domingo, 13 de febrero de 2011

La Via Lactea se zampó un aperitivo galáctico/Milky Way munched on galactic snack


Un reciente estudio ha identificado las migas estelares de lo que puede ser la comida más reciente de la Vía Láctea - una galaxia enana devorada hace 700 millones de años. El descubrimiento proporciona nuevas pruebas para la principal teoría sobre la formación de las galaxias, que sostiene que la Vía Láctea y otras hoy en día grandes galaxias, comenzaron pequeñas y han crecido a costa de consumir o funsionarse con sus vecinas.
Las 15 estrellas del grupo descubierto por Mary Williams, del Instituto Astrofísico de Potsdam en Alemania y sus colegas, tienen una velocidad y composición química similares. Según afirman Williams y sus colegas en la revista Astrophysical Journal, son esas propiedades compartidas las que diferencian al grupo de estrellas, localizado en la constelación de Acuario, de las restantes 250.000 estrellas de la Vía Láctea estudiadas por el Observatorio Astronómico de Australia en Siding Spring.
El grupo de estrellas de Acuario es relativamente compacto, lo cual es un indicio claro de que las estrellas no han tenido tiempo de dispersarse. Según Williams, su forma sugiere que las estrellas proceden de una galaxia que fue capturada hace relativamente poco tiempo y que, durante el proceso, resultó estirada como un chicle debido a la fuerza gravitatoria de la Vía Láctea. La mayoría de los cerca de una docena de grupos similares previamente identificados, están formados por estrellas salpicadas por toda la Vía Láctea, y son los restos de galaxias engullidas hace miles de millones de años .

LAST SUPPER from Science News on Vimeo.

A new study has identified stellar crumbs from what may be the Milky Way’s most recent meal — a dwarf galaxy devoured about 700 million years ago. The discovery provides fresh evidence for the leading theory of galaxy formation, which holds that the Milky Way and other large, modern-day galaxies began small and continue to grow by consuming or merging with their neighbors.
The stream of 15 stars discovered by Mary Williams of the Astrophysical Institute Potsdam in Germany and her colleagues all have similar speeds and chemical compositions. It’s those shared properties that set the elongated grouping of stars, located in the constellation Aquarius, apart from the 250,000 other stars across the Milky Way surveyed by the Australian Astronomical Observatory in Siding Spring, Williams and colleagues report in the Feb. 20 Astrophysical Journal.
The Aquarius star stream is relatively compact, which is a strong clue that the stream hasn’t had time to disperse. Its shape suggests that the stars come from a galaxy that was captured relatively recently and, in the process, stretched like taffy by the Milky Way’s gravity, Williams says. Most of the dozen or so previously identified streams are made up of stars sprinkled throughout the Milky Way and are the remnants of galaxies swallowed billions of years ago.

Tomado de/Taken from Science News

Resumen de la publicación/Abstract of the paper
THE DAWNING OF THE STREAM OF AQUARIUS IN RAVE
M. E. K. Williams, M. Steinmetz, S. Sharma, J. Bland-Hawthorn, R. S. de Jong, G. M. Seabroke, A. Helmi, K. C. Freeman, J. Binney, I. Minchev, O. Bienaymé, R. Campbell, J. P. Fulbright, B. K. Gibson, G. F. Gilmore, E. K. Grebel, U. Munari, J. F. Navarro, Q. A. Parker, W. Reid, A. Siebert, A. Siviero, F. G. Watson, R. F. G. Wyse and T. Zwitter
The Astrophysical Journal 728, Number 2
doi: 10.1088/0004-637X/728/2/102
ABSTRACT
We identify a new, nearby (0.5kpc d 10 kpc) stream in data from the RAdial Velocity Experiment (RAVE). As the majority of stars in the stream lie in the constellation of Aquarius, we name it the Aquarius Stream. We identify 15 members of the stream lying between 30º - l - 75º and –70º - b - –50º, with heliocentric line-of-sight velocities V los ~ –200 km s–1. The members are outliers in the radial velocity distribution, and the overdensity is statistically significant when compared to mock samples created with both the Besançon Galaxy model and newly developed code Galaxia. The metallicity distribution function and isochrone fit in the log g-T eff plane suggest that the stream consists of a 10 Gyr old population with [M/H] ~ –1.0. We explore relations to other streams and substructures, finding that the stream cannot be identified with known structures: it is a new, nearby substructure in the Galaxy's halo. Using a simple dynamical model of a dissolving satellite galaxy, we account for the localization of the stream. We find that the stream is dynamically young and therefore likely the debris of a recently disrupted dwarf galaxy or globular cluster. The Aquarius stream is thus a specimen of ongoing hierarchical Galaxy formation, rare for being right in the solar suburb.