NGC 4656 und NGC 4631

The Wal galaxy NGC 4631 is about the size of the Milky Way and was discovered by William Herschel on March 20, 1787. NGC 4627 is a companion galaxy to the Wal galaxy (NGC 4631) and lies about 2.6' northwest of its center; the two galaxies are listed together in the Arp catalog as Arp 281. The small neighboring galaxy NGC 4627 causes some deformation of the Wal galaxy. In addition, it seems to have come close to the neighboring galaxy NGC 4656/57 more often in the past, as evidenced by hydrogen and other gas remnants found between the two galaxies today.

Of particular interest is the halo of hot gas that surrounds the galaxy and extends to a distance of 25,000 light-years from the galactic plane. High-resolution images of the halo's X-ray emission have been obtained from the Chandra research satellite. It is believed that the Milky Way is also surrounded by a similar halo.

The appearance of the galaxy NGC 4656 is reminiscent of the Small Magellanic Cloud. Because of its characteristic shape, the galaxy is sometimes jokingly called a field hockey stick. The galaxy was apparently in the past in strong interaction with the large neighboring galaxy NGC 4631 a little further to the southeast. One effect of this may be a bright, somewhat detached appearing knot at the northeastern end of the galaxy. This bright knot was cataloged as a separate object when the galaxy was discovered by Wilhelm Herschel on March 20, 1787, which led to it also being listed later in the New General Catalogue under a separate entry as NGC 4657.