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A Superwind from the Cigar Galaxy
What's lighting up the Cigar Galaxy? M82, as this irregular galaxy is also known, was stirred up by a recent pass near large spiral galaxy M81. This doesn't fully explain the source of the red-glowing outwardly expanding gas, however. Recent evidence indicates that this gas is being driven out by the combined emerging particle winds of many stars, together creating a galactic "superwind." The above photograph from the Hubble Space Telescope highlights the specific color of red light strongly emitted by ionized hydrogen gas, showing detailed filaments of this gas. The filaments extend for over 10,000 light years. The 12-million light-year distant Cigar Galaxy is the brightest galaxy in the sky in infrared light, and can be seen in visible light with a small telescope towards the constellation of Ursa Major.
Up until the early 1960s, it was believed that the extended H alpha emission was caused by a single massive explosion at the center of M82. Later, large clouds of molecular hydrogen gas and many supernova remnants were discovered at the center of this galaxy. Further observations with the 45 meter radio telescope at the National Astronomical Observatory of Japan's Nobeyama Radio Observatory showed that the molecular gas is flowing outwards from the nucleus of M82. It is now thought that this outflow is being driven by the copious formation of massive stars (called a starburst) and subsequent supernova explosions. Astronomers call such galaxy-size outflows "superwinds". In addition to providing the ejection mechanism for the material from the galaxy, the superwind heats the gas, causing it to glow with the light of H alpha emission. Studying the M82 galaxy may provide clues to galaxy evolution in general and details of the composition of intergalactic material.