Massive Central Objects Detected in Galaxies

Massive Central Objects Detected in Galaxies
Galaxy Const Type Distance Luminosity Mass DT Comment Sources
Milky Way [Sgr] Sbc 0.028 1.9 2 S Sgr A, Galactic Center Genzel et al. 1997; Ghez et al. 1998
M31 And Sb 2.9 5.2 30 S Andromeda Galaxy Dressler/Richstone 1988; Kormendy 1988b
M32 And E2 2.9 0.25 3 S Satellite of M31 Tonry 1984, 1987; Dressler/Richstone 1988
NGC 3115 Sex SO 27 14.2 2 S Kormendy & Richstone 1992
M106 CVn Sbc 24 1.3 40 M Miyoshi et al. 1995
NGC 4261 Vir E2 90 33 400 G Ferrarese et al. 1996
M87 Vir E0 60 56 3000 G Harms et al. 1994
M104 Vir Sa 50 47 1000 S Sombrero Galaxy Kormendy 1988c
NGC 3377 Leo E5 38 5.2 100 S Kormendy et al. 1998; Richstone et al. 1999
M105 Leo E1 38 13 100 S Gebhardt et al. 1999
NGC 4486B Vir E0 60 0.82 500 S Satellite of M87 Kormendy et al. 1997
M77 Cet Sb 60 10 M Caltech IR detection Greenhill et al. 1996, NRAO PR Jan 15/2000
M84 Vir S0 60 56 300 G HST STIS (May 1997) Bower et al. 1998
NGC 4342 Vir S0 60 50 S Cretton/van den Bosch 1999
NGC 7052 Vul E4 191 300 G van der Marel/van den Bosch 1998
NGC 6251 UMi E2 346 600 G Ferrarese & Ford 1999
NGC 4945 Cen Scd 15 1 M Greenhill et al. 1997


Identification/Catalog number of galaxy
Hubble type
Distance in million light years (of massive central object)
Galaxy luminosity in billion solar luminosities; bulge only for spirals
Central Object's Mass in million solar masses
Detection Type (S: Stellar dynamics, G: Gas dynamics, M: Maser sources)
Common name of galaxy or other comment
Discovery papers

This table summarizes data for some of the well-established massive central objects in the nuclei of galaxies. The masses of these objects are usually estimated from the orbital velocity of stars or gas orbiting the objects at distances of some tens or hundreds of light years, which shows that enormous masses are concentrated in small volumes. Many of these central objects exhibit other signs of violent gravitational action: Accretion disks, emission of strong radio and/or high-energy radiation, or jets of highly accelerated material.

What may be the nature of these mysterious objects ? Many astronomers take it for granted that these objects are supermassive black holes, but none of them is really resolved. To get truely compelling evidence, or better, to reveal the true nature of the massive central objects, a resolution would be required of the order of the Schwarzschild radius (the "horizon" radius of a black hole acording to Einstein's General Relativity theory). The Schwarzschild radius is simply correlated to the mass of an object, as it is defined as that radius where the escape velocity from the mass equals light velocity; this means that it is proportional to the mass. The formal relation can be given as

R_S = 2.94 km * M [solar masses]
Even for the most massive central object (in M87), this yields a value of R_S = 9 billion km, little more than the mean distance of Pluto to the sun and only about 1/1000 of a light year, while the Hubble Space Telescope could only resolve this object to a few tens of light years. So currently, any evidence is indirect at best. It is particularly exaggerated to take our current knowledge of these objects as a further evidence for the validity of Einstein's General Relativity, as was occasionally claimed.

The table above is partly based on STScI-PR97-01 and John Kormendy's CENSUS of Black Hole Candidates in galactic nuclei (more technical version).

Hartmut Frommert
Christine Kronberg

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Last Modification: February 3, 2000