GALEX Space Telescope

Galaxy Evolution Explorer (GALEX) is a space telescope mission launched by the United States National Aeronautics and Space Administration (NASA) in 2003. The primary objective of the mission is to investigate the formation and evolution processes of galaxies in the universe by observing them in the ultraviolet wavelengths.

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Throughout its mission duration, GALEX provided significant data on star formation processes by studying ultraviolet radiation coming from galaxies billions of light-years away.

GALEX was developed under NASA's Small Explorer (SMEX) program. The project was led by the California Institute of Technology (Caltech), with scientific management carried out by Caltech, and spacecraft operations coordinated by NASA's Goddard Space Flight Center.

The satellite was launched on April 28, 2003, from Cape Canaveral Air Force Station aboard a Pegasus XL rocket and was positioned in low Earth orbit.

GALEX is an ultraviolet telescope with a 50 cm diameter mirror. The instrument was designed to observe in both far-ultraviolet (FUV; 135–175 nm) and near-ultraviolet (NUV; 175–280 nm) wavelengths. Ultraviolet observations can only be conducted from space-based platforms since Earth's atmosphere blocks ultraviolet light. In this regard, GALEX had the ability to directly observe star-forming regions in galaxies.

GALEX’s primary scientific goal was to investigate the temporal and spatial distribution of star formation in the universe. Ultraviolet observations are particularly suitable for detecting the radiation emitted by young and hot stars. In this context, GALEX observed hundreds of thousands of galaxies to study star formation rates over a timescale extending up to about 10 billion years into the past.

Thanks to the data obtained by GALEX:

• Galaxy evolution models were supported by observational data,
• Inferences were made regarding early universe star formation processes,
• Star formation maps of galaxies close to the Milky Way were created.

In addition, the satellite’s observations enabled the discovery of many ultraviolet-emitting stars, comets, and galaxies.

Initially, GALEX was planned to operate for 29 months. However, due to the scientific value of the data collected, the mission was extended several times. In 2011, NASA officially ended its support program for the telescope. Subsequently, in 2012, GALEX was transferred to Caltech under a public-private partnership model.

The satellite was fully decommissioned and shut down on June 28, 2013. Throughout its mission, GALEX conducted approximately 500 million ultraviolet source observations, which served as data for numerous academic studies and publications.

GALEX’s data is made publicly available online by NASA and Caltech for researchers’ access. These data are used for research in many astrophysical areas including galaxy evolution, star formation, cosmology, and the interstellar medium. GALEX played a pioneering role, especially in creating wide-field ultraviolet sky maps.