45 research outputs found
Manifestations of a Massive Black Hole in the Galactic Center
A young star cluster is a less contrived explanation than a massive black hole for many of the features seen in the Galactic center. However from a Copernican point of view, this explanation is less attractive than a black hole. The evidence for a ~ 10^6 M_â black hole is becoming progressively less convincing, but the case against it is no stronger. We describe the development of a singular star cluster, as well as the processes of stellar disruption, merging, and gas accretion in such a cluster. Recently merged stars and tidally stripped giants may be detectable within an arcminute of the Galactic Center. We examine the physics of star formation in the inner parsecs of the galaxy, and the problem of maintaining the two parsec molecular torus
Magnetohydrodynamic Simulation of the Interaction between Interplanetary Strong Shock and Magnetic Cloud and its Consequent Geoeffectiveness
Numerical studies have been performed to interpret the observed "shock
overtaking magnetic cloud (MC)" event by a 2.5 dimensional magnetohydrodynamic
(MHD) model in heliospheric meridional plane. Results of an individual MC
simulation show that the MC travels with a constant bulk flow speed. The MC is
injected with very strong inherent magnetic field over that in the ambient flow
and expands rapidly in size initially. Consequently, the diameter of MC
increases in an asymptotic speed while its angular width contracts gradually.
Meanwhile, simulations of MC-shock interaction are also presented, in which
both a typical MC and a strong fast shock emerge from the inner boundary and
propagate along heliospheric equator, separated by an appropriate interval. The
results show that the shock firstly catches up with the preceding MC, then
penetrates through the MC, and finally merges with the MC-driven shock into a
stronger compound shock. The morphologies of shock front in interplanetary
space and MC body behave as a central concave and a smooth arc respectively.
The compression and rotation of magnetic field serve as an efficient mechanism
to cause a large geomagnetic storm. The MC is highly compressed by the the
overtaking shock. Contrarily, the transport time of incidental shock influenced
by the MC depends on the interval between their commencements. Maximum
geoeffectiveness results from that when the shock enters the core of preceding
MC, which is also substantiated to some extent by a corresponding simplified
analytic model. Quantified by index, the specific result gives that the
geoeffectiveness of an individual MC is largely enhanced with 80% increment in
maximum by an incidental shock.Comment: 45 pages, 9 figure