The Galaxy Evolution Explorer, or GALEX, was an orbiting space telescope designed to observe the universe in ultraviolet wavelengths to measure the history of star formation in the universe.

In addition to paving the way for future ultraviolet missions, GALEX allowed astronomers to uncover mysteries about the early universe and how it evolved, as well as better characterize phenomena like black holes and dark matter. The mission was extended three times over a period of 10 years before it was decommissioned in June 2013.

Mission Events

May 28, 2003: GALEX gathers its first celestial images, observing an area of the sky in the constellation Hercules in honor of the crew of the Space Shuttle Columbia.

April 2010: The spacecraft's far-ultraviolet detector experiences an over-current condition, or essentially "shorts out," via a process called electron field emission. Observations continue with GALEX's second ultraviolet detector.

June 2013: The mission is decommissioned after meeting and far exceeding its prime objectives. The spacecraft will remain in orbit for at least 65 years, then fall to Earth and burn up upon re-entering the atmosphere.

Key Discoveries

October 2003: GALEX captures the most sensitive and comprehensive image ever taken of the Andromeda galexy, our nearest large neighbor galaxy.

April 2004: GALEX captures a giant star eruption, or flare, about one million times more energetic than those from our Sun.

December 2004: GALEX spots what appear to be massive "baby" galaxies in our corner of the universe, suggesting our aging universe is still alive with youth.

August 2006: Findings from GALEX indicate that supermassive black holes in some giant galaxies create such a hostile environment, they shut down the formation of new stars.

December 2006: GALEX's observations allow scientists for the first time to see the process of a black hole eating a star.

November 2007: Observations from GALEX prove the "nature" theory of galaxy evolution, which holds that galaxies are evolutionarily linked.

February 2009: GALEX identifies dwarf galaxies forming out of nothing more than pristine gas likely leftover from the early universe, rather than in association with dark matter or gas containing metals.

August 2010: Astronomers, using data from GALEX, find that galaxies presumed "dead" and devoid of star-making can be reignited with star birth, and that galaxy evolution does not proceed straight from the cradle to the grave.

April 2011: Astronomers come up with a new way to identify planets beyond our solar system based on GALEX's use of ultraviolet imaging.

May 2011: GALEX and the Anglo-Australian Telescope on Siding Spring Mountain in Australia complete a five-year survey of 200,000 galaxies stretching back seven billion years in cosmic time. The results lead to one of the best independent confirmations that dark energy is driving our universe apart at accelerating speeds.

Scientific Instrument(s)

- Telescope