, including the first-ever detection of explicit transitions of X-ray pulsars (XRPs) into the "propeller" state (see paper), as well as the identification of a new mode of accretion in XRPs—stable accretion from a "cold" disk (see paper). Furthermore, we demonstrated that dramatic spectral changes accompany the transition of XRPs into their low-level accretion state (see paper). These spectral variations offer valuable insights into the fundamental processes occurring in the magnetized atmospheres of accreting neutron stars. I have contributed a theoretical framework and developed a numerical model to explain the observed spectral changes (see paper).
   In 2018, I was honored to receive a Veni fellowship from the Netherlands Science Foundation (NWO), which enabled me to join a computational astrophysics group at the University of Leiden. During my tenure as a Veni fellow, my research focus has been on the physics of Ultra-Luminous X-ray (ULX) pulsars. Together with the computational astrophysics team at Leiden Observatory, we have been actively involved in developing a numerical model of radiative transfer in strong magnetic fields and extreme accretion scenarios. Our efforts culminated in the development of a comprehensive model of outflows in ULX pulsars, where we established that significant mass losses from accretion discs are feasible only under specific conditions, particularly when the magnetic field strength of a neutron star is sufficiently low (see paper). Furthermore, I have conducted research demonstrating that the apparent luminosity of ULX pulsars is not a mere illusion arising from geometrical beaming; rather, it closely approximates the actual accretion luminosity within these sources (see paper). This finding sheds light on the intrinsic nature of ULX pulsars. Additionally, our investigations have unveiled intriguing parallels between the conditions prevailing inside the central engines of ULX pulsars and those in the early universe, suggesting that the brightest accreting neutron stars may exhibit characteristics akin to those of neutrino pulsars (see paper). These discoveries offer valuable insights into the fundamental properties and evolutionary pathways of ULX pulsars.

Contact information:

Office:
      Astrophysics, Department of Physics, Uni. of Oxford
      Denys Wilkinson Building
     Oxford OX1 3RH, UK

e-mail: alexander.mushtukov@physics.ox.ac.uk