A ground-based telescopic photograph of the peculiar galaxy Arp 220 (image taken by K. Borne, H. Levison, and R. Lucas at USNO Flagstaff Station, Arizona) shows a curious double-lobed structure. This structure was first interpreted as two galaxies merging together, until subsequent observations with highly sensitive CCD detectors revealed a dust lane down the center which made the galaxy appear double lobed.
A "true-color" image of the central pan of the Arp 220 taken with the WFPC on the Hubble Space Telescope. HST reveals a new complex structure within one arc second of the nucleus. HST reveals a new class of object at the core: gigantic young star clusters which are ten times larger than clusters previously observed. They were probably produced by the collision of two spiral galaxies. Stars are produced at a furious rate from the raw dust and gas supplied by the collision.
Astronomers have never before seen such a "starburst galaxy" so close-up. The core of Arp 220 promises to be a unique laboratory for studying the late evolution of massive stars.
Credit: E. Shaya, D. Dowling/U. of Maryland, the WFPC Team, and NASA