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The subject of this week\u2019s circular Hubble\u00a0Picture of the Week\u00a0is situated in the Perseus Cluster, also known as Abell 426, 320 million light-years from Earth. It\u2019s a barred spiral galaxy known as MCG+07-07-072, seen here among a number of photobombing\u00a0stars\u00a0that are much closer to Earth than it is.<\/p>\n
MCG+07-07-072 has quite an unusual shape, for a spiral galaxy, with thin arms emerging from the ends of its barred core to draw a near-circle around its disc. It is classified, using a common extension of the basic Hubble scheme, as an SBc(r) galaxy: the c denotes that its two spiral arms are loosely wound, each only performing a half-turn around the galaxy, and the (r) is for the ring-like structure they create. Rings in\u00a0galaxies\u00a0come in quite a few forms, from merely uncommon, to rare and astrophysically important!<\/p>\n
Lenticular galaxies are a type that sit between\u00a0elliptical\u00a0and\u00a0spiral\u00a0galaxies. They feature a large disc, unlike an elliptical galaxy, but lack any spiral arms. Lenticular means lens-shaped, and these galaxies often\u00a0feature ring-like shapes\u00a0in their discs. Meanwhile, the classification of \u201cring galaxy\u201d is reserved for peculiar galaxies with a round ring of gas and star formation, much like spiral arms look, but\u00a0completely disconnected from the galactic nucleus\u00a0– or even\u00a0without any visible nucleus! They\u2019re thought to be formed in galactic collisions. Finally, there are the famous\u00a0gravitational lenses, where the ring is in fact a distorted image of a distant, background galaxy, formed by the \u2018lens\u2019 galaxy bending light around it.\u00a0Ring-shaped images, called Einstein rings, only form when the lensing and imaged galaxies are perfectly aligned.<\/p>\n
[Image Description:<\/i>\u00a0A galaxy. It is almost circular. It has a glowing bar stretching across its core; from the ends of the bar, thin spiral arms wrap around the galaxy to form a closed disc. The arms are fuzzy from the dust and stars they contain. The galaxy is on a black, mostly-empty background. A few foreground stars with cross-shaped diffraction spikes can be seen, as well as some distant galaxies in the background.]<\/p>\n<\/p><\/div>\n<\/p><\/div>\n