Large galaxies grow by attracting small galaxies as they pass nearby. The Milky Way, our own galaxy practice this kind of galactic cannibalism, absorbing smaller galaxies captured by the gravitational force of the Milky Way. In fact, this practice is common throughout the universe. The images below illustrate the practice against gravity. This beautiful pair of interacting galaxies is in the constellation Eridanus (the river). It is located at more than 50 million light-years away and spans 100,000 light years. The large spiral galaxy NGC 1532 has captured the dwarf galaxy NGC 1531 in its gravitational sphere of influence. The small galaxy is trapped and desperate struggle against the enormous gravitational force that imposes large galaxy. The unequal struggle eventually defeat the small NGC 1531, which will disappear in a merger with NGC 1532. The galaxy NGC 1532/1531 is now an inseparable pair and looks very ready for spring system in the galaxy Whirlpool (right), known as the M51 and its companion NGC 5195.
Image: The galaxy NGC 1532 NGC 1532/1531 which devours the small NGC 1531. Image ESO/Danish 1.5m telescope Chile à La Silla - 2008.
Image: The Whirlpool galaxy NGC 5194 of 60 000 light years in diameter is also known as the M51. It absorbs NGC 5195, his companion on the right. Image Hubble.