NGC 7217
Template:Short description Template:Infobox Galaxy
NGC 7217 is an unbarred spiral galaxy in the constellation Pegasus.
Features
NGC 7217 is a gas-poor system[1] whose main features are the presence of several rings of stars concentric to its nucleus: three main ones –the outermost one being of the most prominent and the one that features most of the gas and star formation of this galaxy –[1] 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.[2] There is also a very large and massive spheroid that extends beyond its disk.[3]
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[4] and two distinct stellar populations: one of intermediate age on its innermost regions and a younger, metal-poor version on its outermost ones.[5]
It has been suggested these features were caused by a merger with another galaxy[6] 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;[5] however right now this galaxy is isolated in space, with no nearby major companions.[5] More recent research presents a somewhat different scenario in which NGC 7217's massive bulge and halo would have been formed in a merger and the disk formed later (and is still growing) either accreting gas from the intergalactic medium or smaller gas-rich galaxies, or most likely from a previously existing reserve.[7]
See also
- Spiral Galaxy NGC 1512
- NGC 7742, a very similar galaxy in the same constellation
References
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