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Milky Way’s far side reveals some secrets

Discovery of “variable stars” could help astronomers map dark matter in the galaxy

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1:50pm, May 14, 2014

FAR, FAR AWAY  Five newly discovered Cepheid variable stars (blue circles, left), seen in an illustration of the Milky Way, sit on the opposite side of the galactic center, roughly 75,000 light-years away from Earth (yellow). The cluster of pale blue dots (right) marks previously known galactic Cepheids. Pink areas show the Milky Way’s hydrogen gas, which flares out toward the edge of the galaxy.

Beyond the galaxy’s center lie mostly uncharted swaths of space. But now astronomers have found some landmarks: five stars roughly 75,000 light-years from Earth. The discovery should help astronomers map the largely unexplored far side of the Milky Way and understand the nature of the enigmatic dark matter thought to hold galaxies together.

The five stars are all Cepheid variables, whose brightness fluctuates steadily. Astronomers use Cepheids as distance markers because the brighter the star, the slower it pulsates. By measuring a Cepheid’s period and how bright it appears from Earth, astronomers can calculate its distance; if the star is in another galaxy, then researchers know how far away the galaxy is as well.

Michael Feast, an astronomer at the University of Cape Town in South Africa, and colleagues found the stars in data from the Optical Gravitational Lensing Experiment, a telescope in Chile. The instrument

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