## Investigation on the origin of superbubbles

Origin of the Fermi Bubble. Fermi has discovered two giant gamma-ray-emitting bubbles that extend nearly 10kpc in diameter north and south of the galactic center (GC). The existence of the bubbles was first evidenced in X-rays detected by ROSAT and later WMAP detected an excess of radio signals at the location of the gamma-ray bubbles. We propose that periodic star capture processes by the galactic supermassive black hole, Sgr A$^*$, with a capture rate $3\times 10^{-5}$yr$^{-1}$ and energy release $\sim 3\times 10^{52}$erg per capture can produce very hot plasma $\sim 10$keV with a wind velocity $\sim 10^8$cm/s injected into the halo and heat up the halo gas to $\sim 1$keV, which produces thermal X-rays. The periodic injection of hot plasma can produce shocks in the halo and accelerate

electrons to $\sim$TeV, which produce radio emission via synchrotron radiation, and gamma-rays via inverse Compton scattering with the relic and the galactic soft photons.  –  Professor K.S. Cheng: “A typical male Chinese with a wife and three kids, I lead a very routine lifestyle, but enjoy doing research in theoretical astrophysics and making a reasonable contribution to understanding the field of neutron-star physics and gamma-ray astronomy. My recent research interests have extended to strange-star physics, gamma-ray bursts and cosmic ray physics. In addition to research, this year I only teach Astrophysics because of too much administration duties. If you are interested in the basic knowledge in astrophysics you are welcome to refer to our foundation course Nature of the Universe.I used to play tennis and badminton, but lately have been playing more with my kids – which has resulted in me gaining weight and losing shape! My advice to prospective physics students is : although majoring in physics may not guarantee you a high-salary job, it can provide you with a good training for the mind – something which will benefit you for the rest of your life.”      My major

research areas are the physics of compact stellar objects ,e.g. structure, cooling ,glitches and other internal activities of neutron stars, and high energy astronomy, e.g. X-ray and gamma-ray emission mechanisms of pulsars and strange stars. In addition I am also interested in gamma-ray bursts, gravitational radiation from compact objects, and properties of strange stars.  –  A giant gamma-ray structure was discovered by processing Fermi all-sky data at energies from 1 to 10 billion electron volts, shown here. The dumbbell-shaped feature (center) emerges from the galactic center and extends 50 degrees north and south from the plane of the Milky Way, spanning the sky from the constellation Virgo to the constellation Grus. PHOTO 1. From end to end, the newly discovered gamma-ray bubbles extend 50,000 light-years, or roughly half of the Milky Way’s diameter, as shown in this illustration. Hints of the bubbles’ edges were first observed in X-rays (blue) by ROSAT, a Germany-led mission operating in the 1990s. The gamma rays mapped by Fermi (magenta) extend much farther from the galaxy’s plane. Credit: NASA’s Goddard Space Flight Center  –  PHOTO 2. The bubbles display a spectrum with higher peak energies than the diffuse gamma-ray glow seen throughout the sky. In addition, the bubbles display sharp edges in Fermi LAT data. Both of these qualities suggest that the structure arose in a sudden, impulsive event. Credit: NASA/DOE/Fermi LAT/D. Sources: Cornell University, University of Hong Kong, NASA.

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