This plot of data from NASA's Spitzer Space Telescope indicates that a
flat, spiral galaxy called NGC 3621 has a feeding, supermassive black hole
lurking within it -- a surprise considering that astronomers thought this
particular class of super-thin galaxies lacked big black holes.
The data were captured by Spitzer's infrared spectrograph, an instrument
that cracks infrared light open to reveal the signatures of elements. In
this case, the data, or spectrum, for NGC 3621, shows the signature of
highly ionized neon -- a sure sign of an active, supermassive black hole.
Only a black hole that is actively consuming gas and stars has enough
energy to ionize neon to this state. The other features in this plot are
polycyclic aromatic hydrocarbons and chlorine, produced in the gas
surrounding stars.
The results challenge current theories, which hold that supermassive black
holes require the bulbous central bulges that poke out from many spiral
galaxies to form and grow. NGC 3621 is the second disk galaxy without any
bulge found to harbor a supermassive black hole; the first, found in 2003,
is NGC 4395. Astronomers have also used Spitzer to find six other mega
black holes in thin spirals with only minimal bulges. Together, the
findings indicate that, for a galaxy, being plump in the middle is not a
necessary condition for growing a rotund black hole.
