ASTRONOMY COLLOQUIUM - FEBRUARY 7, 2006
Ralf Bender, Max-Planck-Institut fuer Extraterrestrische Physik
The Triple Nucleus and Supermassive Black Hole of M31
I report HST STIS observations of the nucleus of M31. It is shown
that the
red double nucleus P1+P2 is well explained by Tremaine's eccentric disk
model. Inside of P2 resides a third, very blue nucleus, P3, which
contains
the supermassive black hole. The blue light of P3 is due to A-type
stars,
presumably formed in starburst 200 Myr ago. Photometric and dynamical
modeling reveals that P3 has the structure of a thin disk in Keplerian
rotation. The disk has an exponential profile and a scale length of
about 1 lightyear. It rotates with >1000 km/s at this radius,
resulting in
a black hole mass of ~1.4*10**8 Msun, considerably higher than previous
measurements indicated. I discuss black hole alternatives and show that
clusters of dark objects are excluded.