Arp 240: A Bridge between Spiral Galaxies from Hubble
Image Credit: NASA, ESA, Hubble Space Telescope; Processing & Copyright: Chris Kotsiopoulos
Explanation: Why is there a bridge between these two spiral galaxies? Made of gas and stars, the bridge provides strong evidence that these two
immense star systems have passed close to each other and experienced violent tides induced by mutual gravity. Known together as
Arp 240 but individually as
NGC 5257 and
NGC 5258, computer modelling and the ages of star clusters
indicate that the two galaxies completed a first passage near each other only about 250 million years ago.
Gravitational tides not only pulled away matter, they compress gas and so caused star formation in both galaxies and the
unusual bridge. Galactic mergers are thought to be common, with Arp 240 representing a
snapshot of a brief stage in this
inevitable process. The Arp 240
pair are about 300 million
light-years distant and can be seen with a small telescope toward the constellation of
Virgo. Repeated
close passages should ultimately result in a
merger and with the emergence of a
single combined galaxy.
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