QUIET BHs in GALACTIC NUCLEI
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Transcript of QUIET BHs in GALACTIC NUCLEI
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?