The galaxy appears similar almost in size and structure to theMilky Way, and is sometimes referred to as "the Milky Way's twin".[5] However, discoveries in the 2000s regarding the structure of the Milky Way may call this similarity into doubt, particularly because the latter is now believed to be a barred spiral, compared to the unbarred status of NGC 7331.[6] In spiral galaxies the central bulge typically co-rotates with the disk but the bulge in the galaxy NGC 7331 is rotating in theopposite direction to the rest of the disk.[7] In both visible light and infrared photos of the NGC 7331, the core of the galaxy appears to be slightly off-center, with one side of the disk appearing to extend further away from the core than the opposite side.
NGC 7331 is the brightest galaxy in the field of a visual grouping known as theNGC 7331 Group of galaxies. In fact, the other members of the group,NGC 7335,NGC 7336,NGC 7337 andNGC 7340, lie far in the background at distances of approximately 300–350 million light years.[8]
All of the members of the NGC 7331 Group, along withNGC 7325,NGC 7326,NGC 7327,NGC 7333,NGC 7338, are listed together asHolm 795 inErik Holmberg'sA Study of Double and Multiple Galaxies Together with Inquiries into some General Metagalactic Problems, published in 1937.[9]
SN 2014C was discovered by theLick Observatory Supernova Search (LOSS) on 5 January 2014.[15][16] The supernova underwent an unusual "metamorphosis" from a hydrogen-poorType Ib to a hydrogen-richType IIn over the course of a year.[17]
SN 2025rbs (TypeIa, mag. 17.07) was discovered byGOTO on 14 July 2025.[18] It got as bright as magnitude 11.9, making it the brightest supernova of 2025.[19] By the end of August 2025, the supernova was still around magnitude 14.4.[20]
In addition to the confirmed supernovae, a 1903 photographic plate fromYerkes Observatory shows a magnitude 16.6 candidate transient that may have also been a supernova.[21]
Image of SN 2014C. The inset images are from NASA's Chandra X-ray Observatory, showing a small region of the galaxy before the supernova (left) and after it (right).
Amateur near-infrared image of SN 2025rbs (marked by red crosshairs)
^abThe quick-look major axis physical diameters given by NED were based on distance estimates of 13.427 ± 2.698 Mpc (43.79×10^6 ± 8.800×10^6 ly) using a scale of 65.1 parsec/arcsec multiplied with given angular diameters.
^Holmberg, Erik (1937). "A Study of Double and Multiple Galaxies Together with Inquiries into some General Metagalactic Problems".Annals of the Observatory of Lund.6: 1.Bibcode:1937AnLun...6....1H.
^"SN1959D".Transient Name Server.IAU. Retrieved30 November 2024.
^Itagaki, K.; Noguchi, T.; Nakano, S.; Elenin, L.; Molotov, I.; Moritani, Y. (2013-04-01). "Supernova 2013bu in NGC 7331 = PSN J22370217+3424052".Central Bureau Electronic Telegrams.3498: 1.Bibcode:2013CBET.3498....1I.
^"SN2013bu".Transient Name Server.IAU. Retrieved30 November 2024.
^Kim, M.; Zheng, W.; Li, W.; et al. (2014-01-01). "Supernova 2014C in NGC 7331 = PSN J22370560+3424319".Central Bureau Electronic Telegrams.3777: 1.Bibcode:2014CBET.3777....1K.
^"SN2014C".Transient Name Server.IAU. Retrieved30 November 2024.
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Media related toNGC 7331 at Wikimedia Commons
