NGC 7217 is an

unbarred spiral galaxy An unbarred spiral galaxyAstronomy Pictures(accessed 18 April 2010) is a type of spiral galaxy without a central bar, or one that is not a barred spiral galaxy. It is designated with an SA in the galaxy morphological classification scheme. Ba ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

Pegasus Pegasus ( grc-gre, Πήγασος, Pḗgasos; la, Pegasus, Pegasos) is one of the best known creatures in Greek mythology. He is a winged divine stallion usually depicted as pure white in color. He was sired by Poseidon, in his role as hor ...

Features

NGC 7217 is a

gas Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma). A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...

-poor system 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 Star formation is the process by which dense regions within molecular clouds in The "medium" is present further soon.-->interstellar space

of this galaxy – plus several others inside the innermost one discovered with the help of the

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versa ...

; a feature that suggests NGC 7217's central regions have suffered several starbursts. There is also a very large and massive

spheroid A spheroid, also known as an ellipsoid of revolution or rotational ellipsoid, is a quadric surface obtained by rotating an ellipse about one of its principal axes; in other words, an ellipsoid with two equal semi-diameters. A spheroid has cir ...

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 population During 1944, Walter Baade categorized groups of stars within the Milky Way into stellar populations. In the abstract of the article by Baade, he recognizes that Jan Oort originally conceived this type of classification in 1926: Baade noticed t ...

s: one of intermediate age on its innermost regions and a younger,

metal-poor In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal physical matter in the Universe is either hydrogen or helium, and astronomers use the word ''"metals"'' as a ...

version 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 A lenticular galaxy (denoted S0) is a type of galaxy intermediate between an elliptical (denoted E) and a spiral galaxy in galaxy morphological classification schemes. It contains a large-scale disc but does not have large-scale spiral arms. L ...

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. More recent research, however, 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. N7217s

References

External links

NGC 7217

* Unbarred spiral galaxies Ring galaxies Pegasus (constellation) 7217 11914 68096 {{Spiral-galaxy-stub

Features

See also

References

External links