November 14, 2002
Subaru Telescope cosponsored a workshop on the center of the Milky Way that was held on the Big Island of Hawaii from November 3 to 8, 2002. Over 100 astronomers from around the world gathered to review recent research on the galactic center. The galactic center is not only the heart of our home galaxy, but it is also the most nearby example of a galaxy nucleus. Studying the center of our own galaxy can help us understand the centers of galaxies in general. The workshop covered phenomena ranging in scale from 1000 light years down to a few light years (roughly the distance between our sun and its nearest neighbor, Proxima Centauri).
In the middle of over 100 billion swirling stars lies the center of the Milky Way, our home. Our own sun is on the outskirts of the Galaxy, about 25000 light years away from the galactic center. In the almost five billion years since our sun was born, it has only gone around the center of the Milky Way about twenty times, even though it is hurling though space at a speed of 240 km or 150 miles per second.
Stars, gas and dust are concentrated in a dense nucleus in the center of our galaxy. When studied in detail, the centers of most nearby galaxies show evidence for black holes more than a million times more massive than our sun, and the Milky Way is no exception. A black hole is an extremely dense concentration of matter whose gravitational pull is so strong that even light can't escape from its surface. The only way astronomers can see black holes is through the effect of their gravitational pull on neighboring gas and stars, and through the light emitted by interstellar material that heats up while falling into a black hole.
Many of the most energetic phenomena in the Universe originate in the centers of galaxies. Some galaxies have extremely bright centers, called Active Galactic Nuclei, which can outshine the starlight from the entire galaxy. The light from quasars, the most distant objects that we have observed in the Universe, probably originate in the centers of galaxies as they were forming.
Combined with theoretical investigations, new observations ranging in wavelength from radio to x-rays from a new generation of telescopes and instruments have greatly enhanced our knowledge of the nucleus of our galaxy in the past several years. A team of astronomers from University of Tokyo, the National Astronomical Observatory of Japan (NAOJ), the Institute of Space and Astronautical Science (ISAS), and Kitasato University presented results obtained with COMICS on Subaru Telescope during the workshop. Although the nucleus of the galaxy is full of stars, it is also full of gas and dust which obscure our view to the center at visible wavelengths. COMICS, the COoled Mid-Infrared Camera and Spectrograph, can observe warm dust heated by the stars. The most recent image from COMICS shows previously unseen detail in the distribution of warm dust. The actual center of the galaxy is so heavily embedded in gas and dust, it is dark even in the mid-infrared.
This image from COMICS shows a 7 by 5 light year region in the center of our galaxy. It is a false color image produced from light detected at wavelengths between 8 and 13 microns.