Pavel Kroupa

Pavel Kroupa (born 24 September 1963 in Jindřichův Hradec, Czechoslovakia) is a Czech-Australian astrophysicist and professor at the University of Bonn.

After the 1968 failure of Prague spring, Kroupa's family fled from Czechoslovakia leaving all possessions behind; as a consequence Kroupa grew up in Germany and South Africa.

He acquired in 1983 his Abitur final exams in Göttingen and afterwards studied physics at The University of Western Australia in Perth.

His research work began in 1987 in Australia with an investigation of Proxima Centauri.

Kroupa is well known for his work for the distribution of stellar masses.

In 1988 he won the Isaac Newton scholarship at the University of Cambridge and in 1992 the senior Rouse Ball research scholarship at Trinity College, Cambridge and attained a doctorate in England in 1992 with a dissertation on the distribution of low mass stars in the Milky Way.

In Cambridge in 1990–1992 by means of observational data on star counts and on binary stars and with detailed computations of stellar structure with Christopher A. Tout and Gerard F. Gilmore he deduced the contemporary, generally used canonical IMF (initial mass function), which describes the distribution of the star masses at their birth.

In Heidelberg he presented the first stellar-dynamic computations in 1993–1995 of star clusters, in which all stars are born as binary stars.

He thus solved the problem that field populations have a significantly lower double star rate than star formation areas, because the binary stars are broken up as the star clusters evolve and disperse.

He mathematically formulated and applied a theory of the evolution of binary stars (eigenevolution), created the method of dynamic population synthesis, and predicted the existence of binary stars forbidden by previous theory (forbidden binaries).

In 1997 and in Heidelberg Kroupa, together with Ulrich Bastian, took the first precise measurement of the spatial movement of two extragalactic systems.

In 1997 he also discovered stellar-dynamic solutions for the satellite galaxies of the Milky Way without the need for exotic dark matter.

His work implies a possible connection of the satellite galaxies with the Bulge of the Milky Way.

This connection can be explained by a collision of the early Milky Way with another young galaxy during which the satellite galaxies formed as tidal dwarf galaxies about 11 Gyr ago.

This is shown in a series of research papers with Manuel Metz and Marcel Pawlowski.

Afterwards Kroupa worked until 2000 in astronomical research groups at Heidelberg University and at the Max Planck Institute for Astronomy, before he went to the University of Kiel and earned his Habilitation there.

He was awarded a Heisenberg Fellowship in 2002.

With this he explained in 2002 the observed heating or thickening with age of the disk of the Milky Way, and with Carsten Weidner he formulated the "IGIMF (integrated galactic initial mass function) theory".

He suggested in co-operation with Ingo Thies and Christian Theis in 2003–2004 in Kiel that brown dwarves and extrasolar planetary systems can develop in circumstellar disks due to passing stars which disturb the disks.

Our Solar System is likely to have been shaped by such events.

In Kiel he also theoretically formulated the concept that galaxies ought to be described by stars forming in populations of embedded star clusters.

In April 2004 he was appointed to the observatory of the University of Bonn, which is today a department of the Argelander Institute for Astronomy.

In 2004 in Kiel together with Carsten Weidner he suggested the existence of a physical maximum star mass of approximately 150 solar masses.

He was honoured in 2007 by a Swinburne University Visiting Professorship in Melbourne and by a Leverhulme Trust Visiting Professorship at the University of Sheffield.

Kroupa leads the research group on stellar populations and stellar dynamics at the University of Bonn.

In 2008 in Bonn together with Jan Pflamm-Altenburg he pointed out that the IGIMF theory implies that disk galaxies have a radial star formation law, in which the star formation density is proportional to the radial gas density.

The IGIMF theory also implies that the star formation rates of irregular dwarf galaxies are proportional to their gas masses and must be corrected to clearly higher values as compared to previous theory.

Simple star-formation laws for galaxies emerge from this work.

The IGIMF theory gives good predictions for the mass distributions of the various metals within galaxies.

As a result of this work and since 2010 Kroupa has concerned himself increasingly with cosmology.

While the cosmological standard model does not offer a unique solution to the cosmic background radiation and to cosmological expansion, he claims that the observed structures on scales of about 1kpc and above falsify the standard model.

The implication of his work is that effective gravity must be non-Newtonian in the ultra-weak field limit.

• Modified Newtonian Dynamics