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The radio source Sgr A* in Sagittarius is thought to be the site of a supermassive black hole lying at the centre of the Milky Way. A study of stellar orbits has identified an object moving towards Sgr A* at a speed of 1,700 kilometres per second. Its low temperature and spectral properties suggest that it is a dusty cloud of ionized gas, three times the mass of Earth, in the process of falling into the black hole. Models predict that as the cloud gets closer to the black hole, X-ray emissions will become much brighter, and a giant radiation flare may be emitted in a few years if the cloud breaks up and feeds gas into the black hole. On the cover, a hydrodynamical simulation set in the year 2025 shows the tidally disrupted gas cloud interacting with the hot accretion flow. In the background are S-stars for which orbits have been determined. (Simulation by M. Schartmann (MPE) using the PLUTO code.)
High-prestige research hogs the money, while the needs — and value — of the US science agencies closest to the public are ignored, says Daniel Sarewitz.
Data from NASA's Kepler space telescope have revolutionized the search for planets outside the Solar System — and are now doing the same for asteroseismology.
Chemist and educator Bassam Shakhashiri is known for his dramatic live demonstrations of chemistry in action. As he takes the helm as president of the American Chemical Society (ACS) this week, he talks about the state of science education and how to engage people in chemistry through the wonders of the lab.
A gas cloud has been spotted approaching the Milky Way's central black hole. Observations of its closest approach, expected to occur in mid-2013, may offer insight into the black hole's immediate surroundings. See Letter p.51
A method developed to allow rapid communication between bacterial cells across long distances enables the cells to detect arsenic collectively, and to report it as an oscillatory output. See Article p.39
As if the idea of a device that makes an object seem invisible was not mind-boggling enough, researchers have now demonstrated a system that can conceal an event in time. See Letter p.62
Cocaine use causes lasting changes in behaviour by altering the strength of connections between neurons. The finding that these changes can be reversed in mice suggests strategies that could be used to treat drug addiction. See Letter p.71
Thousands of quorum-sensing Escherichia coli colonies are synchronized over centimetres using redox signalling to create ‘biopixels’ that can sense trace amounts of arsenic in water.
NMR and single molecule FRET experiments show that antiparallel EmrE dimers interconvert between two identical but oppositely oriented conformations that are each open only to one side of the membrane.
Simulations reproduce previously unexplained features of Titan’s methane cycle, attributing them to atmospheric instabilities and cold-trapping of methane in the polar regions.
Temporal cloaking hides an event in time from being detected; here this is achieved by speeding up one end of a probe beam and slowing down the other to create a ‘time hole’ and to close it afterwards so that the signal amplitude of an event is much reduced.
In mice, cocaine is found to potentiate excitatory transmission in medium-sized spiny neurons expressing the type-1 dopamine receptor; depotentiation reversed cocaine-induced locomotor sensitization, raising the possibility of novel treatments for addiction.
Many TRP ion channels respond to more than one category of cue, and how they discriminate between them is largely unknown; the mechanism by which TRPA1 discriminates between sensory stimuli in Drosophila is now determined.
For the initiation of metastasis, there must be a small population of cancer stem cells at the secondary site and, to maintain this population and allow proliferation, infiltrating cancer cells must induce the expression of stromal periostin.
FBXO11 is identified as the F-box protein that normally targets BCL6 for degradation, and FBXO11 deletions or mutations that prevent this function and thus stabilize BCL6 are found in B-cell lymphomas.
The crystal structure of the calcium-bound gating ring of a calcium- and voltage-activated potassium channel shows in detail how the effect of calcium binding on the gating ring produces the conformational change from closed to open.
The crystal structure of the enzyme MCR from methanogenic archaea shows that it is very similar to that of methanotrophic archaea; the differences observed may tune the enzymes for their respective biological context within the sea mats.