NGC 6946

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NGC 6946
An image of NGC 6946, the fireworks galaxy
Observation data (J2000 epoch)
ConstellationCepheus and Cygnus
Right ascension20h 34m 52.3s[1]
Declination+60° 09′ 14″[1]
Redshift0.000133[1]
Heliocentric radial velocity48 ± 2 km/s[1]
Distance25.2 ± 1.0 Mly
7.72± 0.32 Mpc)[2]
Apparent magnitude (V)+9.6[1]
Characteristics
TypeSAB(rs)cd[1]
Size26.77 kpc (87,300 ly)
(diameter; 25.0 mag/arcsec2 B-band isophote)[1][3]
Apparent size (V)16.0 x 11.2 arcmin[4]
Other designations
UGC 11597, PGC 65001, Arp 29,[1] Caldwell 12

NGC 6946, sometimes referred to as the Fireworks Galaxy, is a grand design, face-on intermediate spiral galaxy with a small bright nucleus, whose location in the sky straddles the boundary between the northern constellations of Cepheus and Cygnus. Its distance from Earth is about 25.2 million light-years or 7.72 megaparsecs,[2] similar to the distance of M101 (NGC 5457) in the constellation Ursa Major.[5] Both were once considered to be part of the Local Group,[6] but are now known to be among the dozen bright spiral galaxies near the Milky Way but beyond the confines of the Local Group.[7] NGC 6946 lies within the Virgo Supercluster.[8]

The galaxy was discovered by William Herschel on 9 September 1798. Based on an estimation by the Third Reference Catalogue of Bright Galaxies (RC3) in 1991, the galaxy has a D25 B-band isophotal diameter of 26.77 kiloparsecs (87,300 light-years).[1][3] It is heavily obscured by interstellar matter due to its location close to the galactic plane of the Milky Way.[9] Due to its prodigious star formation it has been classified as an active starburst galaxy.[7] NGC 6946 has also been classified as a double-barred spiral galaxy, with the inner, smaller bar presumably responsible for funneling gas into its center.[10][11]

Various unusual celestial objects have been observed within NGC 6946. This includes the so-called 'Red Ellipse' along one of the northern arms that looks like a super-bubble or very large supernova remnant, and which may have been formed by an open cluster containing massive stars. There are also two regions of unusual dark lanes of nebulosity, while within the spiral arms several regions appear devoid of stars and gaseous hydrogen, some spanning up to two kiloparsecs across.[7][dubious – discuss] A third peculiar object, discovered in 1967, is now known as "Hodge's Complex".[12] This was once thought to be a young supergiant cluster, but in 2017 it was conjectured to be an interacting dwarf galaxy superimposed on NGC 6946.[7]

Supernovae

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Ten supernovae have been observed in NGC 6946 since 1917. For this reason, NGC 6946 has sometimes been referred to as the "Fireworks Galaxy".[13][14] This is about ten times the rate observed in our Milky Way galaxy,[15] even though the Milky Way has twice as many stars as NGC 6946.

During 2009, a bright star within NGC 6946 flared up over several months to become over one million times as bright as the Sun. Shortly thereafter it faded rapidly. Observations with the Hubble Space Telescope suggest that the star did not survive, although there remains some infrared emission from its position. This is thought to come from debris falling onto a black hole that formed when the star died. This potential black hole-forming star is designated N6946-BH1.[40] The progenitor is believed to have been a yellow hypergiant star.[41]

As of 2017, more supernovae had been seen in NGC 6946 than in any other galaxy,[34] a record that has since been surpassed by NGC 3690.[42]

Supernovae in NGC 6946
Designation Discovery magnitude Type
1917A 14 II
1939C 14.4 ?
1948B 14.9 II
1968D 13.5 II
1969P 13.9 ?
1980K 13 II-L
2002hh 16.5 II
2004et 12.8 II
2008S 17.6 IIn-pec/LBV
2017eaw 12.8 II-P
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See also

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References

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  1. ^ a b c d e f g h i "NASA/IPAC Extragalactic Database". Results for NGC 6946. Retrieved 29 October 2022.
  2. ^ a b Eldridge, J J; Xiao, Lin (2 March 2019). "The distance, supernova rate, and supernova progenitors of NGC 6946". Monthly Notices of the Royal Astronomical Society: Letters. 485 (1): L58 – L61. arXiv:1903.00173. Bibcode:2019MNRAS.485L..58E. doi:10.1093/mnrasl/slz030. S2CID 118831398.
  3. ^ a b De Vaucouleurs, Gerard; De Vaucouleurs, Antoinette; Corwin, Herold G.; Buta, Ronald J.; Paturel, Georges; Fouque, Pascal (1991). Third Reference Catalogue of Bright Galaxies. Bibcode:1991rc3..book.....D.
  4. ^ Jarrett, T. H.; Chester, T.; Cutri, R.; Schneider, S. E.; Huchra, J. P. (2003). "The 2MASS Large Galaxy Atlas". The Astronomical Journal. 125 (2): 525–554. Bibcode:2003AJ....125..525J. doi:10.1086/345794. S2CID 117784410.
  5. ^ Sandage, A.; Bedke, J. (1994). The Carnegie Atlas of Galaxies. Volume I. Carnegie Institution of Washington. Bibcode:1994cag..book.....S.
  6. ^ "NGC 6946". SEDS. Retrieved 20 November 2017.
  7. ^ a b c d Efremov, Yu. N. (2016). "Unusual Objects in the Spiral Galaxy NGC 6946". Open Astronomy. 25 (4): 365–376. Bibcode:2016BaltA..25..369E. doi:10.1515/astro-2017-0255.
  8. ^ "Nearby Groups of Galaxies". ned.ipac.caltech.edu. Retrieved 3 May 2018.
  9. ^ "NED data for some important Non-Messier Galaxies".
  10. ^ Schinnerer, Eva; et, al (2006). "Molecular Gas Dynamics in NGC 6946: A Bar-driven Nuclear Starburst Caught in the Act". The Astrophysical Journal. 649 (1): 181–200. arXiv:astro-ph/0605702. Bibcode:2006ApJ...649..181S. doi:10.1086/506265. S2CID 14717998.
  11. ^ Eibensteiner, Cosima; et, al (2022). "A 2-3 mm high-resolution molecular line survey towards the centre of the nearby spiral galaxy NGC 6946". Astronomy & Astrophysics. 659 (A173): 37. arXiv:2201.02209. Bibcode:2022A&A...659A.173E. doi:10.1051/0004-6361/202142624.
  12. ^ Hodge, P.W. (1967). "A Possible "Super-Supernova" Remnant in NGC 6946". Open Astronomy. 79 (466): 466–470. Bibcode:1967PASP...79...29H. doi:10.1515/astro-2017-0255.
  13. ^ Michaud, Peter (1 January 2015). "Gemini Observatory Welcomes 2005 with Release of Galactic Fireworks Image". NASA. Retrieved 15 October 2017.
  14. ^ Boen, Brooke (20 May 2015). "NGC 6946: The 'Fireworks Galaxy'". NASA. Retrieved 8 December 2016.
  15. ^ "Gemini Observatory Welcomes 2005 with Release of Galactic Fireworks Image", Gemini Observatory, 1 January 2005, retrieved 4 January 2016
  16. ^ Ritchie, G. W. (1917). "Ritchie's Nova H. IV. 76 Cephei in N.G.C. 6946". Harvard College Observatory Bulletin. 641: 1. Bibcode:1917BHarO.641....1R.
  17. ^ "SN 1917A". Transient Name Server. IAU. Retrieved 16 August 2025.
  18. ^ Zwicky, Fritz (2 September 1939). "Supernovae". Central Bureau for Astronomical Telegrams. 793. Observatory Copenhagen, IAU: 1. Retrieved 16 August 2025.
  19. ^ "SN 1939C". Transient Name Server. IAU. Retrieved 16 August 2025.
  20. ^ Mayall, N. U. (1948). "A Supernova in the Spiral Nebula NGC 6946". Publications of the Astronomical Society of the Pacific. 60 (355): 266. Bibcode:1948PASP...60..266M. doi:10.1086/126065.
  21. ^ "SN 1948B". Transient Name Server. IAU. Retrieved 16 August 2025.
  22. ^ a b Wild, P.; Dunlap, J. R. (4 March 1968). "Supernova in NGC 6946". Central Bureau for Astronomical Telegrams. 2057. Smithsonian Astrophysical Observatory, IAU: 1. Retrieved 16 August 2025.
  23. ^ "SN 1968D". Transient Name Server. IAU. Retrieved 16 August 2025.
  24. ^ Rosino, L. (3 February 1971). "New Supernova (1969) in NGC 6946?". Central Bureau for Astronomical Telegrams. 2305. Smithsonian Astrophysical Observatory, IAU: 1. Bibcode:1971IAUC.2305....1R. Retrieved 16 August 2025.
  25. ^ "SN 1969P". Transient Name Server. IAU. Retrieved 16 August 2025.
  26. ^ Wild, P.; Barbon, R. (1980). "Supernova in NGC 6946". International Astronomical Union Circular (3532): 1. Bibcode:1980IAUC.3532....1W.
  27. ^ "SN 1980K". Transient Name Server. IAU. Retrieved 16 August 2025.
  28. ^ Li, W. (2002). "Supernova 2002hh in NGC 6946". International Astronomical Union Circular (8005): 1. Bibcode:2002IAUC.8005....1L.
  29. ^ "SN 2002hh". Transient Name Server. IAU. Retrieved 16 August 2025.
  30. ^ Zwitter, T.; Munari, U.; Moretti, S. (2004). "Supernova 2004et in NGC 6946". International Astronomical Union Circular (8413): 1. Bibcode:2004IAUC.8413....1Z.
  31. ^ Li, W.; Van Dyk, S.D.; Filippenko, A.V; Cuillandre, J.C. (2005). "On the Progenitor of the Type II Supernova 2004et in NGC 6946". Publications of the Astronomical Society of the Pacific. 117 (828): 121–131. arXiv:astro-ph/0412487. Bibcode:2005PASP..117..121L. doi:10.1086/428278. S2CID 17585230.
  32. ^ Arbour, R.; Boles, T. (2008). "Supernova 2008S in NGC 6946". Central Bureau Electronic Telegrams (1234): 1. Bibcode:2008CBET.1234....1A.
  33. ^ "SN 2008S". Transient Name Server. IAU. Retrieved 16 August 2025.
  34. ^ a b Bishop, David (14 May 2017). "Supernova 2017eaw in NGC 6946". Retrieved 29 September 2023. This is our most prolific galaxy with now 10 confirmed supernovae discovered.
  35. ^ Dong, Subo; Stanek, K. Z. (2017). "Confirmation of AT 2017eaw, a Probable Supernova in NGC 6946". The Astronomer's Telegram. 10372: 1. Bibcode:2017ATel10372....1D.
  36. ^ Xiang, Danfeng; Rui, Liming; Wang, Xiaofeng; Fu, Jianning; Xiao, Feng; Zhang, Tianmeng; Zhang, Jujia (2017). "Spectroscopic Classification of SN 2017eaw in NGC 6946 as a Young Type IIP Supernova". The Astronomer's Telegram. 10376: 1. Bibcode:2017ATel10376....1X.
  37. ^ Buta, Ronald J; Keel, William C (21 July 2019). "BVRI photometry of the classic Type II-P supernova 2017eaw in NGC 6946: d 3 to d 594". Monthly Notices of the Royal Astronomical Society. 487 (1): 832–844. arXiv:1905.03084. Bibcode:2019MNRAS.487..832B. doi:10.1093/mnras/stz1291. ISSN 0035-8711. S2CID 147703978.
  38. ^ Szalai, Tamás; Vinkó, József; Könyves-Tóth, Réka; Nagy, Andrea P.; Bostroem, K. Azalee; Sárneczky, Krisztián; Brown, Peter J.; Pejcha, Ondrej; Bódi, Attila; Cseh, Borbála; Csörnyei, Géza (29 April 2019). "The Type II-P Supernova 2017eaw: From Explosion to the Nebular Phase". The Astrophysical Journal. 876 (1): 19. arXiv:1903.09048. Bibcode:2019ApJ...876...19S. doi:10.3847/1538-4357/ab12d0. ISSN 1538-4357. S2CID 84842034.
  39. ^ Kilpatrick, Charles; Foley, Ryan (5 September 2018). "The Dusty Progenitor Star of the Type II Supernova 2017eaw". Monthly Notices of the Royal Astronomical Society. 481 (2): 2536–2547. arXiv:1806.00348. doi:10.1093/mnras/sty2435.
  40. ^ Adams, S. M.; Kochanek, C. S.; Gerke, J. R.; Stanek, K. Z.; Dai, X. (2017). "The search for failed supernovae with the Large Binocular Telescope: conformation of a disappearing star". Monthly Notices of the Royal Astronomical Society. 468 (4): 4968–4981. arXiv:1609.01283v1. Bibcode:2017MNRAS.468.4968A. doi:10.1093/mnras/stx816. S2CID 12919545.
  41. ^ Humphreys, Roberta M. (31 October 2019). "Comments on the Progenitor of NGC 6946-BH1". Research Notes of the AAS. 3 (10): 164. arXiv:1911.02037. Bibcode:2019RNAAS...3..164H. doi:10.3847/2515-5172/ab5191. ISSN 2515-5172. S2CID 207880492.
  42. ^ Bishop, David (27 August 2023). "The most prolific galaxies". Retrieved 29 September 2023.
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