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24 April 2014 11:45 am ,
Vol. 344 ,
Major climate data sets have underestimated the rate of global warming in the last 15 years owing largely to poor data...
The tsetse fly is best known as the vector for the trypanosome parasites that cause sleeping sickness and a disease in...
The National Institutes of Health is revising its "two strikes" rule, which allowed researchers only one chance to...
By stabilizing the components of retromers, molecular complexes that act like recycling bins in cells, a recently...
Fossil fuels power modern society by generating heat, but much of that heat is wasted. Semiconductor devices called...
Researchers are gaining insights into what made Supertyphoon Haiyan so powerful and devastating through post-storm...
Millions around the world got a first-hand look at what it was like to be in Tacloban while it was pummeled by...
- 24 April 2014 11:45 am , Vol. 344 , #6182
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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.