NBIA Colloquium via Zoom by Gordon Baym, University of Illinois, Champaign-Urbana

Neutron stars & matter under extreme conditions: from Copenhagen to the Golden Age

Speaker: Gordon Baym (University of Illinois, Champaign-Urbana)

Title: "Neutron stars & matter under extreme conditions: from Copenhagen to the Golden Age"

Abstract: Neutron stars, first posited in the early thirties, and discovered as pulsars in the late sixties, have had a long association with Copenhagen, from the first musings of Lev Landau in the beginning of the thirties to the first delineation of their unusual nuclear physics in the early seventies.  We are only recently beginning to understand the matter they contain.  I will describe, with a little of the earlier historical context, the ongoing development of a consistent picture of the liquid interiors of neutron stars, now driven by ever increasing observations as well as theoretical advances.  These include in particular observations of three heavy neutron stars of about 2.0 solar masses and higher; ongoing simultaneous inferences of masses and radii of neutron stars by the NICER telescope; and past and future observations of binary neutron star mergers, through gravitational waves as well as across the electromagnetic spectrum. Theoretically an understanding is emerging in QCD of how nuclear matter can turn into deconfined quark matter in the interior, and be capable of supporting heavy neutron stars.  With this basis I will discuss modern quark-hadron crossover equations of state.

Brief bio-sketch: Our speaker today, Gordon Baym, has had a long and lively relationship with physics at the Institute on Blegdamsvej.  After receiving his PhD from Harvard with Julian Schwinger, he came to Copenhagen for the first time as a post-doc when the Institute was still the "Universitetets Institut for Teoretisk Fysik". Here he wrote the well known monograph, Quantum Statistical Mechanics, with Leo Kadanoff. Coming again in 1970 as a Visiting Professor in NORDITA he began the important work, together with Chris Pethick and Hans Bethe, on neutron stars, which he will tell us about today. Gordon remains a frequent visitor to Copenhagen, returning as a NORDITA Professor, then serving on the advisory committee of NBIA, and as an Adjunct Professor in both NORDITA and the NBI.  Ever since leaving Copenhagen for the first time, his day job has been as a professor at the University of Illinois.

Gordon's honors are many, including the 2021 American Physical Society Medal for Exceptional Achievement in Research -- the top honor of the Society -- and earlier both the APS Hans Bethe and Lars Onsager Prizes, as well as the Eugene Feenberg Medal.  He is a member of the U.S. National Academy of Sciences, and the American Philosophical Society.

To participate on Friday, click on


The colloquium will be moderated by Poul Henrik Damgaard and we strongly encourage you to participate actively by asking questions during the talk. Poul Henrik will briefly remind you how this can be done just before the colloquium starts.