Wikipedia:
The Eyes Galaxies (NGC 4435-NGC 4438, also known as Arp 120) are a pair of galaxies about 52 million light-years away in the constellation Virgo. The pair are members of the string of galaxies known as Markarian's Chain.
NGC 4435 is a barred lenticular galaxy currently interacting with NGC 4438. Studies of the galaxy by the Spitzer Space Telescope revealed a relatively young (190 million years) stellar population within the galaxy's nucleus, which may have originated through the interaction with NGC 4438 compressing gas and dust in that region, triggering a starburst. It also appears to have a long tidal tail possibly caused by the interaction; however, other studies suggest the apparent tail is actually foreground galactic cirrus within the Milky Way unrelated to NGC 4435.
NGC 4438 is the most curious interacting galaxy in the Virgo Cluster, due to the uncertainty surrounding the energy mechanism that heats the nuclear source; this energy mechanism may be a starburst region, or a black hole-powered active galactic nucleus (AGN). Both hypotheses are currently under investigation by astronomers.
This galaxy shows a highly distorted disk, including long tidal tails due to the gravitational interactions with other galaxies in the cluster and its companion. The aforementioned features explain why sources differ as to its classification, defining it either as a lenticular or spiral galaxy. NGC 4438 also shows signs of a past, extended - but modest - starburst, a considerable deficiency of neutral hydrogen, as well as a displacement of the components of its interstellar medium - atomic hydrogen, molecular hydrogen, interstellar dust, and hot gas - in the direction of NGC 4435. This observation suggests both a tidal interaction with NGC 4435 and the effects of ram-pressure stripping as NGC 4438 moves at high speed through Virgo's intracluster medium, increased by the encounter between both galaxies.
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