Assessing inflow rates in atomic cooling halos: implications for direct collapse black holes

Supermassive black holes are not only common in the present-day galaxies, but billion solar masses black holes also powered $z\geq 6$ quasars. One efficient way to form such black holes is the collapse of a massive primordial gas cloud into a so-called direct collapse black hole. The main requirement for this scenario is the presence of large accretion rates of $\rm \geq 0.1~M_{\odot}/yr$ to form a supermassive star. It is not yet clear how and under what conditions such accretion rates can be obtained. The prime aim of this work is to determine the mass accretion rates under non-isothermal collapse conditions. We perform high resolution cosmological simulations for three primordial halos of a few times $\rm 10^7~M_{\odot}$ illuminated by an external UV flux, $\rm J_{21}=100-1000$. We find that a rotationally supported structure of about parsec size is assembled, with an aspect ratio between $\rm 0.25 - 1$ depending upon the thermodynamical properties. Rotational support, however, does not halt collapse, and mass inflow rates of $\rm \sim 0.1~M_{\odot}/yr$ can be obtained in the presence of even a moderate UV background flux of strength $\rm J_{21} \geq 100$. To assess whether such large accretion rates can be maintained over longer time scales, we employed sink particles, confirming the persistence of accretion rates of $\rm \sim 0.1~M_{\odot}/yr$. We propose that complete isothermal collapse and molecular hydrogen suppression may not always be necessary to form supermassive stars, precursors of black hole seeds. Sufficiently high inflow rates can be obtained for UV flux $\rm J_{21}=500-1000$, at least for some cases. This value brings the estimate of the abundance of direct collapse black hole seeds closer to that high redshift quasars.Comment: Accepted for publication in MNRAS, comments are still welcom

The formation of supermassive black holes in rapidly rotating disks

Massive primordial halos exposed to moderate UV backgrounds are the potential birthplaces of supermassive black holes. In such a halo, an initially isothermal collapse will occur, leading to high accretion rates of $\sim0.1$~M$_\odot$~yr$^{-1}$. During the collapse, the gas in the interior will turn into a molecular state, and form an accretion disk due to the conservation of angular momentum. We consider here the structure of such an accretion disk and the role of viscous heating in the presence of high accretion rates for a central star of $10$, $100$ and $10^4$~M$_\odot$. Our results show that the temperature in the disk increases considerably due to viscous heating, leading to a transition from the molecular to the atomic cooling phase. We found that the atomic cooling regime may extend out to several $100$~AU for a $10^4$~M$_\odot$ central star and provides substantial support to stabilize the disk. It therefore favors the formation of a massive central object. The comparison of clump migration and contraction time scales shows that stellar feedback from these clumps may occur during the later stages of the evolution. Overall, viscous heating provides an important pathway to obtain an atomic gas phase within the center of the halo, and helps in the formation of very massive objects. The latter may collapse to form a massive black hole of about $\geq 10^4$~M$_\odot$.Comment: Accepted for publication in Astronomy & Astrophysics, comments are still welcom

Biodegradation of rocket propellant waste, ammonium perchlorate

The short term effects of ammonium perchlorate on selected organisms were studied. A long term experiment was also designed to assess the changes incurred by ammonium perchlorate on the nitrogen and chloride contents of soil within a period of 3 years. In addition, an attempt was made to produce methane gas from anaerobic fermentation of the aquatic weed, Alternanthera philoxeroides

A study of the effects of alkalinity and total hardness on postlarvae and juveniles of the giant freshwater prawn Macrobrachium rosenbergii (de Man)

The effects of environmental water hardness and alkalinity on the giant freshwater prawn Macrobrachium rosenbergii (de Man) were investigated. Preliminary studies indicated significant interaction effects between alkalinity and hardness and also that the ratio of calcium to magnesium ions in the water was important for growth. At moderate alkalinity a Ca:Mg ratio of 1:1 allowed better growth than ratios of 4:1 and 1:4. In a series of experiments made with postlarval and juvenile prawns, the levels of alkalinity and hardness in the test waters were adjusted separately so that the influence of each factor could be determined independently as well as in combination. Data on aspects of survival, growth and carapace mineralization were recorded. The results showed that, in contrast to some reports, high water hardness did not necessarily constrain performance provided alkalinity was low (2Smg 1' as CaCOs). On the other hand, high alkalinity (>100mg 1') caused a number of problems. These included increased mortalities (particularly when hardness was low. 20mg 1'), an increased incidence of a pathological condition called "white muscle syndrome” , a reduced size increment achieved at moult while, paradoxically, increasing the moulting frequency, and an enhanced calcium deposition in carapaces during intermoult. In all experiments, postlarvae were more sensitive than juveniles to adverse combinations of alkalinity and hardness. This feature is discussed in relation to Asian prawn farming practises. The activity of dephosphorylating enzymes in gills from immediate postmoult and from intermoult prawns exposed to low and high alkalinity was measured. The activity was maximal at both low and high alkalinity in postmoult prawns i.e. during the time of expected maximum calcium uptake, and significantly lower in intermoult prawns but only when alkalinity was low. At high alkalinity, activity in intermoult prawns remained at postmoult levels suggesting that this activity was associated with the increased calcium deposition observed in intact animals held in high alkalinity waters