Alexander Mushtukov currently holds the position of Stephen Hawking Fellow at the University of Oxford, where he is part of the High Energy Astrophysics group led by Prof. Rob Fender. Additionally, he is a visiting scientist at Leiden Observatory in the Netherlands, collaborating with the computational astrophysics group under the guidance of Prof. Simon Portegies Zwart.

  His research focuses on accretion processes onto compact objects, predominantly neutron stars, but also includes black holes and white dwarfs. He specializes in radiation hydrodynamics, radiative transfer theory, Quantum Electrodynamics (QED) under extreme field conditions, plasma physics, and computational astrophysics. Currently, his focus is on the study of extreme accretion onto strongly magnetized neutron stars, and he is 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).

   Alexander earned his master's degree from Saint Petersburg State University, where he conducted research under the guidance of Prof. Dmitrij Nagirner. Following this, he spent two years engaged in research at Pulkovo Observatory. Subsequently, he transitioned to Finland and became a member of the Relativistic Astrophysics group at the University of Oulu.

   His doctoral studies were completed at the University of Turku, under the supervision of Prof. Juri Poutanen. He was honored to receive the Award for the best thesis of 2015 from the Doctoral Programme in Physical and Chemical Sciences for his dissertation.

   In 2015, Alexander embarked on his postdoctoral journey at the Anton Pannekoek Institute for Astronomy at the University of Amsterdam. There, he became a member of a research group spearheaded by Prof. Michiel van der Klis, where they 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, they developed an analytical model for deciphering aperiodic variability in X-ray binaries, which was detailed in a published paper (see paper). Their 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 this theoretical framework, they introduced a novel method for probing magnetic field strength and geometry in accreting strongly magnetized neutron stars. Alexander also 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 high-energy astrophysics groups at the University of Turku (Finland), Tübingen University (Germany), and the Space Research Institute (Russia), significant strides have been made in understanding low-level accretion phenomena. Their 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, they 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. Alexander contributed a theoretical framework and developed a numerical model to explain the observed spectral changes (see paper).

   In 2018, Alexander was honored to receive a Veni fellowship from the Netherlands Science Foundation (NWO), which enabled him to join a computational astrophysics group at the University of Leiden. During his tenure as a Veni fellow, his research focus has been on the physics of Ultra-Luminous X-ray (ULX) pulsars.

   Together with the computational astrophysics team at Leiden Observatory, they have actively worked on developing a numerical model of radiative transfer in strong magnetic fields and extreme accretion scenarios. This effort culminated in a comprehensive model of outflows in ULX pulsars, establishing 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, Alexander's research has demonstrated that the apparent luminosity of ULX pulsars is not merely an 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, their 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