Messier 82 (also known as NGC 3034, Cigar Galaxy or M82) is a starburst galaxy approximately 12 million light-years away in the constellation Ursa Major. A member of the M81 Group, it is about five times more luminous than the whole Milky Way and has a center one hundred times more luminous than our galaxy's center. The starburst activity is thought to have been triggered by interaction with neighboring galaxy M81. As the closest starburst galaxy to Earth, M82 is the prototypical example of this galaxy type. SN 2014J, a type Ia supernova, was discovered in the galaxy on 21 January 2014. In 2014, in studying M82, scientists discovered the brightest pulsar yet known, designated M82 X-2.
A mosaic image taken by the Hubble Telescope of Messier 82, combining exposures taken with four colored filters that capture starlight from visible and infrared wavelengths as well as the light from the glowing hydrogen filaments.
|Observation data (J2000 epoch)|
|Right ascension||09h 55m 52.2s|
|Declination||+69° 40′ 47″|
|Distance||11.4-12.4 Mly (3.5-3.8 Mpc)|
|Apparent magnitude (V)||8.41|
|Size||~37,000ly in diameter|
|Apparent size (V)||11′.2 × 4′.3|
|Notable features||Edge on starburst galaxy|
|NGC 3034, UGC 5322, Arp 337, Cigar Galaxy, PGC 28655, 3C 231|
M82 was first discovered by Johann Elert Bode on December 31, 1774 together with M81; he described it as a "nebulous patch", about 0.75 deg away from M81, "very pale and of elongated shape". In 1779, Pierre Méchain independently rediscovered both galaxies and reported them to Charles Messier, who added them to his catalog. 
M82 was previously believed to be an irregular galaxy. In 2005, however, two symmetric spiral arms were discovered in near-infrared (NIR) images of M82. The arms were detected by subtracting an axisymmetric exponential disk from the NIR images. Even though the arms were detected in NIR images, they are bluer than the disk. The arms were previously missed due to M82's high disk surface brightness, the nearly edge-on view of this galaxy (~80°), and obscuration by a complex network of dusty filaments in its optical images. These arms emanate from the ends of the NIR bar and can be followed for the length of 3 disc scales. Assuming that the northern part of M82 is nearer to us, as most of the literature does, the observed sense of rotation implies trailing arms.
In 2005, the Hubble Space Telescope revealed 197 young massive clusters in the starburst core. The average mass of these clusters is around 200,000 solar masses, hence the starburst core is a very energetic and high-density environment. Throughout the galaxy's center, young stars are being born 10 times faster than they are inside the entire Milky Way Galaxy.
In the core of M82, the active starburst region spans a diameter of 500 pc. Four high surface brightness regions or clumps (designated A, C, D, and E) are detectable in this region at visible wavelengths. These clumps correspond to known sources at X-ray, infrared, and radio frequencies. Consequently, they are thought to be the least obscured starburst clusters from our vantage point. M82's unique bipolar outflow (or 'superwind') appears to be concentrated on clumps A and C and is fueled by energy released by supernovae within the clumps which occur at a rate of about one every ten years.
The Chandra X-ray Observatory detected fluctuating X-ray emissions from a location approximately 600 light-years away from the center of M82. Astronomers have postulated that this fluctuating emission comes from the first known intermediate-mass black hole, of roughly 200 to 5000 solar masses. M82, like most galaxies, hosts a supermassive black hole at its center with a mass of approximately 3 x 107 solar masses as measured from stellar dynamics.
In April 2010, radio astronomers working at the Jodrell Bank Observatory of the University of Manchester in the UK reported an object in M82 that had started sending out radio waves, and whose emission did not look like anything seen anywhere in the universe before.
There have been several theories about the nature of this object, but currently no theory entirely fits the observed data. It has been suggested that the object could be an unusual "micro quasar", having very high radio luminosity yet low X-ray luminosity, and being fairly stable, it could be an analogue of the low X-ray luminosity galactic microquasar SS 433. However, all known microquasars produce large quantities of X-rays, whereas the object's X-ray flux is below the measurement threshold. The object is located at several arcseconds from the center of M82 which makes it unlikely to be associated with a supermassive black hole. It has an apparent superluminal motion of four times the speed of light relative to the galaxy center. Apparent superluminal motion is consistent with relativistic jets in massive black holes and does not indicate that the source itself is moving above lightspeed.
M82 is being physically affected by its larger neighbor, the spiral M81. Tidal forces caused by gravity have deformed M82, a process that started about 100 million years ago. This interaction has caused star formation to increase tenfold compared to "normal" galaxies.
M82 has undergone at least one tidal encounter with M81 resulting in a large amount of gas being funneled into the galaxy's core over the last 200 Myr. The most recent such encounter is thought to have happened around 2–5×108 years ago and resulted in a concentrated starburst together with a corresponding marked peak in the cluster age distribution. This starburst ran for up to ~50 Myr at a rate of ~10 M⊙ per year. Two subsequent starbursts followed, the last (~4–6 Myr ago) of which may have formed the core clusters, both super star clusters (SSCs) and their lighter counterparts.
Stars in M82's disk seem to have been formed in a burst 500 million years ago, leaving its disk littered with hundreds of clusters with properties similar to globular clusters (but younger), and stopped 100 million years ago with no star formation taking place in this galaxy outside the central starburst and, at low levels since 1 billion years ago, on its halo. A suggestion to explain those features is that M82 was previously a low surface brightness galaxy where star formation was triggered due to interactions with its giant neighbor.
Ignoring any difference in their respective distances from the Earth, the centers of M81 and M82 are visually separated by about 130,000 light-years. The actual separation is +300
−200 kly. 300
On 21 January 2014 at 19.20 UT, a previously unseen star was observed in M82 at magnitude +11.7 by Dr. Steve J. Fossey, along with a team of 4 of his students, at University College London's training observatory, the University of London Observatory. It had brightened to magnitude +10.9 by 23 January. Examination of earlier observations of M82 found the supernova to be present on 15, 16, 17, 19, 20 and 22 January, brightening from magnitude +14.4 to +11.3; there was no sign of it, to limiting magnitude +17, on 14 January. It was initially suggested that it could become as bright as magnitude +8.5, well within the visual range of small telescopes and large binoculars, but it actually peaked at a rather fainter +10.5 on 31 January 2014. Preliminary analysis classified it as "a young, reddened type Ia supernova". The International Astronomical Union (IAU) has designated it SN 2014J. SN 2014J is one of the closest supernovae to Earth observed in recent decades. SN 1993J was at a very similar distance, in M82's larger companion galaxy M81, and SN 1987A in the Large Magellanic Cloud was much closer. 2014J is the closest type Ia supernova since SN 1972E. 
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- http://astropixels.com/galaxies/M82-01.html (dec 2014)
- Barker, S.; de Grijs, R.; Cerviño, M. (2008). "Star cluster versus field star formation in the nucleus of the prototype starburst galaxy M 82". Astronomy and Astrophysics. 484 (3): 711–720. arXiv: . Bibcode:2008A&A...484..711B. doi:10.1051/0004-6361:200809653.
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- Gaffney, N. I.; Lester, D. F. & Telesco, C. M. (1993). "The stellar velocity dispersion in the nucleus of M82". Astrophysical Journal Letters. 407: L57–L60. Bibcode:1993ApJ...407L..57G. doi:10.1086/186805.
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- Tana Joseph, Thomas Maccarone, Robert Fender: The unusual radio transient in M82: an SS 433 analogue?, 2011-07-25
- O'Brien, Tim. "Mystery object in Starburst Galaxy M82 - Jodrell Bank Centre for Astrophysics". www.jb.man.ac.uk. Retrieved 14 April 2018.
- Divakara Mayya, Y.; Carrasco, Luis (2009). "M82 as a Galaxy: Morphology and Stellar Content of the Disk and Halo". Revista Mexicana de Astronomía y Astrofísica (Serie de conferencias). 37: 44–55. arXiv: . Bibcode:2009arXiv0906.0757D.
- Declination separation of 36′.87 and Right Ascension separation of 9′.5 gives via Pythagorean theorem a visual separation of 38′.07; Average distance of 11.65 Mly × sin(38′.07) = 130,000 ly visual separation.
- Separation = sqrt(DM812 + DM822 – 2 DM81 DM82 Cos(38′.07)) assuming the error direction is about the same for both objects.
- "Hubble views new supernova in Messier 82". ESA / HUBBLE. Retrieved 12 March 2014.
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- "Supernova in M82 Passes Its Peak - Sky & Telescope". 17 February 2014. Retrieved 14 April 2018.
- "Supernova in Messier 82 discovered by UCL students". www.ucl.ac.uk. Retrieved 14 April 2018.
|Wikimedia Commons has media related to Messier 82.|
- M82, SEDS Messier pages
- M82 at Chandra
- SST: Galaxy on Fire!
- M82 at NASA/IPAC EXTRAGALACTIC DATABASE
- ESA/Hubble images of M82
- Messier 82 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images
- M82 The Cigar Galaxy
- M82 images with 2 semiprofessional amateur-telescopes as a result of collaboration between 2 observatories!
- M82 at Deep Space Map