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6 March 2014 1:04 pm ,
Vol. 343 ,
Early in April, the first of a fleet of environmental monitoring satellites will lift off from Europe's spaceport in...
Since 2000, U.S. government health research agencies have spent almost $1 billion on an effort to churn out thousands...
Magdalena Koziol, a former postdoc at Yale University, was the victim of scientific sabotage. Now, she is suing the...
Antiretroviral drugs can protect people from becoming infected by HIV. But so-called pre-exposure prophylaxis, or PrEP...
Two studies show that eating a diet low in protein and high in carbohydrates is linked to a longer, healthier life, and...
Considered an icon of conservation science, researchers at World Wildlife Fund (WWF) headquarters in Washington, D.C.,...
The new atlas, which shows the distribution of important trace metals and other substances, is the first product of...
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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.