NGC 7217 is an unbarred spiral galaxy in the constellation Pegasus.
NGC 7217 is a gas-poor system whose main features are the presence of several rings of stars concentric to its nucleus: three main ones -being the outermost one the most prominent and the one that features most of the gas and star formation of this galaxy-, plus several others inside the innermost one discovered with the help of the Hubble Space Telescope, a feature that suggests NGC 7217's central regions have suffered several starbursts, and a very large and massive spheroid that extends beyond its disk.
Other noteworthy features this galaxy has are the presence of a number of stars rotating in the opposite direction around the galaxy's center to most of them and two distinct stellar populations: one of intermediate age on its innermost regions and a younger, metal-poor on its outermost ones.
It has been suggested these features were caused by a merger with another galaxy and, in fact, computer simulations show that NGC 7217 could have been a large lenticular galaxy that merged with one or two smaller gas-rich ones of late Hubble type becoming the spiral galaxy we see today.; however right now this galaxy is isolated in space, with no nearby major companions.
Collaboration between me,
Salvatore Iovene and
Jaime Alemany.
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