This visible-light picture of the central region of galaxy M87 is a specially prepared composite. One image was taken in red light, filtered to emphasize radiation from interstellar gas in the form of hydrogen and singly ionized nitrogen (nitrogen atoms that have each lost one electron). A second image was taken at a wavelength where the radiation from M87 is dominated by the glow from the millions of stars clustered toward the center of the galaxy. Then, the second image, adjusted by an appropriate weighting factor, was subtracted from the first one. The result is a composite picture in which the light from interstellar gas shines brightly and the light from stars is de-emphasized.
The result reveals a previously unknown disk of glowing gas surrounding the very center of M87, which is at the base of the jet that extends toward the right corner of the image. A spiral structure is apparent in the gas disk. The gas has a temperature of roughly 10,000 kelvins. It is extremely unusual to observe spiral structure at the center of an elliptical galaxy.
Camera: WFPC2
Credit: H. Ford (STScl and Johns Hopkins
University), and NASA
