Cold, clumpy accretion onto an active supermassive black hole.

Supermassive black holes in galaxy centres can grow by the accretion of gas, liberating energy that might regulate star formation on galaxy-wide scales. The nature of the gaseous fuel reservoirs that power black hole growth is nevertheless largely unconstrained by observations, and is instead routinely simplified as a smooth, spherical inflow of very hot gas. Recent theory and simulations instead predict that accretion can be dominated by a stochastic, clumpy distribution of very cold molecular clouds--a departure from the 'hot mode' accretion model--although unambiguous observational support for this prediction remains elusive. Here we report observations that reveal a cold, clumpy accretion flow towards a supermassive black hole fuel reservoir in the nucleus of the Abell 2597 Brightest Cluster Galaxy (BCG), a nearby (redshift z = 0.0821) giant elliptical galaxy surrounded by a dense halo of hot plasma. Under the right conditions, thermal instabilities produce a rain of cold clouds that fall towards the galaxy's centre, sustaining star formation amid a kiloparsec-scale molecular nebula that is found at its core. The observations show that these cold clouds also fuel black hole accretion, revealing 'shadows' cast by the molecular clouds as they move inward at about 300 kilometres per second towards the active supermassive black hole, which serves as a bright backlight. Corroborating evidence from prior observations of warmer atomic gas at extremely high spatial resolution, along with simple arguments based on geometry and probability, indicate that these clouds are within the innermost hundred parsecs of the black hole, and falling closer towards it.

Regulation of star formation in giant galaxies by precipitation, feedback and conduction.

The Universe's largest galaxies reside at the centres of galaxy clusters and are embedded in hot gas that, if left undisturbed, would cool quickly and create many more new stars than are actually observed. Cooling can be regulated by feedback from accretion of cooling gas onto the central black hole, but requires an accretion rate finely tuned to the thermodynamic state of the hot gas. Theoretical models in which cold clouds precipitate out of the hot gas via thermal instability and accrete onto the black hole exhibit the necessary tuning. Recent observational evidence shows that the abundance of cold gas in the centres of clusters increases rapidly near the predicted threshold for instability. Here we report observations showing that this precipitation threshold extends over a large range in cluster radius, cluster mass and cosmic time. We incorporate the precipitation threshold into a framework of theoretical models for the thermodynamic state of hot gas in galaxy clusters. According to that framework, precipitation regulates star formation in some giant galaxies, while thermal conduction prevents star formation in others if it can compensate for radiative cooling and shut off precipitation.

Regulation of the X-ray luminosity of clusters of galaxies by cooling and supernova feedback.

Clusters of galaxies are thought to contain about ten times as much dark matter as baryonic matter. The dark component therefore dominates the gravitational potential of a cluster, and the baryons confined by this potential radiate X-rays with a luminosity that depends mainly on the gas density in the cluster's core. Predictions of the X-rays' properties based on models of cluster formation do not, however, agree with the observations. If the models ignore the condensation of cooling gas into stars and feedback from the associated supernovae, they overestimate the X-ray luminosity because the density of the core gas is too high. An early episode of uniformly distributed supernova feedback could rectify this by heating the uncondensed gas and therefore making it harder to compress into the core, but such a process seems to require an implausibly large number of supernovae. Here we show how radiative cooling of intergalactic gas and subsequent supernova heating conspire to eliminate highly compressible low-entropy gas from the intracluster medium. This brings the core entropy and X-ray luminosities of clusters into agreement with the observations, in a way that depends little on the efficiency of supernova heating in the early Universe.

Withholding/withdrawing treatment from neonates: legislation and official guidelines across Europe.

Representatives from eight European countries compared the legal, ethical and professional settings within which decision making for neonates takes place. When it comes to limiting treatment there is general agreement across all countries that overly aggressive treatment is to be discouraged. Nevertheless, strong emphasis has been placed on the need for compassionate care even where cure is not possible. Where a child will die irrespective of medical intervention, there is widespread acceptance of the practice of limiting aggressive treatment or alleviating suffering even if death may be hastened as a result. Where the infant could be saved but the future outlook is bleak there is more debate, but only two countries have tested the courts with such cases. When it comes to the active intentional ending of life, the legal position is standard across Europe; it is prohibited. However, recognising those intractable situations where death may be lingering and unpleasant, Dutch paediatricians have reported that they do sometimes assist babies to die with parental consent. Two cases have been tried through the courts and recent official recommendations have set out standards by which such actions may be assessed.

Saline load test for penetration of periarticular lacerations.

We used a saline load test in 50 consecutive patients with periarticular lacerations suggestive of joint penetration. The surgeon had predicted on clinical grounds whether or not the laceration penetrated the joint. Joint penetration was demonstrated in 14 and was absent in 36. A comparison of the prediction and the test results showed that there were false-positive clinical results in 39% and false-negative in 43%. There were no complications from the use of the test. Our findings support the use of a saline load test in evaluating periarticular lacerations.

The role of computerized tomography in the diagnosis of an occult femoral neck fracture associated with an ipsilateral femoral shaft fracture: case report.

We report a nondisplaced femoral neck and head fracture diagnosed acutely by CT scanning. This case illustrates the potential benefits of an acute femoral neck/head CT scan in obtunded polytrauma patients with high-energy femoral shaft fractures.