| Abstract |
Universe had been explored for thousands of years only by optical observations. From 1960’s space observations onboard spacecrafts became possible to broaden the observational window up to UV and X-rays, which are absorbed by the earth atmosphere. Since electro-magnetic waves in different wave bands are emitted by different mechanisms. X-rays are produced from hot(T > 10^6 K) plasmas or high energy particles, while optical lights are mostly emitted from main sequence stars, infrared light is found from dusts and radio emission are from cold molecule in vibration or rotation modes. Therefore, X-ray observations reveal violent activities of the Universe, which have never been recognized in other wave bands.
In my lecture, the first subject is on the supernovae and their remnants. At the end of the life of massive stars, the gravitational energy of contraction of a star is converted to the kinetic energy of expanding shell with the total energy more than 10^51 ergs. As a shock front propagates in the interstellar medium, kinetic energy is converted to thermal energy to create hot plasmas(T > 10^6 K) there. Imaging spectroscopy of such thermal emission from super nova remnants tells us the elements(abundance), temperature and dynamics of the hot gas, and its environment. In addition, non-thermal emission has been found from SNR without any emission line features of hot plasmas. It suggests non-thermal emission produced by high energy electrons and magnetic fields. Kinetic energy of the SN explosion mentioned above is also converted into high energy particles by acceleration mechanisms.
Black holes (several MSolar) are to be created after the SN explosion of very massive(> 30 MSolar) stars. It may evolve by eating up ambient plasma and merging with black holes. At the center of most of galaxies, it is believed that there are super massive(10^6-9 MSolar) black holes thus evolved. Gravitational energy of accreting matter onto black holes is released from the region close to the black hole radius (Rg= 2GM/c^2). Emission from the region so close to Rg is subject to the gravitational effects, such as gravitational red shifts, as well as relativistic beaming and Doppler effects. Strong radiation from the nucleus irradiates the accretion disc and material around it. Reflection and transmission features can be found in X-ray spectra. Only form such spectral and temporal X-ray data, we are able to examine the geometry and size of structure around the black holes.
In this lecture, I will explain above issues based on X-ray data mostly obtained by Japanese Missions: ASCA(1993-2001) and SUZAKU(2005- ). |
