NGC 6946 is a 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 22.5 million light-years or 6.8 megaparsecs, similar to
the distance of M101 (NGC 5457) in the constellation Ursa Major.
Both were once considered to be part of the Local Group. but are
now known to be among the dozen bright spiral galaxies near the Milky
Way but beyond the confines of the Local Group.
William Herschel on 9 September 1798, this well-studied
galaxy has a diameter of approximately 40,000 light-years, about
one-third of the Milky Way's size, and it contains roughly half the
number of stars as the Milky Way. The galaxy is heavily obscured by
interstellar matter as it lies quite close to the galactic plane of
the Milky Way. Due to its prodigious star formation it has been
classified as an active starburst galaxy.
Various unusual celestial objects have been observed within NGC 6964.
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. A
third peculiar object, discovered in 1967, is now known as "Hodge's
Complex". 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 6964.
RGB image of the galaxy
NGC 6946 from the Liverpool Telescope
Ten supernovae have been observed in
NGC 6946 in the last century: SN
1917A, SN 1939C, SN 1948B, SN 1968D, SN 1969P, SN 1980K, SN 2002hh, SN
2004et, SN 2008S, and SN 2017eaw. For this reason NGC
6946 in 2005 was dubbed the Fireworks Galaxy, a name becoming
NGC 6946 has an unusually high rate of
supernovae production compared to our
Milky Way galaxy, whose rate
averages just one supernova event per century. This is the more
remarkable as our
Galaxy comprises twice as many stars.
On 27 September 2004, the Type II supernova SN 2004et was observed at
magnitude 15.2 and rose to a maximum visual magnitude of 12.7. Images
taken several days earlier revealed no such star, indicating
destruction of the star occurred on the 22 September. The progenitor
of SN 2004et has been identified on earlier images –– only the
seventh time that such an event was directly identified with its host
star. The red supergiant progenitor had an initial mass of about
15M☉ in an interacting binary system shared with a blue
During 2009, a bright star within the galaxy
NGC 6946 flared up over
several months to become over one million times as bright as the Sun.
Shortly thereafter it appeared to vanish. New observations with the
Hubble Space Telescope strongly suggest that the star did not survive,
although a faint trickle of infrared light emanates from where the
star used to be. The remnant glow probably comes from debris falling
onto a black hole that formed when the star died. This potential black
hole-forming star is designated N6946-BH1.
In X-rays, observations using the
Chandra Space Telescope
Chandra Space Telescope have
revealed three of the oldest supernovae so far detected. The attached
composite image also includes optical data from the Gemini Observatory
in red, yellow, and cyan.
^ a b c d e f g h "NASA/IPAC Extragalactic Database". Results for NGC
6946. Retrieved 2006-11-18.
^ a b "Distance Results for NGC 6946". NASA/IPAC Extragalactic
Database. Retrieved 2010-06-18.
^ Sandage, A.; Bedke, J. (1994). The Carnegie Atlas of Galaxies.
Volume I. Carnegie Institution of Washington.
^ "NGC 6946". SEDS. Retrieved 2017-11-20.
^ a b c d Efremov, Yu. N. (2016). "Unusual Objects in the Spiral
Galaxy NGC 6946". 25 (4). Open Astronomy: 365–376.
Bibcode:2016BaltA..25..369E. Retrieved 20 November 2017.
^ Nemiroff, R.; Bonnell, J., eds. (1 January 2011). "NGC 6964 :
the Fireworks Galaxy". Astronomy Picture of the Day. NASA. Retrieved 2
^ Hodge, P.W. (1967). "A Possible "Super-Supernova" Remnant in NGC
6946". 79 (466). Publications of the Astronomical Society of the
Pacific: 466–470. Bibcode:1967PASP...79...29H.
^ a b 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". 117
(828). Publications of the Astronomical Society of the Pacific:
121–131. arXiv:astro-ph/0412487 . Bibcode:2005PASP..117..121L.
^ "List of Supernovae". Harvard-Smithsonian Center for Astrophysics
(IAU). Retrieved 2010-07-12.
^ Michaud, Peter (1 January 2015). "Gemini Observatory Welcomes 2005
with Release of Galactic Fireworks Image". NASA. Retrieved
^ Boen, Brooke (20 May 2015). "NGC 6946: The 'Fireworks Galaxy'".
NASA. Retrieved 2016-12-08.
^ "Gemini Observatory Welcomes 2005 with Release of Galactic Fireworks
Image", Gemini Observatory, 1 January 2005, retrieved 2016-01-04
^ 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.
Galaxy NGC 6946". Retrieved 20 November 2017.
Galaxy NGC 6946
Pictures of NGC 6946
Atlas of the Universe
N6946-BH1 Giant Star Becomes A Black Hole Right Before Our Eyes!
NGC 6946 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray,
Astrophoto, Sky Map, Articles and images
Coordinates: 20h 34m 52.3s, +60° 09′ 14″