Fridolin Weber, Department of Physics, San Diego State University
Background for my research:
It is often stressed that there has never been a more exciting time in the overlapping areas of nuclear physics, particle physics and relativistic astrophysics than today. This comes at a time where new orbiting observatories such as the Hubble Space Telescope, Rossi X-ray Timing Explorer, Chandra X-ray satellite, and the X-ray Multi Mirror Mission have extended the vision of astrophysicists tremendously, allowing them to observe and study astrophysical phenomena with an unprecedented clarity and angular resolution that previously were only imagined. On the Earth, radio telescopes and instruments using adaptive optics and other revolutionary techniques have exceeded previous expectations of what can be accomplished from the ground. Finally, the gravitational wave detectors LIGO, LISA, and VIRGO are opening up a window for the detection of gravitational waves emitted from rotating neutron stars and black holes.
Neutron stars and black holes are among the most striking and bizarre astrophysical objects where two frontiers of modern physics – the strong interaction which holds together atomic nuclei, and general relativity – come together. Neutron stars are so dense that matter in their centers is compressed to densities that are ten to twenty times higher than the density of atomic nuclei! A thimble full of such matter, for instance, would have a mass of one billion tons. At such extraordinary densities atoms themselves collapse, and atomic nuclei are squeezed so tightly together that novel states of matter are formed. These include exotic condensates of elementary particles and the formation of a plasma composed of the most fundamental building blocks of matter – the quarks. Most amazingly, if a plasma of quarks exists in neutron stars, it will be a superconductor with most unusual properties.
My areas of research:
Physicists often summarize the properties of matter over a range of densities and temperatures by drawing a so-called phase diagram. A famous example of such a diagram is the liquid-vapor phase diagram of water. The major goal of my research is to explore the phase diagram not of water but of ultra-dense and ultra-hot (100 billion Kelvin) matter using observed neutron star data provided by the state-of-the-art telescopes mentioned above. The unprecedented advancements in observational astrophysics enable physicists for the first time ever to do that. Naturally such research is performed at the interface between nuclear physics, particle physics, and general relativity. Based on numerical studies, I have been able to predict several possible astrophysical signals that would signal the existence of quarks in the centers of neutron stars (see Fig. 1). These signals are detectable with radio telescopes and X-ray satellites and, thus, have attracted a tremendous interest in the community. The notion "quark astronomy" has been coined by others in the literautre for this kind of research.
My research activities are crucial to obtain the full physics potential of the investments that are made in gravitational radiation detectors, at the Thomas Jefferson Lab, the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory, as well as new investments that are recommended for the Rare Isotope Accelerator (RIA).
Astrophysics provides a natural avenue for science education since most students are deeply touched by natural wonders of the sky and the Universe. Together with my students, I am working on multi-media presentations on how stars work. These presentations will shown to middle and high school students and teachers in the San Diego area.
Fig. 1: Competing structures and novel phases of superdense matter predicted by theory to make their appearance inside of neutron stars (for more details, see F. Weber, “Strange Quark Matter and Compact Stars”, Prog. Part. Nucl. Phys. 54 (2005) 193-288, (astro-ph/0407155).
Recognitions I have received:
Finding out how matter behaves at the most extreme conditions of density and temperature has become a forefront area of modern physics. On the Earth, relativistic particle colliders provide the only tools which allow us to get a glimpse on the properties of such matter. As described above, I follow an alternative approach by studying the properties of neutron stars and other types of compact stellar objects (black holes and white dwarfs). The international interest in this kind of research is simply tremendous. This reflects itself, for instance, in the large number of invitations that I am receiving to speak at major international workshops, conferences, physics schools, and to give colloqia at universities.
In 1999 I published a book entitled "Pulsars as Astrophysical Laboratories for Nuclear and Particle Physics", Studies in High Energy Physics, Cosmology and Gravitation, Institute of Physics (IoP) Publishing Corporation, Bristol, Great Britain, (682 pages). The Institute of Physics is a leading international professional body and learned society, established to promote the advancement and dissemination of physics. The Institute is also one of the major international players in scientific publishing. My book was among the top-ten books of IoP Publishing for may months. It is well recognized as a valuable reference for researchers in the field, a popular text for graduates and advanced undergraduates students entering the field and a self-study guide for interested scientists. I am currently working on the second edition of my book. The new edition will ensure that the book remains a high-quality up-to-date resource for students and researchers.
Since 2003 I am part of the Joint Institute for Nuclear Astrophysics (JINA) which was formed in the same year between the University of Notre Dame, NSCL/MSU, the ASCI Flash Center of the U Chicago, the SciDAT Supernova Center at UC Santa Cruz, and the University of Arizona. One of the main goals of JINA is to explore the fate of matter accreted onto x-ray neutron stars. Such stars are potential sources for the generation of gravitational waves, a subject I am working on since my former stay at the University of Notre Dame.
I would also like to mention that I am an author of Encyclopedia of Astronomy and Astrophysics, UK, and are doing consulting work for the Astronomy Magazine, Waukesha, Wisconsin, USA. As of writing of this text, I have given almost 200 talks and published 115 papers in scientific journals, and about a handful papers in popular journals.
In 2005, I won a 2-year Cottrell College Science Award for research on "Cooling Behavior of Rotating Neutron Stars", and a 3-year award from the National Science Foundation for research on "Neutron Stars as Probes for the Structure of Dense Nuclear Matter". There are currently five undergraduate and graduate students working with me on these as well as related projects, such as
1) Properties of relativistic quantum systems
2) Equation of state of hot and dense stellar matter
3) Superfluidity
4) Stability and evolution of rapidly spinning compact stars (neutron stars, quark stars)
5) Gravity-wave instabilities in compact stars
6) Magnetars
7) Astrophysical signals of quark deconfinement
8) Mass accretion and evolution of X-ray pulsars
9) Physics and astrophysics of strange quark matter
10) Numerical treatment of Einstein's general relativistic field equations
11) General Relativity