Irapuan Rodrigues

Formation of a Black Hole in the Dark

We show that the black hole in the x-ray binary Cygnus X-1 was formed in situ and did not receive an energetic trigger from a nearby supernova. The progenitor of the black hole had an initial mass greater than 40solar masses, and during the collapse to form the ∼10–solar mass black hole of Cygnus X-1, the upper limit for the mass that could have been suddenly ejected is ∼1 solar mass, much less than the mass ejected in a supernova. The observations suggest that high-mass stellar black holes may form promptly, when massive stars disappear silently.

Kinematics and modeling of the inner region of M 83

Two-dimensional kinematics of the central region of Mxa083 (NGCxa05236) were obtained through three-dimensional NIR spectroscopy with the Gemini South telescope. The spatial region covered by the integral field unit (~5 × 13 or ~90 × 240 pc) was centered approximately at the center of the bulge isophotes and oriented southeast-northwest. The Paβ emission at half-arcsecond resolution clearly reveals spider-like diagrams around three centers, indicating the presence of extended masses, which we describe in terms of Satoh distributions. One of the mass concentrations is identified as the optical nucleus (ON), another as the center of the bulge isophotes, similar to the CO kinematical center (KC), and the third as a condensation hidden at optical wavelengths (hidden nucleus, HN), coincident with the largest lobe in 10xa0μm emission. We run numerical simulations that take into account ON, KC, and HN and four more clusters, representing the star-forming arc at the southwest of the optical nucleus. We show that ON, KC, and HN suffer strong evaporation and merge in 10-50 Myr. The star-forming arc is scattered in less than one orbital period, also falling into the center. Simulations also show that tidal striping boosts the external shell of the condensations to their escape velocity. This fact might lead to an overestimation of the mass of the condensations in kinematical observations with spatial resolution smaller than the condensations apparent sizes. Additionally, the existence of two ILR resonances embracing the chain of Hxa0II regions, claimed by different authors, might not exist due to the similarity of the masses of the different components and the fast dynamical evolution of Mxa083 central 300xa0pc.

Light Cores Behind Dark Masks

The dusty circumnuclear environments of many spiral galaxies hide important clues for understanding the tight correlation between the supermassive black hole and the host galaxy bulge mass. Two of the nearest spiral galaxies with nuclear starburst host off-centered compact cores associated with the peak of the infrared emission.These compact objects are lightweight, up to a few million solar masses. Their locations imply that they are triggering the present star formation within the circumnuclear disk. Numerical modeling implies that the giant star clusters formed in the process evaporate in a few system revolutions (due to the strong asymmetric gravitational potential). Therefore the off-center compact object scenario provides a model in which the dynamically cold gaseous component is rapidly converted into a dynamically hot stellar component. Meanwhile only a small fraction of the gas contributes to the growth of the off-centered compact object.