Pavel Kroupa

Pavel Kroupa (born 24 September 1963, Jindřichův Hradec, Czechoslovakia) is a Czech-Australian astrophysicist and professor at the University of Bonn, Germany, where he holds a position at the Helmholtz-Institut für Strahlen- und Kernphysik (HISKP). He also holds an affiliation with the Astronomical Institute of Charles University in Prague, where he was named Professorem Hospitem in 2017.Helmholtz-Institut für Strahlen- und Kernphysik, University of Bonn. http://www.iskp.uni-bonn.deKroupa, Pavel. "Professorem Hospitem, Charles University." https://astro.uni-bonn.de/~pavel/Prof_Hospitem.html

Kroupa leads the Stellar Populations and Dynamics Research (SPODYR) group. He is internationally recognised for his foundational contributions to the theory of the stellar initial mass function (IMF), the dynamics of binary star systems and star clusters, the Integrated Galactic Initial Mass Function (IGIMF) theory, and for his research critically examining the standard ΛCDM cosmological model and exploring Milgromian dynamics (MOND) as an alternative framework.SPODYR Group, University of Bonn. https://astro.uni-bonn.de/~pavel/resea.htmlKroupa, P. (2012). "The Dark Matter Crisis." PASA, 29, 395. http://adsabs.harvard.edu/abs/2012PASA...29..395K

He is the author of 389 refereed publications cited more than 32,800 times, with an h-index of 84 as of March 2026.Kroupa, Pavel. Curriculum Vitae (March 2026) — Publications and grants summary. https://astro.uni-bonn.de/~pavel/life.html In 2024 he was listed among the top-ranked scholars of all time across all fields by ScholarGPS, as the top scholar at Charles University in Prague and sixth at the University of Bonn.ScholarGPS. "Pavel Kroupa — Highly Ranked Scholar." 2024. https://scholargps.com/scholars/72047389554791/pavel-kroupa

Early Life and Background

Kroupa was born on 24 September 1963 in Jindřichův Hradec, Czechoslovakia. When the Prague Spring failed in August 1968 and Warsaw Pact forces invaded, his father fled the country with him on the first night of the invasion.Kroupa, Pavel. "Life's Stations and Career Synopsis." https://astro.uni-bonn.de/~pavel/life.html

The family subsequently lived in: Kassel, West Germany (1968–1972); Pretoria, South Africa (1972–1977); Göttingen, West Germany (1977–1983); and Perth, Western Australia (1983–1988).Kroupa, Pavel. CV — Life's Stations list. https://astro.uni-bonn.de/~pavel/life.html He attended the Christian Brothers' Catholic School in Pretoria and the Theodor-Heuss-Gymnasium in Göttingen, the latter until 1983.Kroupa, Pavel. CV — Theodor-Heuss-Gymnasium, Göttingen. https://astro.uni-bonn.de/~pavel/life.html

Kroupa holds dual Australian and Czech citizenship.

Education

Kroupa commenced physics studies at the University of Western Australia (UWA), Perth, in 1984. In 1986–87 he held a Summer Vacation Scholarship at Mount Stromlo Observatory, Australian National University, Canberra.Kroupa, Pavel. CV (March 2026) — 1986/87 Summer Vacation Scholarship, ANU. He graduated in 1988 with a first-class BSc (Honours) in physics from UWA, supervised by Dr. David Blair and Dr. Ron Burman.Kroupa, P., Burman, R.R., Blair, D.G. (1989). PASA 8, 119. http://adsabs.harvard.edu/abs/1989PASAu...8..119K

In 1988 he was awarded an Isaac Newton Studentship by the University of Cambridge and selected for membership at Trinity College. He commenced his PhD in astrophysics at the Institute of Astronomy, Cambridge, supervised by Dr. Gerard F. Gilmore, with Christopher A. Tout as mentor. In January–March 1991 he was a Visiting Research Fellow at the University of California, Santa Cruz. In October 1991 he was awarded the Senior Rouse Ball Research Studentship by Trinity College.Kroupa, Pavel. CV (March 2026) — Isaac Newton Studentship and Senior Rouse Ball Scholarship, Trinity College Cambridge.

He successfully defended his PhD thesis, The distribution of low-mass stars in the Galactic disc, at Cambridge in May 1992.Kroupa, Pavel. PhD thesis: The distribution of low-mass stars in the Galactic disc. University of Cambridge, 1992.

In 2002 he earned his Habilitation at Kiel University with the thesis Binary Systems, Star Clusters and the Galactic-Field Population.Kroupa, Pavel. Habilitation thesis: Binary systems, star clusters and the galactic-field population. Kiel University, 2002.

Academic Career

Heidelberg (1992–2000)

Following his doctorate, Kroupa took up a five-year research appointment at the Astronomisches Rechen-Institut (ARI), Heidelberg, under Prof. Dr. Roland Wielen. In 1997 he moved to the Institut für Theoretische Astrophysik, University of Heidelberg, under Prof. Dr. Werner Tscharnuter, and subsequently spent periods at the Max-Planck-Institut für Astronomie (MPIA).Kroupa, Pavel. CV — Heidelberg postdoctoral positions 1992–2000 (ARI, MPIA, ITA). In March–July 1999 he was a Smithsonian Short-Term Visitor at the Harvard–Smithsonian Center for Astrophysics.Kroupa, Pavel. CV — Smithsonian Short-Term Visitor, Harvard-Smithsonian CfA, 1999.

Kiel University (2000–2004)

In November 2000 Kroupa moved to Kiel University. He completed his Habilitation there in 2002 and was awarded a five-year Heisenberg Fellowship by the DFG in November 2002.Kroupa, Pavel. CV — Heisenberg Fellowship, DFG, November 2002.

University of Bonn (2004–present)

In April 2004 Kroupa was appointed professor of astronomy at the Sternwarte der Universität Bonn (since 2006 part of the Argelander-Institut für Astronomie, AIfA). In October 2013 he transferred to the HISKP at the University of Bonn.Kroupa, Pavel. CV — Transfer to HISKP, 1 October 2013; Bonn professorship from April 2004. In 2012 he was elected Managing Director of the AIfA for one academic year.Kroupa, Pavel. CV — Elected Managing Director, AIfA, October 2012. In 2023 he was appointed Equal Opportunities Officer (Gleichstellungsbeauftragter) at the University of Bonn.

Charles University in Prague (2016–present)

From 1 August 2016, Kroupa took up an affiliation with the Astronomical Institute of Charles University in Prague. On 3 May 2017 he was named Professorem Hospitem by the Rector of Charles University.Kroupa, Pavel. CV — Affiliation with Charles University from 1 August 2016.

Visiting Positions

ESO Senior Visitor, Santiago, Chile (February–March 2006)Kroupa, Pavel. CV — ESO Senior Visitor, Santiago, February–March 2006. Swinburne Visiting Professor, Melbourne (March 2007)Kroupa, Pavel. CV — Swinburne Visiting Professorship, March 2007. Leverhulme Trust Visiting Professor, University of Sheffield (July–September 2007 and 2008)Kroupa, Pavel. CV — Leverhulme Trust Visiting Professorship, Sheffield, 2007–2008. Guest Professor, University of Vienna (March–April 2014)Kroupa, Pavel. CV — Guest Professorship, University of Vienna, March–April 2014. Visiting Professor, Charles University in Prague (November–December 2015)Kroupa, Pavel. CV — Visiting Professor, Charles University Prague, November–December 2015. ESO Visiting Scientist, Garching (2010)Kroupa, Pavel. CV — ESO Visiting Scientist, Garching, 26 July–26 August 2010. ESO Visiting Scientist, Garching (September–October 2017)Kroupa, Pavel. CV — ESO Visiting Scientist, Garching, 1 July–1 August 2016. ESO Visiting Scientist, Santiago (November 2018)Kroupa, Pavel. CV — ESO Visiting Scientist, Santiago, November 2018. ESO Visiting Scientist, Garching (June–August 2019)Kroupa, Pavel. CV — ESO Visiting Scientist, Garching, June–August 2019.

Research

Initial Mass Function

Kroupa's most widely cited work concerns the stellar initial mass function (IMF). Working in Cambridge (1990–1992) with Christopher A. Tout and Gerard F. Gilmore, he analysed star count and binary star data, incorporating advanced physics of the stellar mass-luminosity relation and corrections for unresolved binary systems and a Galactic field model. This work yielded what became known as the canonical IMF — a two-part power-law form.Kroupa, P., Tout, C.A., Gilmore, G. (1993). MNRAS, 262, 545. http://adsabs.harvard.edu/abs/1993MNRAS.262..545K

The papers Kroupa, Tout & Gilmore (1993) and Kroupa (2001) have together received more than 7,843 citations. The 2002 Science paper "The Initial Mass Function of Stars: Evidence for Uniformity in Variable Systems" was published as an invited review.Kroupa, P. (2002). Science, 295, 82. http://adsabs.harvard.edu/abs/2002Sci...295...82K

IGIMF Theory

In 2003 Kroupa and later PhD student Carsten Weidner introduced the Integrated Galactic Initial Mass Function (IGIMF) Theory, a framework for calculating the galaxy-wide stellar IMF from its constituent embedded star clusters.Kroupa, P., Weidner, C. (2003). ApJ, 598, 1076. https://ui.adsabs.harvard.edu/abs/2003ApJ...598.1076K/abstract

The theory predicts that the galaxy-wide IMF differs systematically from the IMF of individual clusters, with proposed consequences including:

Star-forming dwarf galaxies being Hα-dim relative to their UV luminosityPflamm-Altenburg, J., Weidner, C., Kroupa, P. (2009). MNRAS, 395, 394. http://adsabs.harvard.edu/abs/2009MNRAS.395..394P Disk galaxies displaying radial Hα cutoffsPflamm-Altenburg, J., Kroupa, P. (2008). Nature, 455, 641. http://adsabs.harvard.edu/abs/2008Natur.455..641P The mass-metallicity relation of galaxiesKöppen, J., Weidner, C., Kroupa, P. (2007). MNRAS, 375, 673. http://adsabs.harvard.edu/abs/2007MNRAS.375..673K The chemical enrichment histories of elliptical galaxiesRecchi, S., Calura, F., Kroupa, P. (2009). A&A, 499, 711. http://adsabs.harvard.edu/abs/2009A%26A...499..711R

In 2013 Kroupa and collaborators proposed that the stellar IMF represents an optimally sampled distribution function rather than a probability density distribution.Kroupa, P. et al. (2013). In Stellar Systems and Galactic Structure, Vol. 5, p. 115. https://ui.adsabs.harvard.edu/abs/2013pss5.book..115K/abstract

Binary Stars and Star Cluster Dynamics

Kroupa pioneered the treatment of an initial 100% binary fraction in stellar populations, working in part through interactions with N-body simulation developer Sverre Aarseth. His 1995 papers demonstrated that the lower binary fraction in the Galactic field (~50%) compared to young star-forming regions (~100%) results from dynamical disruption as clusters disperse.Kroupa, P. (1995). MNRAS, 277, 1491. http://adsabs.harvard.edu/abs/1995MNRAS.277.1491K He also derived birth distribution functions of binary star periods, mass ratios, and eccentricities now used as standard inputs for population synthesis.Kroupa, P. (1995). MNRAS, 277, 1507. http://adsabs.harvard.edu/abs/1995MNRAS.277.1507K

Extensions of this work produced predictions for stellar ejections from young clusters,Oh, S., Kroupa, P. (2016). ApJ. http://arxiv.org/abs/1503.08827 new assessments of Cepheid populations,Dinnbier, F. et al. and Kroupa, P. (2024). Cepheid populations study. https://ui.adsabs.harvard.edu/abs/2024A%26A...690A.385D/abstract and quantification of stellar merger frequencies.Dvorakova, N. et al. and Kroupa, P. (2024). Stellar merger frequencies. https://ui.adsabs.harvard.edu/abs/2024A%26A...689A.234D/abstract

Research on tidal tails of open star clusters found an asymmetry in leading and trailing tails, which Kroupa and collaborators argue provides evidence for Milgromian dynamics on open cluster scales.Kroupa, P. et al. (2022). MNRAS. http://adsabs.harvard.edu/abs/2022arXiv221013472KKroupa, P., Pflamm-Altenburg, J., Mazurenko, S., Wu, W., Thies, I. et al. (2024). "Open Star Clusters and Their Asymmetrical Tidal Tails." ApJ, 970, 94. doi:10.3847/1538-4357/ad4c66. https://ui.adsabs.harvard.edu/abs/2024ApJ...970...94K/abstract

Brown Dwarfs and Planetary Systems