QUIET BHs in GALACTIC NUCLEI
• Random motions of stars
– measure random speeds, look for cusps
– example: Milky Way nucleus, M87
• Organized rotation of stars
– example: Andromeda Galaxy (30 million M Solar )
• Rotation of gas clouds
– example: M87
• Disk traced in masers
– example: NGC 4258 (36 million M Solar )
ANDROMEDA GALAXY - M31
BH mass: 30 million Suns
M32:
BH=3million
SOMBRERO GALAXY -
1/2 billion solar masses
“Sombrero” Galaxy
M87 - 3 billion solar masses
MOST ACCURATE MEASUREMENT:
NGC 4258
BH = 36 million Suns
MASER=
Microwave Amplification by Stimulated Emission
of Radiation
MASERS IN NGC 4258
NGC 4258: 36 million solar masses
IS BH MASS RELATED TO
GALAXY BULGE MASS?
Claim:
M BH ~ const. ~ 0.005
M bulge
Is this correlation real
or an artifact of
observational
limitations?
WHY QUIET?
• Need supply of gas for activity
– need ~ 1 solar mass/yr for quasar/luminous
Seyfert
• Probably comes from:
– interstellar “debris”
– gas “dumped” into nucleus during galaxy
mergers
• Gas more plentiful in early stages of galaxy
evolution?
– Accounts for prevalence of quasars at high
redshift?
THE MILKY WAY -
2.6 million solar masses
From Ghez et al. 1998
Infrared picture of the
Galaxy’s Center
(Genzel et al., Germany)
Prof. Andrea Ghez, UCLA
SgrA*
Chandra image (2/00)
ENERGY CHAIN IS BROKEN:
GRAVITY
matter swirling inward
MOTION
friction
HEAT
RADIATION (X-rays, UV…)
THE NEW ENERGY CHAIN:
GRAVITY
MOTION
HEAT
Are black holes
fussy eaters?
ISSUES OF BH FORMATION/GROWTH
Insignificant growth once formed?
Did BHs and galaxies form together?
Infrequent major mergers? rapid spin
or
Frequent minor mergers? slow spin
Grow by swallowing gas? luminous
(Were all galaxies once quasars?)
or
Grow by swallowing stars? less luminous?
BLACK HOLE BINARIES
• Galaxy mergers black hole binaries
• How long does it take them to merge?
• Do we see any galaxies with two active
nuclei?
FLARES FROM TIDALLY
SHREDDED STARS
• Must occur for BHs < a billion solar masses
– more massive stars swallowed whole
• Estimate once per 10,000 yrs for Milky
Way nucleus conditions
• We should “see” one per year if we study
more than 10,000 MW-like galaxies
– … but what do they look like?