HUNGARIANS EXPLORE THE EARLY UNIVERSE

András Patkós
Department of Atomic Physics
Eötvös University, Budapest

Astrophysicists of Hungarian ancestry actively and successfully participate in observational and theoretical investigations of the early history of our Universe. The first part of this article will review the evolution of this kind of research in universities and research institutes of the country. An overview of the actual research directions will be attempted without geographical limitation on the place of activity of Hungarian researchers in the second part. The reason for such an approach is obvious: even those affiliated to academic institutions of the Republic of Hungary mostly work as members of big international collaborations and perform substantial part of their research abroad.

Origins of astrophysical research in Hungary Exploration of the physical nature of cosmic rays is considered to be the precursor of all types of high energy physics research. Due to its origin cosmic particle radiation carries information on the galactic and possibly on the extragalactic magnebc fields.

Full scale experimental study was started in the early fifties when Lajos Jánossy (1902-1974) directed large scale investigations, which he started in Dublin, in the Central Research Institute of Physics (CRIP) of the Hungarian Academy of Sciences (HAS). The experimental and theoretical achievements of this period have been continued to these days when biological effects of the cosmic ray load is studied on spacecrafts with the help of Hungarian produced dosimeters. The physics of the highest energy cosmic rays, accelerated by extragalactic magnetic fields possibly of primordiai nature, is studied by Susan Kövesi-Domokos and Gábor Domokos (Johns Hopkins University), Zoltán Kunszt (Eötvös University, now in Berne) and also by Péter Király (CRIP).

Another source of modern astrophysics is the nuclear research on energy production processes of stars. Early important work on the equation of state of supernovas was done by Judith Németh (Eötvös University), visiting Cornell University in the late sixties, in collaboration with the founder of this subject, Hans Bethe. Today nuclear physics of the cosmic emergence of heavy nuclei in collapsing stars is actively studied by a group at the Debrecen, Institute of Nuclear Research of the HAS (ATOMKI) led by Endre Somorjai. They conduct the experimental part of their research in international collaboration with nuclear astrophysicists in Bochum, Germany.

Investigations of the properties of lighter elementary particles, namely leptons, led George Marx (Eötvös University) towards the study of the role played by neutrinos in stellar environment in the early sixties. Enthusiastic of the solar neutrino experiment proposed by Raymond

Davis, he was the initiator of biannual Neutrino Conferences. The first meeting was held in Balatonfüred at the lake Balaton and came back since then two more times to Hungary. Among leading particle physicists (R. Davis, R. Feynman, T.D. Lee, B. Pontecoruo, F. Reines, V. Weiskopf and others) the legendary personality of the astrophysics of our century, Yakov Zeldovich started to visit Hungary regularly after attending one of these conferences. Pieces of advice given to his Hungarian colleagues laid the basis of modern astroparticle physics research at the Eötvös University.

From the Memoirs of Andrei Sakharov we know how important these visits were for Zeldovich. He appreciated the privilege of being able to escape once in every two years the strict control of his home country. Sakharov complained in Chapter 48 of his Memoirs that his friend has rejected his request for help in an affair of emigration in 1981 by writing him Ihat in case of an intervention he would not be allowed to leave the Soviet Union even for Hungary.

During frequent visits from the second half of the sixties Zeldovich gave many seminars in Budapest and presented also difficult problems to solve to young students. Alexander S. Szalay (now at Johns Hopkins University, Baltimore and Eötvös University) has made the first detailed analysis of the astrophysical bound on neutrinomass in his Ph.D. dissertation written in 1975 under the supervision of G. Marx; following ideas of Dolgov and Zeldovich. In a subsequent series of papers Marx and Szalay have developed the ideas on the role massive neutrinos might have played in galaxy formation via their density fluctuations resulting in Jeans-type instabilities.

Phase transitions occurring in the hot early period of the Universe were first investigated by Kirzhnits and Linde in 1972. These transitions - if realized with strong enough discontinuity - might have influenced both primordial bariogenesis and nucleosynthesis. One of the first realistic field theoretical description of the quarkhadron phase transition was published at the end of the seventies by Julius Kuti (today at UCSD, California), B. Lukács and K. Szlachányi (CRIP) based on the comparison of the free energy density of nuclear matter calculated from Walecka's theory with the result of quantum chromodynamics of quarks. This investigation was promptly followed by the pioneering paper of Kuti, Polónyi and Szlachányi leading the strategy of non-perturbative lattice calculations of finite temperature phase transitions of cosmological interest in 1981. Younger generation of theoretical nuclear and particle physicists continue their internationally highly appreciated work on this subject in three centers of research in Hungary: CRIP, Eötvös University (Budapest) and Kossuth University (Debrecen).

An important change of orientation occurred in the middle of the eighties, when A.S. Szalay became frequent visitor of the leading astrophysical centers of USA (Fermilab/NASA Center, Berkeley, Baltimore). His interest in large scale structure of the Universe, rooted in collaboration with Zeldovich and Sunyaev, has found new impetus in collaboration with important American and Canadian scientists (D.N. Schramm, J.R. Bond and others). He became a leading expert on statistical analysis of astrophysical observational data and initiated the highly successful deep observation program of galaxy densities with the help of pencil beams pointing towards the Northern and Southern galactic poles. A collaboration led by Szalay found an important peak corresponding to the distance scale 128 Mpc in the Fourier spectra of the galaxy densities.

The growing activity of Szalay had its effect on students of Eötvös University where he continued to work actively until 1993, when he accepted a professorship in Baltimore. At the end of the eighties Enikő Regős (now at the University of Cambridge, UK) wrote her MS thesis under the supervision of Szalay on the two-point correlations of the galaxy distribution. Regős visited as a Ph.D. student (enrolled to Eötvös University) the Harvard-Smithsonian Institute and did her Ph.D. research under the supervision of Margareth Geller. Only two years later another student of Szalay, Gábor Tóth entered Princeton University as a full time graduate student. He was followed a year later by Zsolt Frei (a former student of A. Patkós, obtaining his MS degree with a thesis written on the theoretical treatment of the quark-hadron phase transition). Several other students and junior researchers of Eötvös University joined the group of Szalay in Baltimore (István Szapudi, Gyula Szokoly, István Csabai) during the past years. Also close collaboration was established with Péter Boschán (University of Münster, Germany, formerly Eötvös University).

The last important event to be noted in the short but eventful history of astrophysical research in Hungary happened upon the return of two fresh Ph.D.'s from Princeton. Drs. Frei and Tóth have adapted parts of the graduate astrophysics course they undertook in Princeton to the modularized advanced level MS educational program of Eötvös University. A two-year specialization program was started in 1995, attracting 8-10 students every year. Half of them write their MS-thesis on subjects related to astrophysics. The first Ph.D. student of astrophysics started his thesiswork in 1997.

New exciting results concerning the mass of neutrino were presented at the "Neutrino 1998" meeting in Japan, where the closing address was given by the Great Old Man of our community, Prof. George Marx. At present his continued interest in this field is centered on the contribution of neutrinos to the dark matter, indicated by the sustained mean velocity curves of stars located near the edge of galaxies. This interpretation of the observational data is reminiscent of the way the Eötvös torsion balance is able to detect the presence of natural oil reservoirs underground, hidden from direct observations. He also proposed together with I. Ruff an original idea attempting at the non-standard explanation of the solar neutrino puzzle which called wide interest in the early nineties.

Experimental investigations based on observing neutrinos of solar or cosmological origin are promoted in Hungary by Dezső Kiss (CRIP). In reactor experiments at Bugey (France), aiming at observing oscillations of neutrino flavors, due to neutrino-mass Elemér Nagy (Marseille, earlier CRIP) played leading role.

The properties of the quark-hadron phase transition are investigated in terrestrial experiments at CERN with important participation of a group of CRIP led by György Vesztergombi. Theoretical research is done dominantly at CRIP (J. Zimányi, T. Csörgő, T. Biró and P. Lévai) and also at the Kossuth University in Debrecen. Astrophysical implication of a strong first order transition between the two states were studied very actively at the end of eighties, when the possible effects on primordial nucleosynthesis were investigated. Z. Frei and A. Patkós (Eötvös University) have contributed to this field.

Nuclear processes, which are relevant to primordial nucleosynthesis are also actively studied both with experimental and theoretical approaches. A group fed by Ádám Kiss (Eötvös University) achieved advances in studying neutron emission of unstable lithium induced by Coulomb interaction. In their investigation they make use of the radioactive beam technique developed at NSL Michigan (USA) in collaboration with A. Galonsky. Interesting theoretical work on the excitation level structure of some light nuclei of astrophysical interest is being done by Attila Csótó (Eötvös University). The accurate position of certain excited energy levels exerts influence on reaction rates involving boron, lithium and carbon, which has consequences on the nuclear reaction network of primordial nucleosynthesis.

More recently the origins of matter-antimatter asymmetry of our cosmic neighborhood retained the interest of astro-particle physics. Another phase transition taking place at temperatures corresponding to the electroweak mass scale (100 GeV) might have played an important role in the evolution of this asymmetry in the history of the Universe. Theoretical studies are accompanied by large scale numerical simulation work. Two Hungarian groups, both formed at Eötvös University, have made widely quoted work on this subject. Zoltán Fodor and Ferenc Csikor did substantial part of their work in collaboration with a group of DESY (Hamburg, Germany) led by W. Buchmüller. Their most recent work was done in 1998 at the most powerful computer of the world, in collaboration with Japanese scientists. András Patkós and Antal Jakovác have collaborated on numerical simulation projects with the group of the University of Bielefeld. Dynamical (non-equilibrium) aspects of the transition were studied by Jakovác and Buchmüller in Hamburg.

Alex Szalay is one of the central figures of the Sloan Digital Sky Survey which started its operation last July after several years of preparation. The Survey's photometric and spectrometric program covers 10000 square degrees on the North Galactic Cap and three strips, each 2.5 degrees wide and 90 degrees long on the South Galactic Cap. The observations will be performed in 5 wavelength band. A catalog will be produced showing the surroundings of each detected galactic object. The aim is to locate and perform spectroscopic measurements on 900000 field galaxies, 100000 color-selected luminous red galaxies, and 100000 color-selected quasars. The special telescope built for this project is located in New Mexico and is operated by a consortium consisting of Johns Hopkins University, Princeton University and Fermilab (Batavia). Szalay and his collaborators (among them a group of young Hungarians mentioned above) are responsible for the concept and construction of the innovative database, enabling the storage of data on one million galaxies and a fast access for later off-line analysis. The size of the database is comparable to the data processed in the Human Genome Project. Their closer astrophysical interest is the careful statistical analysis of the huge amount of galaxy and quasar characteristics, which is larger than the full data set on these objects assembled in the preceding history of astronomy. They hope that the unprecedented statistics will allow to test the most important ideas on the formation of galaxies and galaxy clusters. The participation of the Eötvös group (István Csabai and students) in these activities is facilitated by a joint American-Hungarian research grant started in 1999.

Another famous name of Hungarian origin among leading astrophysicists is John Kormendy (University of Hawaii) working on black holes in the centers of the galaxies. He is doing observations with help of the Hubble Space Telescope and also investigates dynamical models of galaxies in his quest for the determination of black hole masses. He was able to show that almost every galaxy's core contains a black hole, whose mass is correlated with the mass of the galaxy itself. He was born in the U.S., but visited the country of his ancestors already. Two further professors with Hungarian roots are Mary Barsony (Univesity of California, Riverside) and John Bally (University of Colorado). Both of them work on the problem of star formation. Mary Barsony participates in a proposal for building a mid-infrared camera for the planned Next Generation Space Telescope. Prof. Péter Mészáros (Penn State University) is an expert of cosmic gamma ray bursts, which seem to reach us from cosmological distances. He invited several postdocs from Hungary for research work eventually leading to doctoral degree (Z. Bagoly, I. Horváth).

István Szapudi moved to Fermilab/NASA Astrophysics Center after receiving his Ph.D. from Johns Hopkins University, Baltimore. Now he is associated with University of Durham UK, where he is a leading member of the group doing the largest N-body gravitational simulation at present. He is responsible for the correlational analysis of the results.

Gerry Williger and Frank Varosi are associated with NASA Goddard Space Flight Center, Maryland. Dr. Williger is involved in the Hubble Space Telescope project. His interest related to the Early Universe includes the Helium II Gunn-Peterson effect. Dr. Varosi studies dust in galaxies, performs and interprets observations in the infrared part of the spectra. Zoltán Haiman went to the U.S. for undergraduate studies after completing his high school studies in Budapest. After attending graduate courses in Cambridge (U.K.) he took his Ph.D. from Harvard in 1997 and got his first postdoc position at the NASA/Fermilab Astrophysics center. He did important work on the birth of the first stars and quasars with M. Rees and A. Loeb. Starting from the fall 1999 he joins Princeton University as recipient of one of the distinguished Hubble postdoctoral fellowships awarded this year.

Zsolt Frei and Gábor Tóth both work at the Department of Atomic Physics of Eötvös University as Bolyai Fellows. Dr. Frei is involved in developing automated methods for morphological classification of galaxies. Dr. Tóth developed a highly stable, new magneto-hydrodynamical solver code, and treats also problems of astrophysical interest with its help. His study of galactic flow represents special interest to the Early Universe.

A major group of Hungarian astrophysicists will meet this summer in Szeged using the opportunity of the last total solar eclipse of our century, which can be best "enjoyed" in the Southern part of Hungary. The informal meeting will be hosted by dr. József Vinkó, an astronomer and optical spectrographer of Szeged University. Though not all participants will be able to use the famous Hungaro-Martian language in their short progress reports to be presented, an informal association, supporting the case of modern astrophysics in the institutions of Hungarian higher education and helping young Hungarian students studying astrophysics abroad will be surely formed.

The trace of the total solar eclipse in Hungary (August 11, 1999)