X-ray and Optical Images of Arp 147
These images show Arp 147, a pair of interacting galaxies some 430 million light years from Earth, as seen by the Chandra X-ray Observatory and the Hubble Space Telescope. The ring-shaped object on the right is a remnant of a spiral galaxy that collided with the elliptical galaxy to the left millions of years ago. The collision triggered a wave of star formation. Many of these new young stars raced through their evolution - in a few million years or less - and ended up as supernova explosions or black holes. X-rays from Chandra now reveal a ring of these black holes in the outer arms of the spiral structure. Researchers estimate that the nine sources around the ring are likely 10 to 20 times more massive than the Sun - a rather impressive weight for any Valentine's gift.
(Credit: X-ray: NASA/CXC/MIT/S.Rappaport et al, Optical: NASA/STScI)

Ultraviolet and Infrared Images of Arp 147
Infrared observations with NASA's Spitzer Space Telescope and ultraviolet observations with NASA's Galaxy Evolution Explorer (GALEX) have allowed estimates of the rate of star formation in the ring. These estimates, combined with the use of models for the evolution of binary stars have allowed the authors to conclude that the most intense star formation may have ended some 15 million years ago, in Earth's time frame.
(Credit: X-ray: NASA/CXC/MIT/S.Rappaport et al, Optical: NASA/STScI)