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Volume 481 Issue 7379, 5 January 2012

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.)


  • Editorial |

    Where political leadership on climate change is lacking, scientists must be prepared to stick their heads above the parapet.

World View

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    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.

    • Daniel Sarewitz

Seven Days

  • Seven Days |

    The week in science: researcher arrested for supplying stem-cell clinic; XMRV studies retracted; and a professor faces criminal charges for lab death.


News Q&A


News Feature


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    Regardless of whether the Higgs detection is confirmed, the standard model is incomplete, says John Ellis.

    • John Ellis
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    As models of authorship and collaboration change in the digital age, we must rely on trust to filter the products of research, says Jerome Ravetz.

    • Jerome Ravetz

Books & Arts

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    A view of robotics reveals ethics has not kept up with technology, finds Braden Allenby.

    • Braden Allenby
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    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.

    • Jascha Hoffman


News & Views

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    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

    • Mark Morris
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    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

    • Christopher A. Voigt
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    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

    • Robert W. Boyd
    • Zhimin Shi
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    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

    • Marina E. Wolf


  • Article |

    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.

    • Arthur Prindle
    • Phillip Samayoa
    • Jeff Hasty



  • Feature |

    Female scientists hoping to become entrepreneurs face obstacles — but there are organizations that can help.

    • Virginia Gewin



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