Saturday, December 3, 2011

Voyagers Detect Missing Signal

Voyager 1
Billions of miles from home, the Voyager spacecraft (one illustrated here) are still collecting data. A new study of archival observations has revealed a faint signal from the Milky Way that has long eluded instruments closer to Earth.
NASA / JPL-Caltech
Thirty-four years after their 1977 launches, we’re still hearing about discoveries made by NASA’s Voyager spacecraft. To the tally that includes Jupiter’s faint ring, active volcanoes on Io, and Neptune’s Great Dark Spot — not to mention the ongoing mission to find the outer limit of the Sun’s magnetic influence — add another first: the detection of a particular kind of hydrogen signal called Lyman-alpha emission from the Milky Way itself.

Lyman-alpha is a specific ultraviolet wavelength (121.6 nm, to be exact) emitted when a hydrogen atom’s electron drops down one orbital energy level to the ground state. It’s emitted by hydrogen atoms after they recover from being ionized by hot stars’ ultraviolet radiation or after encountering shock waves from supernovae or stellar winds. Because of these associations, Lyman-alpha is thought to be a good tracer of galaxies’ star-formation rates.


Glenn A. Walsh, Project Director,
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