Washington, Oct 31 : The Hubble space telescope has detected a pair of gravitationally interacting galaxies that appear to mark the number ten.
The galaxies, called Arp 147, were observed by Hubble's Wide Field Planetary Camera 2 (WFPC2).
The left-most galaxy, or the "one" in the image, is relatively undisturbed apart from a smooth ring of starlight. It appears nearly on edge to our line of sight. The right-most galaxy, resembling a zero, exhibits a clumpy, blue ring of intense star formation.
The blue ring was most probably formed after the galaxy on the left passed through the galaxy on the right.
Just as a pebble thrown into a pond creates an outwardly moving circular wave, a propagating density wave was generated at the point of impact and spread outward.
As this density wave collided with material in the target galaxy that was moving inward due to the gravitational pull of the two galaxies, shocks and dense gas were produced, stimulating star formation.
The dusty reddish knot at the lower left of the blue ring probably marks the location of the original nucleus of the galaxy that was hit.
The galaxy pair was photographed on October 27-28, 2008.
Arp 147 lies in the constellation Cetus, and it is more than 400 million light-years away from Earth.
Arp 147 appears in the Arp Atlas of Peculiar Galaxies, compiled by Halton Arp in the 1960s and published in 1966.