Using NASA’s Swift satellite, astronomers at NASA and Pennsylvania State University have used to create detailed ultraviolet light surveys of the Large and Small Magellanic Clouds, the two closest major galaxies to Earth.
The astronomers took thousands of images and assembled them into portraits of the main body of each galaxy, according to Stefan Immler, who led NASA’s contribution from the agency’s Goddard Space Flight Center in Greenbelt, Maryland.
Immler presented a 160-megapixel mosaic image of the Large Magellanic Cloud (LMC) and a 57-megapixel mosaic image of the Small Magellanic Cloud (SMC) at an American Astronomical Society meeting in Indianapolis yesterday.
He said that these images are the highest-resolution surveys of the Magellanic Clouds at ultraviolet wavelengths that have ever been compiled.
NASA said the new images reveal about 1m ultraviolet sources in the LMC, which was assembled from 2,200 images taken by the Swift ultraviolet/optical telescope, and about 250,000 ultraviolet sources in the SMC that were assembled via 656 individual images.
"Prior to these images, there were relatively few UV observations of these galaxies, and none at high resolution across such wide areas, so this project fills in a major missing piece of the scientific puzzle," said Michael Siegel from the Swift Mission Operations Center at Pennsylvania State University.
The LMC is about 163,000 light-years away, while the SMC is about 200,000 light-years away. Each of these galaxies orbit each other as well as our own Milky Way galaxy.
The LMC is about one-tenth the size of the Milky Way and contains only 1pc of the Milky Way’s mass. The SMC is half the size of the LMC and contains about two-thirds of its mass.
Viewing in the ultraviolet allows astronomers to suppress the light of normal stars like the sun to give a clearer picture of the hottest stars and star-formation regions.
NASA said that the Swift ultraviolet/optical telescope is the only telescope that can produce such high-resolution ultraviolet surveys.
"With these mosaics, we can study how stars are born and evolve across each galaxy in a single view, something that’s very difficult to accomplish for our own galaxy because of our location inside it," Immler said.
Both the LMC and SMC are visible from the Southern Hemisphere as faint, glowing patches in the night sky. The galaxies are named after Ferdinand Magellan, the Portuguese explorer who led an expedition to sail around the world in 1519. Together with his crew, Magellan was among the first Europeans to spot the galaxies.
In the following video, Immler narrates a tour of the LMC and SMC galaxies.