deletions | additions       diff --git a/subsection_AGN_feedback_in_galaxies__.tex b/subsection_AGN_feedback_in_galaxies__.tex  index 04cc5bc..eaea588 100644  --- a/subsection_AGN_feedback_in_galaxies__.tex  +++ b/subsection_AGN_feedback_in_galaxies__.tex 
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Hot gas, cold gas, stars, and a supermassive black hole are the main components of a galaxy. Cooling, star formation, AGN accretion and feedback processes can transfer particles from one component to another, and in that way alter the efficiency of all the processes in the galaxy. For example, increased cooling of hot gas will lead to the production of more cold gas. This in turn increases the star formation rate, therefore increasing the rate of supernova. Energy released by from supernovae and ejections from AGN jets and reheats cold gas, leading to a suppression of star formation (negative feedback). In contrast, supernova blast-waves may also compress the surrounding cold gas, thus increasing star formation rate (positive feedback). The formation and evolution of galaxies depends on these feedback loops. (Mo et al, 2011).  If the predecessor dark matter halos contained central galaxies, the galaxies also merge, thus producing a new galaxy. Such a merger may be accompanied by strong star formation or AGN activity if the merging galaxies contained significant amounts of cold gas. (Mo et al, 2011). Black hole growth also depends on accretion and mergers. The merger of two galaxies increases the probability of the merger of the SMBHs at their centres, since black hole mergers are one of the ways through which black holes grow. Even so, the observation of systems with a combined SMBH are not common. (Dean et al, 2015)  These mergers instead produce a binary black hole which is a system consisting of two black holes in close orbit around each other. As the separation of the black holes decreases, they eject stars between them, creating a less dense core which is latter restored after the merger as large amounts of material are accreted towards the newly formed SMBH. (Volonteri et al, 2002). However, galaxy core-depletion can also be attributed to stars falling into to the SMBH(s) as a result of venturing too close to the SMBH(s) event horizon. (Graham 2005).