The Black Hole in the Galactic Center

Approaching the Schwarzschild Radius

Slide 11 of 16
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Because the images become so much less blurred at higher frequencies there is an ongoing race to measure the size of Sagittarius A* at the highest frequencies possible. Recently Sagittarius A* was observed at 86 and 215 GHz which has yielded the smallest size ever observed. Below you can see how the size of Sagittarius A* decreases with frequency (here wavelength is plotted which is inversely proportional to frequency: higher frequencies correspond to lower wavelengths). The size is given as milli-arcseconds (mas) of the angular size on the sky. At 0.1 mas the actual size of the source is still a hundred million kilometers. However, the expected visible size of the black hole - its shadow (roughly 5 times the Schwarzschild radius, see next slides) - is already 40 million kilometers, hence we already observe a region that is very close to the actual black hole.


(Figure: The size of Sagittarius A* as measured with VLBI at different wavelengths of the observed radiation, courtesy of T. Krichbaum)


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Slide 11 of 16

Contact: Heino Falcke