This image shows two clusters of galaxies colliding with one another, the smaller one being known as the Bullet Cluster. NASA's Spitzer Space Telescope obtained these observations during the telescope's warm mission phase, following the depletion of its liquid coolant in 2009.

Spitzer, along with the Hubble Space Telescope, targeted the Bullet Cluster as part of the Spitzer UltRaFaint Survey, or SURFS UP. The joint project will image 10 massive, foreground galaxy clusters whose strong gravity magnifies the light of background objects. This so-called cosmic lensing causes objects such as the distant, dim, young galaxies that SURFS UP is investigating, to appear more than 10 times brighter than they normally would, allowing the team to study the stars within them.

At least one distant, young galaxy has been detected far behind the bullet cluster but magnified by its gravitational lens effect. The overall reddish hue of starlight visible to Spitzer in this distant, young galaxy indicates that the stars in it are already mature. The findings therefore push back the time when the first stars and galaxies arose and began ending a cosmic period known as the Dark Ages.

These Spitzer observations at wavelengths of 3.5 and 4.6 microns are shown in blue and red, respectively.