MCG6 Fe Line
Credit: Tanaka et al. (Nature 375, 659) / P. Nandra NASA/GSFC

A Daily Intake of Iron

So-called "active" galaxies (galaxies which are extremely bright at some wavelengths, or which eject jets of matter ) produce spectacular astrophysical fireworks. It is thought that these fireworks are caused somehow by a "central engine", an active nucleus which probably harbors a supermassive black hole weighing more than 1 million suns. Presumably, matter from the galaxy (gas clouds, stars, perhaps planets and civilizations) near the black hole spiral nearer and near the "event horizon", moving faster and faster until swallowed by the black hole. It's impossible to see into the event horizon, but of course that doesn't stop astronomers from trying. The above image shows an ASCA X-ray measure of an iron emission line from the active galaxy known as MCG-6-30-15. This iron emission line (represented by the red dots) is produced only in extremely hot and/or energetic regions of space. Through the study of this line astronomers can determine the properties of the material producing the line. Astronomers find that the iron emission from MCG-6-30-15 is very peculiar. The width of the line suggests that the material is moving very fast, probably at a velocity approaching 1/3 the speed of light. In addition, the emission line has a peculiar double-peaked structure. This double-peaked structure can be produced by intense gravitational field. Taking all the evidence together, astronomers believe that this emission line is produced by material in a death spiral very close to the supermassive black hole of MCG-6-30-15, just before the material is swallowed into the depths beyond the event horizon. The blue line shows the expected shape of the emission line if the emitting material is at a distance of 3 to 10 times the event horizon.

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Page Author: Dr. Michael F. Corcoran
Last modified August 30, 2000