Messier 77

Messier 77 (M77), also known as NGC 1068 or the Squid Galaxy, is a barred spiral galaxy in the constellation Cetus. It is about 47 million light-years (14 Mpc) away from Earth, and was discovered by Pierre Méchain in 1780, who originally described it as a nebula. Méchain then communicated his discovery to Charles Messier, who subsequently listed the object in his catalog.^[8] Both Messier and William Herschel described this galaxy as a star cluster.^[8] Today, however, the object is known to be a galaxy. It is one of the brightest Seyfert galaxies visible from Earth and has a D₂₅ isophotal diameter of about 27.70 kiloparsecs (90,000 light-years).^[2]

Messier 77
M77 imaged by the Hubble Space Telescope
Observation data (J2000 epoch)
Constellation	Cetus
Right ascension	02h 42m 40.771s[1]
Declination	−00° 00′ 47.84″[1]
Redshift	0.003793[2]
Heliocentric radial velocity	1,137±3 km/s[2]
Distance	47 Mly (14.4 Mpc)[3]
Apparent magnitude (V)	8.9[4]
Characteristics
Type	(R)SA(rs)b[5]
Mass	~1×1012[6] M☉
Size	27.70 kiloparsecs (90,000 light-years)[2] (diameter; D25 isophote)
Apparent size (V)	7.1′ × 6.0′[2]
Notable features	One of the biggest galaxies of Messier's catalog. Inclination estimated to be 40°.[3]
Other designations
Cetus A,, 3C 71, 4C -00.13, IRAS 02401-0013, NGC 1068, Arp 37, UGC 2188, MCG +00-07-083, PGC 10266, CGCG 388-098[7]

Morphology

The morphological classification of NGC 1068 in the De Vaucouleurs system is (R)SA(rs)b,^[5] where the '(R)' indicates an outer ring-like structure, 'SA' denotes a non-barred spiral, '(rs)' means a transitional inner ring/spiral structure, and 'b' says the spiral arms are moderately wound.^[9] Ann et al. (2015) gave it a class of SAa,^[10] suggesting tightly wound arms. However, infrared images of the inner part of the galaxy reveal a prominent bar not seen in visual light,^[11] and for this reason it is now considered a barred spiral.^[12] Messier 77 is the largest member of a small group of galaxies,^[13] which includes NGC 1055, an edge-on spiral galaxy likely twisted by gravitational interactions with Messier 77, and five small irregular galaxies.^[14]

Messier 77 is an active galaxy with an active galactic nucleus (AGN), which is obscured from view by astronomical dust at visible wavelengths. The diameter of the molecular disk and hot plasma associated with the obscuring material was first measured at radio wavelengths by the VLBA and VLA. The hot dust around the nucleus was subsequently measured in the mid-infrared by the MIDI instrument at the VLTI. It is the brightest^[15] and one of the closest and best-studied^[12] type 2 Seyfert galaxies,^[3] forming a prototype of this class.^[12]

Research

Messier 77 is of key interest to scientists due to its relative proximity and luminosity, allowing for study of its active galactic nucleus.^[16] This section contains relevant scientific discoveries that have been made as a result of studying M77.

It has been proposed that type 2 Seyfert galaxies are the same class of object as type 1 Seyfert galaxies, viewed from such an angle that the type 1 core is hidden from view.^[17] An analysis of NGC 1068's spectra using interferometry by Tacconi et al. (1994) suggested that the galaxy's Seyfert 1 core was obstructed by a thick molecular cloud region.^[18]

X-ray source 1H 0244+001 in Cetus has been identified as Messier 77.^[19]

It has a radio jet consisting of a northeast and a southwest region, caused by interactions with the interstellar medium.^[20]The presence of bow shocks in the northeast region due to these interactions overlap with the edges of molecular outflow, suggesting that the jet is responsible for the outflow.^[21]

In February 2022 astronomers reported a cloud of cosmic dust, detected through infrared interferometry observations, located at the centre of Messier 77 that is hiding a supermassive black hole.^[22][23]

In November 2022, the IceCube collaboration announced the detection of a neutrino source emitted by the active galactic nucleus of Messier 77.^[24][25] It is the second detection by IceCube after TXS 0506+056, and only the fourth known source including SN1987A and solar neutrinos. A potential candidate for the source of these neutrinos is the magnetic corona surrounding the active galactic nucleus, providing powerful enough particle acceleration to cause neutron radiation phenomena.^[26] To explain the combination of Messier 77 being an energetic neutrinos source and a weak gamma rays source, a mechanism was suggested whereby helium nuclei collide with ultraviolet photons emitted by the galaxy's central region and break up, releasing neutrons that eventually decay into neutrinos without producing gamma rays.^[27]

Supernova

One supernova has been detected in Messier 77. SN 2018ivc (type II, mag. 14.6523) was discovered by the DLT40 Survey on 24 November 2018.^[28][29]

Gallery

• 
  M77 imaged by the Hubble Space Telescope
• 
  M77 imaged by ESO’s Very Large Telescope (VLT)^[30]
• 
  M77 with SN 2018ivc, November 2018

See also

• List of Messier objects
• NGC 1106 Another galaxy with an active galactic nucleus.