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Whale Galaxy

Herring Galaxy, C32, NGC 4631

This spiral galaxy lies in the constellation of Canes Venatici, near the southern border of that constellation with neighbouring Coma Berenices. Though a barred spiral in structure, seen from the Milky Way it is oriented almost edge-on, so that it appears as an elongated ellipse as seen through a telescope. Its asymmetrical tapering shape gives it a distinctively whale-like or fish-like appearance, an appearance helped by a dense cloud of stars that form an apparent 'fin' extending outwards from the galaxy itself. Its common name of the 'Whale Galaxy' is therefore entirely suitable, and it is also occasionally known as the Herring Galaxy for similar reasons.

The galaxy has a brilliant nucleus, much of whose light is shrouded by intervening spiral arms speckled with a complex tracery of dark patterns formed by interconnecting dustlanes. It contains busy starburst regions in which stars are being born, including short-lived massive stars that erupt into an unusually high number of supernovae within the galaxy. These supernovae produce a galactic superwind, a stream of hot gases extending outward from the galaxy itself.

It is common for large galaxies like this to have smaller satellite galaxies, and the Whale Galaxy has one prominent dwarf spheroidal galaxy in this role, designated NGC 4627. By comparison to the main galaxy, this satellite is far larger than most examples, and the Whale and its attendant are often jointly called the 'Whale and Pup'. The large Whale Galaxy also exerts its gravitational influence over several other surrounding galaxies, notably an interacting pair known collectively as the Hockey Stick (NGC 4656 and 4657). These galaxies and several others form a small galaxy group, the NGC 4631 Group ('NGC 4631' being the NGC designation of the Whale Galaxy at the group's heart.

There are in fact two Whale Galaxies in the sky, of which this one in Canes Venatici is the more prominent, and also the most evidently whale-like in shape. The other is C72 (or NGC 55) in the southern constellation of Sculptor, which is also a barred spiral galaxy seen edge-on from Earth.


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