The Black Hole in the Galactic Center

Approaching the Schwarzschild Radius

Slide 11 of 16
First Prev Next Last Index Homepage
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)


First Prev Next Last Index Homepage
Slide 11 of 16
Contact: Heino Falcke