Messier 87 is a giant elliptical galaxy at the center of the rich Virgo Cluster of galaxies. It is a strong radio source, and carries the alternate designation Virgo A, denoting the brightest radio source in Virgo. This radio galaxy is best known for a jet of gas emanating from the galaxy core and moving at superluminal velocities. This feature is powered by a black hole in the center of Virgo A. Each of the images in this gallery is about the size of half the diameter of the full moon.
Visible: DSS and AAO
The visible-light images of Messier 87 resemble those for M84, displaying a spherical ball of many millions of stars. Let us briefly point out a couple of other interesting objects in the DSS image. First, note the fuzzy objects located to the southwest (lower right) within 3 arcminutes of M87. These galaxies from a galaxy pair known as UGC 7652, and are more than twenty times farther away from us than Messier 87. On the other hand, the bright object located 6 arcmin north of M87 is a foreground star located within our Milky Way Galaxy. Bright stars often show diffraction spikes, an artifact produced by the optics of a telescope whenever looking at a bright point-source of light.
The AAO photograph shows a smaller field of view, and hence the outer regions have been padded with black to keep the absolute size of the image the same as the others in this gallery. It is easier to see the background galaxy pair in this color image because it is not lost in the outer fringes of the slightly over-exposed DSS image.
Where is the famous jet of light from M87? It is not apparent in any of the visible images above. To answer the question, let us turn our attention to the near-infrared picture of Messier 87 (below).
The primary image shows M87 as it appears at near-infrared wavelengths. It is a short exposure (only 7.8 seconds), and thus relatively under-exposed compared to the earlier optical images. However, by avoiding saturation of the central galaxy, 2MASS is able to reveal the presence of the jet. The inset reveals the jet pointing outwards from the central core of M87 at about the 2 o'clock position. This jet is a narrow stream of gas and is about 8000 light-years (2.5 kilo- parsecs, or kpc) in length. The energy necessary to provide the needed power for this remarkable stream is provided by a black hole in the center of M87. Black holes are so massive that even light cannot escape. However, the presence of the central black hole has been inferred from indirect observations with the Hubble Space Telescope. To see closer HST view of this jet, please click here and here.
Mid-Infrared: IRAS (left) and Far-Infrared: IRAS (right)
The longer wavelength infrared photos from IRAS (above) reveal vastly diminished emission from Messier 87. The mid-infrared image is barely able to see M87 at all. If not for the fact that you knew that the galaxy was in the center of the image, you might easily be lost among the random noise fluctuations (green) in the image.
Messier 87 is slightly easier to see as the central red emission peak in the far-infrared image (right). Note that the infrared emission is stretched along a line running from the 2 o'clock position to the 8 o'clock position. This artifact results from the peculiar rectangle-shaped detectors used aboard IRAS. Elliptical galaxies do not generally contain significant amounts of interstellar dust, and therefore are not strong sources of thermal infrared radiation.
The fascinating radio image of Messier 87 (above) was taken with the Very Large Array (VLA) at a frequency of 327 MHz (millions of cycles per second), corresponding to a wavelength of about 92 cm. The astronomers who produced these images have put together a nice explanatory Web site with additional images.
The brightest radio emission is shown in red, and shows a central peak at the same position as M87. There are also jets of emission extending to the west and to the east, producing large radio lobes (yellow). Note that the western lobe (to the right) takes a sudden turn to the south (bottom), suggesting that it is ramming into a denser and unseen intracluster medium.
A large halo of radio emission (green) surrounds the entire galaxy and jets. The halo stretches across a distance of about 80 kiloparsecs, more than twice the diameter of our own Milky Way Galaxy. The central galaxy and its radio halo, meanwhile, are immersed in an even larger cocoon of hot and thin gas which can be seen at x-ray wavelengths (see image below).
Finally, we close our tour of this gallery with a look at the x-ray image (above). Two features in this photo are worth noting. First, the strongest emission source resides at the center of the image, corresponding to Messier 87. A much larger sphere of less intense x-rays surrounds the elliptical galaxy, and results from the hot gas that is found throughout the Virgo Cluster, and in many other galaxy clusters.