Mathematics – Probability
Scientific paper
Apr 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000phdt.........8a&link_type=abstract
Thesis (PhD). CORNELL UNIVERSITY, Source DAI-B 60/10, p. 5113, Apr 2000, 288 pages.
Mathematics
Probability
Scientific paper
Although it has been known for over twenty years that a halo of dark matter surrounds our Galaxy, the composition of the halo is still a mystery. Depending on the number, mass, and size of the dark matter particles, and their agglomerations, the Galactic potential will vary with position and time, leading to ``heating'' of stellar systems in the galaxy, such as the Galactic disk and globular cluster system (GCS). In this thesis, we explore the idea that massive black holes (MBH's) in the mass range 103Msolar<=Mbh<=10 7Msolar could make up the dark matter in the Galactic halo. We place constraints on their allowed mass, Mbh, and fraction of the halo mass density, fbh, by calculating the effect of collisions between them and Galactic clusters. If the Galactic GCS is destroyed or altered to such a degree that it does not resemble the observed GCS, then we can rule out those values of Mbh and fbh. We have constrained halo MBH's using two different arguments. First, requiring the survival over 1010 years of a selected sample of tenously bound clusters, we find that small mass black holes can only have Mbh<=103Msolar if fbh = 1. In the large M bh limit, we cannot constrain the mass of the black hole (other than it is above a certain minimum value to be in the ``large'' limit), however we find that it is unlikely that fbh>~ 0.3 if the selected group of clusters are to survive. Our second constraint comes from requiring that clusters which are conventionally considered unevolved in the absence of MBH's should not be destroyed in 1010 years. Restricting our simulations to tidal encounters between clusters and MBH's, we have found that black holes with masses Mbh>~ (1-3)× 106Msolar can comprise no more than a fraction fbh ~ 0.17 of the total halo density at Galactocentric radius R ~ 8 kpc. This limit comes from requiring stability of the cluster mass function. A more restrictive bound may be derived if we demand that the probability of destruction of any given, low mass (Mc~(2.5-7.5) ×104Msolar) globular cluster not exceed 50%; this bound is fbh<~ 0.025-0.05 at R ~ 8 kpc. This constraint improves those based on disk heating and dynamical friction arguments as well as current lensing results. At smaller radii, the constraint on fbh strengthens, while, at larger radii, an increased fraction of black holes is allowed.
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