The Cigar Galaxy, officially Messier 82 (M82), is a visually dramatic object located approximately 12 million light-years away in the constellation Ursa Major. Its striking, elongated appearance earned it the popular “Cigar” moniker. M82 is the prototype of a starburst galaxy, defined by an extraordinarily high rate of star formation. This peculiar shape only hints at the extreme activity within.
The Official Classification
M82’s formal designation is Irregular Galaxy, primarily because it lacks the defined structure of typical spiral or elliptical galaxies. However, M82 is characterized by its starburst status, making it a clear example of this rare galactic type. A starburst galaxy is defined by star formation occurring at a rate far exceeding that of a typical galaxy, such as the Milky Way. Near-infrared observations suggest M82 may possess a distorted disk structure, but its chaotic star-forming activity overrides this underlying form.
The Starburst Engine
The intensity of star formation in M82’s central region drives its classification and energy output. Stars are created up to ten times faster in the core than the entire Milky Way produces. This activity forms hundreds of young, massive star clusters packed into a starburst region spanning about 500 parsecs. The high density of young stars leads to rapid stellar death, with supernovae occurring roughly every ten years. The resulting stellar radiation and supernova explosions heat the surrounding dust and gas to extreme temperatures, making M82 about five times more luminous than the Milky Way in infrared wavelengths.
The Galactic Interaction and Shaping
M82’s peculiar shape and star-forming activity stem from a close encounter with its larger neighbor, the spiral galaxy Messier 81 (M81). Both galaxies are the most massive members of the M81 Group and are gravitationally bound. This interaction, which began roughly 100 million years ago, subjected M82 to immense tidal forces from M81’s gravity. These forces physically distorted M82, stretching it into the elongated “cigar” profile. The tidal forces also funneled and compressed gas and dust clouds into M82’s central core, triggering the current episode of star formation.
The Superwind Outflow
A direct consequence of M82’s high star formation rate is the massive outflow of material perpendicular to the galactic disk, known as a “superwind” or “galactic chimney.” The rapid sequence of supernovae creates immense pressure and thermal energy, driving gas and plasma out of the core. This bipolar outflow consists of hot gas, dust, and heavy elements manufactured inside massive stars, and is visually captured as fiery red filaments of hydrogen-alpha light. The superwind ejects this material at high speeds, extending thousands of light-years above and below the galactic plane. This expulsion of gas and enriched elements is a feedback mechanism, where the galaxy vents excess energy and seeds the surrounding intergalactic medium.