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 )

• Rotation of gas clouds– example: M87

• Disk traced in masers – example: NGC 4258 (36 million )

SolarM

SolarM

ANDROMEDA GALAXY - M31BH mass: 30 million Suns

M32: BH=3million

SOMBRERO GALAXY - 1/2 billion solar masses

“Sombrero” Galaxy

M87 - 3 billion solar masses

NGC 4258

BH = 36 million Suns

MOST ACCURATE MEASUREMENT:

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:

005.0~.~ constMM

bulge

BH

Is this correlation realor 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?

galcenter-motions.gif

THE MILKY WAY -2.6 million solar masses

Infrared picture of theGalaxy’s Center (Genzel et al., Germany)

From Ghez et al. 1998

Prof. Andrea Ghez, UCLA

SgrA*

Chandra image (2/00)

ENERGY CHAIN IS BROKEN:

GRAVITY

MOTION

HEAT

RADIATION (X-rays, UV…)

matter swirling inward

friction

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

orFrequent 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?