A numerical simulation survey on the outflow from the Galactic center

• Main Authors: Yi-Wen Chang, 張逸雯
• Other Authors: Chung-Ming Ko
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/45157849101064455868

碩士 === 國立中央大學 === 天文研究所 === 101 === In the second half of 2010, Fermi satellite discovered two giant gamma ray bubbles above and below our Galactic plane in the direction of the Galactic center. The bubbles extended 50 degrees in Galactic latitude and 40 degrees in longitude. The spatial distributions correlated with the ROSAT X-ray map at 1.5 keV and the WMAP haze near the Galactic plane. Among many possible origins of the bubbles, we are particular interested in the scenario that stars are repeatedly captured by the supermassive black hole located at the Galactic center. At each capture, a huge amount of energy is release and causes a massive expansion or outflow that forms the bubbles. We adopt the astro-hydrodynamic code PLUTO to study this phenomenon. We carry out 2D (cylindrical coordinates) numerical survey on the formation and evolution of the bubbles under different conditions, such as different energy release at each capture and different time intervals between captures. We also consider the effect of different assumed scale heights of the Galactic gaseous disk. When we compare different single capture cases (with same scale height), we learn that the shape of the bubble from small energy release is rounder and extended further in the lateral direction than the one from large energy release, but the perturbation is weaker. When the energy release is large, the bubble can easily penetrate the disk, but the lateral extend is restricted to about three times the scale heights. The morphology of a single capture case and a repeated captures case with the same total energy is significantly different. The repeated captures case has lesser lateral evolution and a lot more turbulent interior. Moreover, the turbulent level increases when the interval between captures decreases. The X-ray maps from simulations show that the repeated captures cases have slightly thick lower bubble edge than the single capture cases. We also compare the maps with ROSAT data.