The Cigar Galaxy - Messier 82


The Cigar Galaxy emits 5 times more light than the Milky Way, although its diameter is only 1/3rd of the diameter of our galaxy. When so much energy works in so "small region", there must some extraordinary things happen. That is the case with Messier 82 too.

The Cigar Galaxy

It was discovered in the second half of the 18th century, when German astronomer Johann Elert Bode and a few years later Pierre Méchain independently recorded it as a new discovery. Méchain sent the coordinates to Messier, who added the galaxy to his catalogue as object #82 in 1781. Very close to M82, only a degree from it there is another bright galaxy (M81), therefore it was likely to discover them at the same time. Bode and 5 years later Méchain discovered them together. Messier 81 -which was named Bode's Galaxy after its discoverer- is not in this photo, only a very small part of it is visible at the top of the picture. Fortunately Messier 82 located in the centre of the image is interesting enough by its own.

The Cigar Galaxy is about 12 million light-years from us, in the constellation of Big Dipper, quite close to the north celestial pole. It is circumpolar at observing sites north to the 31th parallel, where it is always above the horizon, never sets.

At first sight it seems to be an irregular galaxy. Even professional astronomers classified it irregular until 2005 when special processing of near infrared images of the galaxy showed two symmetrical spiral arms. Those arms could have remained undetected so long because the high surface brightness of the galaxy and the complex structure of dust lanes made them difficult to notice.

There has been intense star formation happened in the past, and is happening currently close to the core of the galaxy. Star formation is triggered by the gravitational effect of the nearby Messier 81. Galaxies with such high rate of star formation are called starburst galaxies. Apart from M82, several other spectacular galaxies are classified as starburst galaxies, like the Antennae Galaxies or the Silver Dollar Galaxy. Newly born stars are heavy and hot. They heat and ionise the remains of the interstellar medium they are formed of. With their strong stellar wind they also sweep away those gases from their close vicinity. Life of massive stars is relatively short, and most of them become supernovae at the end of their life. Energy and shock waves from frequent supernova explosions also increase the temperature and pressure of the interstellar medium. Thermal expansion of the gas clouds and the cumulated pressure of stellar winds make the ionised plasma escape in the direction of the least resistance, which is the direction perpendicular to the main rotational plane of the galaxy. This phenomenon is called the galactic superwind. The bluish colour of the disc of the galaxy is clearly visible in the picture. It's blue colour is caused by the lot of young blue stars of O and B spectral types in the disc. The red-glowing outflows are also visible perpendicular to the main plane of the galaxy, their colour is caused by ionised hydrogen.

Observations made by Hubble Space Telescope in 2005 illustrate the circumstances around the core of the galaxy. 197 young star clusters were identified in the starburst zone around the core of M82. Each of these clusters contain about 200000 solar masses of stars. Star formation rate in M82 is about 10 times higher than in the Milky Way.

On average there is one supernova explosion in the Cigar Galaxy in every 10 years. The latest one identified as SN2014J was in January, 2014. By comparison, in our galaxy the average time between supernova explosions is 50 years, but there hasn't been registered any in the last 150 years, so it is very likely to happen one in the near future.

In addition to these M82 has a very interesting object, the mysteriously named M82 X-2 X-ray pulsar, which was discovered in 2014. M82 X-2 is the brightest pulsar we know, it is 10 million times brighter than our Sun, and 100 times brighter than the maximum brightness an object of its mass can have, the Eddington limit. A couple of theories were suggested to explain the contradiction, but we don't know yet if any of them is right.

M82 X-2 is a binary system containing a magnetised neutron star and a companion star. Gas is flowing from the companion to the neutron star, concentrated in two hot spots around the magnetic poles. The temperature at these hot spots is so high, that they emit mostly X-rays. Rotational axis of the neutron star is not parallel with its magnetic axis, resulting the hot spots rotating with the neutron star, causing its brightness to pulsate. By measuring the pulse period it turned out that the pulsar makes a full rotation in less than 1.5 seconds, and a full orbit around its companion takes only a few days.

Integrated Flux Nebulae

Ten years ago, in 2005 an American communications coach and amateur astronomer Steve Mandel discovered a new type of deep-sky objects while he was testing filters. Very faint, unknown nebulae were visible over the plane of the Milky Way in his pictures. It turned out that they were illuminated by the integrated light of the stars of our galaxy, whereas reflection nebulae which are illuminated by a single or only a few stars. Mandel created the term Integrated Flux Nebulae to describe this kind of objects.

Mandel started to register IFNs in a catalogue, which he calls The Mandel-Wilson Catalogue of Unexplored Nebulae. Wilson's foundation provided financial support for Mandel's work. The faint patches of nebula in the picture around the galaxy are parts of integrated flux nebula MW 3.

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