A mosaic image taken by theHubble Space 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
M82 – December 2013; supernova – January 2014 (bottom)
Messier 82 photographed by amateur astrophotographer Radu Marinescu using a 10" Newtonian telescope, with a high emphasis on the Hydrogen-alpha star-burst areas.
In November 2023, agamma-ray burst was observed in M82, which was determined to have come from amagnetar, the first such event detected outside theMilky Way (and only the fourth such event ever detected).[14][15]
M82, withM81, was discovered byJohann Elert Bode in 1774; he described it as a "nebulous patch", this one about3⁄4 degree away from the other, "very pale and of elongated shape". In 1779,Pierre Méchain independently rediscovered both objects and reported them toCharles Messier, who added them to his catalog.[16]
M82 was believed to be anirregular galaxy. In 2005, however, two symmetricspiral arms were discovered innear-infrared (NIR) images of M82. The arms were detected by subtracting anaxisymmetric exponential disk from the NIR images. Even though the arms were detected in NIR images, they are bluer than the disk. The arms had been missed due to M82's high disksurface brightness, the nearly edge-on view of this galaxy (~80°),[7] and obscuration by a complex network of dusty filaments in its optical images. These arms emanate from the ends of the NIRbar and can be followed for the length of threedisc 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.[17]
In 2005, theHubble Space Telescope revealed 197 young massive clusters in the starburst core.[7] The average mass of these clusters is around 200,000solar masses, hence the starburst core is a very energetic and high-density environment.[7] Throughout the galaxy's center, young stars are being born 10 times faster than they are inside the entireMilky Way Galaxy.[18]
In the core of M82, the active starburst region spans a diameter of 500pc. Four high surface brightness regions or clumps (designated A, C, D, and E) are detectable in this region at visible wavelengths.[7] These clumps correspond to known sources atX-ray,infrared, andradio frequencies.[7] Consequently, they are thought to be the least obscured starburst clusters from our vantage point.[7] M82's unique bipolar outflow (or 'superwind') appears to be concentrated on clumps A and C, and is fueled by energy released bysupernovae within the clumps which occur at a rate of about one every ten years.[7]
TheChandra X-ray Observatory detected fluctuating X-ray emissions about 600 light-years from the center of M82. Astronomers have postulated that this comes from the first knownintermediate-mass black hole, of roughly 200 to 5000solar masses.[19] M82, like most galaxies, hosts asupermassive black hole at its center.[20] This one has mass of approximately 3 × 107 solar masses, as measured from stellar dynamics.[20]
In April 2010, radio astronomers working at theJodrell Bank Observatory of theUniversity of Manchester in theUK 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.[21]
There have been several theories about the nature of this object, but currently no theory entirely fits the observed data.[21] 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 microquasarSS 433.[22] However, all knownmicroquasars produce large quantities of X-rays, whereas the object's X-ray flux is below the measurement threshold.[21] 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 apparentsuperluminal motion of four times the speed of light relative to the galaxy center.[23][24] Apparent superluminal motion is consistent with relativistic jets in massive black holes and does not indicate that the source itself is moving above lightspeed.[23]
M82 is being physically affected by its larger neighbor, thespiralM81. Tidal forces caused bygravity 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.[7] 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.[7] This starburst ran for up to ~50 Myr at a rate of ~10M⊙ per year.[7] 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.[7]
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 billionyears ago, on itshalo. A suggestion to explain those features is that M82 was previously alow surface brightness galaxy where star formation was triggered due to interactions with its giant neighbor.[25]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.[26] The actual separation is300+300 −200 kly.[27][2]
As a starburst galaxy, Messier 82 is prone to frequent supernova, caused by the collapse of young, massive stars. The first (although false) supernova candidate reported was SN 1986D, initially believed to be a supernova inside the galaxy until it was found to be a variable short-wavelength infrared source instead.[28]
The first confirmed supernova recorded in the galaxy was SN 2004am, discovered in March 2004 from images taken in November 2003 by theLick Observatory Supernova Search. It was later determined to be aType II supernova.[29] In 2008, a radio transient was detected in the galaxy, designated SN 2008iz and thought to be a possible radio-only supernova, being too obscured in visible light by dust and gas clouds to be detectable.[30] A similar radio-only transient was reported in 2009, although never received a formal designation and was similarly unconfirmed.[28]
Prior to accurate and thorough supernova surveys, many other supernovae likely occurred in previous decades. TheEuropean VLBI Network studied a number of potential supernova remnants in the galaxy in the 1980s and 90s. One supernova remnant displayed clear expansion between 1986 and 1997 that suggested it originally went supernova in the early 1960s, and two other remnants show possible expansion that could indicate an age almost as young, but could not be confirmed at the time.[31]
On 21 January 2014 at 19.20 UT, a new distinct star was observed in M82, at apparent magnitude +11.7, by astrophysics lecturerSteve Fossey and four of his students, at theUniversity of London Observatory. It had brightened tomagnitude +10.9 two days later. Examination of earlier observations of M82 found the supernova to figure on the intervening day as well as on 15 through 20 January, brightening from magnitude +14.4 to +11.3; it could not be found, to limiting magnitude +17, from images caught of 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,[32] but peaked at fainter +10.5 on the last day of the month.[33] Preliminary analysis classified it as "a young, reddenedType Ia supernova". TheInternational Astronomical Union (IAU) has designated it SN 2014J.[34]SN 1993J was also at relatively close distance, in M82's larger companion galaxyM81.SN 1987A in theLarge Magellanic Cloud was much closer. 2014J is the closest Type Ia supernova sinceSN 1972E.[8][9][10]
^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:0906.0757.Bibcode:2009arXiv0906.0757D.
^Declination separation of 36.87′ and Right Ascension separation of 9.5′ gives viaPythagorean 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.
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![M82 cigar galaxy with its hydrogen emissions taken in France by amateur astrophotographer Anthony MICHEL[35]](/mt/?noimg=&dark=on&url=http%3a%2f%2fen.m.wikipedia.org%2fwiki%2fFile%3aM82_Cigar_Galaxy.png)
