This image shows the center of the colliding galaxies system NGC 7252. Located about 300 million light years from Earth in the direction of the constellation Aquarius, it appears to be a clear example of two disk galaxies in the process of merging after a collision. The orderly spiral pattern is in peaceful contrast to the chaotic outer regions of NGC 7252, as shown in the inset picture at the upper left, A ground-based image from the 4-meter telescope at Cerro Tololo InterAmerican Observatory, in Chile. The two long plumes, consisting of stars and gas ripped out of the merging galaxies by gravitational force, are called 'tidal tails'
The bright dots in this HST image of NGC 7252 are resolved by the telescope. Each appears about 0.04 arc seconds across, the apparent size of a small coin seen from a distance of 100 kilometers (60 miles). Their real diameters are about 60 light years, similar to the sizes of globular clusters in the Milky Way. Researchers have concluded that they are young globular star clusters, formed in the collision of the two disk galaxies that began about one billion years ago. This conclusion is supported by spectrograms obtained with the 5-meter (200-inch) Hale Telescope at Palomar Observatory.
A long-standing theory proposes that elliptical galaxies are formed from collisions between disk galaxies. An objection to the theory is that elliptical galaxies of a given mass tend to contain many more globular clusters than comparable disk galaxies. However, the HST findings suggest that the galaxy collisions themselves may produce new globular clusters, perhaps answering this objection. It appears that the small spiral pattern at the center of NGC 7252 is a relatively short-lived phenomenon and that NGC 7252 is well on the way to becoming an elliptical galaxy.
Camera: WF/PC-I (1992)
Technical Information: False color image
with computer image reconstruction.
Credit (HST image): B. Whitmore (STScl),
and NASA
Credit (inset): F. Schweizer (Carnegie
Institution of Washington)
