BGPhD Calls
Two PhD Positions in Observational Astrophysics: Tracing Cometary Evolution with
Next-Generation Surveys
Institution: Institute of Astronomy and NAO, Bulgarian Academy of Sciences
Research Group: CLIC – Cometary Life Cycle (Supported by the PROMYS component of
the Swiss–Bulgarian Research Programme)
Employment: 100% FTE, fixed-term (3 years)
Start Date: 1st November 2026, or by mutual agreement
Location: Sofia, Bulgaria
The Institute of Astronomy at the Bulgarian Academy of Sciences invites applications for two
PhD positions to investigate the evolution of cometary bodies. These positions are part of the
CLIC project, funded by the PROMYS component of the Swiss–Bulgarian Research
Programme. Our research group aims to build a comprehensive model of the changes
experienced by comet nuclei from their formation, through re-entry into the inner solar
system, until their gradual end.
Comets are considered fossils of planet formation, carrying invaluable information about the
solar system’s origins. As they migrate inward, comet nuclei undergo multiple stages of
evolution - transitioning from trans-Neptunian objects to Centaurs, and finally to active
comets. Throughout this life cycle, they are exposed to diverse evolutionary processes that
leave distinct traces on their physical properties, surface characteristics, and composition.
While individual evolutionary phases have been studied extensively, a unified model
connecting these changes is still missing.
Currently, tracing cometary evolution relies on fragmented observations. Our group will
utilize the upcoming wealth of data from the Vera Rubin Observatory’s Legacy Survey of
Space and Time (LSST), combined with targeted telescope observations, to test hypotheses
on comet evolution on a population-wide scale. The PhD candidates will join a multi-
disciplinary team, including international collaborators, and will have access to the National
Observatory Rozhen, which hosts 2-meter and 1.5-meter optical telescopes.
Position 1: Internal Structure and Fast Rotators
Project Focus: Mining large observational datasets (including the upcoming LSST) to
identify fast-rotating comets and Centaurs. Discovering these fast rotators provides strong
constraints on the bulk physical properties of cometary nuclei, such as their density and
tensile strength. By comparing these properties across different populations - from distant
Centaurs to active Jupiter Family Comets (JFCs), the PhD student will help trace the physical
changes driven by their ongoing evolution in the solar system.
Position 2: Extreme Shapes and Contact Binaries
Project Focus: Using large photometric datasets to identify objects with large lightcurve
amplitudes, which indicate highly elongated or extreme shapes. By analyzing these
lightcurves, the candidate will study how cometary shapes evolve as they migrate closer to
the Sun. This project will also determine the fraction of contact binaries (bi-lobed objects)
across different evolutionary stages, testing long-standing hypotheses about how and where
these complex shapes form.
Candidate Profile
Master’s degree (or equivalent) in Astrophysics, Physics, Data Science, or a related field.
Strong interest in observational astronomy, data analysis, and tackling large datasets. (Prior
experience in planetary science is not required; we welcome applicants who have worked in
other areas of astrophysics).
Experience with scientific programming (e.g., Python) and working in Linux/Unix
environments.
Fluency in written and spoken English.
A proactive mindset, comfortable working independently while contributing to a
collaborative international group.
What We Offer
A fully funded PhD position with a highly competitive academic salary for Bulgaria.
Access to the institute’s observational and computing facilities.
A structured research environment with regular international workshops hosted in Bulgaria,
providing excellent networking and career development opportunities.
Dedicated funding for travel, international conferences, and research visits with our Swiss
and international partners.
Application Process
Please submit your application as a single PDF file to Dr. Rosita Kokotanekova at
rkokotanekova@nao-rozhen.org. The application must include:
A brief motivation letter detailing your experience and interests (maximum 2 pages).
A CV, including any past research projects, internships, or publications.
Academic transcripts for your BSc and MSc degrees.
Contact information for two academic referees (to be included within your PDF application).
Important: In addition to the PDF application, two letters of recommendation must be sent
directly by your referees to Dr. Rosita Kokotanekova at rkokotanekova@nao-rozhen.org
before the deadline.
Qualifying applicants will be interviewed and sit an entrance exam (written and oral), which
can be taken remotely.
Deadline: Applications will be evaluated on a rolling basis starting immediately. Complete
applications (including recommendation letters) received by 30 September 2026 will receive
full consideration.
For informal inquiries or any questions regarding the positions and the application process,
please contact Dr. Rosita Kokotanekova at rkokotanekova@nao-rozhen.org
PhD Position in Computational Heliophysics
Solar and Space Weather Group, Institute of Astronomy, Bulgarian Academy of Sciences, Sofia, Bulgaria
- This PhD position is offered at the Solar and Space Weather Group, Institute of Astronomy, Bulgarian Academy of Sciences.
- The successful applicant will work with Assoc. Prof. Kamen Kozarev on development and application of data processing techniques and machine/deep learning models for the characterization and understanding of the nature of solar eruptive transients. Specifically, he/she will analyze and model EUV imaging observations of coronal mass ejections (CMEs) and shock waves (mostly SDO/AIA), as well as low-frequency radio interferometric observations of thermal and non-thermal CME emission (MWA and LOFAR telescopes).
- PhD position is part of 5-year project “Modeling and ObServAtional Integrated Investigations of Coronal Solar Eruptions” (MOSAIICS) starting in May 2020, funded by the National Science Fund of Bulgaria; Project PI is Assoc. Prof. Kamen Kozarev;
- This 3-year position is open until filled, with a preferable starting date in July 2020; working language is English.
- PhD fees fully covered and a very competitive stipend of approximately €920/month (tax-free) provided for EU-citizens (Average salary in Bulgaria is €600/month, pre-tax). Separate travel funding will be provided as well. Representative numbers for the cost of living can be found at https://bit.ly/2TRohMp;
Requirements:
Master’s degree in Physics/Astrophysics/Data Science or related discipline; demonstrated interest in computational astrophysics/heliophysics, space weather, and machine/deep learning; great writing and communication skills in English;
Previous experience and publications in scientific programming and visualization, especially with Python (SunPy, Pandas, Numpy, Matplotlib, etc.), Linux/Unix environments, version control, machine/deep learning (Torch, Keras, Tensorflow), high-performance computing, and/or data science will be considered an advantage.
How to Apply:
Interested candidates should contact Dr. Kamen Kozarev (kkozarev @ astro.bas.bg), arrange for three letters of recommendation to be sent to him, and provide a curriculum vitae, a cover letter describing their experience and interests, and a list of publications (where available). Qualifying applicants will be interviewed and sit an entrance exam (written and oral), which can be taken remotely.
Additional Information:
- The overall goal of the MOSAIICS project is to adopt an integrated approach providing a deeper understanding of the plasma processes leading to charged particle acceleration by CMEs near the Sun. The project’s high level objectives are to (i) develop and integrate novel image processing and machine learning techniques to reliably analyze radio and EUV remote imaging observations of CMEs and their shocks; (ii) investigate the origins and evolution of radio emission from energetic electron beams in CMEs, comparing with in situ measurements; (iii) develop and apply advanced global data-driven models of particle acceleration and transport to test and improve our theoretical understanding of SEP production and transport.
- Recently, the Institute of Astronomy has installed a new 192-core server cluster, and is adding a multi-GPU server node for advanced computations dedicated to the MOSAIICS project. Supercomputer time on BAS-owned and operated systems is also available.
- The Institute of Astronomy is a leader in astrophysical research in Bulgaria and Southeast Europe. It hosts over 40 researchers working in several areas of astrophysics, namely solar activity and solar system small bodies, stars and stellar systems, galaxies and cosmology. Additionally, IANAO staff have strong expertise in operating and maintaining the National Observatory Rozhen - a dedicated facility in the Rhodopi mountains with a flagship 2-meter reflective optical telescope, as well as a number of smaller research-grade telescopes.
For more information, visit http://astro.bas.bg.
