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Messier 84 is a member of the Virgo Cluster of galaxies, a large and nearby collection of hundreds of galaxies extending over 6 degrees of the celestial sky (about 12 times the diameter of the full moon). There is some ambiguity about the proper classification of this galaxy. Some astronomers believe M84 is an elliptical galaxy, while others regard it as a face-on lenticular galaxy. In either case, there is no obvious spiral structure, and little dust or gas content.
Visible: DSS (left) and Visible: AURA/NOAO/NSF (right), There are very few, if any, distinguishing differences between the visible-light photographs shown above. Can you deduce which image is the most sensitive? The AURA/NOAO color image is more sensitive than the DSS image since the apparent diameter of the galaxy is greatest and the density of foreground stars is highest.
Near-Infrared: 2MASS, Mid-Infrared: IRAS and Far-Infrared: IRAS The near-infrared photo (above, left) looks very similar to the previous visible-light pictures. Despite a relatively short exposure time of less than 8 seconds, Messier 84 is quite luminous at near-IR wavelengths. This is a consequence of the fact that near-IR light is effective for studying older stars and the fact that elliptical/lenticular galaxies are predominantly populated with such stars. Both of the mid-IR and far-IR images taken with IRAS are show relatively weak long-wavelength infrared emission at the same position as the underlying galaxy. The mid-IR photo also displays numerous artifacts (green), which are not real. They are the result of specialized processing undertaken to enhance the relatively weak emission from the galaxy itself. The bright (red) source to the northwest (upper left) does not correspond to any cataloged celestial object, and its reality is in doubt. At even longer infrared wavelengths, the far-IR image (right, above) shows very weak emission at a wavelength of 100 microns. The pixel pattern is an artifact of the data processing, and the elongated features are a signature of the rectangular detectors used to make the photo.
X-Ray: ROSAT The x-ray image essentially shows only the core of M84. The slight (greenish) extension of emission to the southeast (lower left) is probably real, although not associated with Messier 84. It is likely to be weak x-ray emission from a cataloged quasar in the very distant background, with a redshift of z=1.25.
Radio: Laing & Bridle (VLA) Without question, the most interesting image of M84 in this gallery was taken at radio wavelengths with the Very Large Array (VLA) in New Mexico. This picture looks unlike any other in the gallery! The peaks of radio emission are found to straddle both sides of the central galaxy (much like your ear lobes are on opposite sides of your head). This double-lobe structure is a product of the magnetic field configuration of the central galaxy and of the fast-moving cosmic ray particles spiraling around the magnetic field lines. Two thin jets of radio emission (red is brightest) appear to shoot out from the nucleus of M84, to the north and south. These radio streamers produce clouds that appear to be swept into a pinwheel, perhaps by the influence of some unseen force.
This object is an example of one of the more curious beasts in the cosmic zoo:
a
DRAGN (pronounced dragon), Double Radiosource Associated with Galactic
Nucleus. In general, DRAGNs display double lobes (like earlobes!) of radio
emission on either side of an
active galactic nucleus (AGN). Double radio
lobes
are not an uncommon feature of elliptical galaxies and AGN.
Astronomers are not completely certain about the nature of the jets and radio
lobes. However, this radio image essentially maps the distribution of
synchrotron radiation, caused by fast-moving electrons immersed in a magnetic
field. The behavior of the cosmic jets and clouds can be modeled reasonably
well using the similar numerical methods applied in
hydrodynamics. For more
images and information about DRAGNs, please visit here.
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