* Astronomy

The neighbourhood around a black hole seems like no place to raise a star. Violent gravitational forces can rip gas clouds apart, making it hard for stars to condense. But astronomers have spotted evidence of very young stars in a ring of gas close to the heart of the Milky Way, where a massive black hole is thought to reside.
These protostars, 6 to 20 light years from the galaxy's centre, are shrouded by so much gas and dust that they can't be seen with telescopes. Instead, Farhad Yusef-Zadeh of Northwestern University in Evanston, Illinois, and colleagues found them through their radio signals.

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Title: First VLTI infrared spectro-interferometry on GCIRS 7 - Characterising the prime reference source for Galactic center observations at highest angular resolution
Authors: J.-U. Pott, A. Eckart, A. Glindemann, S. Kraus, R. Schodel, A. M. Ghez, J. Woillez, G. Weigelt

 Investigating the environment of the massive black hole SgrA* at the centre of the Galaxy requires the highest angular resolution available to avoid source confusion and to study the physical properties of the individual objects. GCIRS7 has been used as wavefront and astrometric reference. Our studies investigate, for the first time, its properties at 2&10um using VLTI/AMBER and MIDI. We aim at analysing the suitability of IRS7 as an IF-phase-reference for the upcoming generation of dual-field facilities at optical interferometers. We observed with (R~30) and 50m (proj.) baseline, resulting in 9 and 45mas resolution for NIR and MIR, resp. The first K-band fringe detection of a GC star suggests that IRS7 could be marginally resolved at 2um, which would imply that the photosphere of the supergiant is enshrouded by a molecular and dusty envelope. At 10um, IRS7 is strongly resolved with a visibility of approximately 0.2. The MIR is dominated by moderately warm (200 K), extended dust, mostly distributed outside of a radius of about 120 AU (15 mas) around the star. A deep 9.8-silicate absorption in excess of the usual extinction law with respect to the NIR extinction has been found. This confirms recent findings of a relatively enhanced, interstellar 9.8-silicate absorption with respect to the NIR extinction towards another star in the central arcsec, suggesting an unusual dust composition in that region. Our VLTI observations show that interferometric NIR phase-referencing experiments with mas resolution using IRS7 as phase-reference appear to be feasible, but more such studies are required to definitely characterize the close environment around this star. We demonstrate that interferometry is required to resolve the innermost environment of stars at the Galactic centre.

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For years, astronomers speculated that a giant, mysterious force lay at the centre of the Milky Way, but it wasn't until four years ago that UCLA astronomer Andrea Ghez definitively showed what it was.
Using new techniques for peering into the dusty heart of the galaxy, Ghez's observations proved that scores of stars were rapidly orbiting what could only be a black hole. But it wasn't the kind of garden-variety black hole created when a star explodes and dies; it was hundreds of thousands of times as powerful -- a "supermassive" black hole, as they are now known.

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Did the colossal black hole at the centre of the Milky Way devour its baby brother 120 million years ago? Possibly, says a team led by Warren Brown of the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, US.
The grisly suggestion comes from observations of 10 'hypervelocity' stars that are moving so fast they will eventually escape the galaxy altogether.
Since the first such star was discovered in December 2004, astronomers have suspected that the supermassive black hole at the heart of the Milky Way, which weighs 3.6 million times the Sun's mass, is responsible for catapulting the objects outwards at extreme speeds. In that scenario, a pair of stars wanders too close to a single, supermassive black hole, and one star gets captured while the other gets flung outwards at up to 4000 km/sec.
But alternative models have also been proposed, including a scenario in which a second, middleweight black hole lurks near the larger one and together, both black holes fling stars outwards.
It is too soon to say which scenario is correct. But Brown's team says the observations to date point to an intriguing possibility: that a middleweight black hole did exist near the galactic centre at one time, but was swallowed up by its larger neighbour about 120 million years ago.

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