NGC 7331 explained

NGC 7331
Epoch:	J2000
Type:	SA(s)b
Dist Ly:	12.2± ^[1]
Z:	816 ± 1 km/s
Appmag V:	10.4
Size V:	10.5 × 3.7
Size:	120,000 ly (diameter)
Constellation Name:	Pegasus
Names:	UGC 12113, PGC 69327, Caldwell 30

NGC 7331, also known as Caldwell 30, is an unbarred spiral galaxy about 40e6ly away in the constellation Pegasus. It was discovered by William Herschel in 1784.^[2] NGC 7331 is the brightest galaxy in the field of a visual grouping known as the NGC 7331 Group of galaxies. In fact, the other members of the group, NGC 7335, 7336, 7337 and 7340, lie far in the background at distances of approximately 300–350 million light years.^[3]

The galaxy appears similar in size and structure to the Milky Way, and is sometimes referred to as "the Milky Way's twin".^[4] 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.^[5] In spiral galaxies the central bulge typically co-rotates with the disk but the bulge in the galaxy NGC 7331 is rotating in the opposite direction to the rest of the disk.^[6] 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.

Multiple supernova events have been observed in this galaxy. SN 1959D, a Type IIL supernova,^[7] was the first supernova identified within NGC 7331.^[8] The supernova was discovered by Milton Humason and H. S. Gates in a survey at Palomar Observatory.^[9] More recent supernovae are SN 2013bu (type II, mag. 16.6)^[10] and SN 2014C, the latter of which underwent an unusual "metamorphosis" from a hydrogen-poor Type Ib to a hydrogen-rich Type IIn over the course of a year .^[11] A 1903 photographic plate from Yerkes Observatory shows a magnitude 16.6 candidate transient that may have also been a supernova.^[12]

See also

• M94 – another galaxy with a prominent starburst ring
• NGC 1512 – another galaxy with a prominent starburst ring
• Flocculent spiral galaxy

External links

• • Calar Alto Observatory – NGC 7331
• APOD (2004-07-01) – "A Galaxy So Inclined"
• SST – "Morphology of Our Galaxy's 'Twin'"
• NGC 7331 at the astro-photography site of Mr. T. Yoshida
• NGC7331 at W. Kloehr Astrophotography
  • SEDS – NGC 7331

Notes and References

1. Jensen, Joseph B. . 4 . Tonry, John L. . Barris, Brian J. . Thompson, Rodger I. . Liu, Michael C. . Rieke, Marcia J. . Ajhar, Edward A. . Blakeslee, John P. . Measuring Distances and Probing the Unresolved Stellar Populations of Galaxies Using Infrared Surface Brightness Fluctuations . Astrophysical Journal . February 2003 . 583 . 2 . 712–726 . 2003ApJ...583..712J . 10.1086/345430 . astro-ph/0210129 . 551714 .
2. http://www.ngcicproject.org/erdmann/NGC_Discoverers_01.txt The NGC/IC Project
3. Web site: Spiral Galaxy NGC 7331, Galaxy Group (NGC 7335, 7336, 7337).
4. Web site: Seeing Double: Spitzer Captures Our Galaxy's Twin . 2008-04-24 . 2004-06-28 . Spitzer Space Telescope Newsroom . . dead . https://web.archive.org/web/20070517181042/http://www.spitzer.caltech.edu/Media/releases/ssc2004-12/release.shtml . May 17, 2007 .
5. Web site: The Milky Way Has Only Two Spiral Arms . 2008-06-04 . 2008-06-03.
6. https://arxiv.org/abs/astro-ph/9602142 A Counter-rotating Bulge in the Sb Galaxy NGC 7331
7. Web site: NASA/IPAC Extragalactic Database . Results for SN 1959D . 2006-11-10.
8. Web site: NASA/IPAC Extragalactic Database . Results for NGC 7331 . 2006-11-10.
9. M. L. Humason . H. S. Gates . The 1959 Palomar Supernova Search . Publications of the Astronomical Society of the Pacific . 1960 . 72 . 426 . 208–209 . 1960PASP...72..208H . 10.1086/127513. free .
10. https://www.wis-tns.org/object/2013bu Transient Name Server entry for SN 2013bu.
11. Metamorphosis of SN 2014C: Delayed Interaction Between a Hydrogen Poor Core-collapse Supernova and a Nearby Circumstellar Shell . The Astrophysical Journal . 815 . 2 . 120 . D. Milisavljevic. etal. 2015 . 1511.01907. 2015ApJ...815..120M . 10.1088/0004-637X/815/2/120 . 31773513 .
12. Cerny . Chapman . Glusman . Kron . Liang . etal . Precise Photometric Measurements from a 1903 Photographic Plate Using a Commercial Scanner . . 2021 . 133 . 1022 . 044501 . 10.1088/1538-3873/abec20 . 2101.03699. 2021PASP..133d4501C . 231573185 .