Located 12 million light years away in the direction of the constellation Ursa Major, Messier 82 is sometimes called the òÀØCigar GalaxyòÀÙ from its shape. M82 it is too faint to be seen with the naked eye but can be seen through the telescopes of amateurs. Until recently M82 was believed to be an irregular galaxy, but since 2005 M82 has been known to be a spiral galaxy which we are looking at side on. It is the site of one of astronomy’s most intriguing unsolved mysteries.
Along the edge of M82òÀÙs disc we see tangled filaments of dark dust. Blasting out from the galaxyòÀÙs central regions are dramatic plumes of glowing hydrogen gas, driven by the frantic birth of new stars.
(Image credit: ESA, NASA and STScI)
The gravity of M82òÀÙs close neighbouring galaxy M81 is distorting the CigaròÀÙs structure, resulting in the plumes of hydrogen and dust visible in images. This activity is believed to be promoting the unusually high rate of star formation seen in M82. As a result M82 is a òÀØstarburstòÀÙ galaxy’, so called as new stars are being formed in it at an astonishing rate, at least ten times as many new stars are born every year in the centre of M82 as are born in the whole Milky Way Galaxy. These newborn stars are packed closed together and streams of gases escaping from them collide, compressing this hot matter to form even more young stars. This frenzy of creation is a self-limiting process which cannot go on for ever, eventually, tens of millions of years hence, all the gas and dust which are the ingredients for star formation will have been consumed. The starburst then will dwindle to a halt.
Radio image of M82 made with the MERLIN and VLA telescopes. Insets show MERLIN images from April 25th and May 3rd 2009 demonstrating the sudden appearance of the mystery object.ˆà All images are at a frequency of 5 GHz. (Image credit: T.W.B. Muxlow, University of Manchester.)
Near its centre M82 is home to a mysterious object whose place in the astronomical bestiary is still unclear. In 2009, radio astronomers at the UKòÀÙs Jodrell Bank Observatory found this unknown object which had been previously undetectable but was suddenly emitting a unique radio signature as though someone had just hit the On switch. No proposed theory to account for this emission entirely fits the observed data. The best suggestion is the object is an unusual “micro quasar”, a phenomenon formed by a large star orbited by a compact body such as a neutron star or black hole. Material ripped from the larger star by its little parasitical partner is shaped into an accretion disc and emits copious radio and X-ray emissions. The unnamed mystery body in M82 is notably deficient in X-ray emissions, so it would be a very atypical micro quasar. To this day the object’s nature remains an unsolved mystery in our sky.
Artists impression of a microquasar. Microquasars are accreting binary systems which emit very-high-energy gamma-rays.
Further reading
Royal Astronomical Society (RAS) (2010, April 13). Mystery object in Starburst Galaxy M82
(Article by Colin Johnston, Science Communicator)
