The possible impact of Intermediate Mass Black Holes on our Galaxy

University essay from Lunds universitet/Institutionen för astronomi och teoretisk fysik; Lunds universitet/Astronomi

Author: Wilhelm Krüger; [2014]

Keywords: Physics and Astronomy;

Abstract: Orbit integration for three different assumed Intermediate-mass Black Hole (IMBH, defined as black holes with mass MBH in the range 100Mo < MBH 104Mo) populations in the Milky Way for 10 Gyr has been performed. Upon collision with molecular clouds in the galactic disc, the relative velocity between both objects has been measured and the luminosity resulting from the gas accretion process onto the IMBH has been modeled. IMBHs moving on the very same orbits as today observed globular cluster do not create X-Ray luminosities during molecular cloud crossings exceeding 1039 erg/s with the exception of the disc-like orbit of NGC 6838. A population of 5.3 x 105 IMBHs, orbiting on similar orbits as globular cluster do, create on average 1 observable X-Ray object within the galactic disc at any given time. IMBHs orbiting within the galactic disc create high luminosities up to 1043 erg/s due to low relative velocities upon collisions. Assuming those disc-IMBHs have been created in cores of massive star cluster during the lifetime of the Milky Way, the fraction f of cluster creating IMBHs over all cluster capable of doing so has to be fA < 0.35 (fB < 0.018), otherwise ULXs (Ultraluminous X-Ray sources, luminosity ¡ 1039 erg/s ) are predicted to be visible at any given time, contradicting with observations. Index A refers to the model in which all cluster with masses Mcluster > 5 x 104Mo can create IMBHs, while model B assumes cluster have only to obey Mcluster > 2.5 x 103Mo to do so. In turn, given the different mass distributions within the IMBH population assuming model A or B, not more than about 15000 (A) or 16000 (B) IMBHs can be present today within the galactic disc. From the total number of IMBHs formed within star cluster in the disc, 49 % (A) or 54 % (B) have already lost their host cluster due to disruption in molecular cloud encounters. With the exception of NGC 6838, no globular cluster is expected to be destroyed via molecular cloud collisions within 10 Gyr.

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