Seyfert galaxies
Seen with visible light, these are fairly ordinary spiral galaxies.
But they have unusual properties in their cores.
- A large amount of energy is coming from the core of the
galaxy.
- Luminosity of the core is comparable to the luminosity of
a whole galaxy like the Milky Way, up to 1038 W ~ 10 LMW
- The energy emission is non-stellar.
- It is mostly in the form of infrared and radio radiation.
- There are emission lines from highly ionized iron, for example.
- The core lumimosity can vary on time scales of less than one year.
- This indicates that the energy source is small, less than one
light year in size.
- The emission lines are very broad.
- This suggests that the emission is coming from gas that is moving
very fast.
- Some is moving away from us, some toward us.
- The Doppler shift spreads out the spectral line.
What is the energy source?
Recall that there is some evidence of a supermassive black hole
at the
center of our Galaxy.
Let's look at
what theory predicts
for such an oject with its accretion disk.
Maybe there is a ``supermassive'' black hole at the center of a
Seyfert Galaxy.
What we see is lots of energy that isn't from stars, coming from a
small region, with fast moving gas. It all fits.
Suggested masses are 106 to 109 solar masses.
Energy production
Calculations indicate that accretion onto a black hole should be a
pretty efficient energy source. Of the total energy m c2
of a mass m of gas, something like 10% would be radiated away.
(The rest would go into increasing the mass of the black hole.)
The black hole would have to eat 0.1 Msun per year to produce
1038 W of power (10 LMW).
Davison E. Soper, Institute of Theoretical Science,
University of Oregon, Eugene OR 97403 USA
soper@bovine.uoregon.edu