My life with neutron stars Pawe� l Haensel haensel@camk.edu.pl POLNS Conference Warsaw, 26-28th March, 2018 Pawe� l Haensel (CAMK) My life with neutron stars March 27th, 2018 1 / 11
Introduction The idea of this talk is to briefly present neutron stars (NS) as the subject of my research. Topics evolved, and results cumulated with time. I will highlight them with ”most influential” papers and stories on how they came to existence. Plan of this talk First decade - my way to NS Saclay years: I - Phase transitions in NS cores Saclay years: II - Strange quark stars Princeton years: Direct Urca paper Meudon years: I - SLy papers Meudon years: II - Unified EOS St.Petersburg connection - the NS book Concluding remarks Saclay=Centre d’Etudes Nucl´ eaires (CEN) de Saclay (France); Princeton=Princeton University (NJ, USA); Meudon= Observatoire de Paris section de Meudon (France) Pawe� l Haensel (CAMK) My life with neutron stars March 27th, 2018 2 / 11
Starting decade: 1968-1978. From two to 10 57 nucleons My teacher at Warsaw University was Janusz D¸ abrowski (1928-2017) who made important contributions to the theory of nuclear structure, in particular to the theory of nuclear and hyper-nuclear matter. He introduced me to nuclear forces, nuclear many-body theory, and to the quantum theory of many-body systems. First papers on just discovered pulsars were published in 1968, and my know-how was naturally useful to study them. Master Thesis (1968): two-nucleon problem with non-local interactions PhD Thesis (1972): properties of polarized nuclear matter, calculated starting from nucleon-nucleon forces. They were plenty of unsolved problems associated with neutron stars (NS), that I could try to study using my theoretical tools. As a first step, I approximated NS matter by pure neutron matter. Pawe� l Haensel (CAMK) My life with neutron stars March 27th, 2018 3 / 11
1972-1978. NS built of neutron matter Highlights PH ”Magnetic susceptibility of neutron matter” Phys. Rev. C 11, 1822 (1975) PH ”Neutron matter in Brueckner theory with the Reid hard core and Mongan potentials” Nucl. Phys. A 245, 528 (1975) PH and J. Dabrowski ”The deformation of the Fermi surface and the magnetic susceptibility of neutron matter” Nucl. Phys. A254, 211 (1975) Habilitation 1976 ”Properties of neutron matter” Highlights PH ”Zero sound in neutron matter” Nucl. Phys. A 298, 139 (1978) PH ”Isospin and density waves in asymmetric nuclear matter” Nucl. Phys. A 298, 53 (1978) In 1978 I was offered a professorship at Copernicus Astronomical Center (Bartycka 18), and in October 1978 I left the Institute of Theoretical Physics of Warsaw University (Hoza 69) after 10 years of teaching and research. I stayed at CAMK since then. Pawe� l Haensel (CAMK) My life with neutron stars March 27th, 2018 4 / 11
Saclay years I: Phase transitions in neutron-star cores Pion condensation in NS cores Possibility of pion condensation in NS cores was advanced by R.Sawyer and A.Migdal in 1970s. With Mietek Pr´ oszynski (his excellent NS code is still used!) we calculated energy release due to ”minicollapses” of NS generated by the pion condensition (1980-1982); our approach was subsequently used by other authors who tried to apply ”minicollapses” to explain some gamma-ray bursts in 1980s. With Richard Schaeffer we described metastability of NS cores with respect to pion condensation, and ”nucleation” leading to the mini-collapse. General theory of 1st-order phase transition in NS cores With Richard Schaeffer and Leszek Zdunik we developed a semi-analytical theory that allows to calculate the energy release and the changes in NS parameters associated with ”minicollapses” due to any 1st order phase transition in neutron star cores. We got general results in terms of the powers of the condensed-core radius. On revient toujours ` a son premier amour ... Pawe� l Haensel (CAMK) My life with neutron stars March 27th, 2018 5 / 11
Saclay years II: Strange quark stars Possibility of macroscopic bodies of ”strange quark matter” (SQM) (droplets or even stellar mass bodies, composed of u-d-s quark plasma, with strangeness -1 per unit baryon number) was a hot topic in 1983-1984 (Witten 1983, Farhi and Jaffe 1984). Is the SQM the true ground state of the matter? One day in 1984 Richard Schaeffer made a phone call to me, and we decided to construct detailed models of ”strange quark stars”, and study their astrophysical signatures. Leszek Zdunik joined us in this project. After the preprint of our paper started to circulate, we learnt that we had a competing team at the MIT (Charles Alcock, Angela Olinto, and Edward Farhi). They were friendly competitors, they acknowledged our priority - cited our preprint/paper ”Strange quark stars” in their paper ”Strange stars”. P. Haensel, J.L. Zdunik, R. Schaeffer ”Strange quark stars” (1986) 480 A Brazilian postdoc meets me at a conference. He is amazed: ”You are Haensel of the 1986 paper? I did not know that you are still alive...” Our preprint reached Cornell University and SUNY at Stony Brook, and resulted in counter-arguments by Bethe et al. (”Stars of strange matter?” 1986). As a result, Richard Schaeffer was promptly promoted to higher rank at CEN Saclay. Pawe� l Haensel (CAMK) My life with neutron stars March 27th, 2018 6 / 11
Princeton years: the Direct Urca In 1987-1993 I was Visiting Astronomer two month/year at the Astrophysical Sciences Department of Princeton University (NJ), being free to visit also other US institutions. At Princeton, I had a chance to work with late Bohdan Paczynski on accreting neutron stars, X-ray bursts, and gamma-ray bursts. In 1990 a two-week visit at SUNY at Stony Brook resulted in a paper on a neutrino process believed since 1964 to be prohibited. We baptized it ”Direct Urca” and this was generally accepted. It is the most powerful mechanism of NS cooling via neutrino emission. I made preliminary calculations at the initial stage working with Jim Lattimer , Madappa Prakash , in touch with Chris Pethick of NORDITA. The final text was written after I left SUNY. J.M. Lattimer, M. Prakash, C.J. Pethick, PH ”Direct URCA process in neutron stars” (1992) 552 Urca neutrino emission processes were invented by Gamow and Schoeberg (1941) - the name was this of the ”Casino de Urca” in Urca district of Rio de Janeiro, where they first met. Since 1964 (Salpeter & Chiu) it was believed that simplest Urca analogue of → p + ℓ − + ν ℓ , p + ℓ + − n − → n + ν ℓ ( ℓ = e, ν ) in dense NS matter (our Direct Urca) is prohibited. We have shown that for some EOS it is actually open above a certain threshold density, got formula for cooling ( some 10 8 ( T/ 10 8 K ) 2 times faster that previous mechanisms). Some NS seem to cool so rapidly that only DUrca can explain this. Pawe� l Haensel (CAMK) My life with neutron stars March 27th, 2018 7 / 11
Meudon years I: SLy model ”Effective forces” between nucleons in dense nucleon matter are very different from those in vacuum: this is due to the many-body medium effects. T.H.R. Skyrme (1959) showed what are the features of these ”effective force”. Parameters of the ”Skyrme force” are to be determined from experiments. In the early 1990s Richard Schaeffer discussed with me a project relevant for NS: costruct Skyrme-type force by fitting neutron-rich nuclei and relying on the best ”realistic” pure neutron matter calculations available. The hard part (numerical many-body calculations for nuclei) was done by Eric Chabanat - student of Jacques Meyer both from Lyon, and Paul Bonche from Saclay had best know-how for many-body calculations for nuclei. R. Schaeffer and PH took care of astrophysical aspects (NS, supernovae). E. Chabanat, P. Bonche, PH, J.Meyer, R. Schaeffer ”A Skyrme parametrization from subnuclear to neutron star densities” (1997), Part II (1998) 600 + 1165 The ”energy density functional” that we constructed was a great success. It is known as SLy (Skyrme Lyon), to honor our Lyon colleagues. SLy became very popular, because it could be suitable for both neutron-rich nuclei and NS. It also became a ”standard model” co compare with. Pawe� l Haensel (CAMK) My life with neutron stars March 27th, 2018 8 / 11
Meudon years II: Unified SLy EOS Fabrice Douchin was my student at ENS de Lyon. I asked him to apply SLy force to calculate both the crust and the core of NS. This was a huge task for the crust, but he had no previous training in nuclear theory, and therefore was not aware of difficulties. This was actually an advantage... He got training from PH (lectures for one student are the best way of teaching) and in four years the work was completed. It is a pity he had to leave research after a disappointing Postodoc in dense plasma simulations at University of Illinois (Urbana Champaign). F. Douchin, PH ”A unified EOS of dense matter and neutron star structure” (2001), 429 The SLy (4) effective force was used to calculate structure and EOS of both the crust and the core of NS. In this way one obtains correct transition from the crust to the uniform liquid of nucleons and electrons in the core. Maximum mass of NS for the SLy EOS is 2 . 05 M ⊙ . The SLy EOS (sometimes called DH EOS) became a standard in NS calculations. Pawe� l Haensel (CAMK) My life with neutron stars March 27th, 2018 9 / 11
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