The M82 galaxy. Photo: National Astronomical Observatory of Japan

M82 is the 82nd object in Charles Messier's 1784 catalogue of faint nebulae. It is located approximately 12 million light-years from the Earth and is classified as an irregular galaxy because of its disordered shape. The bluish band seen running from the upper-left to the lower-right of the image is due to light from stars in the M82 galaxy. The red filamentary features extending perpendicular to the galaxy are due to ionized hydrogen gas emitting  its characteristic red light (the so-called "H alpha" line) at a wavelength of 6563 Angstroms. The filaments extend for over 10,000 light years in each  direction from the center of the galaxy.

This image was produced using the Subaru Telescope's Faint Object Camera and Spectrograph (FOCAS) on its first night of operation in February of this year. When fully commissioned, FOCAS will also be able to take spectra of many dozens of objects in a single exposure within its 6 arcminute field of view.

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.

The Subaru Telescope had first light in January 1999 and is being continuously adjusted to improve its performance. During this time, test observations are being made with the seven first-phase instruments (including FOCAS). Use of the Subaru Telescope by the worldwide astronomical community will start later this year, and many exciting new scientific results are sure to follow.