Runaway collisions in young star clusters. II. Numerical results

We present a new study of the collisional runaway scenario to form an intermediate-mass black hole (IMBH, MBH > 100 Msun) at the centre of a young, compact stellar cluster. The first phase is the formation of a very dense central core of massive stars (Mstar =~ 30-120 Msun) through mass segregation and gravothermal collapse. Previous work established the conditions for this to happen before the massive stars evolve off the main sequence (MS). In this and a companion paper, we investigate the next stage by implementing direct collisions between stars. Using a Monte Carlo stellar dynamics code, we follow the core collapse and subsequent collisional phase in more than 100 models with varying cluster mass, size, and initial concentration. Collisions are treated either as ideal, ``sticky-sphere'' mergers or using realistic prescriptions derived from 3-D hydrodynamics computations. In all cases for which the core collapse happens in less than the MS lifetime of massive stars (~3 Myr), we obtain the growth of a single very massive star (VMS, Mstar =~ 400-4000 Msun) through a runaway sequence of mergers. Mass loss from collisions, even for velocity dispersions as high as sigma1D ~ 1000 km/s, does not prevent the runaway. The region of cluster parameter space leading to runaway is even more extended than predicted in previous work because, in clusters with sigma1D > 300 km/s, collisions accelerate (and, in extreme cases, drive) core collapse. Although the VMS grows rapidly to > 1000 Msun in models exhibiting runaway, we cannot predict accurately its final mass. This is because the termination of the runaway process must eventually be determined by a complex interplay between stellar dynamics, hydrodynamics, and the stellar evolution of the VMS. [abridged]Comment: 23 pages, 24 figures. For publication in MNRAS. Paper revised to follow requests and suggestions of referee. Companion paper to Freitag, Rasio & Baumgardt 200

Vascular variations of the kidney, retrospective analysis of computed tomography images of ninety-one laparoscopic donor nephrectomies, and comparison of computed tomography images with perioperative findings

Background: In this retrospective study, we aimed to determine the variations of kidney arteries and veins in kidney donor patients who underwent preoperative, computed tomography angiography (CTA).Materials and methods: We analysed kidney CTA findings of 91 donor nephrectomy patients operated from July 2016 through December 2017. Demographics, vascular diameters, abnormalities, numbers, branching variations, routing variations of arteries, and veins were assessed according to CTA images. We also compared the radiological findings with perioperative findings. Two radiologists evaluated CTA images, and the same surgical team performed all donor nephrectomies by laparoscopic approach.Results: Ninety-one of the 96 patients involved to study. Forty-six (50.5%) patients were female. Thirty-five (38.4%) of 91 cases had accessory arteries. Seven (7.6%) right, 1 (1.1%) left and 8 (8.7%) bilateral double hilar artery was observed on CTA. No statistically significant difference was observed in the evaluation of the side of accessory/polar arteries (p > 0.05), and in the evaluation of the distribution of arterial/venous variations according to perioperative findings (p > 0.05). However, in the evaluation of CTA images, we found that the diameter of the kidney artery and vein differed according to gender and side.Conclusions: The knowledge of the vascular variations of the kidney is essential for surgeons performing kidney transplantation. It is also essential for urologist and vascular surgeons. Incompatible with the literature, the right kidney has more vascular variations and, one kidney artery is found in the majority of Turkish kidneydonor patients

Interpreting radiative efficiency in radio-loud AGNs

Author submitted version of unrefereed Nature Astronomy comment. Version in journal format available at https://rdcu.be/KH6WRadiative efficiency in radio-loud active galactic nuclei is governed by the accretion rate onto the central black hole rather than directly by the type of accreted matter; while it correlates with real differences in host galaxies and environments, it does not provide unambiguous information about particular objects.Non peer reviewedFinal Accepted Versio

Cold gas outflows from the Small Magellanic Cloud traced with ASKAP

Feedback from massive stars plays a critical role in the evolution of the Universe by driving powerful outflows from galaxies that enrich the intergalactic medium and regulate star formation. An important source of outflows may be the most numerous galaxies in the Universe: dwarf galaxies. With small gravitational potential wells, these galaxies easily lose their star-forming material in the presence of intense stellar feedback. Here, we show that the nearby dwarf galaxy, the Small Magellanic Cloud (SMC), has atomic hydrogen outflows extending at least 2 kiloparsecs (kpc) from the star-forming bar of the galaxy. The outflows are cold, $T<400~{\rm K}$, and may have formed during a period of active star formation $25 - 60$ million years (Myr) ago. The total mass of atomic gas in the outflow is $\sim 10^7$ solar masses, ${\rm M_{\odot}}$, or $\sim 3$% of the total atomic gas of the galaxy. The inferred mass flux in atomic gas alone, $\dot{M}_{HI}\sim 0.2 - 1.0~{\rm M_{\odot}~yr^{-1}}$, is up to an order of magnitude greater than the star formation rate. We suggest that most of the observed outflow will be stripped from the SMC through its interaction with its companion, the Large Magellanic Cloud (LMC), and the Milky Way, feeding the Magellanic Stream of hydrogen encircling the Milky Way.Comment: Published in Nature Astronomy, 29 October 2018, http://dx.doi.org/10.1038/s41550-018-0608-

Yaşam memnuniyeti üzerinde etkili olan sosyodemografik bileşenler üzerine bir analiz,

Politika yapıcılar toplumu oluşturan bireyleri daha iyi anlamak ve refahı arttırmak amacıyla alınması gereken tedbirleri belirlerken kimin için, nerede, ne zaman hayatın daha iyi olduğunu belirlemek durumundadırlar. Bu amaçla TÜİK Türkiye’de 2003 yılından beri “Yaşam Memnuniyeti Araştırmasını” gerçekleştirmektedir. Toplumun ilerlemesini de ölçmek amacıyla yapılan bu çalışmalardan Türkiye’nin de aralarında bulunduğu OECD Teşkilatı tarafından gerçekleştirilen “Yaşam Memnuniyeti Endeksi” mutluluk algısı ve yaşam memnuniyeti arasındaki kognitif ilişkiyi açıklamaya yöneliktir. ABD tarafından gerçekleştirilen “Genel Sosyal Araştırma/General Social Survey” ve AB ülkelerinin yaptığı “Euro-Barometre” bu bağlamda bilinen diğer geniş kapsamlı araştırmalardır. Yaşam memnuniyeti bileşenlerinin birbirleriyle ilişkisini uygulamalı olarak incelemeye yönelik olan bu çalışma, 2004-2014 yılları arasındaki dönem için belirlenmiştir. Birim kök, granger nedensellik ve regresyon analizleri sonucu elde edilen veriler E-Views 8.0 programı ile analiz edilerek yaşam memnuniyetini en çok etkileyen faktörlerin belirlenmesine çalışılmıştır. Kişisel mutluluk ve aile mutluluğu ile mutluluk kaynağı, memnuniyet ve umut faktörleri arasında nedensellik ilişkisi olduğu, ailenin genel mutluluğunu en çok sevgi ve sağlık hizmetlerinin etkilediği, ailenin en az başarı ve asayiş hizmetlerinden etkilendiğini, bireylerin öz mutluluğunu en çok para ve eğitim hizmetlerinin etkilediğini, en az sağlık ve SGK hizmetlerinden etkilendikleri, gerek bireyin gerekse ailenin öz mutluluğunda en çok kadınların mutlu olmasının etkili olduğu sonucuna varılmıştır

Star formation in the central 0.5 pc of the Milky Way

The supermassive black hole candidate at the Galactic Center is surrounded by a parsec-scale star cluster, which contains a number of early type stars. The presence of such stars has been called a "paradox of youth" as star formation in the immediate vicinity of a supermassive black hole seemed difficult, as well as the transport of stars from far out in a massive-star lifetime. I will recall 30 years of technological developments which led to the current understanding of the nuclear cluster stellar population. The number of early type stars known at present is sufficient to access the 3D structure of this population and its dynamics, which in turn allows discriminating between the various possible origins proposed along the years.Comment: 8 pages, invited review for the conference "The Universe under the Microscope" (AHAR 2008), to be published in Journal of Physics: Conference Series by Institute of Physics Publishin