A star in a 15.2-year orbit around the supermassive black hole at the centre of the Milky Way

Many galaxies are thought to have supermassive black holes at their centres-more than a million times the mass of the Sun. Measurements of stellar velocities and the discovery of variable X-ray emission have provided strong evidence in favour of such a black hole at the centre of the Milky Way, but have hitherto been unable to rule out conclusively the presence of alternative concentrations of mass. Here we report ten years of high-resolution astrometric imaging that allows us to trace two-thirds of the orbit of the star currently closest to the compact radio source (and massive black-hole candidate) Sagittarius A*. The observations, which include both pericentre and apocentre passages, show that the star is on a bound, highly elliptical keplerian orbit around Sgr A*, with an orbital period of 15.2 years and a pericentre distance of only 17 light hours. The orbit with the best fit to the observations requires a central point mass of (3.7 +/- 1.5) x 10(6) solar masses (M(*)). The data no longer allow for a central mass composed of a dense cluster of dark stellar objects or a ball of massive, degenerate fermions.     

Spectroscopic confirmation of a galaxy at redshift z = 8.6

Galaxies had their most significant impact on the Universe when they assembled their first generations of stars. Energetic photons emitted by young, massive stars in primeval galaxies ionized the intergalactic medium surrounding their host galaxies, cleared sightlines along which the light of the young galaxies could escape, and fundamentally altered the physical state of the intergalactic gas in the Universe continuously until the present day. Observations of the cosmic microwave background, and of galaxies and quasars at the highest redshifts, suggest that the Universe was reionized through a complex process that was completed about a billion years after the Big Bang, by redshift z?≈?6. Detecting ionizing Lyman-α photons from increasingly distant galaxies places important constraints on the timing, location and nature of the sources responsible for reionization. Here we report the detection of Lyα photons emitted less than 600?million years after the Big Bang. UDFy-38135539 (ref. 5) is at a redshift of z = 8.5549?±?0.0002, which is greater than those of the previously known most distant objects, at z = 8.2 (refs 6 and 7) and z = 6.96 (ref. 8). We find that this single source is unlikely to provide enough photons to ionize the volume necessary for the emission line to escape, requiring a significant contribution from other, probably fainter galaxies nearby.     

The rapid formation of a large rotating disk galaxy three billion years after the Big Bang

Observations and theoretical simulations have established a framework for galaxy formation and evolution in the young Universe. Galaxies formed as baryonic gas cooled at the centres of collapsing dark-matter haloes; mergers of haloes and galaxies then led to the hierarchical build-up of galaxy mass. It remains unclear, however, over what timescales galaxies were assembled and when and how bulges and disks--the primary components of present-day galaxies--were formed. It is also puzzling that the most massive galaxies were more abundant and were forming stars more rapidly at early epochs than expected from models. Here we report high-angular-resolution observations of a representative luminous star-forming galaxy when the Universe was only 20% of its current age. A large and massive rotating protodisk is channelling gas towards a growing central stellar bulge hosting an accreting massive black hole. The high surface densities of gas, the high rate of star formation and the moderately young stellar ages suggest rapid assembly, fragmentation and conversion to stars of an initially very gas-rich protodisk, with no obvious evidence for a major merger.     

Molecular characterization of the p83/100 proteins of variousBorrelia burgdorferi sensu lato strains

Conclusions As in OspA-serotyping experiments, theB garinii group (OspA-sterotype 3–7) showed highest diversity within this internal fragment of p83/100, whereas theB. afzelii group (OspA-type 2) and theB. burgdorferi sensu stricto group (OspA-type 1) were nearly identical. Determination of the size of the PCR products as well as restriction fragment length polymorphism analysis (DraI) can be used for classification into the three species ofB. burgdorferi sensu lato. Since p83/100 is chromosomally encoded, this protein might be a more stable marker for classification than the plasmid-encoded OspA. In contrast to the flagellin gene a subclassification of theB. garinii group is possible due to the diversity of the p83/100 internal fragment.     

Origin of a 'Southern Hemisphere' geochemical signature in the Arctic upper mantle

The Gakkel ridge, which extends under the Arctic ice cap for approximately 1,800 km, is the slowest spreading ocean ridge on Earth. Its spreading created the Eurasian basin, which is isolated from the rest of the oceanic mantle by North America, Eurasia and the Lomonosov ridge. The Gakkel ridge thus provides unique opportunities to investigate the composition of the sub-Arctic mantle and mantle heterogeneity and melting at the lower limits of seafloor spreading. The first results of the 2001 Arctic Mid-Ocean Ridge Expedition (ref. 1) divided the Gakkel ridge into three tectonic segments, composed of robust western and eastern volcanic zones separated by a 'sparsely magmatic zone'. On the basis of Sr-Nd-Pb isotope ratios and trace elements in basalts from the spreading axis, we show that the sparsely magmatic zone contains an abrupt mantle compositional boundary. Basalts to the west of the boundary display affinities to the Southern Hemisphere 'Dupal' isotopic province, whereas those to the east-closest to the Eurasian continent and where the spreading rate is slowest-display affinities to 'Northern Hemisphere' ridges. The western zone is the only known spreading ridge outside the Southern Hemisphere that samples a significant upper-mantle region with Dupal-like characteristics. Although the cause of Dupal mantle has been long debated, we show that the source of this signature beneath the western Gakkel ridge was subcontinental lithospheric mantle that delaminated and became integrated into the convecting Arctic asthenosphere. This occurred as North Atlantic mantle propagated north into the Arctic during the separation of Svalbard and Greenland.     

一种新型高价锰取代的多金属氧酸盐合成、结构及性质研究

在含有MnⅡ的夹心型多金属氧酸盐水溶液中加入强氧化剂KMnO4,制得一种新型的含有MnⅢ的多金属氧酸盐K5Na3[{MnⅢ(H2O)}2(WO)(H2O) (AsW9O33)2]·18H2O (KNa-1).该化合物的多阴离子结构是基于2个B-α-[AsW9]三缺位Keggin型构筑单元,中间夹着2个{MnⅢ(H2O)}和1个{WⅥO}片段而构成的夹心式构型.对KNa-1进行了变温磁化率测定并采用双核MnⅢ簇为模型进行了拟合,并对该化合物进行了电化学分析.结果表明:KNa-1 中的2个MnⅢ中心存在弱的反铁磁相互作用;化合物中的MnⅢ离子具有不可逆的氧化还原过程.     

Magmatic and amagmatic seafloor generation at the ultraslow-spreading Gakkel ridge,Arctic Ocean

A high-resolution mapping and sampling study of the Gakkel ridge was accomplished during an international ice-breaker expedition to the high Arctic and North Pole in summer 2001. For this slowest-spreading endmember of the global mid-ocean-ridge system, predictions were that magmatism should progressively diminish as the spreading rate decreases along the ridge, and that hydrothermal activity should be rare. Instead, it was found that magmatic variations are irregular, and that hydrothermal activity is abundant. A 300-kilometre-long central amagmatic zone, where mantle peridotites are emplaced directly in the ridge axis, lies between abundant, continuous volcanism in the west, and large, widely spaced volcanic centres in the east. These observations demonstrate that the extent of mantle melting is not a simple function of spreading rate: mantle temperatures at depth or mantle chemistry (or both) must vary significantly along-axis. Highly punctuated volcanism in the absence of ridge offsets suggests that first-order ridge segmentation is controlled by mantle processes of melting and melt segregation. The strong focusing of magmatic activity coupled with faulting may account for the unexpectedly high levels of hydrothermal activity observed.     

Sideband cooling of micromechanical motion to the quantum ground state

The advent of laser cooling techniques revolutionized the study of many atomic-scale systems, fuelling progress towards quantum computing with trapped ions and generating new states of matter with Bose-Einstein condensates. Analogous cooling techniques can provide a general and flexible method of preparing macroscopic objects in their motional ground state. Cavity optomechanical or electromechanical systems achieve sideband cooling through the strong interaction between light and motion. However, entering the quantum regime--in which a system has less than a single quantum of motion--has been difficult because sideband cooling has not sufficiently overwhelmed the coupling of low-frequency mechanical systems to their hot environments. Here we demonstrate sideband cooling of an approximately 10-MHz micromechanical oscillator to the quantum ground state. This achievement required a large electromechanical interaction, which was obtained by embedding a micromechanical membrane into a superconducting microwave resonant circuit. To verify the cooling of the membrane motion to a phonon occupation of 0.34?±?0.05 phonons, we perform a near-Heisenberg-limited position measurement within (5.1?±?0.4)h/2π, where h is Planck's constant. Furthermore, our device exhibits strong coupling, allowing coherent exchange of microwave photons and mechanical phonons. Simultaneously achieving strong coupling, ground state preparation and efficient measurement sets the stage for rapid advances in the control and detection of non-classical states of motion, possibly even testing quantum theory itself in the unexplored region of larger size and mass. Because mechanical oscillators can couple to light of any frequency, they could also serve as a unique intermediary for transferring quantum information between microwave and optical domains.