Download - Artistic concept of a HMXB: a collapsed star (NS or BH) Accretes mass from a massive O or B star
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Artistic concept of a HMXB: a collapsed star (NS or BH) Accretes mass from a massive O or B star
Binary mass function
Radial velocity curve of HD 226868, the O9.7Iab companion star in the HMBX Cyg X-1, folded on the 5.6-day orbital period
Phase (1 = 5.6 days)
km/s
Binary mass function of Cyg X-1: F(Mx) = 0.25 M
Mass of companion ~ 33 M
For i = 90 deg --> Mx = 7 M
It cannot be a neutron star!!
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(erroneously thought to beat 15 Mpc, butactually at 30 Mpc!)
How can we be sure that a SMBH resides at the center ofA galaxy (and not, for instance, a compact star cluster) ?For example, if we notice that the mass-to-light ratio increasesToward the center of the galaxy, is that a proof of SMBH?
No, it is not. It is difficult to get incontrovertible proof.
Hints are fast variability, superluminal motion, very highInferred mass densities, high luminosities….
Most importantly, we must resolve the sphere of influence of the putative central SMBH
Sphere of influence of BH
In the case of SMBHs inhabiting galactic nuclei, the “sphere of influence” is defined as the region of space within which the gravitational potential of the SMBH dominates over that of the surrounding stars.
The radius of the sphere of influence is about e6 times largerThan the Schwarzschild radius of a SMBH.
Beyond a few thousand Schwarzschild radii from the central SMBH, but within the sphere of influence, the motion of stars and gas is predominantly Keplerian (relativistic effects are minimal), with a component due to the combined gravitational potential of stars, dust, gas, dark matter, and anything else contributing mass to within that region. Beyond the sphere of influence, the gravitational dominance of the SMBH quickly vanishes.
For AGNs one can also use accretion disk theory
8600
The SMBH at the centre of our Galaxy
Sgr A* is a compact radio source: VLBI observations at 86 GHz set a limit of 1 AU on its size.
Proper motion studies with adaptive optics in K band (angular resolution of 50 mas ~ 40 AU) for ~40 stars within 1.2 arcsec of Sgr A*. Stellar orbits followed up for years, maximum approach is 45 AU, period of 15.2 yrs, velocity of 12000 km/s !
Very precise determination of SMBH mass:
(4.5+-0.4) e6 M
Ghez et al. 2005, ApJ, 620, 744Ghez et al. 2008, ApJ, 689, 1044 Schoedel et al. 2002, Nature, 419, 694
1”
Stellar orbits in the proximity of the Galactic Center
SMBH mass determination thru stellar dynamics
Stellar dynamics is more precise than gas dynamics becauseGas motion may be not Keplerian, while star orbits are alwaysKeplerian
Continuity equation (Collisionless Boltzmann Equation)And Poisson equation
Many assumptions are necessary
Stellar kinematic is derived from theabsorption lines
Velocity
profiles
arcsec
Dynamical Study of M31 (770 kpc)
Surface brightnessRadial profile
Velocity dispersion radialprofile: it rises toward thenucleus
The rotation curve is Keplerian And matches perfectly the Expectation of an exponential Disk
MBH = (3.0 ± 1.5)×107 M☉
M87 (= Virgo A, 20 Mpc)
The SMBH in M87
MBH = (3.2 ± 0.9)×109 M☉
Microwave Amplification thru Stimulated Emission of Radiation (MASER)
Water maser at 22 GHz observed with VLBI in NGC4258
mas
NGC4258 (7 Mpc)
Water megamasersobserved at 22 GHz with the VLBA:
1 mas = 0.035 pc
H2O is in Keplerian motion
MBH ~ 4×107 M☉
MBH - σ relationship
Beyond cz ~ 10000 km/s (i.e. ~150 Mpc),it becomes very difficult or impossible to measure SMBH masses of inactiveGalaxies. One can rely upon the MBH - relationship
Milky Way !
However, it is possible to measure SMBH masses in activeGalaxies at large distances with various methods
Schematic view of an AGN
AGN have broad (FWHM of several thousands of km/s) and luminous emission lines
Reverberationmapping
Right:Light curves ofContinuum andEmission linesOf Seyfert Galaxy NGC5548
Left:Correlation function of eachCurve with theOptical continuum
Excellent review on Supermassive Black Holes:
Laura Ferrarese and Holland Ford
Supermassive Black Holes in Galactic Nuclei: Past, Present and Future Research
Space Science Reviews 116: 523-624 (2005)[arXiv:astro-ph/0411247]