Géza Csörnyei

I am originally from Hungary; I finished both my bachelor's and master's studies at Eötvös University, Budapest. In the meantime, I worked at Konkoly Observatory as an observatory assistant. After finishing my studies, I was admitted to a PhD position at MPA Garching through the International Max Planck Research School (IMPRS). I received my PhD in April of 2024, and currently I am working in a Fellowship position at the European Southern Observatory!

Research overview

My research topics are diverse, I have tried out a few fields:

• I started by working in the field of Classical Cepheids during my bachelor years, and I have continued pursuing research on this topic since then. My main interest was first investigating the period changes of these stars; however, this was expanded later on to further questions. I mainly work with colleagues from the Seismolab group of the Konkoly Observatory and the H1PStars group of EPFL.
• During my studies, I started pursuing research topics concerning extragalactic spectroscopy. This work resulted in a thesis for both my bachelor's and master's studies. My main focus was investigating emission lines of star-forming and AGN galaxies in the context of photometric redshift estimation and galaxy classification, using spectra from the Sloan Digital Sky Survey.


• My PhD topic was dealing with the spectral modelling of Type II supernovae. Our group at MPA developed a method for fast and reproducible spectral modelling of these transients, which is based on the Monte Carlo based radiative transfer code TARDIS. Using this method, we aim to infer distances to Type II supernovae, with the ultimate goal of estimating the Hubble constant in the nearby Universe independently of all other techniques. My role in this project is mainly about testing the method by applying it to observed data in various setups and looking for biases possibly present in the analysis.


• Lately, my main goal has been to cross-test multiple different distance estimation techniques to find clues about the Hubble Tension. Recent years have brought forward not only a cosmic tension but also a near-universe inconsistency: it turned out that choices and selection effects can substantially alter the Hubble constant. However, owing to recent advancements, today, many techniques allow us to measure independent distances: Cepheids, TRGB, J-AGB, and Type II supernovae... my goal is to find out whether they tell the same tale!



• Click and Find my CV here

Featured works (with brief summary)

Interested in my research? Here are the ones which I first-authored, with some brief summary! Click on the titles to see more!

Clarifying the distance to M 51 based on Cepheids and a Type IIP SN

Despite being a well-known galaxy, the distance to M 51 was quite uncertain, with little to no agreement between methods. Even though somebody surely observes this beautiful galaxy on the globe every day, and despite it having been visited by the Hubble Space Telescope multiple times, no Cepheid distance was inferred to it—up until now!

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Consistency of Type IIP supernova sibling distances

Less known than, say, Cepheids, but Type IIP supernovae are also precise distance indicators. Even better, they do not require external empirical calibrations; one may infer distances to them without the need to calibrate a "ladder" to these SNe based on Cepheids or TRGB. One question, of course, is whether these distances are meaningful, and one way to check this is by applying the method to SNe that exploded in the same galaxy.

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Period changes of Galactic Classical Cepheids

Another study on the Cepheid period changes; however, this time, instead of a single object, we went after a larger, more representative sample of 148 stars! While we were looking for effects that may be tied to the binarity of the objects, we found something else: that they are not perfect clocks. Not only do they evolve, but they fluctuate as well!

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Emission lines and photometric redshifts

Have you ever wondered how strong emission lines affect the accuracy of photometric redshift estimations? Even though they are pretty random, surprisingly, they improve them noticeably. To show this, we analyzed a large sample of SDSS spectra using machine learning and devised a way to generate spectra with realistic emission line ratios.

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Revisiting AU Pegasi

This is my very first article. This project dealt with the period changes of a peculiar Type II Cepheid, among the shortest known binary Type II Cepheids. It was known to exhibit strange and strong period changes, so our plan was to investigate how some additional data clarifies the picture drawn 30 years ago.

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Teaching

• PH2206 webpage / Assigments