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10 April 2014 11:44 am ,
Vol. 344 ,
The Pyrenean ibex, an impressive mountain goat that lived in the central Pyrenees in Spain, went extinct in 2000. But a...
Tight budgets are forcing NASA to consider turning off one or more planetary science projects that have completed their...
Ebola is not a stranger to West Africa—an outbreak in the 1990s killed chimpanzees and sickened one researcher. But the...
In an as-yet-unpublished report, an international panel of geoscientists has concluded that a pair of deadly...
Tropical disease experts tried and failed before to eradicate yaws, a rare disfiguring disease of poor countries. Now,...
Since 2002, researchers have reported that agricultural communities in the hot and humid Pacific Coast of Central...
Balkan endemic kidney disease surfaced in the 1950s and for decades defied attempts to finger the cause. It occurred...
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ScienceShot: Reconstructing Galactic History
31 July 2013 1:00 pm
How did our galaxy form and evolve? To find out, astronomers try to ascertain the ages of the Milky Way's oldest components. Especially useful are globular clusters, old, tight-packed stellar gatherings that serve as time capsules preserving conditions from the Milky Way's youth. Now, as astronomers report online today in Nature, Hubble observations of white dwarf stars have nailed down the age of the great globular cluster 47 Tucanae (shown). Located 15,000 light-years from Earth, this cluster is the second brightest globular in the sky, after Omega Centauri. The new data reveal that 47 Tucanae is 9.9 billion years old, plus or minus 700 million years. For a globular, the cluster is metal-rich—its iron-to-hydrogen ratio is a fifth of the sun's—and is 2 billion years younger than a metal-poor globular dated with the same technique. Metal-poor and metal-rich globulars belong to two different components of the Milky Way, so these ages help reconstruct galactic history. Metal-poor globulars are part of the ancient stellar halo surrounding the Milky Way's disk, while metal-rich globulars reside in the galaxy's bulge and thick disk; therefore, the difference in age means that billions of years elapsed from the formation of the stellar halo to the birth of the thick disk.