Massive Dark Objects Detected in Galaxies

Massive Dark Objects Detected in Galaxies

Massive Dark Objects Detected in Galaxies

Galaxy	Const	Type	Distance	Luminosity	Mass	Comment
Milky Way	[Sgr]	Sbc	0.028	1.9	2	Sgr A, Galactic Center
M31	And	Sb	2.9	5.2	30	Andromeda Galaxy
M32	And	E2	2.9	0.25	3	Satellite of M31
NGC 3115	Sex	SO	27	14.2	2
M 106	CVn	Sbc	24	1.3	40	Maser Detection
NGC 4261	Vir	E2	90	33	400
M87	Vir	E0	60	56	3000
M104	Vir	Sa	50	47	1000	Sombrero Galaxy
NGC 3377	Leo	E5	38	5.2	100
M105	Leo	E1	38	13	50
NGC 4486B	Vir	E0	60	0.82	500	Satellite of M87
M77	Cet	Sb	60			Caltech IR detection
M84	Vir	S0	60	56	300	HST STIS (May 1997)

Key:

Galaxy

Identification/Catalog number of galaxy

Const

Constellation

Type

Hubble type

Distance

Distance in million light years (of massive dark object)

Luminosity

Galaxy luminosity in billion solar luminosities; bulge only for spirals

Mass

Dark Object Mass in million solar masses

Comments

Common name of galaxy or other comment

This table summarizes data for some of the well-established massive dark

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 dark 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 propoertional 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.

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Hartmut Frommert

([email protected])

Christine Kronberg

([email protected])

Last Modification: 14 Feb 1998, 17:30 MET