Artist's rendition of the accretion disk and radio jet around the black hole in the heart of the Seyfert galaxy NGC 4258.
NGC4258 contains one of the very few galactic nuclei for which astronomers
can make images of accretion disk material that lies within a few tenths
of a parsec from a supermassive black hole. The most remarkable
characteristics of the disk are that it is "paper thin," warped, and
rotating differentially according to Kepler's laws (i.e., the square of
rotation velocity is proportional to the reciprocal of radius). In many
other galaxies the characteristics of accretion disks must be inferred
indirectly. In NGC4258, they may be inferred directly from images that
resolve the velocity and angular structure of the disk.
In this artist's conception, the disk is color coded according to Doppler
shift. The blue regions of the disk are moving toward us, while the red
regions move away from us. The inset at the bottom of the graphic is a
radio spectrum (intensity as a function of frequency or velocity) of the
water maser emission. It is the distribution of water emission on the sky
that astronomers map as they trace the outlines of the disk. The white
glints on the disk surface show the locations of regions where maser
emission has been detected.
The blue beam emerging from the black hole represents the relativistic jet
that has also be detected by astronomers on a variety of angular scales,
with instruments such as the Very Large Array and the Very Long Baseline
Array. It lies right along the rotation axis of the innermost portion of
the disk, just as predicted by astronomical theory. Some theories predict
that the black hole will be surrounded by a small region of radio-bright,
intensely hot gas. In a challenge to these suggestions, so far none has
been detected as astronomers have use techniques akin to adaptive optics
to make very sensitive images of the region close to the black hole, and
the hunt continues.
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Type of Observation
Center of Image
RA: 12:18:57.52, Dec: 47:18:14.20 (J2000)
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