NASA Hubble images: Rare Ultra-blue Stars Found in Neighbouring Galaxies

The image at left shows the nearby, majestic Andromeda galaxy.

The rectangular box marks the region probed by NASA’s Hubble Space Telescope (a blend of visible and ultraviolet light).

The photo (top right) is 7,900 light-years across and reveals the galaxy's crowded central region.

The bright area near the center of the image is a grouping of stars nestled around the galaxy's black hole.

The blue dots sprinkled throughout the image are ultra-blue stars whose population increases around the crowded hub. The square box shows a close-up view of an area around the core.

The detailed image, shown at bottom right, reveals a richer population of blue stars huddled around the core.

Dark dust clouds also are visible. The right-hand images, taken with Hubble, are part of a census of stars in M31 called the Panchromatic Hubble Andromeda Treasury survey.

(Credit: NASA; ESA; B. Williams and J. Dalcanton, University of Washington, Seattle)