The Eyes (NGC 4435 and 4438)
The Eyes taken with the FORS2 instrument on the Very Large Telescope. The larger of the galaxies, NGC 4438, at the top of the picture, is thought to have once been a spiral galaxy that was strongly deformed by collisions in the relatively recent past. Credit: ESO/Gems project.
The Eyes (NGC 4435 and 4438) are a pair of adjacent galaxies in the Markarian Chain, 20' east of M86 in the central core of the Virgo Cluster, which were nicknamed by the nineteenth-century observer L. S. Copeland; the likeness to a pair of eyes is emphasized by the fact that NGC 4435 and NGC 4438 are both elongated in a SSW-NNE direction. They lie about 50 million light-years away and are about 100,000 light-years apart.
There is a debate about whether NGC 4435 and NGC 4438 are interacting. Certainly, the two galaxies are very different in appearance. NGC 4435 (magnitude 17.5; R.A. 12h 27.7m, Dec. +13° 5'), at lower right in the image, is oval, compact, with a bright core, and seems to be almost devoid of gas and dust. It appears completely free of any tidal disturbances due to its sky neighbor. In contrast, NGC 4438 (magnitude 17.5; 12h 27.8m; Dec. +13° 1'), the larger galaxy at the upper left, has a lane of obscuring dust visible just below its nucleus, young stars visible to the left of its center, and gas extending at least up to the edges of the image.
NGC 4438 appears to have collided with another galaxy, causing a distortion to spiral shape. One possibility is that NGC 4435 is to blame. According to this theory, the effects seen in NGC 4438 were caused when the two galaxies came within about 16,000 light-years of each other about 100 million years ago. But while the larger galaxy was damaged, the smaller one was significantly more affected by the collision. Gravitational tides from this clash are probably responsible for ripping away the contents of NGC 4438, and for reducing NGC 4435's mass and removing most of its gas and dust.
Another theory is that the giant elliptical galaxy M86, further away from The Eyes, was responsible for the damage to NGC 4438. Recent observations have found filaments of ionized hydrogen gas connecting the two large galaxies, suggesting that they may have collided in the past.
In rich clusters of galaxies, such as the Virgo Cluster, galaxy collisions are fairly frequent, so it's possible NGC 4438 suffered from encounters with both NGC 4435 and Messier 86.