It is often assumed that the strong gravitational field of a super-massive black hole disrupts an adjacent molecular cloud preventing classical star formation in the deep potential well of the black hole. Yet, young stars have been observed across th
e entire nuclear star cluster of the Milky Way including the region close ($<$0.5~pc) to the central black hole, Sgr A*. Here, we focus particularly on small groups of young stars, such as IRS 13N located 0.1 pc away from Sgr A*, which is suggested to contain about five embedded massive young stellar objects ($<$1 Myr). We perform three dimensional hydrodynamical simulations to follow the evolution of molecular clumps orbiting about a $4times10^6~M_{odot}$ black hole, to constrain the formation and the physical conditions of such groups. The molecular clumps in our models assumed to be isothermal containing 100 $M_{odot}$ in $<$0.2 pc radius. Such molecular clumps exist in the circumnuclear disk of the Galaxy. In our highly eccentrically orbiting clump, the strong orbital compression of the clump along the orbital radius vector and perpendicular to the orbital plane causes the gas densities to increase to values higher than the tidal density of Sgr A*, which are required for star formation. Additionally, we speculate that the infrared excess source G2/DSO approaching Sgr A* on a highly eccentric orbit could be associated with a dust enshrouded star that may have been formed recently through the mechanism supported by our models.
We aim at modelling small groups of young stars such as IRS 13N, 0.1 pc away from Sgr A*, which is suggested to contain a few embedded massive young stellar objects. We perform hydrodynamical simulations to follow the evolution of molecular clumps or
biting about a $4times10^6 ~ M_{odot}$ black hole, to constrain the formation and the physical conditions of such groups. We find that, the strong compression due to the black hole along the orbital radius vector of clumps evolving on highly eccentric orbits causes the clumps densities to increase to higher than the tidal density of Sgr A*, and required for star formation. This suggests that the tidal compression from the black hole could support star formation. Additionally, we speculate that the infrared excess source G2/DSO approaching Sgr A* on a highly eccentric orbit could be associated with a dust enshrouded star that may have been formed recently through the mechanism supported by our models.
Supermassive black holes (SMBHs) are fundamental keys to understand the formation and evolution of their host galaxies. However, the formation and growth of SMBHs are not yet well understood. One of the proposed formation scenarios is the growth of S
MBHs from seed intermediate-mass black holes (IMBHs, 10^2 to 10^5 M_{odot}) formed in star clusters. In this context, and also with respect to the low mass end of the M-sigma relation for galaxies, globular clusters are in a mass range that make them ideal systems to look for IMBHs. Among Galactic star clusters, the massive cluster $omega$ Centauri is a special target due to its central high velocity dispersion and also its multiple stellar populations. We study the central structure and dynamics of the star cluster $omega$ Centauri to examine whether an IMBH is necessary to explain the observed velocity dispersion and surface brightness profiles. We perform direct N-body simulations to follow the dynamical evolution of $omega$ Centauri. The simulations are compared to the most recent data-sets in order to explain the present-day conditions of the cluster and to constrain the initial conditions leading to the observed profiles. We find that starting from isotropic spherical multi-mass King models and within our canonical assumptions, a model with a central IMBH mass of 2% of the cluster stellar mass, i.e. a 5x10^4 M_{odot} IMBH, provides a satisfactory fit to both the observed shallow cusp in surface brightness and the continuous rise towards the center of the radial velocity dispersion profile. In our isotropic spherical models, the predicted proper motion dispersion for the best-fit model is the same as the radial velocity dispersion one. (abridged)
Extremely large, rare events arise in various systems, often representing a defining character of their behavior. Another class of extreme occurrences, unexpected failures, may appear less important, but in applications demanding stringent reliabilit
y, the rare absence of an intended effect can be significant. Here, we report the observation of rare gaps in supercontinuum pulse trains, events we term rogue voids. These pulses of unusually small spectral bandwidth follow a reverse-heavy-tailed statistical form. Previous analysis has shown that rogue waves, the opposite extremes in supercontinuum generation, arise by stochastic enhancement of nonlinearity. In contrast, rogue voids appear when spectral broadening is suppressed by competition between pre-solitonic features within the modulation-instability band. This suppression effect can also be externally induced with a weak control pulse.
Optical supercontinuum radiation, a special kind of white light, has found numerous applications in scientific research and technology. This bright, broadband radiation can be generated from nearly monochromatic light through the cooperative action o
f multiple nonlinear effects. Unfortunately, supercontinuum radiation is plagued by large spectral and temporal fluctuations owing to the spontaneous initiation of the generation process. While these fluctuations give rise to fascinating behavior in the form of optical rogue waves [1], they impede many critical applications of supercontinuum. Here, we introduce, and experimentally demonstrate, a powerful means of control over supercontinuum generation by stimulating the process with a very weak optical seed signal [2]. This minute addition significantly reduces the input power threshold for the process and dramatically increases the stability of the resulting radiation. This effect represents an optical tipping point, as the controlled addition of a specialized, but extraordinarily weak perturbation powerfully impacts a much stronger optical field, inducing a drastic transition in the optical system.
