The first edition of INPE's Advanced Course on Astrophysics, in 2005, dealt with prospects and perspectives on Cosmology, literally a "roadmap" to Cosmology.
As an opportune complement, the second edition of the Course reaches aspects of both extragalactic and galactic astrophysics: Compact Objects.
The natural examples of what we call "compact objects" display configurations in which degenerate matter prevails -- white dwarfs, neutron stars and maybe exotic matter stars -- and configurations in which no known pressure mechanism is able to avoid gravitational collapse: the so-called black holes.
Binarity plays a conspicuous role in turning compact configurations of matter observable since companions -- in the form of gaseous stars or even the interstellar medium itself -- provide plenty of gas for accretion. This gas, for its part, converts gravitational potential energy into other forms of energy making such systems visible at great distances. Binarity also plays a crucial role in producing impulsive events of emission of gravitational waves.
The configurations resulting from the exposure of different kinds of compact objects to plenty of gas provide us a plethora of observational phenomena: white dwarfs accreting matter from main sequence stars show up as "Cataclysmic Variables".
Here, the presence or absence of magnetic field in the compact object produce new configurations rich in rare observables such as circular polarized radiation.
No less important, the magnitude of the accretion rate by the compact object defines regimes in which the ambient plasma behaves like a viscous or non-viscous fluid, with associated instabilities that produce the Dwarf Nova eruptions.
The long-term characteristics of accretion onto white dwarfs are equally responsible for a fraction of the pollution of the interstellar medium with nucleosynthetic products -- via Novae and SN I explosions -- and as a consequence, by a fraction of the chemical enrichment of the Galaxy itself.
Neutron stars possess gravitational potential wells a thousand times deeper than the equivalent for white dwarfs. In this circumstance, the phenomenology shifts to proportionally higher energies. Compact objects accreting gas from companion stars or from the interstellar medium show up as X ray and Gamma ray sources. Again, a myriad of effects come up in response to these different physical conditions.
Non-magnetized neutron stars show eruptions of low-Q quality in the repetition rate, as can be seen in relaxation oscillators, while rotating magnetized objects manage to channel the captured matter producing X ray pulsars, and in extreme conditions, powerful releases of energy as observed in magnetars. Tight configurations of neutron stars in inspiralling motion with respect to each other produce strong deformation in the space-time fabric in scales of meter/kilometer and fractions of a millisecond providing, together with supernovae collapses, the most probable sources for the first detections of gravitational waves.
Black Holes, according to the canonical view, do not have firm theoretical limits for their masses. They are observed in Nature from a few solar masses (as in binary
systems) up to 100 million solar masses (as in galactic nuclei). Again, the phenomenology is vast and intervening agents such as magnetic fields are able to produce configurations that mankind only came to know in the 20th century, like extragalactic jets with dimensions exceeding by a factor of a hundred the dimension of a normal galaxy.
The theories to explain the variety of observables presented by Compact Objects will be addressed at INPE's II Advanced Course on Astrophysics by a team of renowned lecturers:
Brian Warner is responsible for several discoveries in the field of Cataclysmic Variables. His textbook "Cataclysmic Variables" is the basic reference for students and researchers. Since the configuration involving a white dwarf as a compact object in binary system was only fully recognized in the second half of the 20th century, we can surely say that Warner has not only created parts of, but fully witnessed the development of this branch of knowledge.
Kostas Kokkotas has important contributions on the study of Quasi-Normal Modes of Pulsating Relativistic Stars.
In particular, working in collaboration with Bernard Schutz and Nils Andersson, he has found a new family of normal mode frequencies: the w-modes, which are mainly modes of the spacetime and not of the fluid. These modes have no analog in Newtonian theory. They have also proven the existence of Axial Modes for normal stars, showing that they are practically spacetime modes. He has also studies on the statistical analysis of the estimators of the Newtonian and post-Newtonian parameters of the gravitational wave signal from a coalescing binary from one or a network of detectors.
Feryal Özel works on physics of compact objects, high energy astrophysics, neutron stars, magnetars, black holes, accretion disks, and gravitational lensing. Among other things she has been working on determining the signatures of ultrahigh magnetic fields and identifying them in Anomalous X-ray Pulsars and Soft Gamma-ray Repeaters. One of her important contributions on the physics of compact objects has to do with the determination of the mass and radius of the neutron star EXO 0748-676 that appears to rule out all the soft equations of state of neutron-star matter. She has received many honours and awards including the NASA Hubble Postdoctoral Fellowship.
The sub-topic "Accretion on neutron stars and black holes" will be presented by Ronald A. Remillard. He is one of the principal investigators behind the All Sky Monitor (ASM) onboard the Rossi X-ray Timing Explorer (RXTE) satellite, a fundamental mission for high energy astrophysics. Ron has scored as chapter author in the two bibles of the high energy community ("X-ray Binaries", from 1995 and its sucessor "Compact Stellar X-ray Sources", 2006), with both observational and theoretical contributions. He is recognized as one of the most important researchers in the field of compact objects.
