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Galactic Center ResearchThe Mass of Sgr A* |
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Galactic Center ResearchThe Mass of Sgr A* |
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| Introduction
Proper Motions |
How do you weight a black hole? One possible way to do this
is by looking at nearby stars and measuring their proper motions. This
is, however, only feasible if you can resolve single stars. The distance
of the galactic center is about 8 kpc, the diffraction-limited resolution
of our pictures is 0.15", so with our high-resolution images, we were able
to resolve this highly crowded region and derive proper motions.  Once
you determined the speed of these stars (and their mass), you can calculate
(given the speed of the black hole) the enclosed mass using Newton's laws
of gravitation. This way we were able to estimate the mass of Sgr A* to
be at least 105 solar masses. The left
picture shows how the stars in the very center move around the yellow cross.
At this location the compact radio source Sgr A* is located which coincides
with the position of the massive black hole. This movie is also available
in MPEG (120 kB) and AVI
(2.7 MB) format. |
This is a plot of enclosed mass versus distance from Sgr A*, done using several different methods. The dashed lines show different model estimates. It is clear to be seen that the best model is a single enclosed mass of about 106 solar masses.
If you have comments or suggestions, email me at ott@mpe.mpg.de